THE STRUCTURE OF A CELL AND MICROORGANISMS

Cell wall: covering of the cell.

(1) Protects inner

parts of the cell.

(2) Regulates the

flow of substances

that enter

into or pass out

of the cell.

(3) Maintains the

shape of the

cell.

(2) Cell wall Present only in

plant cells. It is

made up of cellulose.

(1) Substances can

pass into the

cell or out of the

cell through the

cell wall.

Cell Organelle Structure Function

(2) Gives strength

to the cell.

(3) Gives a definite

shape to the cell.

(4) Protects inner

components of

the cell.

(3) Nucleus (1) Central, round

and largest part

of the cell.

(1) Controls all the

functions of cell.

(2) Porous nuclear

membrane

around it.

(2) Takes part in

cell division.

(3) Inside it, are

chromosomes

made up of

DNA and genes.

(3) Transmits

inherited characters

through

DNA and genes.

(4) Cytoplasm (1) Substance filling

the cell,

apart from the

nucleus.

Cell organelles

which perform all

the functions of the

cell are embedded

in it.

(2) Semi-fluid substance

with

water soluble

organic and

inorganic substances.

(5) Mitochondria (1) Mainly tubular

in shape.

(1) Produce energy

from the food

material in the

cell.

(2) It has double

walls.

(2) Supply energy

to the cell

whenever

required.

Cell Organelle Structure Function

(3) Inner wall has

folds.

(6) Golgi bodies Stacks of flat,

membrane bound

sacs

Storage of enzymes.

(7) Vacuoles (1) An empty space

covered by a

single membrane.

They store products

of excretion and

secretions temporarily.

(2) Plant cells have

large vacuoles.

4. Differences between animal cell and plant cell :

Character Animal Cell Plant cell

(1) Cell wall      Absent              Present

(2) Vacuole       Small                Large

(3) Plastids       Absent              Present

5. Microorganisms : In our surroundings, there are countless

microorganisms. Viruses, bacteria, algae, fungi, yeast cells,

protozoa, etc. are some of the types of microorganisms. Some

microorganisms are harmful while some are useful.

6. Virus :

(1) A virus can be studied only by an

electron microscope. (2) Viruses do not

have cell organelles and cytoplasm.

(3) There is a protein covering around a

virus. (4) It has DNA or RNA molecules.

(5) Viruses cause different diseases in

plants and animals.

7. Bacteria : (1) Bacteria can be seen by a

compound microscope. (2) They have cell

wall, cell membrane, cytoplasm and cell

organelles. (3) They have free chromosomes,

as nuclear membrane is absent. (4) Some

bacteria are useful while some are

harmful.

Bacteria Occurrence Functions

(1) Useful

(a) Rhizobium In the root

nodules of

leguminous

plants

(1) Nitrogen fixation.

(2) Transform

nitrogen in the air to

nitrogen compounds.

(3) Make the soil fertile.

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

(b) Azotobacter In the soil (1) Fixes atmospheric

nitrogen.

(2) Independent

existence.

(3) Make soil fertile.

(2) Harmful

(a) Staphylococcus Grows on

foodstuffs

Produce enterotoxin. If

enterotoxin enters the

body, it causes diarrhoea

and vomiting.

(b) Clostridium Grows in canned

foodstuffs after

their date of

expiry.

Produce toxic substances.

8. Algae : (1) Algae grow in wet and

damp places. (2) They are autotrophic

plants, possessing chlorophyll.

(3) Most of them are useful. (4) Diatom

is a type of alga.

9. Fungi : (1) Fungi grow in damp places

on organic substances. (2) They do

not have chlorophyll. They are

saprophytic. (3) Some fungi are useful

and some are harmful. Harmful fungi

cause skin diseases and also cause

damage to substances. (4) From the

fungus Penicillium, antibiotic

penicillin is manufactured. In 1928 , Alexander Fleming

discovered that a substance produced during the growth of

Penicillium kills microorganisms

10. Antibiotics : Certain microorganisms are able to produce

some specific antibiotics. These antibiotics can kill only

particular types of microorganisms.

