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Page No 105:

Question 1:

Cell membrane is present in
(a) a plant cell.
(b) an animal cell.
(c) both plant and animal cells.
(d) none of them.

Answer:

(c) both plant and animal cells
The cell membrane surrounds the cytoplasm of the cell and is present in both plant and animal cells.

Page No 105:

Question 2:

Which one of the following is not paired correctly?
(a) Golgi body : making of proteins
(b) cell membrane : protection
(c) mitochondria : energy
(d) ER : transport

Answer:

(a) Golgi body: Making of proteins
Golgi bodies are associated with the packaging and sorting of materials.

Page No 105:

Question 3:

The membrane that surrounds vacuole is called __________.
(a) cell wall
(b) cell membrane
(c) tonoplast
(d) chloroplast

Answer:

(c) tonoplast
The membrane of a vacuole is known as the tonoplast.

Page No 105:

Question 4:

The organelle generally not seen in an animal cell is ____________.
(a) a vacuole
(b) a ribosome
(c) the cell wall
(d) mitochondria

Answer:

(c) the cell wall
Animal cells do not possess cell wall. Cell wall is present in plant cells.

Page No 105:

Question 5:

What structural adaptations of cells in the lining of nose make it possible to keep dust and germs away?
(a) big cells with thin cell membrane and mucus-producing cells
(b) small cells with thin cell membrane
(c) ciliated cells and mucus-producing cells
(d) cells with thin cell membrane and mucus-producing cell

Answer:

(c) ciliated cells and mucus-producing cells
The lashing movement of the cilia in the nose keeps dust and germs away.

Page No 105:

Question 6:

The longest cell in the human body is
(a) a nerve cell.
(b) a muscle cell.
(c) a white blood cell.
(d) both nerve and muscle cells.

Answer:

(a) a nerve cell
Nerve cells have a long projection called the axon, because of which they are very long .



Page No 106:

Question 7:

Mark the following statements 'true' or false. Rewrite the wrong ones correctly.
(a) All cells have nuclei.
(b) Chloroplasts are present in all plant cells.
(c) Animal cells usually do not have vacuoles.
(d) Animal and plant cells have cell membranes.
(e) Ribosomes are called 'suicide bags'.
(f) The cell wall is made of cellulose which is a living substance.
(g) The cell membrane is freely permeable to all substances.
(h) All living organisms are made up of cells.
(i) Structures present in the cell are called organs.
(j) Cell respiration takes place in mitochondria.

Answer:

(a) All cells have nuclei.
False. Cells such as red blood cells do not have nuclei.

(b) Chloroplasts are present in all plant cells.
False. Chloroplasts are present in the leaf cells of plants.

(c)  True

(d)  True

(e) Ribosomes are called 'suicide bags'.
False. Lysosomes are called suicide bags.

(f) The cell wall is made of cellulose, which is a living substance.
False. The cell wall is made of cellulose, which is a non-living substance.

(g) The cell membrane is freely permeable to all substances.
False. The cell membrane is semi-permeable.

(h) True

(i) Structures present in the cell are called organs.
False. Structures present in the cell are called organelles.

(j) True

Page No 106:

Question 8:

In each part, choose one correct answer from the following.
A. Which is the organelle responsible for recycling of materials?
(a) ribosome
(b) lysosome
(c) mitochondria
(d) Golgi bodies
B. Which of the following is not a cell organelle?
(a) lysosome
(b) ribosome
(c) protein
(d) nucleus
C. A cell has a defect that results in the loss of its ability to control the passage of substances in and out of the cell. In which of the organelles, is the defect most likely to be present?
(a) ribosomes
(b) endoplasmic reticulum
(c) cell membrane
(d) none of these
D. A red blood cell does not reproduce because
(a) it is short lived.
(b) after it delivers oxygen, its function is over.
(c) it does not have a nucleus.
(d) none of the above.
E. Nida was given two unlabelled cells. She was asked to identify the plant cell from the two. What structures she must look for?
(a) vacuoles
(b) cell wall
(c) only chloroplast
(d) cell wall and vacuole

Answer:

A. (b) Lysosome

Lysosome is the organelle responsible for recycling materials.
 
B. (c) Protein

Protein is not a cell organelle.

C. (b) Endoplasmic reticulum

The endoplasmic reticulum controls the passage of substances in and out of the cell.

