Cell Structure and Functions

Q57. Why plant cells need cell walls?
Or
What is the function of cell wall in a plant cell?

Ans. Cell membrane gives shape to the cell. In addition to the cell membrane, there is an outer thick layer in cells of plants called cell wall. This additional layer surrounding the cell membrane is required by the plants for protection. Plant cells need protection against variations in temperature, high wind speed, atmospheric moisture, etc. They are exposed to these variations because they cannot move.

Q58. What are the functions of the cell membrane?

Ans. Functions of the cell membrane

                          i.        The cytoplasm and nucleus are enclosed within the cell membrane, also called the plasma membrane.

                         ii.        The membrane separates cells from one another and also the cell from the surrounding medium.

                        iii.        The plasma membrane is porous and allows the movement of substances or materials both inward and outward.

Q59. State the difference between eukaryotes and prokaryotes.

Ans.

Q60. Make a sketch of the human nerve cell. What function do nerve cells perform?

Ans.

The nerve cell receives and transfers messages, thereby helping to control and coordinate the working of different parts of the body.

Q61. Write short notes on the following:
(a) Cytoplasm
(b) Nucleus of a cell

Ans. Cytoplasm - It is the jelly-like substance present between the cell membrane and the nucleus. Various other components, or organelles, of cells are present in the cytoplasm. These are mitochondria, golgi bodies, ribosomes, etc.

Nucleus of a cell - It is generally spherical and located in the centre of the cell. It is composed of the following components:

      a.   Nuclear membrane - Nucleus is separated from the cytoplasm by a membrane called the nuclear membrane. This membrane is also porous and allows the movement of materials between the cytoplasm and the inside of the nucleus.

      b.   Nucleolus - A smaller spherical body in the nucleus is called the nucleolus.

      c.   Chromosomes – nucleus contains thread-like structures called chromosomes.  These carry genes and help in inheritance or transfer of characters from the parents to the offspring. The chromosomes can be seen only when the cell divides.

Q62. Make sketches of animal and plant cells. State three differences between them.

Ans. Figure ‘a’ – Plant Cell

Figure ‘b’ – Animal Cell