Antibiotics Microorganisms

producting the

antibiotic

Type of

microorganism

Germs destroyed

Penicillin Penicillium

chrysogenum

Fungus Germs of

diphtheria and

pneumonia

Chloromycetin Streptomyces

venezuelae

Bacterium Germs of typhoid

Streptomycin Streptomyces

griseus

Bacterium Germs of

tuberculosis

Tetracycline Streptomyces

aureofaciens

Bacterium Various germs

Erythromycin Streptomyces

erythreus

Bacterium Various germs

11. Yeast cells : (1) The fungal cells which cause fermentation are

known as yeast cells. (2) During such fermentation by microorganisms,

organic substances with excellent taste and flavour

are produced. Bread, idli and dosa are some foodstuffs formed

by fermentation. (3) Some unpalatable and harmful substances

are also produced due to fermentation. Such substances are not

suitable for consumption.

12. Protozoa : (1) Protozoa are unicellular organisms having

nucleus and cell membrane. (2) They do not have chlorophyll

and grow by taking ready-made food. (3) Some protozoa are

harmful. Amoeba is one such protozoan that causes illness

(Amoebic dysentery), diarrhoea and vomiting.

Q. 1 Answer the following questions :

(1) When, how and by whom was the cell discovered ?

Ans. (1) Around 350 years ago, in the year 1665, an English

scientist named Robert Hooke discovered the cell. (2) He was

observing the thin sections of cork under microscope. (3) He saw

the section of the cork like a honeycomb. It was made up of small

compartments which he named cells.

(3) What are the instruments used for studying the cells ?

What is the magnification of these instruments?

Ans. (1) Cells are studied with the help of a compound

microscope. (2) For magnifying and observing small objects which

cannot be seen by a compound microscope, an electron microscope

7. THE STRUCTURE OF A CELL AND MICROORGANISMS 83

is used. (3) With the help of compound microscope, the cells can

be magnified to 100 or 1000 times. (4) With the help of electron

microscope the objects are magnified 2 billion times, i.e 2_10

times.

(4) What are cell organelles? Name the cell organelles.

Ans. (1) Cell has various constituents inside its cytoplasm.

(2) These constituents are called cell organelles. (3) The following

are the cell organelles : cell wall, cell membrane, cytoplasm,

nucleus, mitochondria. Golgi body, ribosomes, lysosomes, plastids

and vacuoles.

* (5) List the characteristics of the cell membrane.

Ans. (1) Cell membrane is located on the outer side of the cell.

(2) In plant cells, a cell wall lies on the outer side of cell membrane.

(3) It is a thin and flexible layer. (4) Functions of the cell membrane

are as follows : (i) It protects the inner parts of the cell (ii) It

regulates the flow of the substances which enter into the cell and

pass out from the cell. (iii) It maintains the shape of the cell.

(6) Explain the structure of the nucleus.

Ans. Structure of the nucleus :

(1) The nucleus is the largest and the central part of the cell.

(2) The shape of the nucleus is usually round. (3) The membrane

surrounding the nucleus is porous. (4) The nucleus contains

chromosomes. (5) The chromosomes are made up of DNA

(Deoxyribonucleic acid) molecules. (6) A DNA thread of a specific

length is called a gene.

* (7) Explain the functions of the nucleus.

Ans. Functions of the nucleus :

(1) The nucleus controls and regulates all the functions of a

cell. (2) It takes an active part in the process of cell division.

(3) Chromosomes in the nucleus are made up of DNA molecules.

The specific length of DNA, is called a gene which helps in the

transmission of inherited characters from parental generation to

the next one.

(8) What is cytoplasm ? What is its function ?

Ans. 1. Cytoplasm : (1) Inside the cell there are two parts,

the nucleus and the cytoplasm. The substance which fills up the cell

except the nuclear region is called cytoplasm. (2) The cytoplasm is

84 NAVNEET GENERAL SCIENCE DIGEST : STANDARD VIII

semi-fluid in nature. (3) Water-soluble organic and inorganic

substances are suspended in the cytoplasm.

2. Function of cytoplasm : The cell organelles which perform

various functions of the cell lie in the cytoplasm.

(9) What is a vacuole ?

Ans. (1) A vacuole is a cell organelle. (2) It has an empty space

which is covered over by a membrane. (3) Plant cells have large

vacuoles. (4) Animal cells have small vacuoles.

