CLASS 8 Chapter 8 Cell- Structure and Functions

Exercise Questions

Question 1. Indicate whether the following statements are True (T) or False (F).

(a) Unicellular organisms have a one-celled body. (T/F)

(b) Muscle cells are branched. (T/F)

(c) The basic living unit of an organism is an organ. (T/F)

(d) Amoeba has irregular shape. (T/F)

Solution 1.

1. a) Unicellular organisms have one-celled bodies. True
2. b) Muscle cells are branched. False
3. c) The basic living unit of an organism is an organ. False
4. d) Amoeba has an irregular shape. True

Question 2. Sketch the human nerve cell. What function do nerve cells perform?

Solution 2.

Transmission of messages from receptive organs of the body to the brain and vice-versa is the main function of the nerve cell. It controls and coordinates the working of different parts of the body.

Question 3. Write short notes on the following.

(a) Cytoplasm

(b) Nucleus of a cell

Solution 3.

(a) Cytoplasm:

A fluid that contains all the cell organelles such as the Mitochondria, Ribosomes, Golgi bodies, etc. is called cytoplasm. It is found between the plasma membrane and the nucleus. the exchange of materials between cell organelles takes place with the help of cytoplasm. It is usually clear and colourless and made up of eighty per cent water

(b) The nucleus of a cell:

A double-membrane-bound cell organelle present in eukaryotic cells is known as the nucleus. It contains genetic material, called DNA. It has a spherical shape and is called the command centre of the cell. It has the following components:

• Nuclear membrane
• Nucleolus
• Chromosomes

1. Nuclear membrane:

The nuclear membrane has a double-layered membrane. the contents of the nucleus from the cytoplasm are separated by this. the transfer of certain substances in and out of the cell is done through the pores present in it.

2. Nucleolus:

The nucleolus is a small dense spherical body. It is not surrounded by any membrane.

3. Chromosome:

The thread-like structure that carries genes is called chromosomes. These genes stored all the necessary information required for the transfer of characteristics from the parents to their offspring. Only chromosomes are responsible for the inheritance of characteristics.

Question 4. Which part of the cell contains organelles?

Solution 4.  The cytoplasm contains all the cell organelles such as the Mitochondria, Ribosomes, Golgi bodies, etc

Question 5. Make sketches of animal and plant cells. State three differences between them.

Solution 5.

Plant cell	Animal cell
Plant cells are large.	Animal cells are smaller ithan plant cells.
The cell wall is present in a plant cell.	The cell wall is absent in an animal cell.
Vacuoles are large in plant cells.	Vacuoles are small in animal cells.
Plastids could be seen in plant cells.	Plastids could not be seen in animal cells, Except for Euglena.

 

                                             Plant Cell                                    Animal Cell    

                

Question 6. State the difference between eukaryotes and prokaryotes.

Solution 6.

Prokaryotes	Eukaryotes
Most prokaryotes are unicellular.	Most eukaryotes are multicellular
There is no nuclear membrane in prokaryotes. So, the nucleus is poorly defined.	A nuclear membrane is present in eukaryotes. So, the nucleus is well-defined.
Not all cell organelles are present in prokaryotes.	All the cell organelles are present in eukaryotes.
The nucleolus is absent in prokaryotes.	The nucleolus is present in eukaryotes.
Eg: Blue-green algae, Bacteria	Eg: Plant, Animal cells, and Fungi.

 

Question 7. Where are chromosomes found in a cell? State their function.

Solution 7. Chromosomes are present in the nucleus of a cell that carries genes. Chromosomes are thread-like structure that carries genes called chromosomes. These genes stored all the necessary information required for the transfer of characteristics from the parents to their offspring. Only chromosomes are responsible for the inheritance of characteristics.

Question 8. ‘Cells are the basic structural units of living organisms. Explain.

Solution 8. ‘Cells are the basic structural units of living organisms because cells constitute various components of plants and animals. The cell is known as the smallest unit of life and is the building block of life. There is a variety of shapes and sizes of cells. Cells perform their function based on their sizes and shapes.

Question 9. Explain why chloroplasts are found only in plant cells.

Solution 9. Plants make their food and in this process of making food chloroplasts are required, that is why chloroplasts are found only in plant cells.