Cell Structure and Functions Class 8 Extra Questions Science Chapter 8

Cell Structure and Functions Class 8 Extra Questions Science Chapter 8

Cell Structure and Functions Class 8 Extra Questions Science Chapter 8

Q. What is the basic, functional and structural unit of life?

Answer: Cell

Q. Which cell does not have a nucleus?

Answer: Red blood cell (RBC)

Q. What is the name of the organism which can be seen only with the help of a microscope?

Answer: Microorganisms

Q. What are the organisms which are composed of many cells packed together called?

Answer: Multicellular organisms

Q. What is the name of the powerhouse of the cell?

Ans: Mitochondria

Question 6.
Name one example of prokaryotic cell.
Answer:
Blue-green algae

Question 7.
Amoeba and Paramecium belong to which category of organisms?
Answer:
Unicellular

Question 8.
Which instrument is used to observe cells?
Answer:
Microscope

Question 9.
Why we do not sense any pain when we cut nails and hair?
Answer:
Nails and hair are made up of dead cells.

Question 10.
What is the name of living substance present in cell?
Answer:
Protoplasm

Question 11.
What is the other name of cell membrane?
Answer:
Plasma membrane

Question 12.
What is the name of thread-like structure present in nucleoplasm?
Answer:
Chromatin

Question 13.
What is the name of cell which has a well-defined nucleus?
Answer:
Eukaryotic cell

Question 14.
Name the two types of cell.
Answer:
Prokaryotic cells and eukaryotic cells.

Question 1.
What is the function of cell wall?
Answer:
The major function of the cell wall is to provide rigidity, tensile strength, structural support, protection against mechanical stress and infection.

Question 2.
Name the parts of the nucleus and state its function.
Answer:
Nucleus consists of three main parts—nuclear membrane, nucleoplasm and nucleolus.

Nucleus plays an important role during cell division. It also controls the activities of the cell.

Question 3.
What is an organ?
Answer:
The structure that contains more than one type of tissues and is visible to the naked eyes are called organs.

Question 4.
What do you mean by unicellular and multicellular organisms?
Answer:
Organisms which consist of only one cell are called unicellular organisms while organisms made up of more than one cell are called multicellular organisms.

Question 5.
Give a brief description of nucleus.
Answer: Nucleus is a dense round body found in the centre of an animal cell and mostly on the periphery of the plant cell. The nucleus controls all the activities in a cell.

Question 6. Name the following:

a) Controls the function of a cell.

Ans: Nucleus

b) Selectively allows things to get in and out of the cell.

Ans: Cell membrane

c) Transfer characters from parents to offspring.

Answer: Genes

Question 7. What is nucleolus?

Answer: A spherical body present at the centre of the nucleus is called the nucleolus.

Question 8. What is endoplasmic reticulum?

Answer: Endoplasmic Reticulum (ER) is the tubular membrane inside the cytoplasm of the cell. Ribosomes cover their surface. Besides, the ER has both smooth and rough surfaces. In addition, they help in the transportation process.

Question 9.
What are cell organelles?
Answer:
The tiny components present in the cytoplasm are called cell organelles.

Question 10.
What is cell membrane?
Answer:
The thin and delicate membrane surrounding the cell cytoplasm is called cell membrane.

Question 1.
Differentiate between
(a) Cell wall and cell membrane
(b) Leucoplast and chloroplast
(c) Vacuole in a plant cell and an animal cell
(d) A tissue and an organ
Answer:
(a)

Cell wallCell membrane
(i) It is present in only plant cells.(i) It is present in both plant and animal cells.
(ii) It is a rigid, thick structure.(ii) It is a delicate, thin structure.
(iii) It is completely permeable to ordinary molecules.(iii) It is selectively permeable to molecules.
(iv) It is metabolically inactive and non­living.(iv) It is metabolically active and living.

(b)

LeucoplastChloroplast
(i) It is colourless plastid.(i) It is green plastid.
(ii) It is found in underground parts of plants like roots, and underground modified stems.(ii) It is found in green parts of plants like leaves, stems and sepals.
(iii) It helps in storage of food.(iii) It helps in photosynthesis.

(c)

Vacuoles in plantsVacuoles in animals
(i) Plant cell vacuoles are large in size.(i) Animal cell vacuoles are smaller in size.
(ii) Usually a large central vacuole is found.(ii) Many vacuoles are found.
(iii) It is usually a permanent structure.(iii) It is mostly a temporary structure.

(d)

TissueOrgan
It is made of similar cells.It is made of similar tissues.