* (10) What functions do vacuoles perform?

Ans. (1) Vacuoles store products of excretion. (2) Vacuoles

also store temporarily secretions of cells within it.

(11) What is a virus ? Explain the structure of a virus.

Ans. (1) Virus is an ultramicroscopic microorganism that

does not have a cellular structure. (2) It has a simple structure.

(3) It can be observed only under an electron microscope.

(4) Viruses have a protein covering around them. (5) Viral DNA or

RNA is present inside the virus. (6) Viruses are harmful and cause

variety of diseases among plants and animals.

(12) What are bacteria ? Explain the structure of a

bacterium.

Ans. (1) Bacteria are microscopic microorganisms which can

be seen only through a compound microscope. (2) They are larger

than viruses. (3) There are free chromosomes in bacteria. Nucleus

is not clearly formed in bacteria. (4) Bacterial cell shows cell wall,

cell membrane, cytoplasm and cell organelles. (5) Some bacteria

are useful to man while some are harmful. Harmful bacteria cause a

variety of diseases.

(13) What are protozoa? Give an example of a harmful

protozoan.

Ans. (1) Protozoa is the class of unicellular animals. (2) They

do not have chlorophyll and they cannot synthesize food like plants.

(3) Protozoa grow by obtaining ready-made food. (4) Amoeba is a

harmful protozoan. It causes amoebic dysentery. (5) It enters the

body through contaminated food or water and causes diarrhoea and

vomiting. (6) If the patient is not given treatment these disorders

cause chronic problems.

* (1) How many chromosomes are there in the nucleus

of the human cell ?

Ans. The nucleus of human cell has 46 chromosomes.

* (2) Why is Euglena said to belong to both animal as

well as plant kingdom?

Ans. Euglena shows behaviour like animals. However,

since it has chlorophyll, it is an autotrophic organism. Hence

it is said to belong to both animal and plant kingdoms.

Q. 2 Write short notes on the following :

(1) Cell wall * (2) Mitochondria * (3) Harmful bacteria

* (4) Useful bacteria * (5) Antibiotics (6) Yeast cells.

Ans. (1) Cell wall : (1) The covering outside the cell

membrane is cell wall. (2) It is present only in plant cells. (3) The

cell wall is made up of cellulose. (4) Cell wall gives strength to the

cell. (5) It gives a definite shape to the cell. (6) Inner components of

the cell get protection due to cell wall. (7) Cell wall regulates the

passage of substances in and out of the cell.

(2) Mitochondrion (Pl. Mitochondria) : (1) Mitochondrion

is an important cell organelle. (2) It is mainly tubular in shape. But

other shapes of mitochondria also occur. (3) The mitochondrion

has a double wall. (4) The inner wall of mitochondria is folded.

(5) Mitochondria produce energy from the food material present

in the cell. (6) This energy is supplied to cell when required.

(7) Mitochondria, therefore, are called the powerhouse of the cell.

(3) Harmful bacteria : (1) Some varieties of bacteria are

harmful. (2) Staphylococcus bacteria grows on foodstuffs. (3) It

produces a toxic substance called, enterotoxin. (4) This substance

after entering the body causes vomiting and diarrhoea. (5) Another

harmful bacteria is Clostridium. It grows on the canned food after

its expiry. (6) This bacterium too produces poisonous substance.

Such foodstuffs, if consumed, cause diarrhoea and vomiting.

(7) Diseases like typhoid, tuberculosis, diphtheria and pneumonia

are also caused due to bacterial infections.

(4) Useful Bacteria : Some bacteria are useful for man.

(1) The Rhizobium bacterium which lives inside the nodules on the

roots of leguminous plants does the function of nitrogen fixation.

 (2) Rhizobium bacteria convert the nitrogen in the air into

nitrogenous compounds. (3) Due to this soil becomes fertile.

(4) Another bacterium, Azotobacter which lives independently also

fixes atmospheric nitrogen into nitrogenous compounds.

(5) Several bacteria in the soil, carry out decomposition of dead and

decaying matter. (6) They in turn make humus from them. Fertility

of the soil is thus increased due to such bacteria.

