NCERT Solutions For Class 8 Science Chapter – 8

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NCERT Solutions For Class 8 Science CHAPTER – 8 Cell Structure and Functions

 

Q1. Indicate whether the following statements are True or False.

  • Unicellular organisms have one –  celled body.
  • Muscle cells are branched.
  • The basic living unit of an organisms is an organ.
  • Amoeba has irregular shape.

Answer:-

 

  • True
  • False
  • False
  • True

 

Q2. Make a sketch of the human nerve cell. What functions do nerve cells perform?

Answer:-

 

Human Nerve cell

 

 

 

 

The main function of the nerve cell is to transmit messages to the brain from receptor organs and vice versa . It has controls over the working of different parts of the body.

 

Q3. Write short note on the following

  • Cytoplasm
  • Nucleus of a cell

 

Answer:-

 

  • Cytoplasm:- The cytoplasm is a fluid that contains all the cell organelles such as the Mitochondria Ribosomes Golgi bodies etc. It is present between the nucleus and the plasma membrane It helps in the exchange of materials between the cell  organelles. It is made up of eighty percent water and is usually clear and colourless.

 

  • The nucleus of a cell: The Nucleus is a doubled – membrane bound cell organelle present in eukaryotic cells . It contains in the DNA the genetic material. It is the command center of the cell and is spherical in shape It has the following components:

 

Cell and Nucleaus Diagram

 

 

 

Nuclear membrane

Nucleolus

Chromosomes

 

  1. Nuclear membrane : It has is double – layered membrane . It separates the contents of the nucleus from the cytoplasm  and acts as a wall. It  has pores that allow the transfer of certain substances in and out of the cell.

 

  1. Nucleolus: It is a small dense spherical body. It is not bound by any membrane.

 

  1. Chromosomes:  These are thread – like structures that carry genes. All the necessary information required for the transfer of characteristics from the parent to to offspring are stored in the genes. Inheritance of characteristics is possible only because of chromosomes.

 

Q4. Which part of the cell contains organelles?

Answer:-

 

Various cell organelles are present in the cytoplasm. It is a  clear and  colorless fluid that  contains organelles like Mitochondria , Ribosomes , Golgi bodies.

 

Q5. Make sketches of animal and plant cells State three differences between   them.

 

Answer:-

 

Plant cells Animals Cell
They are large in size. They are smaller than plant cells
The cell wall is present The cell wall is absent.
Vacuoles are large. Vacuoles are small.
Plastids could be seen Expect for Euglena, Plastids  could not be seen in animals cells.

  

 

Animal and plant cell

 

 

 

 

 

 

 

 

 

 

Q6. State the difference between eukaryotes and prokaryotes.

Answer:-

 

Prokaryotes Eukaryotes
Most them are unicellular Most of them are multicellular
There is no nuclear membrane  the nucleus is poorly defined There is a nuclear membrane. So  the nucleus well defined.
Not all cell organelles are present All the cell organelles are preset
Nucleolus is absent Nucleolus is present.
Eg: Blue – green algae, Bacteria Eg: Plant, Animal cell and Fungi.

 

Q7. Where are chromosomes  found in cell? State their function.

Answer:-

 

Chromosomes are thread – like structures 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. Inheritance of characteristics is possible only because of chromosomes.

 

Q8. ‘Cells are the basic structural units of living organisms’.

Answer:-

 

Various components of plants and animals are constituted by cells. It is the smallest unit of life and is capable of all living fuctions They are the building blocks of life That is the reason why cells are referred to as ‘the basic structural and functional blocks of life’

Cells exist in various shapes and sizes and perform a wide range of activities.

Their shapes and sizes are related to the functions it performs.

 

Q9. Explain why chloroplasts are found only  in plants cells.

Answer:-

 

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

 

Q10. 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.

  1. The living substances in the cell.
  2. Units of inheritance present in the chromosomes.

 

Down

  1. Green plastids.
  2. Formed by collection of tissues

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

  1.  Empty structures in the cytoplasm.
  2. A group of cells.

 

Crossword Puzzle on Cell-Structure and Functions-1

 

 

 

 

Answer:-

 

Across

  1. Chlorophyll
  2. Organelle
  3. Protoplasm
  4. Genes

 

Down

  1. Chloroplasts
  2. Organ
  3. Membrane
  4. Vacuole
  5. Tissue

Crossword Puzzle on Cell-Structure and Functions