NCERT solutions for class 8 Science Chapter 8 Cell Structure And Function

Solution for Exercise

Q.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)


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Answer :

a)True
b) False
c) False
d) True

Q.2 Make a sketch of the human nerve cell. What function do nerve cells perform?


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Answer :

Function of nerve cells: The function of the nerve cell is to receive and transfer messages, it helps to control and coordinate the working of different parts of the body.

Q.3 Write short notes on the following.
(a) Cytoplasm
(b) Nucleus of a cell


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Answer :

(a) Cytoplasm:


It is a jelly like substance. It is found between the nucleus and the cell membrane. It is made up of eighty percent water and is usually clear and colourless. It contains Mitochondria, Ribosomes, Golgi bodies, etc.

(b) Nucleus of a cell

Nucleus of a cell is an important component of the living cell. It is located at the centre of the cell. It is separated from the cytoplasm by a membrane called nuclear membrane. It contains genetic material.

Q.4 Which part of the cell contains organelles?


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Answer :

Cytoplasm

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


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Answer :


animal cell

(i) The outermost covering is a cell wall and it is made of cellulose
(ii) Plastids are present in plant cells.
(iii) Large vacuoles are present in plant cells.

plant

(i) The outer most covering is a cell membrane.
(ii) plastids are absent in animal cells.
(iii) No or very small vacuoles are present in animal cells.

Q.6 State the difference between eukaryotes and prokaryotes.


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Answer :

prokaryotes

(i) Most of them are unicellular.
(ii) Nucleus is absent.
(iii) There is no nuclear membrane. So, the nucleus is poorly defined.
(iv) Example: bacteria and blue-green algae.

eukaryotes

(i)Most of them are multicellular.
(ii) Nucleus is present.
(iii) There is a nuclear membrane. So, the nucleus is well defined.
(iv) Example : Plant and animals

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


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Answer :

Chromosomes are thread-like structure. it is present in the nucleus that carry genes. All the necessary information required for the transfer of characteristics from the parents to the offspring are stored in the genes.

Q.8 Cells are the basic structural units of living organisms’. Explain.


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Answer :

Cell is the smallest structural unit of living organisms because the Different cells combine to form tissues and tissues combine to form organs. Similarly, organs combine to form body. Thus they are termed as the basic structural unit of every living organism.

Q.9 Explain why chloroplast are found only in plant cells?


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Answer :

Chloroplasts are plastids required for the food making process, called photosynthesis, and thus they are only present in plant cells.

Q.10 Complete the crossword with the help of clues given below.

Across


i). This is necessary for photosynthesis.
ii) Term for component present in the cytoplasm.
iii). The living substance in the cell.
iv) Units of inheritance present on the chromosomes.

Down


i) Green plastids.
ii) Formed by collection of tissues.
iii) It separates the contents of the cell from the surrounding medium.
iv) Empty structure in the cytoplasm.
v) A group of cells.


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Answer :

Across


i) Chlorophyll
ii) Organelle
iii) Protoplasm
iv) Genes

Down


i) Chloroplasts
ii) Organ
iii) Membrane
iv) Vacuole
v) Tissue



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