(5) Antibiotics : (1) Antibiotics are substances which can kill

a particular microorganism. (2) Antibiotics can control spread of

disease by killing specific microorganisms. (3) In 1928, Alexander

Fleming first discovered the antibiotic properties in the fungus,

Penicillium. He discovered that a particular substance from this

fungus can kill microorganisms. (4) Based on this discovery the

well known antibiotic, penicillin was discovered from Penicillium

fungus. (5) Similarly antibiotics such as, Chloromycetin,

Streptomycin, Tetracycline, Erythromycin can be produced from

different microorganisms. (6) These antibiotics can cure diseases

such as typhoid, tuberculosis and pneumonia.

(6) Yeast cells : (1) Yeast belongs to the class of Fungi.

(2) Yeast cells are used in fermentation reaction. (3) Yeast helps in

the formation of organic substances with excellent taste and

flavour. (4) In the preparation of bread, yeast cells are used for the

process of fermentation.

Q. 3 Distinguish between the following :

* (1) Plant cell and Animal cell :

Ans. Plant cell Animal cell

1. The cell wall is the outermost

covering of the plant cell.

1. The cell membrane is the

outermost covering of the

animal cell.

2. Cell wall is present in the

plant cell.

2. Cell wall is absent in animal

cell.

3. Vacuoles in plant cell are

large.

3. Vacuoles in animal cell are

small.

4. Chloroplastids are present in

plant cell.

4. Chloroplastids are absent in

animal cell.

5. Chlorophyll is present in

plant cell.

5. Chlorophyll is absent in

animal cell.

* (2) Cell Membrane and Cytoplasm :

Ans. Cell Membrane Cytoplasm

1. Cell membrane is the outer

covering of the cell.

1. Cytoplasm is a substance

inside the cell.

2. Cell membrane protects the

inner parts of the cell.

2. Cytoplasm has cell organelles

embedded in it.

3. Cell membrane is a thin,

flexible membranous solid

substance.

3. Cytoplasm is a semi-fluid

substance.

4. Cell membrane is made up of

lipids and proteins.

4. Cytoplasm is made up of

organic and inorganic

components.

5. Cell membrane regulates the

flow of substances in and out

of the cell.

5. All the cell organelles

embedded in the cytoplasm

carry out the various life

processes of the cell.

(3) Virus and Bacteria :

Ans. Virus Bacteria

1. Virus does not have cellular

structure.

1. Bacteria have cellular

structure.

2. Virus does not have

cytoplasm and cell

organelles.

2. Bacteria have cytoplasm, cell

membrane and free

chromosomes.

3. Virus can be observed only

through electron microscope.

3. Bacteria can be observed

under a compound microscope.

4. Viruses are smaller than

bacteria.

4. Bacteria are larger than

viruses.

5. Virus may have DNA or RNA

as its genetic material.

5. Bacterial DNA and RNA both

are present in bacterial cells.

6. There is covering of protein

around the viral cell.

6. There is covering of cell wall

around the bacterial cell.

7. Viruses cannot be killed by

antibiotics.

7. Bacteria can be killed by a

specific antibiotic.

8. All the types of viruses are

harmful.

8. All bacteria are not harmful.

Some of them are useful too.

 (4) Algae and Fungi :

Ans. Algae Fungi

1. In algae, chlorophyll is

present.

1. In Fungi, chlorophyll is

absent.

2. The algae are autotrophic. 2. The fungi are saprophytic.

3. Most of the algae are useful. 3. Most of the fungi are harmful.

Only few are useful.

4. Antibiotics cannot be

prepared from algae.

4. Antibiotics are prepared

from fungi.

5. Algae are producers in the

food chains.

5. Fungi are decomposers in the

food chain.

Q. 4 Give scientific reasons :

(1) Mitochondria are called the powerhouses of the cell.

Ans. (1) Mitochondria produce energy from food materials

within the cells. (2) Whenever required this energy is supplied to

the cell. (3) Mitochondria, therefore are called the powerhouses of

the cell.

(2) Viruses are studied by an electron microscope.

Ans. (1) Viruses are very small. (2) Their structure cannot be

observed by a compound microscope. (3) With the electron

microscope, magnification of infinitesimally small objects can be

done. (4) The object gets magnified two billion times by the electron

microscope. (5) Viruses therefore, are studied by an electron microscope.

