Cell Structure and Functions Class 8 Extra Questions and Answers Science Chapter 8

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Class 8 Science Chapter 8 Extra Questions and Answers Cell Structure and Functions

Extra Questions for Class 8 Science Chapter 8 Cell Structure and Functions with Answers

Cell Structure and Functions Class 8 Extra Questions Very Short Answer Type

Question 1.
List some of the basic functions carried out by all living organisms.
Answer:
Growth and development, movement, digestion, respiration, excretion, reproduction, etc.

Question 2.
What is a cork?
Answer:
Cork is a part of the bark of a tree.

Question 3.
What is meant by cell in Latin?
Answer:
Cell in Latin means “hollow space”.

Question 4.
What instrument helped in studying the living cells ?
Answer:
Microscope helped in studying the living cells.

Question 5.
How many cells are there in a human body ? What about their shape and size ?
Answer:
Human body has trillions of cells, which vary in shape and size on the basis of their functions.

Question 6.
What is the name of organism made of more than one cell?
Answer:
They are called multicellular.

Question 7.
What is meant by unicellular organisms?
Answer:
The single-celled organisms are called unicellular organisms, (uni = one, cellular = cell).

Question 8.
What is the size of cell of a bacteria?
Answer:
0.1 to 0.5 micrometre (mm).

Question 9.
What is tissue?
Answer:
Tissue is a group of similar cells performing a specific function.

Question 10.
Is cell wall present or absent in animal cell?
Answer:
It is absent.

Question 11.
When can chromosomes be seen?
Answer:
The chromosomes can be seen only when the cell divides.

Question 12.
Name two organisms which are made of single cell.
Answer:
Amoeba and Paramecium.

Cell Structure and Functions Class 8 Extra Questions Short Answer Type 1

Question 1.
When you cut your hair and nail, you do not feel pain. Why?
Answer:
When nail and hair are cut, we do not feel any pain because the cells of nails and hair are dead cells.

Question 2.
Why are we able to know a lot about cell structure today?
Answer:
Today, we know a lot about cell- structure and its functions because of the improved microscopes having higher magnification.

Question 3.
How are cells in the living organisms arranged?
Answer:
The cells in the living organisms are arranged in the similar manner as bricks are arranged to make a building.

Question 4.
What are basic structural units in buildings and living organisms ?
Answer:
Bricks in buildings and cells in the living organisms are the basic structural units.

Question 5.
Does egg of a hen represent a single cell ?
Answer:
Yes, egg of a hen represents a single cell and is big enough to be seen by unaided eye. _

Question 6.
While studying living cells with microscope, why do we use stains ?
Answer:
Stains (dyes) are used to colour the parts of the cell to observe and study their detailed structure clearly under microscope.

Question 7.
What is the difference between the functions of organisms with one cell and the organisms with multi cells?
Answer:
A single-celled organism captures and digests food, respires, excretes, grows and reproduces with its single cell. Similar functions in multicellular organisms are carried out by groups of specialised cells forming different tissues which in turn form organs.

Question 8.
What are the projections in Amoeba called? What do they do?
Answer:
The projections in Amoeba are known as pseudopodia (pseudo = false; podia = feet). These projections are in fact false feet and these appear and disappear as Amoeba moves or feeds.

Question 9.
What is the size of cells in living organisms.
Answer:
The size of cells in living organisms may be as small as a millionth of a metre or a few centimetre. However, most of the cells are microscopic in size and are not visible to the unaided eye.

Question 10.
What is the size of smallest cell? What is the size of red blood cells (RBCs) found in the human body?
Answer:
The size of the smallest cell is 0.1 to 0. 5 micrometres (pm) found in bacteria and that of red blood cells in the human body measure seven micrometres.

Question 11.
Give example of a large cell. State the size of the largest cell.
Answer:
The hen’s egg is an example of large. cell, which is quite large that it can be seen by an unaided eye. The largest cell, measuring 170 x 130 mm, is the egg of an ostrich.

Question 12.
What are white and yellow parts of an egg called?
Answer:
In an egg, a white material surrounds the yellow part. The white material is called albumin, and the yellow component is called yolk.

Question 13.
Define the terms tissue and organ.
Answer:

• Tissue: A tissue is a group of similar cells performing a specific function.
• Organ: It is a group of tissues performing a specific function.

Question 14.
Define nucleus. What is its role?
Answer:
The central dense round body in the centre of the cell is called nucleus. In addition to its role in inheritance, nucleus acts as control centre of the activities of the cell.

Question 15.
Define the term cytoplasm.
Answer:
The jelly-like substance found between the nucleus and the cell membrane is called cytoplasm.

