PSEB 12th Class Biology Important Questions Chapter 4 Reproductive Health

Punjab State Board PSEB 12th Class Biology Important Questions Chapter 4 Reproductive Health Important Questions and Answers.

PSEB 12th Class Biology Important Questions Chapter 4 Reproductive Health

Very short answer type questions

Question 1.
Reproductive health refers only to healthy reproductive functions. Comment. [NCERT Exemplar]
Answer:
Reproductive health refers to the total well-being in all aspects of reproduction, i.e., physical, behavioural, psychological and social.

Question 2.
The present population growth rate in India is alarming. Suggest ways to check it. [NCERT Exemplar]
Answer:

  • By increasing marriageable age.
  • By promoting use of birth control measure.
  • By educating people about consequences of un- controlled population growth.

Question 3.
Why do intensely lactating mothers not generally conceive? [NCERT Exemplar]
Answer:
Due to suppression of gonadotropins, ovulation and menstrual cycle do not take place.

PSEB 12th Class Biology Important Questions Chapter 4 Reproductive Health

Question 4.
Name an IUD that you would recommend to promote the cervix hostility to sperms.
Answer:
The hormone releasing IUD’s, e.g. progestasert, LNG-20 are , recommended to promote the cervix hostility to sperms.

Question 5.
Mention any tvgo events that are exhibited by the intake of oral contraceptive pills to prevent pregnancy in humans.
Answer:
Two events that are exhibited by the intake of oral contraceptive pills to prevent pregnancy in humans are ovulation and implantation.

Question 6.
Why is tubectomy considered a contraceptive method?
Answer:
Tubectomy involves cutting a piece of the fallopian tube and tying its ends. This way, the sperms are not able to reach the egg and it acts as a contraceptive method.

Question 7.
Mention the primary aim of the ‘Assisted Reproductive Technology’ (ART) programme. [NCERT Exemplar]
Answer:
‘Assisted Reproductive Technology’ (ART) is the collection of certain I1 special techniques. The primary aim of the ART programmes is to assist infertile couples to have children through certain special techniques (like ZIFT, IUT, GIFT, ICSI, AI, etc.), when corrective treatment for infertility problems is not possible.

Question 8.
Expand GIFT and ICSI.
Answer:
GIFT: Gamete Intra Fallopian Transfer.
ICSI: Intra Cytoplasmic Sperm Injection.

PSEB 12th Class Biology Important Questions Chapter 4 Reproductive Health

Short answer type questions

Question 1.
Comment on the RCH programme of the government to improve the reproductive health of the people. [NCERT Exemplar]
Answer:
The basic aims of the RCH programmes are creating public awareness f regarding reproduction-related aspects and providing facilities to build up a healthy society with added emphasis on the health of mother and child.

Question 2.
(a) List any four characteristics of an ideal contraceptive.
(b) Name two intrauterine contraceptive devices that effect the motility of sperms.
Answer:
(a) An ideal contraceptive should be:

  • user friendly,
  • easily available,
  • effective,
  • reversible with no or least side-effects,
  • non-interfering with the sexual drive/desire and/or the sexual act of the user, (any four)

(b) Intrauterine Devices (IUDs): Lippes loop, copper releasing IUDs (Cu-T, Cu-7, multiload 375).

Question 3.
Name two hormones that are constituents of contraceptive pills. Why do they have high and effective contraceptive value? Name a commonly prescribed non-steroidal oral pill.
Answer:
Hormonal preparations (progestogens or progesterons and estrogens) are highly effective contraceptive because they inhibit ovulation and implantation, e.g., Mala-D, Mala-L. Morning after pills are used as emergency contraceptives, to avoid pregnancy due to rape or casual unprotected intercourse.

“Saheli”, a new oral pill is used “once-a-week” a non-steroidal preparation With very less side effects and high contraceptive value developed by CDRI in Lucknow, India.

PSEB 12th Class Biology Important Questions Chapter 4 Reproductive Health

Question 4.
Name and explain the surgical method advised to human males and females as a means of birth control. Mention its one advantage and one disadvantage.
Answer:
In the males-Vasectomy. In this method, a small part of the vas deferens is removed or tied up through a small incision on the scrotum. In the females-Tubectomy. In this method, a small part of the fallopian tube is removed or tied up through a small incision in the abdomen or through vagina.
Advantage: Highly effective
Disadvantage: Reversibility is very poor

Question 5.
A childless couple has agreed for a test tube baby programme. List only the basic steps of the procedure would involve to conceive the baby.
Answer:
IVF is the technique used in the case of childless couple. In IVF or In Vitro fertilisation, fertilisation is carried out in a glass container outside the body of the mother. Purified semen is poured over the mature retrieved oocytes. The fertilised eggs are separated and allowed to remain in culture medium, maintained in incubator for 48-72 hours. During the period, the fertilised egg undergoes cleavage and reach 4-8 celled stage, 2-3 fertilised 4-8 celled embryos are transferred or implanted .into the uterus of the recipient surrogate mother, for further development up to delivery.
Note: Excess fertilised oocytes are cryopreserved for use in case of implantation failure.

Question 6.
Why is medical termination of pregnancy (MTP) carried out?
Answer:
MTP is carried out to get rid of unwanted pregnancies. It is also essential when the foetus is suffering from an incurable disease or when continuation of the pregnancy could be harmful or even fatal to the mother and/or foetus.

PSEB 12th Class Biology Important Questions Chapter 4 Reproductive Health

Long answer type questions

Question 1.
Your school has been selected by the Department of Education to organise and host an interschool seminar on “Reproductive Health-Problems and Practices.” However, many parents are reluctant to permit their wards to attend it. Their argument is that the topic is “too embarrassing.”
Put forth four arguments with appropriate reasons and explanation to justify the topic to be very essential and timely.
Answer:
The selection of your school, to host a seminar on “Reproductive Health-Problems and Practices” is a matter great pride for the prestigious institute. The students will have an opportunity to listen to the diverse ideas, suggested by the learned speakers.

It is sad that many parents are reluctant to permit their wards to attend the seminar assuming that the topic is too embarrassing. The following arguments will justify the relevance of the topic in the present time:
(i) Introduction of sex education and the proper information about reproductive organs, adolescence and related changes will protect the youth from social evils like sex-abuse and sex-related crimes.

(ii) Right information about safe, healthy and hygienic sexual practices, sexually transmitted diseases (STDs) would help the people to lead a reproductive healthy life.

(iii) Decline in sex-ratio is a matter of great concern. The Govt, has put a I statutory ban on female foeticide. Both girls and boys have equal rights and equal opportunities in all spheres of life.

(iv) India is facing another problem of population explosion. It is eating, almost all the benefits of overall development. The benefits of development are not trickling down to the poor at lower strata. There is need for family planning, socially conscious healthy families of desired size i.e., Hum Do Humare Do.

PSEB 12th Class Biology Solutions Chapter 4 Reproductive Health

Punjab State Board PSEB 12th Class Biology Book Solutions Chapter 4 Reproductive Health Textbook Exercise Questions and Answers.

PSEB Solutions for Class 12 Biology Chapter 4 Reproductive Healths

PSEB 12th Class Biology Guide Reproductive Health Textbook Questions and Answers

Question 1.
What do you think is the significance of reproductive health in a society?
Answer:
Reproductive health is the total well being in all aspects of reproduction. It includes physical, emotional, behavioural, and social well being. Sexually transmitted diseases such as AIDS, gonorrhoea, etc. are transferred from one individual to another through sexual contact. It can also lead to unwanted pregnancies.

Hence, it is necessary to create awareness among people, especially the youth, regarding various reproduction related aspects as the young individuals are the future of the country and they are most susceptible of acquiring sexually transmitted diseases. Creating awareness about the available birth control methods, sexually transmitted diseases and their preventive measures, and gender equality will help in bringing up a socially conscious healthy family. Spreading. awareness regarding uncontrolled population growth and social evils among young individuals will help in building up a reproductively healthy society.

Question 2.
Suggest the aspects of reproductive health which need to be given special attention in the present scenario.
Answer:
Reproductive health is the total well being in all aspects of reproduction. The aspects which have to be given special attention in the present scenario are as follows:
1. Counselling and creating awareness among people, especially the youth, about various aspects of reproductive health, such as sexually transmitted diseases, available contraceptive methods, case of pregnant mothers, adolescence, etc.

2. Providing support and facilities such as medical assistance to people during pregnancy, STDs, abortions, contraceptives, infertility, etc. for building a reproductively healthy society.

PSEB 12th Class Biology Solutions Chapter 4 Reproductive Health

Question 3.
Is sex education necessary in schools? Why?
Answer:
Yes, introduction of sex education in schools is necessary. It would provide right information to young individuals at the right time about various aspects of reproductive health such as reproductive organs, puberty, and adolescence related changes, safe sexual practices, sexually transmitted diseases, etc.

The young individual or adolescents are more susceptible in acquiring various sexually transmitted diseases. Hence, providing information to them at the right time would help them to lead a reproductively healthy life and also protect them from the myths and misconceptions about various sex related issues.

Question 4.
Do you think that reproductive health in our country has improved in the past 50 years? If yes, mention some such areas of improvement.
Answer:
Yes, the reproductive health has tremendously improved in India in the last 50 years. The areas of improvement are as follows:

  1. Massive child immunisation programme, which has lead to a decrease in the infant mortality rate.
  2. Maternal and infant mortality rate, which has been decreased drastically due to better post natal care.
  3. Family planning, which has motivated people to have smaller families.
  4. Use of contraceptive, which has resulted in a decrease in the rate of sexually transmitted diseases and unwanted pregnancies.

Question 5.
What are the suggested reasons for population explosion?
Answer:
The human population is increasing day by day, leading to population explosion. It is because of the following two major reasons:
(a) Decreased death rate
(b) Increased birth rate and longevity
The death rate has decreased in the past 50 years. The factor leading to decreased death rate and increased birth rate are control of diseases, awareness and spread of education, improvement in medical facilities, ensured food supply in emergency situation, etc. All this has resulted in an increase in the longevity of an individual.

Question 6.
Is the use of contraceptives justified? Give reasons.
Answer:
Yes, the use of contraceptives is absolutely justified. The human population is increasing tremendously. Therefore, to regulate the population growth by regulating reproduction has become a necessary demand in the present times. Various contraceptive devices have been devised to reduce unwanted pregnancies, which help in bringing down the increased birth rate and hence, in checking population explosion.

PSEB 12th Class Biology Solutions Chapter 4 Reproductive Health

Question 7.
Removal of gonads cannot be considered as a contraceptive option. Why?
Answer:
Contraceptive devices are used to prevent unwanted pregnancy and to prevent the spreading of STDs. There are many methods, such as natural, barrier, oral, and surgical methods, that prevent unwanted pregnancy. However, the complete removal of gonads cannot be a contraceptive option because it will lead to infertility and unavailability of certain hormones that are required for normal functioning of accessory reproductive parts. Therefore, only those contraceptive methods can be used that prevent the chances of fertilisation rather than making the person infertile forever.

