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Cell - Structure And Functions

Class 8th Science CBSE Solution

Exercises
Question 1.

Indicate whether the following statements are True (T) or False (F).
(a) Unicellular organisms have 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)


Answer:

(a) Unicellular organisms have one-celled body: True

Explanation: Unicellular organisms are single cell organisms. Example: Bacteria

(b) Muscle cells are branched: False

Explanation: It is the characteristic of the muscle cells that they are involuntary and branched.

(c) The basic living unit of an organism is an organ: False

Explanation: The cell is the basic unit of an organism. It is also called as the building block.

(d) Amoeba has irregular shape: True

Explanation: Yes, Amoeba has an irregular shape because it moves through pseudopodia.


Question 2.

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


Answer:

The function of a nerve cell is to transmit messages to the brain and also to take away messages from the brain to the receptor organs.

A sketch of the human nerve cell is shown below:




Question 3.

Write short notes on the following.

Cytoplasm:


Answer:

Cytoplasm is a fluid inside the cell that fills the regions between the plasma membrane and the nucleus. Cell organelles such as mitochondria, ribosomes, Golgi bodies, etc. are suspended in the cytoplasm. It is made up of mostly water and salt. Cytoplasm is present within the cell membrane of all cell types and contains all organelles and cell parts. The cytoplasm helps in the exchange of materials between cell organelles.


Question 4.

Write short notes on the following.
Nucleus of a cell:


Answer:

Nucleus is the manager of the cell. It regulates all the functioning of the cell. It is generally located in the center of the cell and is spherical in shape. A membrane called nuclear membrane separates it from cytoplasm. It contains the genetic material DNA and RNA in it. Nucleus contains a dense body called Nucleolus which actually contains Chromosomes, the genetic material.


Question 5.

Which part of the cell contains organelles?


Answer:

Cytoplasm is the part of the cell that contains various organelles such as mitochondria, ribosomes, Golgi bodies, etc.



Question 6.

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


Answer:

The sketches of animal and plant cells are shown below:



Question 7.

State the difference between eukaryotes and prokaryotes.


Answer:
Question 8.

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


Answer:

Chromosomes are present inside the nucleus of a cell. Their function is to carry characteristic features i.e the genetic information, of parent cells to the daughter cell means, from parent to offspring.


Question 9.

'Cells are the basic structural units of living organisms'. Explain.


Answer:

The ‘cell’ is the smallest structural unit of living matter that is capable of functioning independently.As bricks assemble to make a building, cells assemble to make the body of every organism hence is called as basic building block of life . A group of cells form a tissue which performs a specific function, A group of tissue forms an organ and in the same way a group of organs form an organism. therefore cells are responsible for every vital function of our body hence, cell are called structural unit of living organisms


Question 10.

Explain why chloroplasts are found only in plant cells?


Answer:

Chloroplasts are found only in plant cells because They are green organelle which contain photosynthetic pigment chlorophyll , chlorophyll function is to absorbs sunlight and stores it in the energy-storage molecules ATP during photosynthesis . Hence, found only in green plants and algae


Question 11.

Complete the crossword with the help of clues given below.

Across

1. This is necessary for photosynthesis.

3. Term for component present in the cytoplasm.

6. The living substance in the cell.

8. Units of inheritance present on the chromosomes.

Down

1. Green plastids.

2. Formed by collection of tissues.

4. It separates the contents of the cell from the surrounding Medium.

5. Empty structure in the cytoplasm.

7. A group of cells.



Answer: