Lakhmir Singh Solutions of Class 9 Biology Chapter 2 Fundamental Unit of Life – Cell are provided here. We know that cells are the fundamental unit of life. The cell is the structural unit and building block of life. All living organisms in this universe are made up of cells. They are either unicellular or multicellular. This chapter mainly deals with the structure and cells present in both plants and animals and how a plant cell is entirely different from an animal cell. Besides, we will learn about the cell structure, size, shape and organelles present in it. Each cell organelle has its own characteristic behaviour and function. The whole biology of an animal or plant is determined by its cell.
Lakhmir Singh Solutions for Class 9 Biology Chapter 2 Fundamental Unit of Life – Cell
Access Lakhmir Singh Solutions for Class 9 Biology Chapter 2 Fundamental Unit of Life – Cell
Short Answer Type Questions
1. Distinguish between prokaryotic and eukaryotic cells.
Answer
| Prokaryotic | Eukaryotic |
| Organisms are always unicellular | Organisms are always unicellular and multicellular |
| Nucleus is absent | Nucleus is present |
| Cell division takes place through binary fission | Cell division takes place through mitosis |
| DNA arrangement is circular | DNA arrangement is linear |
| Example: Bacteria, Blue-green algae | Example: Plant and animal cell |
2. Write down the differences between organ and organelle.
Answer
| Organ | Organelle |
| These are the parts of a body | These are the parts of a cell |
| These are found in multicellular organisms | These are found in unicellular organisms |
| These are macroscopic in nature | These are microscopic in nature |
| Example: Brain, Heart, Lungs | Example: Cytoplasm, mitochondria |
3. Write down the differences between the nucleus and nucleoid.
Answer
| Nucleus | Nucleoid |
| A nucleus is a membrane-bound structure in which eukaryotes store their genetic materials. | Nucleoid is a particular area in which prokaryotes store their genetic materials. |
| Contains many chromosomes. | Contains one chromosome |
| It is a spherically shaped organelle. | It is an irregularly shaped organelle. |
| Nucleoplasm and Nucleolus are present in the nucleus. | Nucleoplasm and Nucleolus are absent in the nucleoid. |
4. Mention the differences between a light microscope and an electron microscope.
Answer
| Light microscope | Electron microscope |
| It uses light as an illuminating source | It uses an electron beam as an illuminating source |
| Both live and dead specimens can be seen | Only dead and the dried specimen can be seen |
| It has low resolution | It has a high resolution |
5. Give a brief account of the discovery of the cell.
Answer
Cells are the basic structural and functional unit of life. The term cells was first coined in 1665 by a British scientist Robert Hooke. He was the first person to study living things under a microscope, and he examined a thin slice of cork under a microscope and observed honeycomb-like structures. Robert Hooke called these structures as cells.
6. Describe the proteins of the plasma membrane.
Answer
There are two types of proteins molecules found in the plasma membrane:
(i) Intrinsic proteins -They completely cover the lipid bilayer.
(ii) Extrinsic proteins – These occur either on the outer surface or on the inner surface of the lipid layer.
7. Enumerate functions of the plasma membrane.
Answer
- The plasma membrane forms a barrier between the cell organelles from the outside environment.
- It allows only certain molecules to pass through it.
- It facilitates communication and signalling between the cells.
8. Give an example of diffusion across the plasma membrane.
Answer
In unicellular organisms like Amoeba, gaseous exchange takes place through the process of diffusion.
9. Set up an experiment to demonstrate osmosis.
Answer
1. Take three raisins and weigh them on a common balance. Let this value be W1.
2. Keep these raisins in a bowl containing water for 2 hours.
3. Take the raisins out of the water and gently dry them with the help of blotting paper.
4. Weigh the soaked swollen raisins again on the common balance. Let this value be W2.
The soaked swollen raisins (W2) weigh more than the dry raisins (W1). This is because the raisins absorbed water through the process of endosmosis.
