Class 8 Science NCERT Solutions for Chapter – 8 Cell Structure and Functions

Cell Structure and Functions

Question 1.
Indicate whether the following statements are True (T) or False (F).

(a) Unicellular organisms have a one-celled body.
Answer:
True

(b) Muscle cells are branched.
Answer:
False

(c) The basic living unit of an organism is an organ.
Answer:
False

(d) Amoeba has an irregular shape.
Answer:
True

Question 2.
Make a sketch of a human nerve cell. What function, do nerve cells perform?

Answer:
The nerve cell receives and transfers messages, thereby helping to control and coordinate the working of different parts of the body.
NCERT Solutions for Class 8 Science img 13

Question 3.
Write short notes on the following

(1) Cytoplasm

Answer:
It is the jelly-like substance found between the nucleus and the cell membrane. It contains the nucleus and many small structures called organelles. Cytoplasm, along with nucleoplasm, forms the living substance of the cell, called the protoplasm.

(2) The Nucleus of a cell

Answer:
It is an important component of the living cell. It is generally spherical and located in the center of the cell. The Nucleus is separated from the cytoplasm by a membrane called the nuclear membrane. The liquid substance of the nucleus is termed as nucleoplasm.

There is a smaller spherical body in the nucleus which is called the nucleolus. The Nucleus also contains thread-like structures called chromosomes. These carry genes and help in inheritance. The Nucleus acts as the control center of the activities of the cell.

Question 4.
Which part of the cell contains organelles?

Answer:
The Cytoplasm contains organelles of the cell.

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

Answer:
NCERT Solutions for Class 8 Science img 14

Animal CellPlant Cell
The Cell wall is absent.The Cell wall is present.
Plastids are absent.Plastids are present.
Presence of a number of small vacuoles.Presence of a large vacuole.

Question 6.
State the difference between eukaryotes and prokaryotes.

Answer:
Eukaryotes have a well-organized nucleus with a nuclear membrane while prokaryotes do not have this.

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

Answer:
Chromosomes are found in the nucleus of the cell. They carry genes and help in inheritance i.e., transfer of characters from the parents to the offspring.

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

Answer:
Cells are assembled to make the body of every organism. There are millions of living organisms. They are of different shapes and sizes. Even an organism with billions of cells begins its life as a single cell which is a fertilized egg. The fertilized egg cell multiplies and the number of cells increases as development proceeds.
So, the cell is called the basic structural unit of living organisms.

Question 9.
Explain why chloroplasts are found only in plant cells?

Answer:
Chloroplasts contain chlorophyll which synthesizes food in plants by the process of photosynthesis. As photosynthesis does not occur in animals, they do not contain chloroplasts.

Question 10.
Complete the crossword puzzle with the help of clues given below.

Across
1. This is necessary for photosynthesis.
3. Term for component present in the cytoplasm.
8. 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.

Answer:
NCERT Solutions for Class 8 Science img 15

InText Questions and Answers

Question 1.
Can you list the basic functions carried out by all living organisms?

Answer:
Some of the basic functions carried out by all living organisms are :

  1. Growth and development
  2. Movement
  3. Nutrition
  4. Respiration
  5. Excretion
  6. Reproduction, etc.

8.2 Cell

Question 2.
A hen’s egg can be seen easily. Is it a cell or a group of cells?

Answer:
The egg of a hen represents a single cell and is big enough to be seen by the unaided eye.

Shape of Celt

Question 3.
What advantage does amoeba derive by changing shape?

Answer:
The change in shape is due to the formation of pseudopodia which facilitates amoeba in its movement and capturing food.

Question 4.
Can you guess, which part of the cell gives it shape?

Answer:
Cell membrane.

Size of Cell

Question 5.
Are the cells in an elephant larger than the cells in a rat?

Answer:
The size of the cells has no relation to the size of the body of the animal or plant. It is not necessary that the cells in the elephant be much bigger than those in a rat. The size of the cell is related to its function.

8.5 Parts of the Cell

Question 6.
I want to know why plant cells need cell walls?

Answer:
The Cell wall is an additional layer surrounding the cell membrane which is required by plants for protection. Plant cells need protection against variations in temperature, high wind speeds, atmospheric moisture, etc.

8.6 Comparison of Plant and Animal Cells

Question 7.
Let us tabulate the similarities and distinguishing features of plant and animal cells. Only a few features are mentioned. You may add more in Table 8.1 (Textbook Page 96).

Answer:

S.NO.PartPlant cellAnimal cell
1.Cell membranePresentPresent
2.Cell wallPresentAbsent
3.NucleusPresentPresent
4.Nuclear membranePresentPresent
5.CytoplasmPresentPresent
6.PlastidsPresentAbsent
7.VacuolePresentPresent

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