Lakhmir Singh Solutions of Class 9 Biology Chapter 2 Fundamental Unit Of Life - Cell

We all know that cells are the fundamental unit of life. The cell is the structural and building block of life. All living organisms in this universe are made up of cells. They are either unicellular or multicellular. This lesson mainly deals with the structure and cells present in both plants and animals. Here, we learn how a plant cell is entirely different from an animal cell. We also 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.

Download PDF Of Lakhmir Singh Solutions for Class 9 Biology Chapter 2 Fundamental Unit Of Life – Cell

 

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Access Lakhmir Singh Solutions for Class 9 Biology Chapter 2

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 chromosomes

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 differences between light microscope and electron microscope.

Answer

Light microscope

Electron microscope

Uses light as an illuminating source

Uses electrons beam as an illuminating source

Both live and dead specimen can be seen

Only dead and the dried specimen can be seen

It has low resolution

It has 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 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 are 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 signaling 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 the 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 by 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 the 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 Mitochondria in animal

(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 ripening of fruits

Chloroplast has a structure called chlorophyll which functions by trapping the solar energy and used for the synthesis of food in all green plants.

(b)

Ribosome

Centrosome

Helps in protein synthesis

Plays major role in cell division

Found in both plants and animals

Found in only plants

Ribosomes are scattered everywhere inside the cell

Centrosome found inside 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 center 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 looks green, papaya yellow and 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 color 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, inducing the death of the cell.


Also, visit Lakhmir Singh Solutions for Class 9 Biology to get complete solutions for all chapters.

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