1. Select the correct word from the following list and fill in the blanks. Float, water, crop, nutrients, preparation

 (a) The same kind of plants grown and cultivated on a large scale at a place is called _____________.

Answer (a): Crop.

(b) The first step before growing crops is _____________ of the soil.

Answer (b): Preparation.

(c) Damaged seeds would _____________ on top of water.

Answer (c): Float.

(d) For growing a crop, sufficient sunlight and _____________ and _____________ from the soil are essential.

Answer (d): Water, nutrients

 

2. Write a paragraph in your own words on each of the following.

(a) Preparation of soil

(b) Sowing

(c) Weeding

(d) Threshing

Solution (2):

(a) Preparation of soil:

Turning up the soil and loosening it is the first step before growing a crop. This allows the roots to penetrate deep into the soil. The loose soil allows the roots to breathe easily even when they go deep into the soil. The loosened soil helps in the growth of earthworms and microbes present in the soil. These organisms are friends of the farmer since they further turn and loosen the soil and add humus to it.

(b) Sowing:

Sowing of seeds at proper depths and distances gives a good yield. High-grade variety of seeds are sown after the selection of healthy seeds. Sowing is done by seed drills.

(c) Weeding:

Weeding involves the removal of unwanted and uncultivated plants called weeds. Weeding is essential as weeds compete with the crop plants for water, nutrients, space and light. It affects the growth of the crop. Some weeds are even poisonous for animals and human beings.

(d) Threshing:

Separation of the grains from the chaff is called threshing. It is either done manually by sickle or by a machine called harvester.

3. Explain how fertilisers are different from manure.

Solution (3):

Difference between fertilisers and manure:

https://www.jagranjosh.com/imported/images/E/Articles/ncert-solutions-8th-ch-1-a-5-difference-between-fertiliser-manure.jpg

4. What are weeds? How can we control them?

Solution (4)

Undesirable plants that grow naturally along with the crop are known as weeds. It can be controlled by the process of weeding. Weeding involves the removal of unwanted and uncultivated plants called weeds. Weeding is essential as weeds compete with the crop plants for water, nutrients, space and light. It affects the growth of the crop. Some weeds are even poisonous for animals and human beings.

Some methods to control weeds are

Physical removal of weeds by uprooting or cutting them close to the ground, from time to time.

Weeds are also controlled by using certain chemicals, called weedicides

 

5. Match the organisms in Column A with their action in Column B.

A

B

(i) Bacteria

(a) Fixing nitrogen

(ii) Rhizobium

(b) Setting of curd

(iii) Lactobacillus

(c) Baking of bread

(iv) Yeast

(d) Causing malaria

(v) A protozoan

(e) Causing cholera

(vi) A virus

(f) Causing AIDS

 

(g) Producing antibodies

Sol:-

A

B

(i) Bacteria

(e) Causing cholera

(ii) Rhizobium

(a) Fixing nitrogen

(iii) Lactobacillus

(b) Setting of curd

(iv) Yeast

(c) Baking of bread

(v) A protozoan

(d) Causing malaria

(vi) A virus

(f) Causing AIDS

 

 

6. Can microorganisms be seen with the naked eye? If not, how can they be seen?

Soln:

Microorganisms cannot be seen by naked eye because they are very small. They can be seen by using microscope.

 

7. Write 10 lines on the usefulness of microorganisms in our lives.

Soln:

Uses of microorganisms are listed below

  • They are helpful in cleaning up of the environment. For example, the organic wastes (vegetable peels, remains of animals, faeces, etc.) are broken down into harmless and usable substances by bacteria.
  • Curd contains several microorganisms. Of these, the bacterium, Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd.
  • Bacteria are also involved in the making of cheese, pickles and many other food items.
  • Bacteria and yeast are also helpful for fermentation of rice idlis and dosa batter.
  • Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume. This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes.
  • Microorganisms are used for the large scale production of alcohol, wine and acetic acid (vinegar).
  • Antibiotics are being produced from bacteria and fungi.
  • Microorganisms are helpful in producing vaccines against disease causing agents.
  • Some bacteria (Fig. 2.7) are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility.
  • Microorganisms decompose dead organic waste of plants and animals to convert them into simple substances. These substances are again used by other plants and animals. Thus, microorganisms can be used to degrade the harmful and smelly substances and thereby clean up the environment.

8. What are antibiotics? What precautions must be taken while taking antibiotics?

Soln:

Chemical agents that kill or stop the growth of disease causing microorganisms are called antibiotics. Antibiotics should be taken only on the advice of a qualified doctor. Also one must complete the course prescribed by the doctor.