Question 8.
Amniocentesis for sex determination is banned in our country. Is this ban necessary? Comment.
Answer:
Amniocentesis is a pre-natal diagnostic technique that is used to determine the sex and metabolic disorders of the developing foetus in the mother’s uterus through the observation of the chromosomal patterns. This method was developed so as to determine any kind of genetic disorder present in the foetus. However, unfortunately, this technique is being misused to detect the sex of the child before birth and the female foetus is then aborted. Thus, to prevent the increasing female foeticides, it is necessary to ban the usage of amniocentesis technique for determining the sex of a child.

PSEB 12th Class Biology Solutions Chapter 4 Reproductive Health

Question 9.
Suggest some methods to assist infertile couples to have children.
Answer:
Infertility is the inability of a couple to produce a baby even after unprotected intercourse. It might be due to abnormalities present in either male or female, or might be even both the partners. The techniques used to assist infertile couples to have children are as follows:
(a) Test Tube Babies: This involves in-vitro fertilisation where the sperms meet the egg outside the body of a female. The zygote, hence produced, is then transferred in the uterus or fallopian tube of a normal female. The babies produced from this method are known as test tube babies.

(b) Gamete Intra Fallopian Transfer (GIFT): It is a technique that involves the transfer of gamete (ovum) from a donor into the fallopian tube of the recipient female who is unable to produce eggs, but has the ability to conceive and can provide right conditions for the development of an embryo.

(c) Intra Cytoplasmic Sperm Injection (ICSI): It is a method of injecting sperm directly into the ovum to form an embryo in laboratory.

(d) Artificial Insemination: Artificial insemination is a method of transferring semen (sperm) from a healthy male donor into the vagina or uterus of the recipient female. It is employed when the male partner is not able to inseminate the female or has low sperm counts.

Question 10.
What are the measures one has to take to prevent from contracting STDs?
Answer:
Sexually transmitted diseases (STDs) get transferred from one individual to the other through sexual contact. Adolescents and young adults are at the greatest risk of acquiring these sexually transmitted diseases. Hence, creating awareness among the adolescents regarding its after-effects can prevent them from contracting STDs. The use of contraceptives, such as condoms, etc. while intercourse, can prevent the transfer of these diseases. Also, sex with unknown partners or multiple partners should be avoided as they may have such diseases. Specialists should be consulted immediately in case of doubt so as to assure early detection and cure of the disease.

Question 11.
State True/False with explanation.
(a) Abortions could happen spontaneously too. (True/False)
(b) Infertility is defined as the inability to produce a viable offspring and is always due to abnormalities/defects in the female partner. (True/False)
(c) Complete lactation could help as a natural method of contraception. (True/False)
(d) Creating awareness about sex related aspects is an effective method to improve reproductive health of the people. (True/False)
Answer:
(a) False
Abortion is term given for medical termination of pregnancy.

(b) False
Infertility is defined as the inability of the couple to produce baby even after unprotected coitus. It might occur due to abnormalities/defects in either male or female or both.

(c) False
Complete lactation or lactational amenorrhea is a natural method of contraception. Flowever, it is limited till lactation period, which continues till six months after parturition.

(d) True.

PSEB 12th Class Biology Solutions Chapter 4 Reproductive Health

Question 12.
Correct the following statements:
(a) Surgical methods of contraception prevent gamete formation.
(b) All sexually transmitted diseases are completely curable.
(c) Oral pills are very popular contraceptives among the rural women.
(d) In E. T. techniques, embryos are always transferred into the uterus.
Answer:
(a) Surgical methods of contraception prevent the flow of gamete during intercourse.
(b) Some of the sexually transmitted diseases are curable if they are detected early and treated properly. AIDS is still an incurable disease.
(c) Oral pills are very popular contraceptives among urban women.
(d) In embryo transfer technique, 8 celled embryos are transferred into the fallopian tube while more than 8 celled embryos are transferred into the uterus.

PSEB 12th Class Biology Important Questions Chapter 3 Human Reproduction

Punjab State Board PSEB 12th Class Biology Important Questions Chapter 3 Human Reproduction Important Questions and Answers.

PSEB 12th Class Biology Important Questions Chapter 3 Human Reproduction

Very short answer type questions

Question 1.
Why are the human testes located outside the abdominal cavity? Name the pouch in which they are present.
Answer:
The human testes need lower temperature, 2-2.5°C less than the body temperature, for the formation of sperms which is provided outside the body. Testes are present in scrotal sac or scrotum.

Question 2.
Write the location and function of the sertoli cells in humans.
Answer:
Sertoli cells are present in seminiferous tubules. They provide nutrition to the germ cells or sperms.

Question 3.
Mention the location and the function of leydig cells in humans.
Answer:
Leydig cells are present in seminiferous tubules. They synthesise and secrete androgens.

PSEB 12th Class Biology Important Questions Chapter 3 Human Reproduction

Question 4.
The path of sperm transport is given below. Provide the missing steps in blank boxes. [NCERT Exemplar]
PSEB 12th Class Biology Important Questions Chapter 3 Human Reproduction 1
Answer:
Vasa efferentia, Vas deferens.

Question 5.
Female reproductive organs and associated functions are given below in column A and B. Fill in the blank boxes. [NCERT Exemplar]

Column A Column B
Ovaries Ovulation
Oviduct A
B Pregnancy
Vagina Birth

Answer:
A – Fertilisation
B – Uterus

Question 6.
What is the role of cervix of the human female system in reproduction? [NCERT Exemplar]
Answer:
Cervix helps in regulating the passage of sperms into the uterus and forms the birth canal to facilitate parturition.

Question 7.
When do the oogenesis and the spermatogenesis initiate in human females and males respectively?
Answer:
In females; oogenesis initiates during foetal life. In males, spermatogenesis begins at the time of puberty.

PSEB 12th Class Biology Important Questions Chapter 3 Human Reproduction

Question 8.
Mention the importance of LH surge during menstrual cycle. [NCERT Exemplar]
Answer:
LH surge is essential for the events leading to ovulation.

Question 9.
Menstrual cycles are absent during pregnancy. Why? [NCERT Exemplar]
Answer:
The high levels of progesterone and estrogens during pregnancy suppress the release of gonadotropins required for the development of new follicles. Therefore, new cycle cannot be initiated.

Question 10.
How does the sperm penetrate through the zona pellucida in [ human ovum?
Answer:
The sperm penetrates through zona pellucida with the help of secretions from acrosome.

Question 11.
Mention the function of trophoblast in human embryo.
Answer:
Trophoblast is the outer layer of blastocyst which helps in the attachment of blastocyst to the endometrium of the uterus.

Question 12.
Explain the function of umbilical cord.
Answer:
It transports nutrients and respiratory gases and metabolic wastes to and from mother and foetus.

PSEB 12th Class Biology Important Questions Chapter 3 Human Reproduction

Question 13.
Given below are the stages in human reproduction. Write them ‘ in correct sequential order.
Insemination, Gametogenesis, Fertilisation, Parturition, Gestation, Implantation. [NCERT Exemplar]
Answer:
Gametogenesis, Insemination, Fertilisation, Implantation, Gestation, Parturition.

Question 14.
What stimulates pituitary to release the hormone responsible for parturition? Name the hormone.
Answer:
The signal from the fully developed foetus and placenta or the foetal , ejection reflex induces mild uterine contraction. The hormone released is oxytocin.

Question 15.
Name the important mammary gland secretions that help in resistance of the new bom baby. [NCERT Exemplar]
Answer:
Colostrum

Question 16.
Mention the function of mitochondria in sperm.
Answer:
It provide energy for the movement of sperm tail.

Short answer type questions

Question 1.
Write the function of each of the following:
(a) Middle piece in human sperm.
(b) Luteinising hormone in human males.
Answer:
(a) Provides energy for movement.
(b) Stimulates synthesis and secretion of androgens or male hormones for spermatogenesis.

PSEB 12th Class Biology Important Questions Chapter 3 Human Reproduction

Question 2.
Differentiate between mayor structural changes in the human ovary during the follicular and luteal phase of the menstrual cycle.
Answer:

Follicular phase Luteal phase
1. During this, primary follicles grow to become fully mature Graafian follicle. During this, remaining part of Graafian follicle transforms into corpus luteum.
2. Endometrium regenerates through proliferation. Endometrium further thickens secreting progesterone for implantation after fertilisation. If fertilisation does not occur, corpus luteum degenerates.

Question 3.
Explain the events in a normal woman during her menstrual cycle on the following days :
(a) Pituitary hormone levels from 8 to 12 days.
(b) Uterine events from 13 to 15 days.
(c) Ovarian events from 16 to 23 days.
Answer:
(a) The level of LH and FSH secreted by anterior lobe of pituitary, stimulated by GnRH, increases.

(b) The endometrium of the uterus regenerates through proliferation. It grows and become thickened. There is repair of ruptured blood vessels and new blood capillaries develop. Uterine glands elongate.

(c) The remnant of Graafian follicle forms corpus luteum which secretes large amount of progesterone essential for maintenance of endometrium for implantation and for pregnancy.

Question 4.
What happens to corpus luteum in human female if the ovum is (a) fertilised, (b) not fertilised?
Answer:
(a) In case the ovum is fertilised, the corpus luteum persists and secretes a large amount of progesterone. The progesterone is essential for maintenance of endometrium, a necessity for implantation and for pregnancy.

(b) In the absence of fertilisation, corpus luteum degenerates. The level of LH and progesterone decreases very low. The absence of hormonal support, leads to the disintegration of endometrium and results in menstrual flow.

PSEB 12th Class Biology Important Questions Chapter 3 Human Reproduction

Question 5.
A large number of married couples the world over are childless. It is shocking to know that in India the female partner is often blamed for the couple being childless.
(a) Why in your opinion the female partner is often blamed for such situations in India? Mention any two values that you as a biology student can promote to check this Social evil.
(b) State any two reasons responsible for the cause of infertility.
(c) Suggest a technique that can help the couple to have a child where the problem is with the male partner.
Answer:
(a) The female partner is wrongly blamed for not bearing the child. It is due to the lack of proper information and knowledge about the reproduction and reproductive organs. Being a biology student I will advise and explain the couple as well as their other family members. Both male and female are equally responsible for bearing child. The two value, promoted are (i) concern for others (ii) scientific
temperament.

(b) Infertility is the inability to produce children inspite of unprotected sex and sexual co-habitation. It may be due to (i) physical/congenital disease (ii) immuno- logical or even physiological reason.

(c) In case, the problem is with male partner, artificial insemination (AI) is adopted. Semen collected either from the husband or a healthy donor is artificially introduced in the vagina or into the uterus of the female.

Question 6.
Name and explain the role of inner and middle walls of the human uterus.
Answer:
The inner wall of the uterus is called endometrium. It supports foetal growth and helps in placenta formation after implantation.
The middle wall of the uterus is called myometrium, exhibits strong contraction during delivery of baby.

Question 7.
Write a brief account of the structure and functions of placenta. [NCERT Exemplar]
Answer:
Placenta connects the foetus to the uterus through an umbilical chord. Both the foetal and the maternal tissues contribute to its formation. The foetal part is the chorionic villi and the maternal part is the uterine mucosa.