D. (c) It does not have a nucleus.
A red blood cell does not reproduce because it does not have a nucleus.

E. (d) Cell wall and vacuole
Nida must look for cell walls and a vacuole to identify the plant cell.

Page No 106:

Question 9:

Name six organelles common to plant and animal cells.

Answer:

The nucleus, lysosomes, Golgi body, endoplasmic reticulum, cell membrane and mitochondria are common to both plant and animal cells.

Page No 106:

Question 10:

Name two organelles not found in animal cells.

Answer:

Cell walls and chloroplasts are not found in animal cells.

Page No 106:

Question 11:

Explain why nerve cells are long, while ciliated cells are short and have cilia?

Answer:

Nerve cells have to carry messages in the form of electrical signals from the different parts of the body to the spinal cord and the brain and back from them to the body parts. In order to carry messages over a long distance, they have long 'arms'; hence, they are long.
Ciliated cells are short and have hair-like projections called cilia, the lashing movement of which keeps dust and germs away.

Page No 106:

Question 12:

Give one function each of the following organelles:
mitochondria, endoplasmic reticulum, ribosomes, nucleus, Golgi bodies, lysosomes

Answer:

Mitochondria are the powerhouse of the cell, as cellular respiration, takes place in mitochondria.

The endoplasmic reticulum acts as a transport channel for materials to pass through.

Ribosomes act as protein factories of the cell.

The nucleus controls all the functions of the cell.

Golgi bodies package and sort materials.

Lysosomes are the suicide bags of the cell and help in recycling material.

Page No 106:

Question 13:

Clearly differentiate between the following pairs of words
(a) chromosomes and ribosomes
(b) cytoplasm and nucleoplasm
(c) cell wall and plasma membrane
(d) tissue and organ

Answer:

(a)

Chromosomes Ribosomes
They are present inside the nucleus. They are present on the rough endoplasmic reticulum.
They carry hereditary information. They are the protein factory of the cell.

(b)
Cytoplasm Nucleoplasm
It is the jelly-like material in the cell outside the nucleus. It is the jelly-like material present inside the nucleus.
It contain all the organelles, which are suspended in it. It has chromosomes suspended in it.

(c)
Cell wall Plasma membrane
It is the thick covering outside the cell membrane in plant cells. It is the thin elastic covering present outside the cells.
It is permeable to all substances. It is selectively permeable.

(d)
Tissue Organ
It is a group of cells that together perform specific functions. Various tissues together form an organ.
Examples: Muscle tissues and skin tissues. Examples: Heart and stomach.



Page No 107:

Question 14:

Can you say why cells were not observed before late seventeenth century?

Answer:

Cells are very tiny and cannot be seen by naked eyes. We need a microscope to see cells. There were no microscopes before late seventeenth century, which is why cells were not observed at that time.

Page No 107:

Question 15:

Why are mitochondria called the 'power houses' of the cells?

Answer:

Mitochondria are called the 'powerhouses' of the cells because the energy generating process of the body i.e., cellular respiration, takes place in mitochondria.

Page No 107:

Question 16:

Compare the cell to a factory. There are various areas in the factory. Now place the organelles listed below against corresponding factory areas.

ribosomes, lysosomes, mitochondria, cell membrane, Golgi bodies, nucleus, nuclear membrane, endoplasmic reticulum, cytoplasm
AREAS IN A FACTORY
(a) main office_______________.
(b) office wall _______________.
(c) area surrounding main office _____________.
(d) production units _______________.
(e) supply channels ________________.
(f) recycling units _________________.
(g) power house __________________.
(h) boundary wall of factory ______________.
(i) packaging unit ________________.

Answer:

AREAS IN A FACTORY

(a) Main office: Nucleus
 
(b) Office wall: Nuclear membrane

(c) Area surrounding the main office: Cytoplasm

(d) Production units: Ribosomes

(e) Supply channels: Endoplasmic reticulum

(f) Recycling units: Lysosomes

(g) Powerhouse: Mitochondria

(h) Boundary wall of factory: Cell membrane

(i) Packaging unit: Golgi body

Page No 107:

Question 17:

What is division of labour? Explain how this happens in a cell, with the help of suitable examples.

Answer:

Division of labour is a system of assigning different work to different organs, tissues, cells and even cellular organelle.
An organism can work more efficiently if there is division of work. In cells, there are different organelles performing different functions, such as mitochondria, which produce energy; ribosomes, which make proteins; and the nucleus, which controls all the cellular activities. Thus, in a cell, all organelles work in a coordinated manner because of division of work.



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