PSEB 9th Class Science Notes Chapter 5 The Fundamental Unit of Life

This PSEB 9th Class Science Notes Chapter 5 The Fundamental Unit of Life will help you in revision during exams.

PSEB 9th Class Science Notes Chapter 5 The Fundamental Unit of Life

→ All living organisms around us are complex structural compartments called cells.

→ A.V. Leeuwenhoek (1674) first studied the living cell. He examined bacteria, sperms, and erythrocytes (RBC).

→ The biosphere is the highest level of organisation of living organisms.

→ Level of organisation is Atoms → Elements → Cell → Tissue → Organ → Organ System → Living Organisms.

→ Robert Hooke (1665) examined dead cells,

→ Rober Brown (1831) observed the nucleus in the centre of cell.

PSEB 9th Class Science Notes Chapter 5 The Fundamental Unit of Life

→ Huxley regarded protoplasm as the ‘Physical basis of life’.

→ The cytoplasm is the fluid content of cells present between the nucleus and plasma membrane.

→ It contains metabolites and organelles.

→ Organelles are special components of cells performing specific functions.

→ Cells are of two types i.e. prokaryotic cell and eukaryotic cell.

→ Organisms may be single-celled e.g. Amoeba, CMamydomonas (an algal plant), Paramecium or they are multicellular.

→ Higher plants and animals are made up of a large number of cells.

→ A true nucleus is present, It is generally single-spherical and central in position.

→ The nucleus is separated from the cytoplasm by a double-layered membrane called nuclear membrane. It controls the functioning of cells.

→ The nucleus contains chromosomes composed of DNA and protein.

→ A functional segment of DNA is called a gene.

→ All living organisms start their life cycle from a single cell.

PSEB 9th Class Science Notes Chapter 5 The Fundamental Unit of Life

→ Cell size varies from 0.2 – 0.5 micron to 30 micron (one micron = 1/1000 mm ). Nerve cells may be as long as a few metres.

→ A plant cell is bounded by a protective cell wall.

→ A plasma membrane is a living membrane.

→ Mitochondria are rod-shaped, double-membranous, light-microscopic, eukaryotic structures. Inner membranes have cristae and exosomes.

→ Functions: These act as powerhouses or ATP mills as they are sites for cellular respiration and release energy.

→ The centrosome is an animal structure and is formed of two microtubular centrioles, each being formed of 9 triplet microtubules showing a 9 + 0 arrangement.

→ Function: These help in cell division.

→ Basal bodies give rise to cilia or flagella centrioles form.

→ Contractile vacuoles are present in freshwater protozoans.

→ The cell is a Latin word for a little room’.

→ The electron microscope was discovered in 1942.

→ Water obeys the laws of diffusion.

PSEB 9th Class Science Notes Chapter 5 The Fundamental Unit of Life

→ The nucleus plays a central role in cellular reproduction, the process by which a cell divides and forms two new cells.

→ Plastids are the largest-sized eukaryotic structures of plant cells. These are of three types: Leucoplasts (colourless and store the food).

→ The primary function of the leucoplast is storage. Chloroplasts (green coloured and are sites of photosynthesis, so-called kitchens of cells)

→ Each chloroplast is a double-membranous structure having grana in its inner chamber.

→ Each granum is formed of many chlorophyll-containing thylakoids present in stacks.

→ Functions: Chloroplasts are sites for photosynthesis.

→ Chromoplasts (coloured and help in pollination of dowers and dispersal of seeds and fruits).

→ The endoplasmic reticulum is an electron-microscopic interconnected network of cisternae, vacuoles, and tubules.

→ It is of two types: RER (cisternae are studded with ribosomes and involved in protein synthesis) and SER (tubules are without ribosomes).

→ Functions:

  • It is a passageway for intracellular and intercellular transport of materials.
  • It gives internal support to the cell.
  • SER is involved in the synthesis of lipids and steroids.
  • RER is concerned with protein synthesis.

PSEB 9th Class Science Notes Chapter 5 The Fundamental Unit of Life

→ Lysosomes are electron-microscopic single membrane-bound vesicular structures of animal cells and contain hydrolytic enzymes.

→ Functions:

  • These are centres of intracellular digestion and act as both digestive bags and suicidal bags.
  • They destroy foreign substances.
  • They remove cellular debris.

→ Living organisms are composed of one or a large number of cells. The cell is the structural and functional unit of life.

→ A large number of build-up and breakdown reactions take place in the cell.

→ Life is passed on from one generation to the next generation in the form of cells.

→ Robert Hooke (1665) first discovered cells on the basis of compartments observed in a thin section of the bark of a tree.

→ Prokaryotic cells lack a well-organized nuclear membrane and membrane-bound organelles. They have 70 S type of ribosomes.

→ Eukaryotic cells have a proper nucleus and membrane-bound organelles. 80 S ribosomes are present.

→ The Golgi body is formed of stacked cisternae with swollen ends, vacuoles, and vesicles.

→ Functions:

  • It is involved in cell secretions such as mucous, enzymes, and hormones.
  • It helps in the storage of secretory products.

→ Cell inclusions include reserve food in the form of glycogen granules or lipid droplets or starch grains.

→ Vacuoles and fluid-filled membrane-bound spaces each containing cell sap within a tonoplast, wastes, gases, secretions, etc.

PSEB 9th Class Science Notes Chapter 5 The Fundamental Unit of Life

→ Functions: They help in the storage of food, water, and other wastes.

→ Ribosomes are composed of RNA and proteins, granular electron-microscopic particles without membrane.

→ Functions: These act as protein factories.

→ Prokaryotes: The simple organisms called Monerans without a proper nucleus. e.g. Bacteria, Blue-green algae.

→ Eukaryotes: Organisms with true nucleus (plant and animal cells).

→ Organelles: Special living components of cells each performing a definite function.

→ Leucoplasts: Colourless plastids.

→ Centriole: Star-shaped structure present near the nucleus in an animal cell. It forms a spindle during cell division.

→ Genes: They are present on chromosomes and act as carriers of characters from parents to offspring.

→ Lysosome: These are electro-microscopic structures bounded by a single membrane. They are full of digestive enzymes. They are called ‘suicidal bags.’

→ DNA (Deoxyribose nucleic acid): It controls cellular functions and also acts as genetic material.

PSEB 9th Class Science Notes Chapter 5 The Fundamental Unit of Life

→ RNA (Ribose nucleic acid): It plays important role in protein synthesis.

→ Cyclosis: Streaming movements of cytoplasm.

→ Autolysis: Self-digestion of the cell by its lysosomal enzymes.

→ Autophagy: Digestion of its own cell organelles or reserve food by the lysosome.

→ Cristae: Infolds of the inner mitochondrial membrane.

→ Chloroplast: Chlorophyll-containing green coloured photosynthetic plastids.

→ Chromoplast: A pigmented plastid.

→ Tonoplast: Vacuolar membrane present around cell sap.

→ Camillo Golgi discovered Golgi bodies and shared Noble Prize in 1906 with Santiago Ramony Cajal for their work on the structure of the nervous system.

→ Nucleoid: A primitive nucleus of prokaryotes, not covered by a nuclear membrane.

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