NCERT Class 8 Science Chapter 8 - Cell - Structure and Functions

Chapter 8 Cell - Structure and Functions

Question and Answers
Question 1: Define the following:
a) Cell - The cell is the basic structural and functional unit of life. All organisms are made up of living cells.

b) Unicellular - The organisms that are made up of only one cell are called unicellular. Example: Amoeba, Paramecium

c) Multicellular - The organisms that are made up of many cell are called multicellular. Example: Humans, Animals

d) Pseudopodia - The finger-like structures are called pseudopodia. These are the false feet of amoeba. Amoeba encircles the pseudopodia around food particle and takes it inside its body.

e) Tissue - A tissue is a group of cell that perform a similar function.

Question 2:  Make a sketch of human nerve cell. What function does nerve cell perform?
Answer:

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

Question 3: Write short notes on following:
a) Cytoplasm - It is a jelly like substance present between cell membrane and nucleus. It contains other components (organelles) like mitochondria, golgi bodies, ribosome, vacuoles etc.

b) Nucleus of a cell - The nucleus is a spherical body generally found in the centre of the cell. It has a membrane called nuclear membrane. It has a spherical body called nucleolus and thread like structure called chromosomes. The chromosomes carry genes which help in the transfer of the characters from parents to offspring.

Question 4: Draw the following diagrams
a) Spherical red blood cells
b) Spindle shaped muscle cells
c) Long branched nerve cell
Answer:

Question 5: Which part of cell contains organelle?
Answer: Various cell organelles are present in cytoplasm. It is a colorless fluid that contains organelles like mitochondria, plastids, golgi bodies, ribosomes etc.

Question 6: State difference between eukaryotes and prokaryotes.
Answer:
Eukaryotes
1. Eu = true; karyon = nucleus
2. The cells have a well - organized nuclear membrane is called eukaryotic cells.
3. Membrane bound cell organelle are present.
4. Example: Onion cell (plant cell), cheek cells

Prokaryotes
1. Pro = primitive; karyon = nucleus
2. The cells having nuclear material without membrane are called prokaryotic cell.
3. Membrane bound cell organelles are absent.
4. Example: Bacteria and blue green algae

Question 7: Where are chromosomes found in a cell? State their function.
Answer: Chromosomes are found in the nucleus of cell. They carry genes, which help in inheritance, the transfer of characters from parents to the offspring.

Question 8: ‘Cells are the basic structural units of living organism’. Explain.
Answer:
1. All basic functions of an organism take place inside the cell. As bricks assemble to make a building, cell makes a body of an organism.
2. A group of cells form tissue which performs specific function.
3. A group of tissues form an organ, a group of organs form an organism. That's why cells are considered as basic structural unit of living organism.

Question 9: Define
a) Prokaryotic cell - The cell having nuclear material without nuclear membrane are called prokaryotic cell.

b) Eukaryotic cell - The cell that have well - organized nucleus with nuclear membrane are called eukaryotic cell.

Question 10: Explain why chloroplasts are found only in plant cell?
Answer: Chloroplasts are plastids required for the food making process, called photosynthesis, and thus they are only present in plant cells.

Question 11: Draw plant and animal cell.
Answer:

Question 12: Draw and label the following diagram
a) Cell observed in an onion peel
b) Human Cheek cell
Answer:

Question 12: State three differences between plant and animal cell.
Answer:
Plant cell
1. Cell wall is present.
2. Plastids are present.
3. Presence of larger vacuoles.

Animal cell
1. Cell wall is absent.
2. Plastids are absent.
3. Absence of vacuoles if present then smaller in size.

Question 13: Why do plant cells need cell wall?
Answer: Plant cells need protection against variation in temperature, high wind speed, atmospheric moisture etc. They are exposed to the variations because they can't move. That is why plants need cell wall.