(3) Some bacteria increase the fertility of the soil.

Ans. (1) Many useful bacteria are there in the soil. These

bacteria decompose dead plant and animal bodies and produce

humus from them. (2) This humus increases the fertility of the soil.

(3) Bacteria like Rhizobium that live inside the root nodules of

leguminous plants bring about nitrogen fixation. (4) Bacteria such

as Azotobacter also converts atmospheric nitrogen into nitrogenous

compounds. (5) Rhizobium and Azotobacter increase the fertility of

the soil by adding nitrogenous compounds to it. (6) Some bacteria

therefore, increase the fertility of the soil.

 (4) We should not eat foodstuffs from the cans whose

expiry date is over.

Ans. (1) Canned foodstuffs have to be used within a specific

period. (2) After this period is over, the harmful bacteria like

Clostridium start growing in it. (3) These bacteria produce toxic

substances in such cans. (4) The consumption of such food causes

diarrhoea and vomiting. (5) In order to prevent such hazard, on

every can expiry date is specified. This means that a person should

consume canned food only during the stipulated time. (6) So to

avoid poisoning we should not eat foodstuffs from the cans whose

expiry date is over.

(5) Water from overhead tanks give bad odour at times.

Ans. (1) Water in overhead tanks may contain algae. (2) If

sunlight reaches here, these algae start growing. (3) The growth

of algae cause bad odour. (4) Therefore, water from overhead

tanks give bad odour at times.

(6) Fungi are called saprophytic.

Ans. (1) Saprophytic means utilizing dead and decaying

organic food and converting it into inorganic substances, (2) This

mode of nutrition is seen in fungi. (3) Fungi can grow on any

organic matter if there is humidity in the air. (4) Therefore, fungi

are called saprophytic.

(7) We should not use uncovered food.

Ans. (1) There are countless microorganisms in our

surroundings. (2) The air, water and soil are occupied by

microorganisms. (3) Some of these microorganisms are harmful as

they cause many diseases. (4) Viruses, bacteria, fungi and

Protozoan like Amoeba can cause infection. (5) The uncovered food

may carry some of these microorganisms. (6) Therefore, in order to

protect our health, we should not use uncovered food.

(8) We should not use contaminated food or water.

Ans. (1) Contaminated food or water contain harmful and

disease-causing viruses, bacteria, fungi or Protozoa. (2) Some

bacteria like Staphylococcus produce enterotoxin which can cause

poisoning. (3) Infections such as diarrhoea and vomiting can be

caused due to such contaminated food. (4) Therefore, we should not

use contaminated food.

5 Answer the following questions in one sentence

each :

Who gave the term ‘cell’ ?

Ans. The English Scientist Robert Hooke gave the term ‘cell’.

  When is an electron microscope used ?

Ans. When infinitesimally small object which cannot be seen

under a compound microscope, has to be magnified to view a large

image then an electron microscope is used.

 In which cells are the cell walls found?

Ans. Cell walls are found only in plant cells.

Of which substance is cell wall made up of ?

Ans. Cell wall is made up of cellulose.

 Which is the largest and central organelle of the cell ?

Ans. Nucleus is the largest and central organelle of the cell.

What is a gene ?

Ans. DNA thread of a specific length is known as gene.

(7) How does transmission of inherited characterstics

take place ?

Ans. Inherited characteristics are transmitted to the next

generation according to the genes on the chromosomes in the

nucleus.

Which organelle is called the powerhouse of a cell ?

Ans. The organelle mitochondrion (Pl. mitochondria) is called

the powerhouse of a cell.

 What is the shape of Golgi bodies ? What is stored in

them?

Ans. Golgi bodies are stacks of flat membrane bound sacs in

the cytoplasm storing enzymes.

 Which microorganism does not have cell organelles

and cytoplasm?

Ans. Virus is the microorganism that does not have cell

organelles and cytoplasm.

  Which type of bacterium is found in the nodules on

the roots of leguminous plants ? What is its function?

Ans. The bacteria found in the nodules on the roots of

leguminous plants are Rhizobium which help to convert nitrogen

from air into nitrogenous compounds.