PSEB 12th Class Biology Important Questions Chapter 3 Human Reproduction

Long answer type questions

Question 1.
(a) Briefly explain the events of fertilisation and implantation in an adult human female.
(b) Comment on the role of placenta as an endocrine gland.
Or
Name the stage of human embryo of which it gets implanted.
Explain the process of implantation.
Or Draw a labelled diagram of a human blastocyst. How does it get implanted in the uterus?
Answer:
(a) (i) Fertilisation : Fertilisation occurs, if the ovum and sperms are transported simultaneously to the ampullary-isthmic junction and involve fusion of sperm with an ovum.
Secretions of acrosome of sperm help it to enter into the cytoplasm of ovum through zona pellucida and the plasma membrane. It induces meiotic division-II to form haploid ovum (ootid) and secondary polar body. The fusion of sperm with ovum to form diploid zygote is called fertilisation.
PSEB 12th Class Biology Important Questions Chapter 3 Human Reproduction 2
(ii) Implantation: Zygote undergoes cleavage to form a solid mass of 16 cells-morula, with daughter cells called blastomeres. Morula develops into a embryo with about 64 cells and with a cavity called blastocoel and the embryo is termed as blastocyst. It consists of outer layer of cells-trophoblast and inner cell mass.

The trophoblast gets attached to the endometrium- uterine wall of mother, after 7 days of fertilisation by a process called implantation leading to pregnancy. The uterine cells divide rapidly and cover blastocyst. The blastocyst gets embedded in the endometrium. Inner cell mass forms embryo.
PSEB 12th Class Biology Important Questions Chapter 3 Human Reproduction 3

(b) Placenta beside providing nutrients to the foetus also act as an endocrine gland. Placenta secretes human chorionic gonadotrophin (hCG), human placental lactogen (hPL), estrogen, progesterone etc., and later relaxin is secreted by ovary which facilitates parturition. Increased level of hormones like cortisol, prolactin and thyroxine etc., help in foetal growth, metabolic changes in the mother and maintenance of pregnancy.

PSEB 12th Class Biology Important Questions Chapter 15 Biodiversity and Conservation

Punjab State Board PSEB 12th Class Biology Important Questions Chapter 15 Biodiversity and Conservation Important Questions and Answers.

PSEB 12th Class Biology Important Questions Chapter 15 Biodiversity and Conservation

Very short answer type questions

Question 1.
Why is genetic variation important in the plant Rauwolfia vomitoria? [NCERT Exemplar]
Answer:
Genetic variation affects the variation in potency and concentration of me drug reserpine in the medicinal plant Rauwolfia vomitoria.

Question 2.
Name the type of biodiversity represented by the following:
(i) 50,000 different strains of rice in India
(ii) Estuaries and alpine meadows in India.
Answer:
(i) Genetic diversity
(ii) Ecological diversity

Question 3.
Identify ‘a’ and ‘b’ in the figure given below representing proportionate number of major vertebrate taxa.
PSEB 12th Class Biology Important Questions Chapter 15 Biodiversity and Conservation 1
Answer:
(a) Mammals
(b) Amphibians

Question 4.
Suggest two practices giving one example by each, that help protect rare or threatened species.
Answer:

  1. By using cryopreservation (preservation at -196°C) technique, sperms, eggs, tissues, and embryos can be stored for long period in gene banks, seed banks etc.
  2. Plants are propagated in vitro using tissue culture methods.

Question 5.
According to David Tilman, greater the diversity greater is the primary productivity. Can you think of a very low diversity man-made ecosystem that has high productivity? [NCERT Exemplar]
Answer:
Agricultural fields like wheat field or paddy field which are also examples of monoculture practices.

PSEB 12th Class Biology Important Questions Chapter 15 Biodiversity and Conservation

Question 6.
What is Red Data Book? [NCERT Exemplar]
Answer:
The Red Data Book is a compilation of data on species threatened with extinction and is maintained by IUCN. ‘

Question 7.
What is the expanded form of IUCN? [NCERT Exemplar]
Answer:
International Union for Conservation of Nature.

Question 8.
Why Western Ghats in India have been declared as biological hotspots?
Answer:
Western Ghats are biological hotspots because they have species richness and species evenness.

Question 9.
What is a national park?
Answer:
It is a protected area reserved for wildlife where human activities are not permitted.

Question 10.
What is the difference between endemic and exotic species? [NCERT Exemplar]
Answer:
Endemic species are native species restricted to a particular geographical region. Exotic species are species which are introduced from other geographical regions into an area.

Question 11.
How is the presently occurring species extinction different from the earlier mass extinctions? [NCERT Exemplar]
Answer:
Species extinction occurring at present is due to anthropogenic or man-made causes whereas the earlier extinction was due to natural causes.

Question 12.
Differentiate between in situ and ex situ approaches of conservation of biodiversity.
Answer:

In situ approach Ex-situ approach
1. It involves protection of endangered species of plants and animals. It involves protection of endangered species by removing them from the natural habitat.
2. This is done by protecting the natural habitat or ecosystem. This is done by placing the species under special care.

Short answer type questions

Question 1.
What is biodiversity? Why is it a matter of concern now?
Answer:
Biodiversity is the occurrence of different types of genes, gene pools, species, habitats and ecosystems at a particular place and various parts of earth. It is a matter of concern because species are continuously lost, limiting the diversity and this will affect our survival and well-being on earth due to the changes in environment.

PSEB 12th Class Biology Important Questions Chapter 15 Biodiversity and Conservation

Question 2.
Where would you expect more species biodiversity-in tropics or in polar regions? Give reasons in support of your answer.
Answer:
More biodiversity is found in the tropics. This is because tropical regions remain undisturbed from frequent glaciations as in polar regions. Also, the tropics are less seasonal/more constant.

Question 3.
Is it true that there is more solar energy available in the tropics? Explain briefly. [NCERT Exemplar]
Answer:
As one moves from the equator to the polar regions, the length of the day decreases and the length of the night increases. The length of day and night are same at the equator. Therefore, it is true that there is more solar energy available in the tropics.

Question 4.
The given graph alongside shows species-area relationship. Write the equation of the curve ‘a’ and explain.
Answer:
PSEB 12th Class Biology Important Questions Chapter 15 Biodiversity and Conservation 2
The equation of the curve ‘a’ is S = CAZ.
(i) Within a region, species richness increases with increasing explored area but only up to a limit.
(ii) Relationship between species richness and area for a wide variety of taxa turns out to be a rectangular hyperbola.

Question 5.
Explain ‘rivet popper hypothesis. Name the ecologist who proposed it.
Answer:
Paul Ehrlich proposed the rivet popper hypothesis. This hypothesis states that in an airplane (ecosystem) all parts are joined together using thousands of rivets (species). If every passenger traveling in it starts popping a rivet to take home (causing a species to become extinct), it may not affect flight safety (proper functioning of the ecosystem) initially but as more and more rivets are removed, the plane becomes dangerously weak over a period of time. Also, which rivet is removed may also be critical like loss of rivets on the wings (key species) is more serious threat to flight safety than loss of few rivets on the seats or windows inside the plane.

Question 6.
How do human activities cause desertification?
Answer:
Human activities like over-cultivation, unrestricted grazing, deforestation, and poor irrigation practices result in arid patches of land. The fertile topsoil that may take centuries to develop is eroded due to these activities. When large barren patches extend and meet over time, a desert is created. Increased urbanization is also one of the causes of desertification.

Question 7.
Why are conventional methods not suitable for the assessment of biodiversity of bacteria? [NCERT Exemplar]
Answer:
Many bacteria are not culturable under normal conditions in the laboratory. This becomes a problem in studying their morphological, biochemical, and other characterizations which are useful for their assessment.

Question 8.
List any four techniques where the principle of ex-situ conservation of biodiversity has been employed.
Answer:
Ex-situ Conservation (off-site conservation)

  1. Zoological parks and botanical gardens.
  2. Wildlife safari parks, aquaria.
  3. Preservation of germplasm-seed gene banks, tissue culture, cryopreservation.
  4. Sacred plants grown in homes, villages, and religious places.

Long answer type questions

Question 1.
(a) Why should we conserve biodiversity? How can we do it?
(b) Explain the importance of biodiversity hotspots and sacred groves.
Or
Why should biodiversity be conserved? List any two ethical arguments in its support. ‘
Answer:
(a) Need for Conservation of Biodiversity: Reasons for conservation of biodiversity can be grouped into three categories :

  1. narrowly utilitarian
  2. broadly utilitarian and
  3. ethical.

(i) Narrowly Utilitarian: The reasons for conserving biodiversity are obvious because of their :
(a) direct economic benefits such as

  • food (cereals, pulses, fruits)
  • firewood
  • fiber
  • construction material
  • products of medicinal importance
  • industrial products (tannins, gums, lubricants, dyes, resins, perfumes).

(b) More than 25% of the drugs are derived from plants.

PSEB 12th Class Biology Important Questions Chapter 15 Biodiversity and Conservation

(c) 25,000 species of plants are used as traditional medicines by native people.

(ii) Broadly Utilitarian: Biodiversity plays a major role in providing ecosystem services that nature provides and which cannot be given a price tag are :

  • Production of Oxygen
  • Pollination of flowers by bees, bumblebees, birds, and bats, etc.
  • Resulting in the formation of fruits and seeds.
  • Aesthetic pleasures like bird watching, walking through the thick forests, waking up to bulbul’s song, etc.

(iii) Ethical :
(a) We share this planet with millions of plants, animals, and microbe species. Every species has an intrinsic value even if it is not of current or any economic value to us.

(b) We have an essential duty to care for their well-being and pass on the biological legacy in a proper form to our future generations. We can conserve biodiversity by two major approaches

  • In situ conservation (on site/ conservation)
  • Ex situ conservation (off-site conservation).

(c) Hotspots are the areas identified by conservationists for the very high level of species richness and high degree of endemism (species confined to a particular area and not found anywhere else). Hotspots help in protection of certain biodiversity-rich regions.

Sacred groves are the tracts of forest set aside where all the trees and wildlife within are given religious sanctity and total protection. Such sacred groves are found in Khasi and Jaintia hills in Meghalaya, Aravalli Hills of Rajasthan etc.

PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction

Punjab State Board PSEB 12th Class Biology Book Solutions Chapter 3 Human Reproduction Textbook Exercise Questions and Answers.

PSEB Solutions for Class 12 Biology Chapter 3 Human Reproduction

PSEB 12th Class Biology Guide Human Reproduction Textbook Questions and Answers

Question 1.
Fill in the blanks:
(a) Humans reproduce …………………. .(asexually/sexually)
Answer:
sexually.

(b) Humans are …………………… .(oviparous/viviparous/ovoviviparous)
Answer:
viviparous.

(c) Fertilisation is ………………………. in humans, (external/internal)
Answer:
internal

(d) Male and female gametes are …………………. .(diploid/haploid)
Answer:
haploid.

(e) Zygote is ………………….. .(diploid/haploid)
Answer:
diploid.

(f) The process of release of ovum from a mature follicle is called ……………………. .
Answer:
ovulation.

(g) Ovulation is induced by a hormone called …………………… .
Answer:
luteinising hormone.

(h) The fusion of male and female gametes is called ……………………… .
Answer:
fertilisation.

(i) Fertilisation takes place in ………………… .
Answer:
fallopian tube (ampullary-isthmic junction).

(j) Zygote divides to form ……………….., which is implanted in uterus.
Answer:
blastocyst

(k) The structure which provides vascular connection between foetus and uterus is called …………………… .
Answer:
placenta.

PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction

Question 2.
Draw a labelled diagram of male reproductive system.
Answer:
PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction 1
PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction 2

Question 3.
Draw a labelled diagram of female reproductive system.
Answer:
PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction 3
PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction 4

PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction

Question 4.
Write two major functions each of testis and ovary.
Answer:
Functions of the testis
(a) They produce male gametes called spermatozoa by the process of spermatogenesis.
(b) The leydig cells of the seminiferous tubules secrete the male sex hormone called testosterone. Testosterone aids the development of secondary sex characteristics in males.

Functions of the ovary
(a) They produce female gametes called ova by the process of oogenesis.
(b) The growing Graafian follicles secrete the female sex hormone called estrogen. Estrogen aids the development of secondary sex characteristics in females.

Question 5.
Describe the structure of a seminiferous tubule.
Answer:
The production of sperms in the testes takes place in a highly coiled structure called the seminiferous tubules. These tubules are located in the testicular lobules. Each seminiferous tubule is lined by germinal epithelium. It is lined on its inner side by two types of cells namely spermatogonia aid sertoli cells respectively. Spermatogonia are male germ cells which produce primary spermatocytes by meiotic divisions. Primary spermatocytes undergo further meiotic division to form secondary spermatocytes and finally, spermatids. Spermatids later metamorphoses into male gametes called spermatozoa. Sertoli cells are known as nurse cells of the testes as they provide nourishment to the germ cells. There are large polygonal cells known as interstitial cells or leydig cells just adjacent to seminiferous tubules. These cells secrete the male hormone called testosterone.
PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction 5

Question 6.
What is spermatogenesis? Briefly describe the process of spermatogenesis.
Answer:
Spermatogenesis is the process of the production of sperms from the immature germ cells in males. It takes place in seminiferous tubules present inside the testes. During spermatogenesis, a diploid spermatogonium (male germ cell) increases its size to form a diploid primary spermatocyte. This diploid primary spermatocyte undergoes first meiotic division (meiosis I), which is a reductional division to form two equal haploid secondary spermatocytes. Each secondary spermatocyte then undergoes second meiotic division (meiosis II) to form two equal haploid spermatids. Hence, a diploid spermatogonium produces four haploid spermatids. These spermatids are transformed into spermatozoa (sperm) by the process called spermiogenesis.
PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction 6

PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction

Question 7.
Name the hormones involved in regulation of spermatogenesis.
Answer:
Follicle-stimulating hormones (FSH) and luteinising hormones (LH) are secreted by gonadotropin releasing hormones from the hypothalamus. These hormones are involved in the regulation of the process of spermatogenesis. FSH acts on sertoli cells, whereas LH acts on leydig cells of the testis and stimulates the process of spermatogenesis.

Question 8.
Define spermiogenesis and spermiation.
Answer:
Spermiogenesis : It is the process of transforming spermatids into matured spermatozoa or sperms.
Spermiation : It is ‘the process when mature spermatozoa are released from the sertoli cells into the lumen of seminiferous tubules.

Question 9.
Draw a labelled diagram of sperm.
Answer:
PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction 7

Question 10.
What are the major components of seminal plasma?
Answer:
Semen (produced in males) is composed of sperms and seminal plasma. The major components of the seminal plasma in the male reproductive system are mucus, spermatozoa, and various secretions of accessory glands. The seminal plasma is rich in fructose, calcium, ascorbic acid, and certain enzymes. It provides nourishment and protection to sperms.

PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction

Question 11.
What are the major functions of male accessory ducts and glands?
Answer:
The male accessory ducts are vasa efferentia, epididymis, vas deferens, and rete testis. They play an important role in the transport and temporary storage of sperms. On the contrary, male accessory glands are seminal vesicles, prostate glands, and bulbourethral glands. These glands secrete fluids that lubricate the reproductive system and sperms. The sperms get dispersed in the fluid which makes their transportation into the female body easier. The fluid is rich in fructose, ascorbic acid, and certain enzymes. They also provide nutrients and activate the sperm.

Question 12.
What is oogenesis? Give a brief account of oogenesis.
Answer:
Oogenesis is the process of the formation of a mature ovum from the oogonia in females. It takes place in the ovaries. During oogenesis, a diploid oogonium or egg mother cell increases in size and gets transformed into a diploid primary oocyte. This diploid primary oocyte undergoes first meiotic division i.e., meiosis I or reductional division to form two unequal haploid cells. The smaller cell is known as the first polar body, while the larger cell is known as the secondary oocyte. This secondary oocyte undergoes second meiotic division i.e., meiosis II or equational division and gives rise to a second polar body and an ovum. Hence, in the process of oogenesis, a diploid oogonium produces a single haploid ovum while two or three polar bodies are produced.
PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction 8

Question 13.
Draw a labelled diagram of a section through ovary.
Answer:
PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction 9

PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction

Question 14.
Draw a labelled diagram of a Graafian follicle.
Answer:
PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction 10

Question 15.
Name the functions of the following:
(a) Corpus luteum
(b) Endometrium
(c) Acrosome
(d) Sperm tail
(e) Fimbriae
Answer:
(a) Corpus Luteum: It is formed from the ruptured Graafian follicle. It secretes progesterone hormone during the luteal phase of the menstrual cycle. A high level of progesterone inhibits the secretions of FSH and LH, thereby preventing ovulation. It also allows the endometrium of the uterus to proliferate and to prepare itself for implantation.

(b) Endometrium: It is the innermost lining of the uterus. It is rich in glands and undergoes cyclic changes during various phases of the menstrual cycle to prepare itself for the implantation of the embryo.

(c) Acrosome: It is a cap-like structure present in the anterior part of the head of the sperm. It contains hyaluronidase enzyme, which hydrolyses the outer membrane of the egg, thereby helping the sperm to penetrate the egg at the time of fertilisation.

(d) Sperm Tail: It is the longest region of the sperm that facilitates the movement of the sperm inside the female reproductive tract.

(e) Fimbriae: They are finger-like projections at the ovarian end of the fallopian tube. They help in the collection of the ovum (after ovulation), which is facilitated by the beating of the cilia.

Question 16.
Identify True/False statements. Correct each false statement to make it true.
(a) Androgens are produced by Sertoli cells. (True/False)
(b) Spermatozoa get nutrition from Sertoli cells. (True/False)
(c) Leydig cells are found in ovary. (True/False)
(d) Leydig cells synthesise androgens. (True/False)
(e) Oogenesis takes place in corpus luteum. (True/False)
(f) Menstrual cycle ceases during pregnancy. (True/False)
(g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience. (True/False)
Answer:
(a) Androgens are produced by Sertoli cells.
False Correct : Leydig cells.

(b) Spermatozoa get nutrition from Sertoli cells.
True

(c) Leydig cells are found in ovary.
False Correct : spermatogonia.

(d) Leydig cells synthesise androgens.
True

(e) Oogenesis takes place in corpus luteum.
False Correct : ovaries

(f) Menstrual cycle ceases during pregnancy.
True

(g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience.
True

PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction

Question 17.
What is menstrual cycle? Which hormones regulate menstrual cycle? ,
Answer:
The menstrual cycle is a series of cyclic physiologic changes that take place inside the female reproductive tract in primates. The whole cycle takes around 28 days to complete. The end of the cycle is accompanied by the breakdown of uterine endothelium, which gets released in the form of blood and mucus through the vagina. This is known as menses.

The follicle stimulating hormone (FSH), luteinising hormone (LH), L estrogen, and progesterone are the various hormones that regulate the menstrual cycle. The level of FSH and LH secreted from the anterior pituitary gland increases during the follicular phase. FSH secreted under the influence of RH (releasing hormone) from the hypothalamus , stimulates the conversion of a primary follicle into a graafian follicle.

The level of LH increases gradually leading to the growth of follicle and f secretion of estrogen. Estrogen inhibits the secretion of FSH and stimulates the secretion of luteinising hormone. It also causes the thickening of the uterine endometrium. The increased level of LH causes the rupturing of the graafian follicle and release the ovum into the fallopian tube. The ruptured graafian follicle changes to corpus luteum and starts secreting progesterone hormone during the luteal phase.

Progesterone hormone helps in the maintenance and preparation of endometrium for the implantation of the embryo. High levels of progesterone hormone in the blood decrease the secretion of LH and FSH, therefore inhibiting further ovulation.

Question 18.
What is parturition? Which hormones are involved in induction of parturition?
Answer:
Parturition is the process of giving birth to a baby as the development of the foetus gets completed in the mother’s womb. The hormones involved in this process are oxytocin and relaxin. Oxytocin leads to the contraction of smooth muscles of myometrium of the uterus, which directs the full term foetus towards the birth canal. On the other hand, relaxin hormone causes relaxation of the pelvic ligaments and prepares the uterus for child birth.

Question 19.
In our society the women are often blamed for giving birth to [ daughters. Can you explain why this is not correct?
Answer:
All human beings have 23 pairs of chromosomes. Human males have 22 pairs of autosomes and contain one or two types of sex chromosome. They are either X or Y. On the contrary, human females have 22 pairs of autosomes and contain only the X sex chromosome. The sex of an individual is determined by the type of the male gamete (X or Y), which fuses with the X chromosome of the female. If the fertilising sperm is X, then the baby will be a girl and if it is Y, then the baby will be a boy.
Hence, it is incorrect to blame a woman for the gender of the child.

PSEB 12th Class Biology Solutions Chapter 3 Human Reproduction

Question 20.
How many eggs are released by a human ovary in a month? How many eggs do you think would have been released if the mother gave birth to identical twins? Would your answer change if the twins bom were fraternal?
Answer:
An ovary releases an egg every month. When two babies are produced in succession, they are called twins. Generally, twins are produced from a single egg by the separation of early blastomeres resulting from the first zygotic cleavage. As a result, the young ones formed will have the same genetic make-up and are thus, called identical twins.

If the twins born are fraternal, then they would have developed from two separate eggs. This happens when two eggs’ (one from each ovary) are released at the same time and get fertilised by two separate sperms. Hence, the young ones developed will have separate genes and are therefore, called non-identical or fraternal twins.

Question 21.
How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies?
Answer:
Dogs and rodents are polyovulatory species. In these species, more than one ovum is released from the ovary at the time of ovulation. Hence, six eggs were released by the ovary of a female dog to produce six puppies.

PSEB 12th Class Biology Solutions Chapter 15 Biodiversity and Conservation

Punjab State Board PSEB 12th Class Biology Book Solutions Chapter 15 Biodiversity and Conservation Textbook Exercise Questions and Answers.

PSEB Solutions for Class 12 Biology Chapter 15 Biodiversity and Conservation

PSEB 12th Class Biology Guide Biodiversity and Conservation Textbook Questions and Answers

Question 1.
Name the three important components of biodiversity.
Answer:
Biodiversity is the variety of living forms present in various ecosystems. It includes variability among life forms from all sources including land, air, and water. Three important components of biodiversity are as follows :

  • Genetic diversity
  • Species diversity
  • Ecological diversity

Question 2.
How do ecologists estimate the total number of species present in the world?
Answer:
The diversity of living organisms present on the Earth is very vast. According to an estimate by researchers, it is about seven million. the total number of species present in the world is calculated by statistical comparison between species richness of a well-studied group of insects of temperate and tropical regions. Then, these ratios are extrapolated with other groups of plants and animals to calculate the total species richness present on the Earth.