9. Explain why plastic containers are favored for storing food.

Soln:

Because plastic is non-reactive and will not react with the ingredients of the food items.

10. Explain the difference between thermoplastic and thermosetting plastics.

Soln:

The difference between the thermosetting plastics and thermoplastics are

Thermosetting plastic

Thermoplastic

Cannot be bent, it will break if we attempt to bend thermo setting plastic

Thermoplastic can be bent easily

On heating thermosetting plastics, it cannot be softened. This is the reason it cannot be reshaped once it is molded.

On heating the thermoplastics, it becomes softened and can be molded and reshaped easily.

11. Explain why the following are made of thermosetting plastics.

(a) Saucepan handles

(b) Electric plugs/switches/plug boards

Soln:

a) Thermosetting plastics are used to make saucepan handles because they are bad conductors of heat and also on heating, these plastics do not get softened.

b) Bakelite is a kind of thermosetting plastic which is a bad conductor of heat and electricity. Because of this property it is used for making electric plugs, switches, plug boards, etc.

 

12. ‘Avoid plastics as far as possible’. Comment on this advice.

Soln:

We should avoid plastics as far as possible because plastics are non-biodegradable in nature. Once introduced into the environment they cause pollution. If burnt they release poisonous gases and the the plastic bags thrown in the garbage dumb are swallowed by animals choke their respiratory system and causes fatalities in animals.

13. Match the terms of column A correctly with the phrases given in column B

A

B

(i) Polyester

(a) Prepared by using wood pulp

(ii) Teflon

(b) Used for making parachutes and stockings

(iii) Rayon

(c) Used to make non-stick cookwares

(iv) Nylon

(d) Fabrics do not wrinkle easily

Soln:

A

B

(i) Polyester

(d) Fabrics do not wrinkle easily

(ii) Teflon

(c) Used to make non-stick cookwares

(iii) Rayon

(a) Prepared by using wood pulp

(iv) Nylon

(b) Used for making parachutes and stockings

14. ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.

Soln:

The manufacturing of synthetic fibers is helpful in the conservation of forests because if we use natural fibers, the raw materials for them have to be derived from the plants, which require cutting off lots of trees. This proves to be helpful in the conservation of forests.

 

 

1. Select the correct word from the following list and fill in the blanks. Float, water, crop, nutrients, preparation

 (a) The same kind of plants grown and cultivated on a large scale at a place is called _____________.

Answer (a): Crop.

(b) The first step before growing crops is _____________ of the soil.

Answer (b): Preparation.

(c) Damaged seeds would _____________ on top of water.

Answer (c): Float.

(d) For growing a crop, sufficient sunlight and _____________ and _____________ from the soil are essential.

Answer (d): Water, nutrients

 

2. Write a paragraph in your own words on each of the following.

(a) Preparation of soil

(b) Sowing

(c) Weeding

(d) Threshing

Solution (2):

(a) Preparation of soil:

Turning up the soil and loosening it is the first step before growing a crop. This allows the roots to penetrate deep into the soil. The loose soil allows the roots to breathe easily even when they go deep into the soil. The loosened soil helps in the growth of earthworms and microbes present in the soil. These organisms are friends of the farmer since they further turn and loosen the soil and add humus to it.

(b) Sowing:

Sowing of seeds at proper depths and distances gives a good yield. High-grade variety of seeds are sown after the selection of healthy seeds. Sowing is done by seed drills.

(c) Weeding:

Weeding involves the removal of unwanted and uncultivated plants called weeds. Weeding is essential as weeds compete with the crop plants for water, nutrients, space and light. It affects the growth of the crop. Some weeds are even poisonous for animals and human beings.

(d) Threshing:

Separation of the grains from the chaff is called threshing. It is either done manually by sickle or by a machine called harvester.

3. Explain how fertilisers are different from manure.

Solution (3):

Difference between fertilisers and manure:

https://www.jagranjosh.com/imported/images/E/Articles/ncert-solutions-8th-ch-1-a-5-difference-between-fertiliser-manure.jpg

4. What are weeds? How can we control them?

Solution (4)

Undesirable plants that grow naturally along with the crop are known as weeds. It can be controlled by the process of weeding. Weeding involves the removal of unwanted and uncultivated plants called weeds. Weeding is essential as weeds compete with the crop plants for water, nutrients, space and light. It affects the growth of the crop. Some weeds are even poisonous for animals and human beings.

Some methods to control weeds are

Physical removal of weeds by uprooting or cutting them close to the ground, from time to time.