Which bacteria fix nitrogen of the air independently?

Ans. Azotobacter bacteria fix the nitrogen of the air independently.

 Which bacterium produces the poisonous

enterotoxin? Where is it produced?

Ans. The bacterium Staphylococcus produces the poisonous

enterotoxin in the foodstuffs.

Where does Clostridium grow?

Ans. Clostridium grows on the canned foodstuffs which have

crossed their date of expiry.

What was the discovery of Alexander Fleming?

Ans. Alexander Fleming discovered that a substance produced

during the growth of fungus Penicillium can kill certain

microorganisms.

 6 Find the odd man out and give reasons :

(1) Cell membrane, Cell wall, Cytoplasm, Mitochondria.

(2) Virus, Bacteria, Algae, Protoza.

(3) DNA, RNA, Nucleus, Gene.

(4) Penicillin, Tetracycline, Enterotoxin, Erythromycin.

(5) Mitochondria, Ribosomes, Lysosomes, Humus.

(6) Bread, Canned food, Idli, Dosa.

(7) Nucleus, Fungi, Cytoplasm, Cell membrane.

(8) Rhizobium, Amoeba, Harmful fungi, Clostridium.

Ans. (1) Cell wall. Others are cell organelles of animal cell.

(2) Virus. Others have cell organelles and cytoplasm. (3) Nucleus.

Others are found inside the chromosome. (4) Enterotoxin. Others

are antibiotics. (5) Humus. Others are cell organelles. (6) Canned

food. Others are foodstuffs made by fermentation. (7) Fungi.

Others are important constituents of cell. (8) Rhizobium. Others

are harmful microorganisms.

7 Considering the correlation between the words of

the first pair, match the third word with the most appropriate

answer :

(1) Cytoplasm : Organelles : : Chromosomes : ……… .

(2) Cell wall : Cellulose : : Covering of virus : ……… .

(3) Supply of energy : Mitochondria : : Storage of

enzymes : : ……… .

(4) Overhead tanks of water : Algae : : Canned food : ……… .

(5) Chloromycetin : Typhoid : : Streptomycin : ……… .

(6) Penicillium : Penicillin : : Staphylococcus : ……… .

(7) Unicellular Protozoa : Amoeba : : Unicellular algae : ……… .

Ans. (1) Genes (2) Proteins (3) Golgi body (4) Clostridium

(5) Tuberculosis (6) Enterotoxin (7) Diatom

Q. 8 State whether the following statements are True

or False. If a Statement is false, correct it and rewrite :

(1) All living things are not made up of cells.

(2) All the life processes are carried out by cells.

(3) The cell wall gives strength to animal cells.

(4) The membrane around the nucleus is continuous.

(5) Mitochondria are mainly triangular.

(6) Vacuoles in the plant cells are small in size and few in

number.

(7) Animal cells do not have chlorophyll.

(8) Viruses do not have cytoplasm and cell organelles.

(9) In Amoeba, instead of nucleus, there are free chromosomes.

(10) Humus reduces the fertility of the soil.

(11) Algae grow in damp places on organic substances.

(12) Some harmful fungi cause diseases of the skin.

(13) Yeast cells belong to the class of Algae.

(14) When Amoeba enters our stomach, we get trouble only for a

small period of time.

(15) The cell is the basic constituent of every living thing.

Ans. (1) False. All living things are made up of cells.

(2) True. (3) False. The cell wall gives strength only to plant cells.

(4) False. The membrane around the nucleus is porous. (5) False.

Mitochondria are mainly tubular. (6) False. Vacuoles in the plant

cells are large in size and many in number. (7) True. (8) True.

(9) False. In bacteria, instead of nucleus there are free

chromosomes. (10) False. Humus increases the fertility of the soil.

(11) True. (12) True. (13) False. Yeast cells belong to the class of

Fungi. (14) False. When Amoeba enters our stomach, we get

chronic type of illness. (15) True.

Q. 9 Fill in the blanks :

1. (1) The study of cells is called ……… .

* (2) The name cell was first used by the scientist ……… .

* (3) The cell wall of plant cell consists of a substance ……… .

* (4) The cell wall is found only in the ……… cells.

