Punjab State Board PSEB 11th Class Biology Book Solutions Chapter 12 Mineral Nutrition Textbook Exercise Questions and Answers.
PSEB Solutions for Class 11 Biology Chapter 12 Mineral Nutrition
PSEB 11th Class Biology Guide Mineral Nutrition Textbook Questions and Answers
‘All elements that are present in a plant need not be essential to its survival’. Comment.
All elements that are present in a plant need not be essential to its survival because they do not directly involved in the composition of their body. However, if the concentration of micronutrients such as Fe, Mn, Cu, Zn, Cl, etc., rise above their critical values, they appear to be toxic for the plant.
Why is purification of water and nutrient salts so important in studies involving mineral nutrition using hydroponics?
It is to know the essentiality of a mineral element in the life cycle of a plant. Further, it helps in improving the deficiency symptoms of the plants. The nutrient solution must be adequetly aerated to obtain the optimal growth.
Explain with examples : macronutrients, micronutrients, beneficial nutrients, toxic elements and essential elements.
(i) Macronutrients: These are generally present in plant tissues in large amount (in excess 10 m mole kg’1 of dry matter). The macronutrients include carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, potassium, calcium and magnesium.
(ii) Micronutrients: Micronutrients or trace elements, are needed in very small amount (less than 10m mole kg~: of dry matter). These include iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel.
(iii) Beneficial Nutrients: The elements which are not essential for plants, but their presence are beneficial for the growth and development. Such, elements are called beneficial elements.
(iv) Toxic Elements: Any mineral ion concentration in tissues, that reduces the dry weight of tissues by about 10 % is considered toxic. For example, Mn inhibit the absorption of other elements.
(v) Essential Elements: The macronutrients including carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, potassium, calcium and magnesium, which are require directly for the growth and metabolism of the plants and whose deficiency produces certain symptoms in the plants are known as essential elements.
Name at least five different deficiency symptoms in plants. Describe them and correlate them with the concerned mineral deficiency.
The kind of deficiency symptoms shown in plants include chlorosis, necrosis, stunted plant growth, premature fall of leaves and buds, and inhibition of cell division.
- Chlorosis is the loss of chlorophyll leading to yellowing in leaves. This symptom is caused by the deficiency of elements N, K, Mg, S, Fe, Mn, Zn and Mo.
- Necrosis or death of tissue, particularly leaf tissue, is due to the deficiency of Ca, Mg, Cu, K.
- Lack or low level of N, K, S, Mo causes an inhibition of cell division.
- Some elements like N, S, Mo delay flowering if their concentration in plants is low.
If a plant shows a symptom which could develop due to deficiency of more than one nutrient, how would you find out experimentally, the real deficient mineral element?
Every element shows certain characteristic deficiency symptoms in the plants. The deficiency of any one element cannot be met by supplying some other element. So, by absorbing the type of deficiency symptom, we can determine the real deficient mineral element.
Why is that in certain plants deficiency symptoms appear first in younger parts of the plant, while in others they do so in mature organs?
For elements that are actively mobilised within the plants and exported to young developing tissues, the deficiency symptoms tend to appear first in the older tissues. For example, the deficiency symptoms of nitrogen, potassium and magnesium are visible first in the senescent leaves. In the older leaves, biomolecules containing these elements are broken down, making these elements available for mobilising to younger leaves.
The deficiency symptoms tend to appear first in the young tissues, whenever the elements are relatively immobile and are not transported out of the mature organs. For example, elements like sulphur and calcium are a part of the structural component of the cell and hence are not easily released.
How are the minerals absorbed by the plants?
Mechanism of Absorption of Minerals: The process of absorption can occur into following two main phases :
(i) In the first phase, an initial rapid uptake of ions into the ‘free space’ or ‘outer space’ of cells the apoplast is passive.
(ii) In the second phase of uptake, the ions are taken in slowly into the ‘inner space’ the symplast of the cells. The passive movement of ions into the apoplast usually occurs through ion-channels, the trans-membrane proteins that function as selective pores. On the other hand, the entry or exit of ions to and from the symplast requires the expenditure of metabolic energies. The movement of ions is usually called the inward movement into the cells is influx and the outward movement, efflux.
What are the conditions necessary for fixation of atmospheric nitrogen by Rhizobium ? What is their role in Nitrogen-fixation?
The first essential condition for nitrogen fixation is legume-bacteria relationship. Rhizobium bacteria cause nodule formation for this association. The enzyme nitrogenase is highly sensitive to the molecular oxygen. The nodules protect these enzymes by an oxygen scavenger called leghaerrloglobin.
Rhizobium bacteria are free living in soil. They are symbionts, which can fix atmospheric nitrogen for plants.
What are the steps involved in formation of a root nodule?
Steps in Nodule Formation: Nodule formation involves a sequence of multiple interactions between Rhizobium and roots of the host plant. Principal stages in the nodule formation are given below:
- Rhizobia multiply and colonise the surroundings of roots and get attached to epidermal and root hair cells.
- The root-hairs curl and the bacteria invade the root-hair.
- An infection thread is produced carrying the bacteria into the cortex of the root, where they initiate the nodule formation in the cortex of the root. Then the bacteria are released from the thread into the cells which leads to the differentiation of specialised nitrogen fixing cells.
- The nodule thus formed, establishes a direct vascular connection with the host for exchange of nutrients.
Which of the following statements are true? If false, correct them:
(a) Boron deficiency leads to stout axis.
(b) Every mineral element that is present in a cell is needed by the cell.
(c) Nitrogen as a nutrient element, is highly immobile in the plants.
(d) It is very easy to establish the essentiality of micronutrients because they are required only in trace quantities.
(b) All the mineral elements present in a cell are not needed by the cell. For example, plants growing near radioactive mining sites tend to accumulate large amounts of radioactive compounds. These compounds are not essential for the plants.
(c) Nitrogen as a nutrient element is highly mobile in plants. It can be mobilised from the old and mature parts of a plant to its younger parts.