Weeds are also controlled by using certain chemicals, called weedicides

 

5. Match the organisms in Column A with their action in Column B.

A

B

(i) Bacteria

(a) Fixing nitrogen

(ii) Rhizobium

(b) Setting of curd

(iii) Lactobacillus

(c) Baking of bread

(iv) Yeast

(d) Causing malaria

(v) A protozoan

(e) Causing cholera

(vi) A virus

(f) Causing AIDS

 

(g) Producing antibodies

Sol:-

A

B

(i) Bacteria

(e) Causing cholera

(ii) Rhizobium

(a) Fixing nitrogen

(iii) Lactobacillus

(b) Setting of curd

(iv) Yeast

(c) Baking of bread

(v) A protozoan

(d) Causing malaria

(vi) A virus

(f) Causing AIDS

 

 

6. Can microorganisms be seen with the naked eye? If not, how can they be seen?

Soln:

Microorganisms cannot be seen by naked eye because they are very small. They can be seen by using microscope.

 

7. Write 10 lines on the usefulness of microorganisms in our lives.

Soln:

Uses of microorganisms are listed below

  • They are helpful in cleaning up of the environment. For example, the organic wastes (vegetable peels, remains of animals, faeces, etc.) are broken down into harmless and usable substances by bacteria.
  • Curd contains several microorganisms. Of these, the bacterium, Lactobacillus promotes the formation of curd. It multiplies in milk and converts it into curd.
  • Bacteria are also involved in the making of cheese, pickles and many other food items.
  • Bacteria and yeast are also helpful for fermentation of rice idlis and dosa batter.
  • Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume. This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes.
  • Microorganisms are used for the large scale production of alcohol, wine and acetic acid (vinegar).
  • Antibiotics are being produced from bacteria and fungi.
  • Microorganisms are helpful in producing vaccines against disease causing agents.
  • Some bacteria (Fig. 2.7) are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility.
  • Microorganisms decompose dead organic waste of plants and animals to convert them into simple substances. These substances are again used by other plants and animals. Thus, microorganisms can be used to degrade the harmful and smelly substances and thereby clean up the environment.

8. What are antibiotics? What precautions must be taken while taking antibiotics?

Soln:

Chemical agents that kill or stop the growth of disease causing microorganisms are called antibiotics. Antibiotics should be taken only on the advice of a qualified doctor. Also one must complete the course prescribed by the doctor.

9. Explain why plastic containers are favored for storing food.

Soln:

Because plastic is non-reactive and will not react with the ingredients of the food items.

10. Explain the difference between thermoplastic and thermosetting plastics.

Soln:

The difference between the thermosetting plastics and thermoplastics are

Thermosetting plastic

Thermoplastic

Cannot be bent, it will break if we attempt to bend thermo setting plastic

Thermoplastic can be bent easily

On heating thermosetting plastics, it cannot be softened. This is the reason it cannot be reshaped once it is molded.

On heating the thermoplastics, it becomes softened and can be molded and reshaped easily.

11. Explain why the following are made of thermosetting plastics.

(a) Saucepan handles

(b) Electric plugs/switches/plug boards

Soln:

a) Thermosetting plastics are used to make saucepan handles because they are bad conductors of heat and also on heating, these plastics do not get softened.

b) Bakelite is a kind of thermosetting plastic which is a bad conductor of heat and electricity. Because of this property it is used for making electric plugs, switches, plug boards, etc.

 

12. ‘Avoid plastics as far as possible’. Comment on this advice.

Soln:

We should avoid plastics as far as possible because plastics are non-biodegradable in nature. Once introduced into the environment they cause pollution. If burnt they release poisonous gases and the the plastic bags thrown in the garbage dumb are swallowed by animals choke their respiratory system and causes fatalities in animals.

13. Match the terms of column A correctly with the phrases given in column B

A

B

(i) Polyester

(a) Prepared by using wood pulp

(ii) Teflon

(b) Used for making parachutes and stockings

(iii) Rayon

(c) Used to make non-stick cookwares

(iv) Nylon

(d) Fabrics do not wrinkle easily

Soln:

A

B

(i) Polyester

(d) Fabrics do not wrinkle easily

(ii) Teflon

(c) Used to make non-stick cookwares

(iii) Rayon

(a) Prepared by using wood pulp

(iv) Nylon

(b) Used for making parachutes and stockings

14. ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.

Soln:

The manufacturing of synthetic fibers is helpful in the conservation of forests because if we use natural fibers, the raw materials for them have to be derived from the plants, which require cutting off lots of trees. This proves to be helpful in the conservation of forests.