NCERT Solutions for Class 8 Science - Cell Structure and Functions

Exercises

Q1. Indicate whether the following statements are True (T) or False (F).
(a) Unicellular organisms have a one-celled body. ( )
(b) Muscle cells are branched. ( )
(c) The basic living unit of an organism is an organ. ( )
(d) Amoeba has an irregular shape. ( )
Ans:

(a) True. 

• Organism made up of one cell is called unicellular or unicellular organism.

(b) True. 

• Muscle tissue is of three types- Striated muscle, Cardiac muscle, Smooth muscle. Muscle cells usually branched cells.

(c) False. 

• Cell is the basic, structural and fundamental unit of life.

(d) True. 

• Amoeba has no definite shape.

Q2. Make a sketch of the human nerve cell. What function do nerve cells perform?
Ans:

Human Nerve Cell

Q3. Write short notes on the following:

(a) Cytoplasm
(b) Nucleus of a cell

Ans:
(a) Cytoplasm 

• The cytoplasm is the jelly-like substance present between the cell membrane and the nucleus. Various other components or organelles like Mitochondria, Golgi bodies, Ribosomes, etc. are present in the cytoplasm.
• Cytoplasm helps the exchange and storage of substances among cell organelles.
• Most of the metabolic activities occur inside the cytoplasm.

(b) Nucleus of a Cell

• The nucleus is an important component of the living cell. It is mostly spherical and located in the center of the cell.
  Plant and Animal Cell
• It is separated from the cytoplasm by a membrane called the nuclear membrane. 
• In addition, the nucleus contains thread-like structures called chromosomes. These carry genes and help in the inheritance or transfer of characters from the parents to the offspring. 
• The nucleus, in addition to its role in inheritance, acts as the control centre of the activities of the cell.

Q4. Which part of the cell contains organelles?
Ans: Cell organelles are suspended in the cytoplasm of the cell . Cytoplasm is the gel like substance present between the cell membrane and the nucleus. Various other components, or organelles, of cells are present in the cytoplasm. These are mitochondria, Golgi bodies, ribosomes, etc.

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

Q6. State the difference between eukaryotes and prokaryotes.
Ans:


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

• Chromosomes are found inside the nucleus of a typical cell. 
• Chromosomes contain genes that are carriers of genetic information. 

Chromosome

• Chromosomes govern distinct features of an organism.
• Chromosomes take part in cell division.

Q8. ‘Cells are the basic structural units of living organisms’. Explain.
Ans: Cells are the smallest units from which a living organism is made. A cell contains all the necessary structures which are required to carry out various biological processes. A group of cells makes a tissue which further makes organs and finally an organism. Thus, cells are called the basic structural unit of living organisms.

Q9. Explain why chloroplasts are found only in plant cells?
Ans: Chloroplasts are a type of plastids that contain chlorophyll. Chlorophyll is a green colour pigment that plays important role in photosynthesis. Since green plants need to prepare their food, hence chloroplast is present in them.Structure of Chloroplast

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.
6. The living substance in the cell.
8. Units of inheritance present on the chromosomes.
Down-
1. Green plastids.
2. Formed by a 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.

Ans:
Across:
1. Chlorophyll
3. Organelle
6. Protoplasm
8. Genes
Down:
1. Chloroplast
2. Organ
4. Membrane
5. Vacuole
7. Tissue