(5) ……… is the central and largest component of the cell.

Ans. (1) cytology (2) Robert Hooke (3) cellulose (4) plant

(5) Nucleus.

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

2. (1) Cytoplasm is a ……… substance.

(2) ……… are made up of DNA and are present inside the

nucleus.

* (3) ……… are the powerhouses of the cell.

* (4) The cell membrane is ……… .

(5) Golgi bodies store ……… .

Ans. (1) semifluid (2) Chromosomes (3) Mitochondria

(4) the outer covering of the cell (5) enzymes.

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

3. (1) Nucleus takes part in ……… .

(2) Some kinds of ……… are used as food.

(3) ……… are a kind of unicellular algae.

(4) ……… can kill specific microorganisms.

(5) Disease becomes ……… if not treated in time.

Ans. (1) cell division (2) algae (3) Diatoms (4) Antibiotics

(5) chronic.

Q. 10 Choose the correct alternative and complete the

following sentences :

(1) Electron microscope magnifies the object two …… times.

(a) thousand (b) million (c) billion (d) lac

(2) The ……… regulates the flow of substances that enter into

or pass out of the cell.

(a) vacuole (b) cell membrane

(c) cytoplasm (d) mitochondrion

(3) …… thread of a specific length is called a gene.

(a) Chromosomal (b) DNA (c) Protein (d) Amino acid

(4) ……… store products of excretion and secretions

temporarily.

(a) Vacuoles (b) Golgi bodies

(c) Mitochondria (d) Lysososmes

* (5) The ……… is an organelle found only in plant cells.

(a) ribosome (b) mitochondrion (c) plastid (d) nucleus

* (6) Chromosomes are found in the organelle called ……… .

(a) plastid (b) mitochondrion (c) nucleus (d) Golgi body

* (7) The ……… cell carries out photosynthesis.

(a) plant (b) yeast (c) muscle (d) nerve

(8) The antibiotic penicillin is used to kill germs of ……… and

……… .

(a) diphtheria, pneumonia

(b) tuberculosis, typhoid

(c) cough, cold

(d) asthma, diarrhoea

(9) Some harmful fungi cause ……… diseases.

(a) chest (b) throat (c) skin (d) mouth

(10) Fermentation caused by microorganisms results into the

formation of ……… substances.

(a) inorganic (b) organic

(c) proteinaceous (d) fatty

Ans. (1) billion (2) cell membrane (3) DNA (4) Vacuoles

(5) plastid (6) nucleus (7) plant (8) diphtheria, pneumonia

(9) skin (10) organic.

Q.1 Match the following :

[1] ‘A’ ‘B’

(1) Robert Hooke

(2) Alexander Fleming

(3) Cellulose

(4) DNA

(a) Genes

(b) Cell wall

(c) Penicillin

(d) Cell

Ans. (1) Robert Hooke– Cell (2) Alexander Fleming –

Penicillin (3) Cellulose – cell wall (4) DNA– Genes.

[2] ‘A’ ‘B’

(1) Bacteria living inside the

nodules of the root

(2) Bacteria inside the canned food

after its date of expiry

(3) Bacteria living in the soil

(4) Bacteria secreting enterotoxins

(a) Azotobacter

(b) Staphylococcus

(c) Rhizobium

(d) Clostridium

Ans. (1) Bacteria living inside nodules of the root – Rhizobium.

(2) Bacteria inside the canned food after its date of expiry –

Clostridium. (3) Bacteria living in soil – Azotobacter. (4) Bacteria

secreting enterotoxins – Staphylococcus.

[3] ‘A’ ‘B’

(1) Penicillin

(2) Chloromycetin

(3) Streptomycin

(4) Tetracycline

(5) Erythromycin

(a) Streptomyces griseus

(b) Streptomyces erythreus

(c) Streptomyces aureofaciens

(d) Streptomyces venezuelae

(e) Penicillium chrysogenum

Ans. (1) Penicillin – Penicillium chrysogenum (2) Chloromycetin

– Streptomyces venezuelae (3) Streptomycin – Streptomyces

griseus (4) Tetracycline – Streptomyces aureofaciens (5) Erythromycin–

Streptomyces erythreus.