Question 2.
What are the main functional regions of a cell? Explain.
Answer:
The main functional regions of a cell are:

a) Plasma membrane: This is the membrane which makes the outer boundary of the cells. It is very thin, delicate and selectively permeable.

b) Cytoplasm: Cytoplasm is viscous, the transparent jelly-like substance of the cell. It contains cell organelles.

c) Nucleus: The nucleus controls the working of the cell. It is a dense oval body lying in the protoplasm of the cell.

Question 3. Define cell membrane and state its functions.
Answer: A cell membrane or plasma membrane is a thin, delicate membrane surrounding the cytoplasm. Following are the functions of cell membrane:

a) It separates the cells from one another and also separates the cells from the surrounding medium.

b) It gives a definite shape to the cell.

c) Being porous, it allows the movement of substances from both inside and outside the cells.

d) Its porous structure helps in regulating the movement of materials through the cells.

Question 1. Which organism is more efficient in its functioning—unicellular or multicellular? Why?
Answer: Multicellular organisms are more efficient in their functioning because labour is divided among the cells and have a great capacity to survive than unicellular organisms.

Question 2. What would happen if animals have a cell wall?
Answer: All parts of the animal would become rigid which will make the movement of limbs and body parts difficult.

Question 3. Cells consist of many organelles, yet we do not call any of these organelles as structural and functional units of living organisms. Explain.
Answer: Organelles cannot function outside the cell as an independent unit. They can perform their functions only when they are within the living cells.

Question 4. Why do plant cells need cell walls?
Answer: As plants cannot move, they need protection against variations in temperature, high wind speed, atmo¬spheric moisture, etc.

Question 1.
In a cell, every cell organelle perform its own function. They coordinate the functions of cell.

  • Can a cell work if any of its organelle stops working?
  • What does a cell represent in a real life?
  • What values do we get from the above paragraph?

Answer:

  • Cell would not work if any of its organelle stops working.
  • Cell represent our society where various people do their work to maintain it.
  • We should perform our duty regularly and honestly for the betterment of the whole world.

Question 2.
Shyam being very inquisitive, didn’t listen to the teacher’s instruction properly. He took the thin layer of onion peel with a drop of water on the glass slide. He placed the coverslip on it and start observing the slide under a microscope. But he was unable to see the cells of onion peel properly.

  • What do you think he might have forgotten?
  • What is the function of a dye?
  • What values do you get from the above incidence?

Answer:

  • He might have forgotten using dye.
  • Dye stains the cell and its component and make them visible.
  • We must always follow teacher’s instruction. In laboratory we must not hurry and keep patience.

Question 2.
Talk to the senior biology teacher in your school or a neighbouring school. Find out if there are diseases which are passed on from parents to the offspring. Find out how these are carried and also if these diseases can be treated. For this you can also visit a doctor.
Answer:
Diseases which are passed from parents to offspring are colour blindness, haemophilia, thalassemia, etc. Most of these diseases cannot be treated. (For more information search internet).

Question 3.
Visit an agriculture extension centre in your area. Find out about genetically modified (GM) crops. Prepare a short speech for your class on this topic.
Answer:
Genetically Modified (GM) crops have a great role to play in Indian agriculture, when we need more from lesser resources. The transgenics have the potentiality to resist biotic and abiotic stresses and result in increased productivity in addition to better nutritional quality. The hue and cry on the impact of GM crops on biodiversity has created hypes regarding economic, social and ethical concerns. Though several workers have contradicted the fears expressed regarding the risks and hazards of GM crops, concerns on the safety of a GM foods are still creating controversies. India must avoid taking extreme decisions and has to develop a symbiotic relationship between the public and private sectors, to use new technological inputs to complement the traditional methods for making an ‘Evergreen Revolution’.

Question 4.
Find out about Bt cotton from an agriculture expert (or from envfor.nic.in/divisions/csnrv/ btcotton/bgnote.pdf). Prepare a short note on its advantages/disadvantages.
Answer:
Bt cotton is a Genetically Modified Organism (GMO) cotton variety, which produces an insecticide to bollworm. It is produced by Monsanto. Strains of the bacterium Bacillus thuringiensis produce over 200 different Bt toxins, each harmful to different insects. Most notably, Bt toxins are insecticidal to the larvae of moths and butterflies, beetles, cotton bollworms and ghtu flies but are harmless to other forms of life. The gene coding for Bt toxin has been inserted into cotton as a transgene, causing it to produce this natural insecticide in its tissues. In many regions, the main pests in commercial cotton are lepidopteran larvae, which are killed by the Bt protein in the genetically modified cotton they eat.
Advantages:

  • It eliminates the need to use large amounts of broad-spectrum insecticides to kill these pests.
  • It spares natural insect predators in the farm ecology.
  • It kills only targeted pest.