10. Write down the differences between diffusion and osmosis.
Answer
| Diffusion | Osmosis |
| This occurs in all mediums – Solid, Liquid and gas. | This occurs only in the liquid medium. |
| Do not require a semipermeable membrane. | Requires a semipermeable membrane. |
| The flow of particles occurs in all directions. | The flow of particles occurs only in one direction. |
11. Write a note on endocytosis.
Answer
Endocytosis is defined as the process of trapping a particle or substance from the external environment by engulfing it. Endocytosis is of two types viz phagocytosis, also known as cellular eating and pinocytosis, also referred to as cellular drinking. There are three types of endocytosis:
1. Phagocytosis, 2. Pinocytosis, and 3. Receptor-mediated endocytosis.
12. What would happen when eukaryotic cells are placed in hypotonic, hypertonic and isotonic solutions?
Answer
When eukaryotic cells are placed in the following solutions, the changes observed are as follows:
- Hypotonic Solution: The water moves from a region of low osmolarity to a region of high osmolarity. In this case, since the extracellular fluid has low osmolarity, the water would rush into the cell. The cell would then expand and eventually lyse or burst.
- Hypertonic Solution: In this case, water will leave the cell since the cell has a lower osmolarity than the extracellular fluid. As a result, the cell would shrink in what is called plasmolysis.
- Isotonic Solution: The osmolarity of both fluids is equal. As such, though water diffuses in and out, there is no net change in the volume of the cell.
13. Name the following:
(a) Smallest cell organelle
(b) Largest cell organelle;
(c) ER studded with ribosomes
(d) Functional segments of the DNA molecule.
Answer :
(a) Ribosome
(b) Plastid in plants and Nucleus in animal cell
(c) Rough endoplasmic reticulum contains a ribosome attached to its surface
(d) Genes
14. Distinguish between the following:
(a) Chromoplast and chloroplast
(b) Ribosome and centrosome
Answer
(a)
| Chromoplast | Chloroplast |
| Chromoplasts are plastids and contain carotenoids | Chromoplasts – is a name given to an area for all the pigments to be kept and synthesized in the plant. |
| They lack in chlorophyll | They have a high concentration of chlorophyll |
| Chromoplasts may develop from green chloroplasts. Chlorophyll and thylakoid membranes disappear, and carotenoids are accumulated, e.g. during the ripening of fruits | Chloroplast has a structure called chlorophyll which functions by trapping solar energy and is used for the synthesis of food in all green plants. |
(b)
| Ribosome | Centrosome |
| It helps in protein synthesis | It plays a major role in cell division |
| Found in both plants and animals | Found in only plants |
| Ribosomes are scattered everywhere inside the cell | Centrosomes are found inside the nucleus only |
15. Write the main differences between plant and animal cells.
Answer
| Plant cell | Animal cell |
| Cell wall is present | Cell wall is absent |
| Nucleus lies on one side of the cell | Nucleus lies on one centre of the cell |
16. What will happen in a cell if its nucleus is removed? Give reasons in support of your answer.
Answer
If the nucleus of a cell is removed, the cell will not be able to carry out its vital functions and will die.
17. Explain why do spinach look green, papaya yellow and the edible part of watermelon red?
Answer
Spinach is green because of the presence of green pigment chlorophyll. Papaya is yellow because of the presence of caricaxanthin. The edible part of a watermelon is red in colour because of the presence of lycopene which is a red pigment.
18. Write down two main functions of
(a) Endoplasmic reticulum
(b) Lysosome
Answer
(a) Endoplasmic reticulum
- It plays a major role in the production, processing, and transport of proteins and lipids.
- It produces transmembrane proteins and lipids for its membrane and for many other cell components, including lysosomes, secretory vesicles, the Golgi apparatus, the cell membrane, and plant cell vacuoles.
(b) Lysosomes
- Intracellular digestion
- Removal of dead cells
19. Name the following
(a) The cell organelle which synthesizes protein.
(b) The type of plastid which stores food.
Answer:
(a) Ribosome
(b) Leucoplasts
20. Lysosomes are known as suicide bags.” Why?
Answer:
Lysosomes are known as suicide bags of the cell because they contain lytic enzymes capable of digesting cells and unwanted materials. When lysosomes burst, the lytic enzymes within the organelle spill all over the cell, rupturing the cell membrane or cell wall and inducing the death of the cell.
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