Cell Structure and Functions Class 8 Extra Questions Short Answer Type 2

Question 1.
How do we observe the cell by microscope?
Answer:
To observe the cell by microscope, sometimes an organ has to be cut into sections to observe various smaller components. Some components in these sections are visible through the microscope after staining (dying) with coloured dyes.

Question 2.
What was the observation of a part of the bark of a tree (cork) by Robert Hooke?
Answer:
Robert Hooke in 1665 observed slices of cork under a simple magnifying device. He took thin slices of cork and observed them under a microscope. He noticed partitioned boxes or compartments in the cork slice. These boxes appeared like a honey-comb. He coined the term cell for each box.

Question 3.
Describe the differences and similarities between cell and brick.
Answer:
The cells in the living organisms are arranged and appear like bricks in a building. Both bricks in the building and cells in the living organisms are basic structural units. The buildings, though built of similar bricks, have different designs, shapes and sizes. Similarly, in the living world, organisms differ from one another but all are made up of cells. But, cells in the living organisms are complex living structures unlike non-living bricks.

Question 4.
Which part of the cell gives shape to it?
Answer:
Components of cells are enclosed in a membrane ealled cell membrane. This membrane provides shape to the cells in plants and animals. Cell wall is an additional covering over the cell membrane in plant cells. It gives shape and rigidity.

Question 5.
Is there any relation between the size of the body of the animal or plant with the size of the cell?
Answer:
The size of the cell, in fact, has no relation with the size of the body of the animal or plant. The size of the cell is related to its function. For example, nerve cells, both in the elephant and rat, are long and branched. They perform the same function of transferring messages in bigger as well as in the smaller organism.

Question 6.
How do cells/groups of cells perform different functions in multicellular organisms?
Answer:
The cell in a living organise is the basic structural unit. Cells combine to form tissues and a group of tissues is called an organ. These organs together constitute different systems in living beings and perform different functions. Each organ in the system performs different functions.

Question 7.
What constitutes cytoplasm?
Answer:
Cytoplasm is a fluid present between the cell membrane and the nucleus and is made up of basic elements like carbon (C), hydrogen (H), oxygen (O) and nitrogen (N). These are found in the form of chemical substances like carbohydrates, proteins and water.

Question 8.
What are the components present in cytoplasm?
Answer:
Besides nucleus, various other components-or organelles of cells are present in the cytoplasm. These are mitochondria, golgi bodies, ribosomes, etc. Cytoplasm, along with nucleus, forms the living substance of a cell. This living substance is called protoplasm.

Question 9.
What is nucleolus? Describe its function in brief.
Answer:
Nucleolus is a small, spherical, dense body in the nucleus. The function of nucleolus is to assemble ribosomes.

Question 10.
What are prokaryotic cells and eukaryotic cells ?
Answer:
The cells having nuclear material without nuclear membrane are termed prokaryotic cells. The organisms with these kinds of cells are called prokaryotes (pro = primitive; karyon = nucleus). Examples are bacteria and blue-green algae.

The cells having a well-organised nucleus with a nuclear membrane are designated as eukaryotic cells. The organisms having these cells are called eukaryotes (eu = true; karyon = nucleus). Examples are onion, cells and cheek cells.

Question 11.
What is the function of nucleoplasm?
Answer:
Nucleoplasm of nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance.

Cell Structure and Functions Class 8 Extra Questions Long Answer Type

Question 1.
Define the function of following:
(a) Plasma membrane
(b) Mitochondria
(e) Gene
(d) Vacuole
(e) Plastid

Answer:
(a) Plasma membrane: It is the outer covering of the cell which separates its contents from the surrounding medium. It is made up of lipids and protein. The main function of cell membrane is to regulate the movement of molecules in and out of the cell.

(b) Mitochondria: Mitochondria are the powerhouses of the cell because energy is released from the mitochondria after respiration. They are the sites cellular respiration of or oxidation of food.

(c) Gene: Genes carry information of heredity help in inheritance or transfer of characters from the parents to the offspring.

(d) Vacuoles: Cells contain water-filled, sac-like structures called as vacuoles. They are large-sized in plant cells while either absent or small-sized in animal cells.

(e) Plastids: The coloured bodies in the cytoplasm of the cells are called plastids. Plastids are found in plant cells only. Chloroplast i.e., the green plastids contains chlorophyll for the process of photosynthesis. Through this process, plant cell prepares food which is ultimately stored in the form of starch.

Question 2.
What are the basic components of a cell? Describe their functions.
Answer:
The basic components of a cell are:
(i) Cell membrane
(ii) Cytoplasm
(iii) Nucleus

(i) Cell membrane separates the inside contents of the cell from outside. It being porous, allows movement of substances or materials both inwards and outwards of the cell.
(ii) Cytoplasm contains the cell organelle, which performs different functions.
(iii) Nucleus acts as a control centre of a cell. In addition to it, it also facilitates inheritance.

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