Question 3.
Give three hypotheses for explaining why tropics show greatest levels of species richness.
Answer:
There are three different hypotheses proposed by scientists for explaining species richness in the tropics.

  1. Tropical latitudes receive more solar energy than temperate regions, which leads to high productivity and high species diversity.
  2. Tropical regions have less seasonal variations and have a more or less constant environment. This promotes the niche specialization and thus, high species richness.
  3. Temperate regions were subjected to glaciations during the ice age, while tropical regions remained undisturbed which led to an increase in the species diversity in this region.

Question 4.
What is the significance of the slope of regression in a species-area relationship?
Answer:
The slope of regression (z) has a great significance in order to find a species-area relationship. It has been found that in smaller areas (where the species-area relationship is analyzed), the value of slopes of regression is similar regardless of the taxonomic- group or the region. However, when a similar analysis is done in larger areas, then the slope of regression is much steeper.

PSEB 12th Class Biology Solutions Chapter 15 Biodiversity and Conservation

Question 5.
What are the major causes of species losses in a geographical region?
Answer:
Biodiversity is the variety of living forms present in various ecosystems. It includes variability among life forms from all sources including land, air, and water. Biodiversity around the world is declining at a very fast pace. The following are the major causes for the loss of biodiversity around the world :

(i) Habitat Loss and Fragmentation: Habitats of various organisms are altered or destroyed by uncontrolled and unsustainable human activities such as deforestation, slash and burn agriculture, mining, and urbanisation. This results in the breaking up of the habitat into small pieces, which effects the movement of migratory animals and also, decreases the genetic exchange between populations leading to a declination of species.

(ii) Over-exploitation: Due to over-hunting and over-exploitation of various plants and animals by humans, many species have become endangered or extinct (such as the tiger and the passenger pigeon).

(iii) Alien Species Invasions: Accidental or intentional introduction of non-native species into a habitat has also led to the declination or extinction of indigenous species. For example, the Nile perch introduced in Lake Victoria in Kenya led to the extinction of more than two hundred species of native fish in the lake.

(iv) Co-extinction: In a native habitat, one species is connected to the other in an intricate network. The extinction of one species causes the extinction of other species, which is associated with it in an obligatory way. For example, the extinction of the host will cause the extinction of its parasites.

Question 6.
How is biodiversity important for ecosystem functioning?
Answer:
An ecosystem with high species diversity is much more stable than an ecosystem with low species diversity. Also, high biodiversity makes the ecosystem more stable in productivity and more resistant towards disturbances such as alien species invasions and floods.

If an ecosystem is rich in biodiversity, then the ecological balance would not get affected. As we all know, various trophic levels are connected through food chains. If anyone organism or all organisms of any one trophic level is killed, then it will disrupt the entire food chain. For example, in a food chain, if all plants are killed, then all deer’s will die due to the lack of food.

If all deer’s are dead, soon the tigers will also die. Therefore, it can be concluded that if an ecosystem is rich in species, then there will be other food alternatives at each trophic level which would not allow any organism to die due to the absence of their food resource. Hence, biodiversity plays an important role in maintaining the health and ecological balance of an ecosystem.

Question 7.
What are sacred groves? What is their role in conservation?
Answer:
Sacred groves are tracts of forest which are regenerated around places of worship. Sacred groves are found in Rajasthan, Western Ghats of Karnataka, and Maharashtra, Meghalaya, and Madhya Pradesh. Sacred grows help in the protection of many rare, threatened, and endemic species of plants and animals found in an area. The process of deforestation is strictly prohibited in this region by tribals. Hence, the sacred grove biodiversity is a rich area.

Question 8.
Among the ecosystem services are control of floods and soil erosion. How is this achieved by the biotic components of the ecosystem?
Answer:
The biotic components of an ecosystem include the living organisms such as plants and animals. Plants play a very important role in controlling floods and soil erosion. The roots of plants hold the soil particles together, thereby preventing the top layer of the soil to get eroded by wind or running water. The roots also make the soil porous, thereby allowing groundwater infiltration and preventing floods. Hence, plants are able to prevent soil erosion and natural calamities Fucii as floods and droughts. They also increase the fertility of soil and biodiversity.

PSEB 12th Class Biology Solutions Chapter 15 Biodiversity and Conservation

Question 9.
The species diversity of plants (22 percent) is much less than that of animals (72 percent). What could be the explanations to how animals achieved greater diversification?
Answer:
72 percent of species recorded on the Earth are animals and only 22 percent species are plants. There is quite a large difference in their percentage This is because animals have adapted themselves to ensure their survival in changing environments in comparison to plants. For example, insects and other animals have developed a complex nervous system to control and coordinate their body structure. Also, repeated body/ segments with paired appendages and external cuticles have made insects versatile and have given them the ability to survive in vain JUS habitats as compared to other life forms.

Question 10.
Can you think of a situation where we deliberately want to make a species extinct? How would you justify it?
Answer:
Yes, there are various kinds of parasites and disease-causing microbes that we deliberately want to eradicate from the Earth. Since these micro-organisms are harmful to human beings, scientists are working hard to fight against them.

Scientists have been able to eliminate smallpox virus from the world through the use of vaccinations. This shows than humans deliberately want to make these species extinct. Several other eradication programs such as polio and Hepatitis B vaccinations are aimed to eliminate these disease-causing microbes.

PSEB 12th Class Biology Important Questions Chapter 2 Sexual Reproduction in Flowering Plants

Punjab State Board PSEB 12th Class Biology Important Questions Chapter 2 Sexual Reproduction in Flowering Plants Important Questions and Answers.

PSEB 12th Class Biology Important Questions Chapter 2 Sexual Reproduction in Flowering Plants

Very short answer type questions

Question 1.
An anther with malfunctioning tapetum often fails to produce viable male gametophytes. Give any one reason.
Answer:
A malfunctioning tapetum does not provide enough nourishment to the developing male gametophytes and thus fail to produce viable male gametophytes.

Question 2.
Complete the following flow chart
Pollen mother cell → Pollen tetrad
PSEB 12th Class Biology Important Questions Chapter 2 Sexual Reproduction in Flowering Plants 1
[NCERT Exampler]
Answer:
Generative cell.

PSEB 12th Class Biology Important Questions Chapter 2 Sexual Reproduction in Flowering Plants

Question 3.
Gynoecium of a flower may be apocarpous or syncarpous. Explain with the help of an example each.
Answer:
Gynoecium of a flower may be apocarpous means the carpels are free from one another and there is no fusion of any part e.g., Ranunculus, Rose. Gynoecium of a flower is syncarpous, means the carpels are fused by their ovaries. The number of fusing carpels may vary from 2 (Petunia) to ∞ (Hibiscus).

Question 4.
Name the parts of the gynoecium which develop into fruit and seeds. [NCERT Exemplar]
Answer:
Ovary develops into fruit and ovules develop into seeds.

Question 5.
How many haploid cells are present in a mature female gametophyte of a flowering plant? Name them.
Answer:
One dikaryotic polar cell with two haploid nuclei and six haploid cells, viz, 3 antipodal, 2 synergids and 1 egg.

Question 6.
Name the type of pollination in self-incompatible plants. [NCERT Exemplar]
Answer:
Xenogamy.

Question 7.
How do flowers of Vallisneria get pollinated?
Answer:
In Vallisneria, the female flower stalk is coiled to reach the water surface to receive the pollen grains carried by water currents.

PSEB 12th Class Biology Important Questions Chapter 2 Sexual Reproduction in Flowering Plants

Question 8.
What is pollen-pistil interaction and how is it mediated?
Answer:
The pistil accepts the right type (compatible) of pollen and promotes fertilisation and rejects the pollen of other species and incompatible pollen of the same species. It is the result of interaction between the chemicals of the pollen and those of stigma.

Question 9.
State the function of filiform apparatus found in mature embryo sac of an angiosperm.
Answer:
Filiform apparatus plays an important role in guiding the path of pollen tubes into the synergids.

Question 10.
Normally one embryo develops in one seed but when an orange seed is squeezed many embryos of different shapes and sizes are seen. Mention how it has happened?
Answer:
An orange seed has many embryos because of polyembryony.

Question 11.
Name the component cells of the ‘egg apparatus’ in an embryo sac. [NCERT Exemplar]
Answer:
Two synergids and an egg.

Question 12.
Name the common function that cotyledons and nucellus perform. [NCERT Exemplar]
Answer:
Cotyledons and nucellus provide nourishment.

PSEB 12th Class Biology Important Questions Chapter 2 Sexual Reproduction in Flowering Plants

Question 13.
In the embryos of a typical dicot and a grass, which are the true homologous structures? [NCERT Exemplar]
Answer:
Cotyledons and scutellum.

Question 14.
In a case of polyembryony, if an embryo develops from the synergid and *another from the nucellus, which is haploid and which is diploid? [NCERT Exemplar]
Answer:
Synergid embryo is haploid and nucellar embryo is diploid.

Short answer type questions

Question 1.
Name the organic materials the exine and intine of an angiosperm pollen grains are made up of. Explain the role of exine.
Answer:
Exine is made up of sporopollenin and intine is made up of cellulose and pectin.
Due to the sporopollenin, exine can withstand high temperature and strong acids. It is also not affected by enzymes. It is because of this reason that pollen grains are well preserved as fossils.

Question 2.
Differentiate between geitonogamy and xenogamy in plants. Which one between the two will lead to inbreeding depression and why?
Answer:

Geitonogamy Xenogamy
1. It is transfer of pollen grains from the anther to the stigma of another flower of same plant. It is transfer of pollen grains from the anther to the stigma of a different plant.
2. The pollen grains are genetically similar to the plant. The pollen grains are genetically different from the plant.

Geitonogamy will lead to inbreeding depression because the pollen grains are genetically similar, which results in inbreeding. Continued inbreeding will thus reduce fertility and productivity.

PSEB 12th Class Biology Important Questions Chapter 2 Sexual Reproduction in Flowering Plants

Question 3.
Double fertilisation is reported in plants of both, castor and groundnut. However, the mature seeds of groundnut are non-albuminous and castor are albuminous. Explain the post fertilisation events that are responsible for it.
Answer:
The development of endosperm (preceding the embryo) takes place from primary endosperm nucleus (PEN) in both, castor and groundnut. The developing embryo derives nutrition from endosperm.

PEN undergoes repeated division to give free nuclei. Subsequently cell wall is formed and endosperm becomes cellular. At this stage endosperm is retained in castor or is not fully consumed but in groundnut endosperm is consumed by growing embryo.

Question 4.
Differentiate between albuminous and non-albuminous seeds, giving one example of each.
Answer:

  • Albuminous seeds have residual endosperm ip them. For example, maize.
  • Non-albuminous seeds do not have any residual endosperm. For example, pea.

Question 5.
A non biology person is quite shocked to know that apple is a false fruit, mango is a true fruit and banana is a seedless fruit. As a biology student how would you satisfy this person?
Answer:
In apple only the thalamus (along with ovary) portion contributes to fruit. Therefore, it is a false fruit. Mango develops only from the ovary, therefore it is a true fruit.
Banana develops from ovary but without fertilisation. The method is known as parthenocarpy. Since there is no fertilisation, no seeds are formed.

