ICSE Class 7 Biology Important Questions Chapter 9 Life Under a Microscope

Biology ICSE Class 7 Important Questions Chapter 9 Life Under a Microscope

Extra Questions

Question 1.
What are microorganisms ? Name its categories.
Answer:
Organisms that can be seen through a microscope only arc
called microorganisms. They are divided into five categories – bacteria, algae, protozoa, fungi and viruses.

Question 2.
What are algae ?
Answer:
Algae are a large group of autotrophic organisms that are mostly found in aquatic habitats like ponds, puddles and oceans or even in moist soil, rocks and tree barks. They may be unicellular, multicellular or colonial

Question 3.
Classify algae on the basis of their pigments.
Answer:
All algae contain green pigment chlorophyll. Some algae have pigments of other colours also and classified as :
(i) Green algae
(ii) Brown algae
(iii) Red algae

Question 4.
How do bacteria survive harsh conditions ?
Answer:
Bacteria can survive under harsh conditions due to the formation of a hard protective covering around them called a cyst or a spore. They remain inactive in the cyst during unfavourable conditions. The hard protective covering
protect it from the unfavourable conditions and it becomes active during favourable conditions by breaking the cyst wall.

Question 5.
How are anaerobic bacteria different from aerobic bacteria ?
Answer:
Anaerobic bacteria :

• They grow in the absence of oxygen.
• For example : Tetanus is caused by anaerobic bacteria.

Aerobic bacteria:

• They grow in the presence of oxygen.
• For example : Tuberculosis is caused by aerobic bacteria.

Question 6.
List the three main groups of fungi. Give one example of each group.
Answer:
The three major groups of fungi are :
(a) thread like fungi
(b) club fungi
(c) sac fungi
(a) Thread like fungi : They grow in the form of fine threads that form a cotton-like mass on the surface. These thread like structures are hyphae. Most hyphae grow along the surface of the substrate which may be cheese or bread. Some of the hyphae are root like and grow downward. For example.

(a) Rhizopus and Mucor.

(b) Club fungi : Mushrooms and bracket are club fungi. Some of these may reach a height of 20 or 30 cm. Most mushrooms are hyphae. The part above the ground is the reproductive structure of a mushroom. The upright part of mushroom is called the stalk. The umbrella shaped part of mushroom is called die cap. Both stalk and cap are made of hyphae that are tightly packed.

(c) Sac Fungi :
These fungi vary from single celled microscopic yeast to the large morels.

Question 7.
Give reasons
(i) The dough prepared for making idli rises when kept overnight.
Answer:
Dough prepared for making idli rises when kept overnight due to the action of yeast. It becomes light, fluffy and sour.
Yeast multiply and produces carbondioxide which raises the dough.

(ii) Food is kept in the refrigerator to prevent spoilage.
Answer:
Food is kept in the refrigerator to prevent spoilage as microorganisms do not multiply in cold conditions.

(iii) It is difficult to set curd in winters.
Answer:
It is difficult to set curd in winters as microorganisms do not multiply in cold conditions. As the temperature is very low in winters.

(iv) How do bacteria help in maintaining fertility of the soil?
Answer:
Bacteria along with certain fungi play an important role in maintaining the fertility of the soil. Some bacteria live in the root nodules of plants, such as pea, gram and beans. These bacteria absorb the nitrogen of the atmosphere and convert it in to nitrates these nitrates are transferred to the soil, which are used by the plants.

Question 8.
Who discovered microorganisms ?
Answer:
Anton van Leeuwenhoek.

Question 9.
Name few unicellular and multicellular organisms ?
Answer:
Microorganisms mae up of only one cell are called unicellular microorganisms. For example, bacteria, certain algae (diatoms, chlorella, chlamydomonas), yeast (a fungus), Paramecium and Euglena (protozoans)
Microorganisms which are made of many cells are called multicellular microorganisms. For example, Volvox, Spirogyra, bread mould.

Question 10.
Classify bacteria on the basis of their shape.
Answer:
(i) Cocci – spherical shaped
(ii) Bacilli – rod shaped bacteria. Example – E scherichia coli.
(iii) Spirilla – spiral shaped bacteria.
(iv) Vibrios – curved or comma shaped bacteria. Example – Vibrio choleraL

Question 11.
Why is Cyanobacteria named so when it is a blue- green algae ?
Answer:
It has blue pigment along with chlorophyll (green pigment) and is a blue green algae. However, it is more like a bacteria as it does not have a nucleus, hence named Cyanobacteria.

Question 12.
Name two brown algae.
Answer:
Laminaria and Fucus

Question 13.
What is algin ?
Answer:
It is a gummy substance present in kelps (a brown algae) which is used in the preparation of ice cream and toothpaste.