Disadvantages:

  • By cotton is ineffective against many cotton pests such as plant bugs, stink bugs, and aphids.
  • GM seeds are expensive.
  • GM crops cannot be use as fodder for cattles.
  • Effectiveness up to 120 days, after that the toxin producing efficiency of the Bt gene drastically reduces.

I. Multiple Choice Questions (MCQs)
Choose the correct option.
Question 1.
Nucleus is separated from cytoplasm by
(a) nuclear membrane
(b) nucleoplasm
(c) organs
(d) cell membrane

Question 2.
The liquid material in the nucleus is
(a) chromosomes
(b) bacteria
(c) nucleoplasm
(d) nucleolus

Question 3.
Tissues combine to form
(a) nucleus
(b) cells
(c) organism
(d) organs

Question 4.
Cells present in living organism differ in
(a) numbers
(b) shape
(c) size
(d) all of these

Question 5.
Cells which lack nuclear membrane are
(a) eukaryotic cells
(b) prokaryotic cells
(c) single cells
(d) multicells

Question 6.
The control centre of all the activities of a cell is
(a) nucleus
(b) nucleoplasm
(c) cytoplasm
(d) organelles

Question 7.
The coloured organelles which are found in plants only are
(a) chlorophyll
(b) plastids
(c) vacuoles
(d) WBC

Question 8.
Genes are located in
(a) chrpmosomes
(b) plastids
(c) cytoplasm
(d) lysosome

Question 9.
A group of similar cells combine to form
(a) tissue
(b) organ
(c) organisms
(d) organelles

Question 10.
The organism containing only a single cell is called
(a) unicellular organism
(b) multicellular organism
(c) organelle
(d) all of these

Question 11.
Cell walls is found in
(a) plant cells only
(b) animal cells only
(c) both (a) and (b)
(d) none of them

Question 12.
The empty blank looking structures in the cytoplasm is
(a) vacuoles
(b) plastids
(c) plasma membrane
(d) nucleus

Question 13.
The other name of cell membrane is
(a) plasma membrane
(b) cell wall
(c) nuclear membrane
(d) none of these

Question 14.
The basic structural and functional unit of all living organism is
(a) cell
(b) cell wall
(c) cell membrane
(d) chloroplasts

Question 15.
Chromosomes are found in
(a) nucleus
(b) nucleolus
(c) nucleoplast
(d) vacuole
Answer:
1. (a)
2. (c)
3. (d)
4. (d)
5. (b)
6. (a)
7. (b)
8. (a)
9. (a)
10. (a)
11. (a)
12. (a)
13. (a)
14. (a)
15. (a)

II. Fill in the Blanks
Fill in the blanks with suitable word/s.
1. Cells are the __________ unit of all living organisms.
2. __________ cells are branched.
3. Amoeba has __________ shape.
4. The __________ cell transfers the messages.
5. __________ is a group of tissues.
6. Protoplasm is __________ inside the cell.
7. Eukaryotes cells have a well-developed __________.
8. The jelly-like substance found between the nucleus and the cell-membrane is __________
9. Nucleus is separated from the cytoplasm by __________.
10. An __________ is a group of organs.
11. __________ are present in plant cells but in animal cells.
12. __________ is the process of making food in plants.
13. __________ is absent in animal cell.
14. The kitchen of plant cell is __________.
15. __________ is the power house of the cell.
Answer:
1. basic
2. Muscle
3. irregular
4. nerve
5. Organ
6. viscous fluid
7. nucleus
8. cytoplasm
9. nuclear membrane
10. organ system
11. Plastids, absent
12. Photosynthesis
13. Cell wall
14. plastid
15. Mitochondria

III. Match the following
Match the items given in column I suitably with those given in column II
Cell Structure and Functions Class 8 Extra Questions Science Chapter 8 1
Answer:
1. (e)
2. (a)
3. (b)
4. (c)
5. (d)
6. (h)
7. (g)
8. (f)
9. (j)
10. (i)

IV. True or False
State whether the given statements are true or false.
1. Cytoplasm is not a part of cell.
2. Cell wall surrounds the cell membrane.
3. A group of similar cells is called tissue.
4. Tissues combine to form an organism.
5. Cell are of different sizes.
6. Chloroplasts are blue in colour.
7. Plastid occur in plant cells only.
8. Chromosomes contain basic hereditary units called genes.
9. Nucleus is the control unit of cell.
10. The shape and size of cell is related to its function.
11. Organs make up tissues.
12. The cytoplasm and nucleoplasm make up the protoplasm.
13. The smallest unit of life is chloroplast.
14. Unicellular organisms have one-celled body.
15. The cell wall is living in nature.
Answer:
1. False
2. True
3. True
4. False
5. True
6. False
7. True
8. True
9. True
10. True
11. False
12. True
13. False
14. True
15. False

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