Question 6.
Why are some seeds referred to as apomictic seeds? Mention one advantage and one disadvantage to a farmer who uses them.
Answer:
Seeds produced without fertilisation are referred to as apomictic.
Advantage: Desired characters are retained in offspring (progeny) as there is no segregation of characters in offspring (progeny). Seed production is assured in absence of pollinators.

Disadvantage: Cannot control accumulation of deleterious genetic mutation. These are usually restricted to narrow ecological niches and lack ability to adapt to changing environment.

PSEB 12th Class Biology Important Questions Chapter 2 Sexual Reproduction in Flowering Plants

Long answer type questions

Question 1.
A flower of brinjal plant following the process of sexual reproduction produces 360 viable seeds.
Answer the following questions giving reasons:
(a) How many ovules are minimally involved?
(b) How many megaspore mother cells are involved?
(c) What is the minimum number of pollen grains that must land on stigma for pollination?
(d) How many male gametes are involved in the above case?
(e) How many microspore mother cells must have undergone reduction division prior to dehiscence of another in the above case?
Answer:
(a) 360 ovules are involved. One ovule after fertilisation forms one seed.
(b) 360 megaspore mother cells are involved. Each megaspore mother cell forms four megaspores out of which only one remains functional.
(c) 360 pollen grains. One pollen grain participates in fertilisation of one ovule.
(d) 720 male gametes are involved. Each pollen grain carries two male gametes (which participate in double fertilisation) (360 × 2 = 720).
(e) 90 microspore mother cells undergo reduction division. Each microspore mother cell meiotically divides to form four pollen grains (360/4 = 90).

PSEB 12th Class Biology Important Questions Chapter 16 Environmental Issues

Punjab State Board PSEB 12th Class Biology Important Questions Chapter 16 Environmental Issues Important Questions and Answers.

PSEB 12th Class Biology Important Questions Chapter 16 Environmental Issues

Very short answer type questions

Question 1.
Why are lichens regarded as pollution indicators?
Answer:
Lichens are regarded as pollution indicators because they do not grow in areas that are polluted. So their presence indicates no pollution in that area and their absence indicates that the area is polluted.

Question 2.
Why is the use of unleaded petrol recommended for motor vehicles equipped with catalytic converters?
Or
Why are owners of motor vehicles equipped with catalytic converters advised to use unleaded petrol?
Or
Why is it desirable to use unleaded petrol in vehicles fitted with catalytic converters?
Answer:
Vehicles fitted with catalytic converters need to use unleaded petrol because lead inactivates the catalyst in the catalytic converter and increases hydrocarbon emission, thereby harming the environment.

Question 3.
In which year was the Air (Prevention and Control of Air Pollution) Act amended to include noise as air pollutant? [NCERT Exemplar]
Answer:
The Air (Prevention and Control of Air Pollution) Act 1981 was amended in 1987 to include noise as an air pollutant.

PSEB 12th Class Biology Important Questions Chapter 16 Environmental Issues

Question 4.
Name an industry which can cause air pollution, thermal pollution, and eutrophication. [NCERT Exemplar]
Answer:
Fertilizer factory.

Question 5.
Mention two advantages for preferring CNG over diesel as an automobile fuel.
Answer:
Advantages of CNG :

  1. It burns more efficiently than petrol or diesel.
  2. It is cheaper than petrol or diesel and cannot be siphoned off by thieves or adulterated.

Question 6.
What is an algal bloom? [NCERT Exemplar]
Answer:
The excessive growth of algae (free-floating) that causes coloration of water bodies is called algal bloom.

Question 7.
Write the name of the organism that is referred to as the ‘Terror of Bengal’.
Or
Why is Eichhomia crassipes nicknamed as* ‘Terror of Bengal’?
Answer:
Eichhornia crassipes is nicknamed as ‘Terror of Bengal’ because it grows very fast in the water body and depletes the dissolved oxygen. Hence, disturbing the ecosystem dynamics of the water body.

Question 8.
What is the raw material for polyblend? [NCERT Exemplar]
Answer:
Polyblends are natural man-made fibres, made by the mixture of two or more polymers, especially plastic waste products.

Question 9.
Mention the effect of UV rays on DNA and proteins in living organisms.
Answer:
The high energy of UV rays breaks the chemical bonds within DNA and protein molecules.

Question 10.
Write the unit used for measuring ozone thickness.
Answer:
Dobson unit.

Question 11.
State the purpose of signing the Montreal Protocol.
Answer:
Montreal Protocol was signed at Montreal, in 1987 to curb the emission of ozone-depleting substances.

PSEB 12th Class Biology Important Questions Chapter 16 Environmental Issues

Question 12.
What is reforestation? [NCERT Exemplar]
Answer:
Reforestation is the process of restoring a forest that once existed but was removed at some point of time in the past.

Short answer type questions

Question 1.
It is a common practice to plant trees and shrubs near the boundary walls of buildings. What purpose do they serve?
[NCERT Exemplar]
Answer:
The practice of growing and maintaining trees and shrubs near the boundary wall of residential or official buildings is a common practice. This is because it acts as a barrier for sound and check noise pollution. This green belt of trees and shrubs also acts as an effective measure to check primary air pollutants like dust, fly ash, etc.

Question 2.
‘Determination of Biological Oxygen Demand (BOD) can help in suggesting the quality of a water body. Explain.
Answer:
Biochemical Oxygen Demand (BOD) is the amount of dissolved oxygen required for microbial breakdown of biodegradable organic matter. Aerobic organisms use a lot of oxygen and as a result, there is a sharp decline in Dissolved Oxygen (DO) in the water body. This Can cause death of fishes and other aquatic species. The relationship between BOD and sewage can be understood from the graph given below :
PSEB 12th Class Biology Important Questions Chapter 16 Environmental Issues 1
Determination of BOD is thus an important parameter in suggesting the quality of a water body. The presence of more organic waste increases the microbial activity thus decreasing the DO. BOD is higher in polluted water and lesser in clean water.

Question 3.
Explain the process of secondary treatment given to the primary effluent up to the point it shows a significant change in the level of biological oxygen demand (BOD) in it.
Answer:
The primary effluent is passed into large aeration tanks where it is constantly agitated. Air is pumped into it mechanically. This allows vigorous growth of useful aerobic microbes into floes. These microbes consume the major part of organic matter in the effluent (this significantly reduces the BOD of the effluent).

PSEB 12th Class Biology Important Questions Chapter 16 Environmental Issues

Question 4.
Excessive nutrients in a freshwater body cause fish mortality. Give two reasons.
Answer:
Excessive nutrients in the water body result in the excessive and rapid growth of plants and animals, resulting in formation of increased organic matter, death of plants and animals increased the organic matter at the bottom which decomposes, increased BOD deplete the oxygen content, resulting in fish mortality.

Question 5.
Is it true that, if the dissolved oxygen level drops to zero, the water will become septic? Give an example which could lower the dissolved oxygen content of an aquatic body. [NCERT Exemplar]
Answer:
Yes, it is true. In case of zero level of Dissolved Oxygen (DO), the water becomes septic. Organic pollutants like fertilizer in aquatic bodies are responsible for lowering (up to zero) the level of dissolved oxygen.

Question 6.
Explain giving reasons why thermal power plants are not considered eco-friendly?
Answer:
Thermal power plants release particulate and gaseous pollutants in the environment. Inhalation of these pollutants can cause breathing or respiratory symptoms^irritation, inflammation, damage to lungs, and even premature death.

Question 7.
Blend of polyblend and bitumen, when used, helps to increase road life by a factor of three. What is the reason? [NCERT Exemplar]
Answer:
Polyblend is a fine powder of recycled modified plastic. The binding property of plastic makes the road last longer besides giving added strength to withstand more loads. This is because: plastic increases the melting point of the bitumen which would prevent it from melting in India’s hot and extremely humid climate, where temperature frequently crosses 50°C. rainwater will not seep through because of the plastic in the blend.

Question 8.
What is the main idea behind ‘Joint Forest Management Concept’ introduced by the Government of India?
[NCERT Exemplar]
Answer:
The main idea behind joint forest management concept introduced by the Government of India was involving the local communities in forest conservation. This concept was adopted considering the extraordinary courage and dedication the local people showed in protecting the wildlife through the movements like Bishnoi’s movement in Jodhpur and Chipko Movement in Garhwal Himalayas.

Long answer type questions

Question 1.
Explain giving reasons the cause of appearance of peaks ‘a’ and ‘b’ in the graph shown below:
img
Answer:
‘a’-High BOD due to sewage discharge.
‘b’-Increase in dissolved oxygen due to sewage decomposition. Micro-organisms involved in biodegradation of organic matter consume a lot of oxygen, therefore, there is a sharp decline in dissolved oxygen. When the sewage is completely degraded, oxygen concentration again increases.

Question 2.
Why is the concentration of toxins found to be more in the organisms occupying the highest trophic level in the food chain in a polluted* water body? Explain with the help of a suitable example.
Answer:
The concentration of toxic materials like heavy metals and pesticides increase at each trophic level of a food chain and is more in organisms of highest trophic level due to their accumulation at each trophic level For example, when DDT was used to control mosquitoes in a lake of USA, 800 times more DDT was found in the phytoplanktons than in the water of the lake. Zooplanktons had about 13 times more DDT than phytoplanktons. It was also observed that the fishes population had 9-40 times more DDT than zooplanktons and fish-eating birds had 25 times more DDT than fish.

Question 3.
Refrigerants arc considered to be a necessity in modem living but are said to be responsible for ozone holes detected in Antarctica. Justify.
Answer:
The widely used refrigerants are CFCs or. chlorofluorocarbons. CFCs discharged in the lower part of atmosphere move upwards to the stratosphere. Here, the UV rays act on them and release chlorine atoms. These free chlorine atoms react with ozone to release molecular oxygen. Chlorine atoms are not consumed in this reaction and hence, these continuously degrade ozone and have resulted in ozone holes.

PSEB 12th Class Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants

Punjab State Board PSEB 12th Class Biology Book Solutions Chapter 2 Sexual Reproduction in Flowering Plants Textbook Exercise Questions and Answers.

PSEB Solutions for Class 12 Biology Chapter 2 Sexual Reproduction in Flowering Plants

PSEB 12th Class Biology Guide Sexual Reproduction in Flowering Plants Textbook Questions and Answers

Question 1.
Name the parts of an angiosperm flower in which development of male and female gametophyte take place.
Answer:
The male gametophyte or the pollen grain develops inside the pollen chamber of the anther, whereas the female gametophyte (also known as the embryo sac) develops inside the nucellus of the ovule from the functional megaspore.

Question 2.
Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.
Answer:

Microsporogenesis Megasporogenesis
1. It is the process of the formation of microspore tetrads from a microspore mother cell through meiosis. It is the process of the formation of the four megaspores from a megaspore mother cell in the region of the nucellus through meiosis.
2. It occurs inside the pollen sac of the anther. It occurs inside the ovule.

(b) Both events (microsporogenesis and megasporogenesis) involve the process of meiosis or reduction division which results in the formation of haploid gametes from the microspore and megaspore mother cells.

(c) Microsporogenesis results in the formation of haploid microspores from a diploid microspore mother cell. On the other hand, megasporogenesis results in the formation of haploid megaspores from a diploid megaspore mother cell.