Question 14.
Name few green algae which are :
(i) Unicellular
(ii) Multicellular
(ill) Colonial
Answer:
(i) Unicellular green algae — Chlorella, Chlamydomonas, desmids, diatoms.
(ii) Multicellular green algae — Spirogyra
(iii) Colonial green algae — Volvox

Question 15.
Name an autotrophic protozoa and a heterotrophic protozoa.
Answer:
Heterotrophic protozoa — Amoeba, paramecium. Autotrophic protozoa — Euglena

Question 16.
Why are viruses regarded as a link between the living organisms and the non-living world ?
Answer:
Viruses are not free living. They grow and multiply only in living cells of host. They neither reproduce nor respire outside a living host

Question 17.
Draw the structure of a typical virus (bacteriophage)
Answer:

Question 18.
What is fermentation ?
Answer:
Fermentation is a process by which carbohydrates are changed into alcohols and carbon dioxide by bacteria or yeast under anaerobic conditions.

Question 19.
How do bacteria help in maintaining fertility of the soil?
Answer:
Bacteria along with certain fungi play an important role in maintaining the fertility of the soil. Some bacteria live in the root nodules of plants, such as pea, gram and beans. These bacteria absorb the nitrogen of the atmosphere and convert it in to nitrates. These nitrates are transferred to the soil, which are used by the plants.

Question 20.
Give few uses of fungi.
Answer:
Uses of fungi –

• Scavenging – They decompose the dead, decaying bodies of plants and animals and are nature’s scavengers and make die soil fertile.
• Food – Some mushrooms are eaten as food.
• Yeast is used in the manufacturing of wine and bakery products to make them light and fluffy.
• Antibiotics – Penicillin, an antibiotic is obtained from a fungus, Penicillium.

Question 21.
Name the microorganisms causing the following diseases.

1. Typhoid and food poisoning
2. Tuberculosis
3. Amoebic dysentery
4. Sleeping sickness
5. Malaria

Answer:

1. Salmonella bacteria
2. Mycobacterium tuberculosis
3. Entamoeba (protozoa)
4. Trypanosoma (protozoa)
5. Plasmodium (protozoa)

Question 22.
Name some common diseases caused by different types of microorganisms.
Answer:

Question 23.
Mention few ways to prevent the spoilage of food.
Answer:

• Refrigeration
• Drying
• Adding salt, sugar, vinegar and oil as preservatives.
• Canning
• Pasteurization

Question 24.
What is pasteurization ? Who invented it ?
Answer:
It is a process in which a liquid food item (mostly milk) is first heated to a very high temperature and then immediately cooled to a very low temperature. This kills the bacteria in it and preserves the food. Louis Pasteur invented it.

Question 25.
What is a vaccine ?
Answer:
A vaccine is introduction of a preparation containing a small amount of a pathogen (disease causing organism) in changed or weakened form inside the body. This provides protection against any future infection by that pathogen.

Question 26.
Who developed small pox vaccine ?
Answer:
Edward Jenner

Question 27.
Mention few preventive measures to avoid infection.
Answer:

• Avoid direct or indirect contact with patient suffering from any contageous disease.
• Trim your nails regularly.
• Drink filtered or boiled water.
• Keep food and water in covered containers.
• Get yourself vaccinated against diseases.
• Maintain personal hygiene, wash your hands before eating.

Question 28.
Fill in the blanks.
(i) The science dealing with the study of microorganisms is known as …………
Answer:
The science dealing with the study of microorganisms is known as microbiology.

(ii) Agar is obtained from …………. algae.
Answer:
Agar is obtained from red algae.

(iii) Dead cells of diatoms sink to the ocean floor and form large deposits of ………….
Answer:
Dead cells of diatoms sink to the ocean floor and form large deposits of diatomaceous earth.

(iv) …………. are called jewels of the plant world as their cell wall produces beautiful living-dot-like impressions. ‘
Answer:
Diatoms are called jewels of the plant world as their cell wall produces beautiful living-dot-like impressions.

(v) …………. is the simplest known protozoan.
Answer:
Amoeba is the simplest known protozoan.

(vi) …………. is a slipper shaped protozoan.
Answer:
Paramecium is a slipper shaped protozoan.

(vii) The hyphae of fungus are collectively called ………….
Answer:
The hyphae of fungus are collectively called mycelium.

(viii) Yeast reproduces by
Answer:
Yeast reproduces by budding.

(ix) The separation of fibres from the long stem of fibre plants such as flax and jute is called …………. of fibres.
Answer:
The separation of fibres from the long stem of fibre plants such as flax and jute is called retting of fibres.

(x) A …………. is a small particle which consists of DNA surrounded by a protein coat.
Answer:
A virus is a small particle which consists of DNA surrounded by a protein coat

(xi) ………… are blue-green algae.
Answer:
Cyanobacteria are blue-green algae.

(xii) A …………. colony is a hollow sphere made of many identical cells.
Answer:
A Volvox colony is a hollow sphere made of many identical cells.

(xiii) ………… bacteria decompose the dead remains of plants and animals.
Answer:
Saprophytic bacteria decompose the dead remains of plants and animals.

(xiv) All fungi are ………….
Answer:
All fungi are heterotrophic.

ICSE Class 7 Biology Important Questions