CBSE Class 8 Biology: Cell Structure and Functions Questions & Answers

1. Indicate whether the following statements are True (T) or False (F).
   (a) Unicellular organisms have one-celled body. (T / F ) - True.
   (b) Muscle cells are branched. - (T / F) - False
   (c) The basic living unit of an organism is an organ. (T / F) - False
   (d) Amoeba has irregular shape. - (T / F) - True.


2. Make a sketch of the human nerve cell. What function do nerve cells perform?
   Ans
   Nerve cells receive and transfer messages, thereby helps to control and coordinate the working of different parts of the body.


3. Write short notes on the following:
   (a) Cytoplasm
   (b) Nucleus of a cell
   Ans.
   (a) Cytoplasm: The jelly-like substance present between the cell membrane and the nucleus. It contains various other components or organelles like mitochondria, golgi bodies, ribosomes etc.
   
   (b) Nucleus of a cell:
   • It is an important component of the living cell.
   • It acts as control centre of all the activities in a cell.
   • It is generally spherical and is located in the centre of the cell.
   • It is separated from the cytoplasm by a membrane called nuclear membrane.
   • The nuclear membrane is porous and allows the movements of materials between the cytoplasm and inside of the nucleus.
   • It contains a smaller spherical body called the nucleolus and thread-like structures called chromosomes that that appear only during cell division.
   • These chromosomes carry genes which help in the transfer of characters from parents to offsprings.


4. Which part of the cell contains organelles?
   Ans.
   Cytoplasm contains the nucleus and various other components or organelles like mitochondria, golgi bodies, ribosomes etc.


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


6. State the difference between eukaryotes and prokaryotes.
   Ans.
   All the organisms other than bacteria and blue green algae that are made of cells with a well-organized nucleus having a nuclear membrane are called eukaryotes. Whereas bacterial cells that are not well-organized and the nuclear material is not bound by a nuclear membrane are called prokaryotes.


7. Where are chromosomes found in a cell? State their function.
   Ans. Chromosomes are found in the nucleus of a cell. They carry genes which help in the transfer of characters from parents to their offsprings. Chromosomes are seen only during cell division.


8. 'Cells are the basic structural units of living organisms'. Explain.
   Ans.
   Living organims differ from one another in shape and size. However all living organisms are made up of cells which are complex living structures. Hence, cells are called the basic structural units of living organisms.


9. Explain why chloroplasts are found only in plant cells.
   Ans.
   Chloroplasts are the green colored plastids present in the leaves. They contain chlorophyll which is essential for photosynthesis as they are capable of trapping sunlight.


10. Complete the crossword with the help of clues given below:
    Across
    1. This is necessary for photosynthesis.
    3. Term for component present in 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.