PSEB 12th Class Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants

Question 3.
Arrange the following terms in the correct developmental sequence:
Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
Answer:
The correct developmental sequence is as follows:
Sporogenous tissue, pollen mother cell, microspore tetrad, pollen grain, male gametes.
During the development of microsporangium, each cell of the sporogenous tissue acts as a pollen mother cell and gives rise to a microspore tetrad, containing four haploid microspores by the process of meiosis (microsporogenesis). As the anther matures, these microspores dissociate and develop into pollen grains. The pollen grains mature and give rise to male gametes.

Question 4.
With a neat, labelled diagram, describe the parts of a typical ’ angiosperm ovule.
Answer:
An ovule is a female megasporangium where the formation of megaspores takes place.
PSEB 12th Class Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants 1

The various parts of a typical angiospermic ovule are as follows :
1. Funiculus: It is a stalk-like structure which represents the point of attachment of the ovule to the placenta of the ovary.

2. Hilum: It is the point where the body of the ovule is attached to the funiculus.

3. Integuments: They are the outer layers surrounding the ovule that provide protection to the developing embryo.

4. Micropyle: It is a narrow pore formed by the projection of integuments. It marks the point where the pollen tube enters the ovule at the time of fertilisation.

5. Nucellus: It is a mass of the parenchymatous tissue surrounded by the integuments from the outside. The nucellus provides nutrition to the developing embryo. The embryo sac is located inside the nucellus.

6. Chalaza: It is the based swollen part of the nucellus from where the integuments originate.

Question 5.
What is meant by monosporic development of female gametophyte?
Answer:
The female gametophyte or the embryo sac develops from a single functional megaspore. This is known as monosporic development of the female gametophyte. In most flowering plants, a single megaspore mother cell present at the micropylar pole of the nucellus region of the ovule undergoes meiosis to produce four haploid megaspores. Later, out of these four megaspores, only one functional megaspoxe develops into the female gametophyte, while the remaining three degenerate.

PSEB 12th Class Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants

Question 6.
With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
Answer:
Structure of the mature embryo sac
PSEB 12th Class Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants 2
The female gametophyte (embryo sac) develops from a single functional megaspore. This megaspore undergoes three successive mitotic divisions to form eight nucleate embryo sacs.
The first mitotic division in the megaspore forms two nuclei. One nucleus moves towards the micropylar end while the other nucleus moves towards the chalazal end. Then, these nuclei divide at their respective ends and re-divide to form eight nucleate stages. As a result, there are four nuclei each at both the ends i.e., at the micropylar and the chalazal end in the embryo sac. At the micropylar end, out of the four nuclei only three differentiate into two synergids and one egg cell. Together they are known as the egg apparatus.

Similarly, at the chalazal end, three out of four nuclei differentiates as antipodal cells. The remaining two cells (of the micropylar and the chalazal end) move towards the centre and are known as the polar nuclei, which are situated in a large central cell. Hence, at maturity, the female gametophyte appears as a 7-celled structure, though it has 8-nucleate.

Question 7.
What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
Answer:
There are two types of flowers present in plants namely Oxalis and Viola – chasmogamous and cleistogamous flowers. Chasmogamous flowers have exposed anthers and stigmata similar to the flowers of other species.

Cross-pollination cannot occur in cleistogamous flowers. This is because cleistogamous flowers never open at all. Also, the anther and the stigma lie close to each other in these flowers. Hence, only self-pollination is possible in these flowers.

Question 8.
Mention two strategies evolved to prevent self-pollination in flowers.
Answer:
Self-pollination involves the transfer of pollen from the stamen to the pistil of the same flower. Two strategies that have evolved to prevent self-pollination in flowers are given on next page:
1. Self-incompatibility: In certain plants, the stigma of the flower has the capability to prevent the germination of pollen grains and hence, prevent the growth of the pollen tube. It is a genetic mechanism to prevent self-pollination called self-incompatibility. Incompatibility may be between individuals of the same species or between individuals of different species. Thus, incompatibility prevents breeding.

2. Protandry: In some plants, the gynoecium matures before the androecium or vice-versa. This phenomenon is known as protogyny or protandry respectively. This prevents the pollen from coming in contact with the stigma of the same flower.

PSEB 12th Class Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants

Question 9.
What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Answer:
Self-incompatibility is a genetic mechanism in angiosperms that prevents self-pollination. It develops genetic incompatibility between ‘ individuals of the same species or between individuals of different
species.

The plants which exhibit this phenomenon have the ability to prevent germination of pollen grains and thus, prevent the growth of the pollen tube on the stigma of the flower. This prevents the fusion of the gametes along with the development of the embryo. As a result, no seed formation takes place.

Question 10.
What is bagging technique? How is it useful in a plant breeding programme?
Answer:
Various artificial hybridisation techniques (under various crop improvement programmes) involve the removal of the anther from bisexual flowers without affecting the female reproductive part (pistil) through the process of emasculation. Then, these emasculated flowers are wrapped in bags to prevent pollination by unwanted pollen grains. This process is called bagging.

This technique is an important part of the plant breeding programme as
it ensures that pollen grains of only desirable plants are used for fertilisation of the stigma to develop the desired plant variety.

Question 11.
What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Answer:
Triple fusion is the fusion of the male gamete with two polar nuclei inside the embryo sac of the angiosperm. This process of fusion takes place inside the embryo sac.

When pollen grains fall on the stigma, they germinate and give rise to the pollen tube that passes through the style and enters into the ovule. After this, the pollen tube enters one of synergids and releases two male gametes there.

Out of the two male gametes, one gamete fuses with the nucleus of the egg cell and forms the zygote (syngamy). The other male gamete fuses with the two polar nuclei present in the central cell to form a triploid primary endosperm nucleus. Since this process involves the fusion of three haploid nuclei, it is known as triple fusion. It results in the formation of the endosperm.
One male gamete nucleus and two polar nuclei are involved in this process.

Question 12.
Why do you think the zygote is dormant for sometime in a fertilised ovule?
Answer:
The zygote is formed by the fusion of the male gamete with the nucleus of the egg cell. The zygote remains dormant for some time and waits for the endosperm to form, which develops from the primary endosperm cell resulting from triple fusion. The endosperm provides food for the growing embryo and after the formation of the endosperm, further development of the embryo from the zygote starts.

PSEB 12th Class Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants

Question 13.
Differentiate between:
(a) hypocotyl and epicotyl;
(b) coleoptile and coleorrhiza;
(c) integument and testa;
(d) perisperm and pericarp.
Answer:
(a)

Hypocotyl Epicotyl
1. The portion of the embryonal axis which lies below the cotyledon in a dicot embryo is known as the hypocotyl. The portion of the embryonal axis which lies above the cotyledon in a dicot embryo is known as the epicotyl.
2. It terminates with the radicle. It terminates with the plumule.

(b)

Coleoptile Coleorrhiza
It is a conical protective sheath that encloses the plumule in a monocot seed. It is an undifferentiated sheath that encloses the radicle and the root cap in a monocot seed.

(c)

Integument Testa
It is the outermost covering of an ovule. It provides protection to it. It is the outermost covering of a seed. It provides protection to the young embryo.

(d) Perisperm

Perisperm Pericarp
It is the residual nucellus which persists. It is present in some seeds such as beet and black pepper. It is the ripened wall of a fruit, which develops from the wall of an ovary.

PSEB 12th Class Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants

Question 14.
Why is apple called a false fruit? Which part(s) of the flower forms the fruit?
Answer:
Fruits derived from the ovary and other accessory floral parts are called false fruits. On the contrary, true fruits are those fruits which develop from the ovary, but do not consist of the thalamus or any other floral part. In an apple, the fleshy receptacle forms the main edible part. Hence, it is a false fruit.

Question 15.
What is meant by emasculation? When and why does a plant breeder employ this technique?
Answer:
Emasculation is the process of removing anthers from bisexual flowers without affecting the female reproductive part (pistil), which is used in various plant hybridisation techniques.

Emasculation is performed by plant breeders in bisexual flowers to obtain the desired variety of a plant by crossing a particular plant with the desired pollen grain. To remove the anthers, the flowers are f covered with a bag before they open. This ensures that the flower is pollinated by pollen grains obtained from desirable varieties only. Later, the mature, viable, and stored pollen grains are dusted on the
bagged stigma by breeders to allow artificial pollination to take place and obtain the desired plant variety.

Question 16.
If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
Answer:
Parthenocarpy is the process of developing fruits without involving the process of fertilisation or seed formation. Therefore, the seedless varieties of economically important fruits such as orange, lemon, water melon etc. are produced using this technique. This technique involves inducing fruit formation by the application of plant growth hormones such as auxins.

Question 17.
Explain the role of tapetum in the formation of pollen-grain wall.
Answer:
Tapetum is the innermost layer of the microsporangium. It provides nourishment to the developing pollen grains. During microsporogenesis, the cells of tapetum produce various enzymes, hormones, amino acids, and other nutritious material required for the development of pollen grains. It also produces the exine layer of the pollen grains, which is composed of the sporopollenin.

PSEB 12th Class Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants

Question 18.
What is apomixis and what is its importance?
Answer:
Apomixis is the mechanism of seed production without involving the process of meiosis and syngamy. It plays an important role in hybrid seed production. The method of producing hybrid seeds by cultivation is very expensive for farmers. Also, by sowing hybrid seeds, it is difficult to maintain hybrid characters as characters segregate during meiosis. Apomixis prevents the loss of specific characters in the hybrid. Also, it is a cost-effective method for producing seeds.

PSEB 12th Class Biology Solutions Chapter 16 Environmental Issues

Punjab State Board PSEB 12th Class Biology Book Solutions Chapter 16 Environmental Issues Textbook Exercise Questions and Answers.

PSEB Solutions for Class 12 Biology Chapter 16 Environmental Issues

PSEB 12th Class Biology Guide Environmental Issues Textbook Questions and Answers

Question 1.
What are the various constituents of domestic sewage? Discuss the effects of sewage discharge on a river.
Answer:
Domestic sewage is the waste originating from the kitchen, toilet, laundry, and other sources. It contains impurities such as suspended solid (sand, salt, clay), colloidal, material (faecal matter, bacteria, plastic and cloth fibre), dissolved materials (nitrate, phosphate, calcium, sodium, ammonia), and disease-causing microbes. When organic wastes from the sewage enter the water bodies, it serves as a food source for micro-organisms such as algae and bacteria. As a result, the population of these micro-organisms in the water body increases.

Here, they utilise most of the dissolved oxygen for their metabolism. This results in an increase in the levels of Biological oxygen demand (BOD) in river water and results in the death of aquatic organisms. Also, the nutrients in the water lead to the growth of planktonic algal, causing algal bloom. This causes deterioration of water quality and fish mortality.

Question 2.
List all the wastes that you generate, at home, school or during your trips to other places. Could you very easily reduce the generation of these wastes? Which would be difficult or rather impossible to reduce?
Answer:
Wastes generated at home include plastic bags, paper napkins, toiletries, kitchen wastes (such as peelings of vegetables and fruits, tea leaves), domestic sewage, glass, etc.

Wastes generated at schools include waste paper, plastics, vegetable and fruit peels, food wrappings, sewage etc.
Wastes generated at trips or picnics include plastic, paper, vegetable and fruit peels, disposable cups, plates, spoons etc.

Yes, wastes can be easily reduced by the judicious use of the above materials. Wastage of paper can be minimised by writing on both sides of the paper and by using recycled paper. Plastic and glass waste can also be reduced by recycling and re-using.

Also, substituting plastic bags with biodegradable jute bags can reduce wastes generated at home, school, or during trips. Domestic sewage can be reduced by optimising the use of water while bathing, cooking, and other household activities. Non-biodegradable wastes such as plastic, metal, broken glass, etc. are difficult to decompose because micro-organisms do riot have the ability to decompose them.

Question 3.
Discuss the causes and effects of global warming. What measures need to be taken to control global warming?
Answer:
Global warming is defined as an increase in the average temperature of the Earth’s surface. Causes of Global Warming: Global warming occurs as a result of the increased concentration of greenhouse gases in the atmosphere. Greenhouse gases include carbon dioxide, methane, and water vapour. These gases trap solar radiations released back by the Earth. This helps in keeping our planet warm and thus, helps in human survival. However, an increase in the amount of greenhouse gases can lead to an excessive increase in the Earth’s temperature, leading to global warming. Global warming is a result of industrialisation, burning of fossil fuels, and deforestation.

Effects of Global Warming: It has been observed that in the past three decades, the average temperature of the Earth has increased by 0.6°C. As a result, the natural water cycle has been disturbed resulting in changes in the pattern of rainfall. It also changes the amount of rainwater. Also, it results in the melting of Polar ice caps and mountain glaciers, which has caused a rise in the sea level, leading to the inundation of coastal regions.

Control Measures for Preventing Global Warming:

  • Reducing the use of fossil fuels
  • Use of bio-fuels
  • Improving energy efficiency
  • Use of renewable source of energy such as CNG etc.
  • Reforestation.
  • Recycling of materials

PSEB 12th Class Biology Solutions Chapter 16 Environmental Issues

Question 4.
Match the items given in column A and B:

Column A Column B
(a) Catalytic converter (i) Particulate matter
(b) Electrostatic precipitator (ii) Carbon monoxide and nitrogen oxides
(c) Earmuffs (iii) High noise level
(d) Landfills (iv) Solid wastes

Answer:

Column A Column B
(a) Catalytic converter (ii) Carbon monoxide and nitrogen oxides
(b) Electrostatic precipitator (i) Particulate matter
(c) Earmuffs (iii) High noise level
(d) Landfills (iv) Solid wastes

Question 5.
Write critical notes on the following:
(a) Eutrophication
(b) Biological magnification
(c) Groundwater depletion and ways for its replenishment
Answer:
(a) Eutrophication:
It is the natural ageing process of a lake caused due to nutrient enrichment. It is brought down by the runoff of nutrients such as animal wastes, fertilisers, and sewage from land which leads to an increased fertility of the lake. As a result, it causes a tremendous increase in the primary productivity of the ecosystem. This leads to an increased growth of algae, resulting, into, algal blooms. Later, the decomposition of these algae depletes the supply of oxygen, leading to the death of other aquatic animal life.

(b) Biological Magnification: Unknowingly some harmful chemicals enter our bodies through the food chain. We use several pesticides and other chemicals to protect our crops from diseases and pests. These chemicals are either washed down into the soil or into the water bodies. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies, these are taken up by aquatic plants and animals. This is one of the ways in which they enter the food chain. As these chemicals are not degradable, these get accumulated progressively at each trophic level. As human beings occupy the topmost level in any food chain, the maximum concentration of these chemicals get accumulated in our bodies. This phenomenon is known as biological magnification.

(c) Ground Water Depletion and Ways for its Replenishment: The level of groundwater has decreased in the recent years. The source of water supply is rapidly diminishing each year because of an increase in the population and water pollution. To meet the demand of water, water is withdrawn from water bodies such as ponds, rivers etc. As a result, the source of groundwater is depleting.

This is because the amount of groundwater being drawn for human use is more than the amount replaced by rainfall. Lack of vegetation cover also results in very small amounts of water seeping through the ground. An increase in water pollution is another factor that has reduced the availability of groundwater.

Measures for Replenishing Ground Water:

  • Preventing over-exploitation of groundwater
  • Optimising water use and reducing water demand
  • Rainwater harvesting
  • Preventing deforestation and plantation of more trees.

Question 6.
Why does ozone hole form over Antarctica? How will enhanced ultraviolet radiation affect us?
Answer:
The ozone hole is more prominent over the region of Antarctica. It is formed due to an increased concentration of chlorine in the atmosphere. Chlorine is mainly released from chlorofluorocarbons (CFC’s) widely used as refrigerants. The CFC’s magnate from the troposphere to the stratosphere, where they release chlorine atoms by the action of UV rays on them.

The release of Chlorine atoms causes the conversion of ozone into molecular oxygen. One atom of chlorine can destroy around 10,000 molecules of ozone and causes ozone depletion. The formation of the ozone hole will result in an increased concentration of UV – B radiations on the Earth’s surface. UV -B damages DNA and activates the process of skin ageing. It also causes skin darkening and skin cancer. High levels of UV -B cause corneal cataracts in human beings.

PSEB 12th Class Biology Solutions Chapter 16 Environmental Issues

Question 7.
Discuss the role of women and communities in protection and conservation of forests.
Answer:
Women and communities have played a major role in environmental conservation movements.
(i) Case Study of the Bishnoi Community: The Bishnoi community in Rajasthan strictly believes in the concept of living peacefully with nature. In 1731, the king of Jodhpur ordered his ministers to arrange wood for the construction of his new palace. For this purpose, the minister and 1116 workers went to Bishnoi village.

There, a Bishnoi woman called Amrita Devi along with her daughter and hundreds of other Bishnois showed the courage to step forward and stop them from cutting trees. They embraced the trees and lost their lives at the hands of soldiers of the king. This resistance by the people of the village forced the king to give up the idea of cutting trees.

(ii) Chipko Movement: The Chipko movement was started in 1974 in the Garhwal region of the Himalayas. In this movement, the women from the village stopped the contractors from cutting forest trees by embracing them.

Question 8.
What measures, as an individual, would you take to reduce environmental pollution?
Answer:
The following initiatives can be taken to prevent environmental pollution:
Measures for Preventing Air Pollution

  • Planting more trees
  • Use of clean and renewable energy sources such as CNG and bio-fuels
  • Reducing the use of fossil fuels
  • Use of catalytic converters in automobiles

Measures for Preventing Water Pollution:

  • Optimising the use of water
  • Using kitchen wastewater in gardening and other household purposes

Measures for Controlling Noise Pollution:

  • Avoid burning crackers on Diwali
  • Plantation of more trees

Measures for Decreasing Solid Waste Generation:

  • Segregation of waste
  • Recycling and reuse of plastic and paper
  • Composting of biodegradable kitchen waste
  • Reducing the use of plastics.

Question 9.
Discuss briefly the following:
(a) Radioactive wastes
(b) Defunct ships and e-wastes
(c) Municipal solid Wastes
Answer:
(a) Radioactive Wastes: Radioactive wastes are generated during the process of generating nuclear energy from radioactive materials. Nuclear waste is rich in radioactive materials that generate large quantities of ionising radiations such as gamma rays. These rays cause mutation in organisms, which often results in skin cancer. At high dosage, these rays can be lethal.

Safe disposal of radioactive wastes is a big challenge. It is recommended that nuclear wastes should be stored after pre-treatment in suitable shielded containers, which should then be buried in rocks.

(b) Defunct Ships and E-wastes: Defunct ships are dead ships that are no longer in use. Such ships are broken down for scrap metal in countries such as India and Pakistan. These ships are a source of various toxicants such as asbestos, lead, mercury etc. Thus, they contribute to solid* wastes that are hazardous to health.

E-waste or electronic wastes generally include electronic goods such as computers etc. Such wastes are rich in metals such as copper, iron, silicon, gold etc. These metals are highly toxic and pose serious health hazards. People of developing countries are involved in the recycling process of these metals and therefore, get exposed to toxic substances present in these wastes.

(c) Municipal Solid Wastes: Municipal solid wastes are generated from schools, offices, homes, and stores. It is generally rich in glass, metal, paper waste, food, rubber, leather, and textiles. The open dumps of municipal wastes serve as a breeding ground for flies, mosquitoes, and other disease-causing microbes. Hence, it is necessary to dispose of municipal solid waste properly to prevent the spreading of diseases. Sanitary landfills and incineration are the methods for the safe disposal of solid wastes.

Question 10.
What initiatives were taken for reducing vehicular air pollution in Delhi? Has air quality improved in Delhi?
Answer:
Delhi has been categorised as the fourth most polluted city of the world in a list of 41 cities. Burning of fossil fuels has added to the pollution of air in Delhi.
Various steps have been taken to improve the quality of air in Delhi.

(a) Introduction of CNG (Compressed Natural Gas): By the order of the supreme court of India, CNG-powered vehicles were introduced at the end of year 2006 to reduce the levels of pollution in Delhi. CNG is a clean fuel that produces very little unburnt particles.
(b) Phasing out of old vehicles
(c) Use of unleaded petrol
(d) Use of low-sulphur petrol and diesel
(e) Use of catalytic converters
(f) Application of stringent pollution-level norms for vehicles
(g) Implementation of Bharat stage I, which is equivalent to euro II norms in vehicles of major Indian cities.

The introduction of CNG-powered vehicles has improved Delhi’s air quality, which has lead to a substantial fall in the level of CO2 and SO2. However, the problem of suspended particulate matter (SPM) and respiratory suspended particulate matter,(RSPM) still persists.

PSEB 12th Class Biology Solutions Chapter 16 Environmental Issues

Question 11.
Discuss briefly the following:
(a) Greenhouse gases
(b) Catalytic converter
(c) Ultraviolet B
Answer:
(a) Greenhouse Gases: The greenhouse effect refers to an overall increase in the average temperature of the Earth due to the presence of greenhouse gases. Greenhouse gases mainly consist of carbon dioxide, methane, and water vapour. When solar radiations reach the Earth, some of these radiations are absorbed.

These absorbed radiations are Released back into the atmosphere. These radiations are trapped by the greenhouse gases present in the atmosphere. This helps in keeping our planet warm and thus, helps in human survival.
However, an increase in the amount of greenhouse gases can lead to an excessive increase in the Earth’s temperature, thereby causing global warming.

(b) Catalytic Converter: Catalytic converters are devices fitted in automobiles to reduce automobile or vehicle pollution. These devices contain expensive metals such as platinum, palladium, and rhodium that act as catalysts.
As the vehicular discharge -passes through the catalytic converter, the unburnt hydrocarbons present in it get converted into carbon dioxide and water. Carbon monoxide and nitric oxide released by catalytic converters are converted into carbon dioxide and nitrogen gas respectively.

(c) Ultraviolet B: Ultraviolet-B is an electromagnetic radiation which has a shorter wavelength than visible light.
It is a harmful radiation that comes from sunlight and penetrates through the ozone hole onto the Earth’s surface.
It induces many health hazards in humans. UV -B damages DNA and activates the process of skin ageing. It also causes skin darkening and skin cancer. High levels of UV -B cause corneal cataracts in human beings.