8th Science Notes and MCQs

CHAPTER - 1

Crop Production and Management 

Textbook Questions and Answers

Question 1. Select the correct word and fill in the blanks.

Float, water, crop, nutrients, preparation.

1. The same kind of plants grown on a large scale at a place is called _________
2. An important task in growing crops is _________ of soil.
3. Damaged seeds would ___________ on top of the water.
4. For growing crop sufficient sunlight and _________ and _________ from the soil are essential.

Answer:

1. crop
2. preparation
3. float
4. water, nutrients

 Question 2. Match items in column ‘A’ with those in column ‘B’:

(A)                 (B)

(i) Kharif crops         (a) Food for cattle

(ii) Zayed crops (b) Urea and superphosphate

(iii) Chemical fertilizers (c) Animal excreta, cowdung, urine

(iv) Organic manure         (d) Wheat, gram, pea

(e) Paddy and maize

Answer:

(A)                 (B)

(i) Kharif crops         (e) Paddy and maize

(ii) Zayed crops (d) Wheat, gram, pea

(iii) Chemical fertilizers (b) Urea and superphosphate

(iv) Organic manure         (c) Animal excreta, cow dung, urine, and plant waste.

Question 3.Give two examples of each of the following:

(а) Kharif crop

(b) Rabi crop

Answer:

(a) Kharif crop – Maiz, paddy, soybean

(b) Rabi crop – Wheat, gram, pea

Question 4.Write a paragraph in your own words on each of the following:

(а) Preparation of soil

(b) Sowing

(c) Weeding

(d) Threshing

Answer:

(a) Preparation of soil. Preparation of soil involves two main steps-ploughing and levelling. Ploughing is the process of loosening and turning the soil so that the circulation of air is improved in the soil. It is done with the help of various types of ploughs like wooden iron for hard soil, bullock drawn, or tractor driven. Loosening of soil permits easy and deeper penetration of the roots and it provides good aeration to the roots. The ploughed land is levelled and pressed lightly with the help of a wooden plank or iron leveller.

(b) Sowing. Sowing is the process of putting seeds in the soil. Sowing can be done manually or by using a seed drill.

(c) Weeding. The removal of weeds is called weeding. It is necessary since weeds use nutrients from the soil. They compete for water and light and thus, affect the growth of crops by reducing the yield. Some weeds even interfere in the harvesting. Weeds can sometimes be poisonous for animals and human beings.

(d) Threshing. The process of separating grains from the harvested crop is called threshing. It may be done manually by striking the harvested crop against a hard surface or by using a machine called a thresher.

 

Question 5.Explain how fertilizers are different from manure.

Answer:

Differences between Fertiliser and Manure

Fertilizer                                                                                     Manure

1. A fertilizer is an inorganic salt. 1. Manure is a natural substance obtained by the decomposition of cattle dung, human waste, and plant residues.

2. A fertilizer is prepared in factories. 2. Manure can be prepared in the fields.

3. A fertilizer does not provide any humus to the soil. 3. Manure provides a lot of humus to the soil.

4. Fertilisers are very rich in plant nutrients like nitrogen, phosphorus, and potassium. 4. Manure is relatively less rich in plant nutrients.

Question 6.What is irrigation? Describe two methods of irrigation which conserve water.

Answer:
The supply of water to crops at different intervals is called irrigation.

Methods of irrigation which conserve water are:

1.Sprinkler system: This system is useful on uneven lands where water is available in smaller quantities. In this system, the perpendicular pipes, having rotating nozzles on the top, are joined to the main pipe at regular intervals. When the water flows through the main pipe with the help of a pump, it escapes from the rotating nozzles. It is sprinkled on the crop as if it is raining.

2.Drip system. In this system, the waterfalls drop by drop just at the position of the roots. This system consists of the main pipe to which lateral pipes are joined. The specially prepared nozzles are attached to these lateral pipes. The nozzles are grounded just near the roots of the plants. It provides water to plants drop by drop. Water is not wasted at all.

 Question 7.If wheat is sown in Kharif season, what would happen? Discuss.
Answer:
If wheat is sown in the Kharif season then it would not grow because a lot of water due to rain will spoil the seeds. Wheat crops require low temperature which it does not get in the Kharif season. Therefore, the quantity of wheat produced will be very less and quality will also be very poor.

Question 8.Explain how the soil is affected by the continuous plantation of crops in a field.

Answer:

Continuous plantation of crops in a field year after year makes the soil barren in a few years because all the nutrients present in the soil will be depleted.

Question 9.What are weeds? How can we control them?

Answer:

The undesirable plants in the field are called weeds which have to be removed, otherwise, our own crop plants may not get sufficient water, space, and light. The various methods to control the weeds are:

• Mechanical method. Uprooting weeds with khurpi or hand, ploughing, burning, and flooding.
• Cultural method, lb prepare proper seedbed and sowing of seed timely and intercropping and crop rotation are the methods included under cultural method.
• Chemical method. By spraying chemicals known as herbicides or weedicides e.g. 2,4-D fluchloralin etc.

 Question 10.Arrange the following boxes in proper order to make a flow chart of sugarcane crop production:

Question 11.Complete the following word puzzle with the help of clues given below.

Down

1. Providing water to the crops.

2. Keeping crop grains for a long time under proper conditions.

5. Certain plants of the same kind grown on a large scale.

Across

3. A machine used for cutting the matured crop.

4. A rabi crop that is also one of the pulses.

6. A process of separating the grain from the chaff.

Crop Production and Management 

Additional Questions and Answers

Question 1.Why do organisms need energy?

Answer:

Organisms need energy for carrying out their various body functions, such as digestion, respiration, and excretion.

Question 2.What is agriculture?

Answer:

Agriculture is the study of science and the art of production of plants and animals useful to man.

• The loosened soil allows the roots to penetrate freely, deeper, and breathe easily.
• The loosened soil also helps in the growth of earthworms and microbes, who are friends of the farmer, since they aid in further turning and loosening the soil and add humus to it.

 Question 8.What is sowing?

Answer:

Sowing is the process of putting seeds in the soil.

Question 9.What is meant by good quality seeds?

Answer:

Good quality seeds mean clean and healthy seeds of a good variety.

Question 10.What are manures?

Answer:

Manures are organic materials which supply all the elements a plant needs in small amounts. Besides serving as a source of nutrients, organic manures improve the physical conditions of the soil.

Question 11.What is organic manure?

Answer:

Any organic matter obtained from plant or animal wastes is called organic manure.

Question 12.How do farmers make manure?

Answer:

Farmers dump plant and animal wastes at open places and allow them to be decomposed by organisms like bacteria and fungi. The decomposed matter is called manure.

Question 13.What is irrigation?

Answer:

Once the seeds or the seedlings establish themselves in the field, water is again given in the field. This is known as irrigation.

Question 14.What are the sources of irrigation?

Answer:

The sources of irrigation are wells, tubewells, ponds, lakes, rivers, dam,s and canals.

 

Question 15.Draw a diagram to show’ sprinkler system and drip system.

Answer:

Question 16.What are weeds?

Answer:

Weeds are undesirable plants which grow along with crops and compete for sunlight, water, and nutrients, thus decreases the yield of the main crop.

Question 17.Give two examples of weeds?

Answer:

Wild oat, Chenopodium, Amaranthus.

Question 18.What is weeding? Why is it necessary?

Answer:

The removal of weeds is called weeding. It is necessary since weeds use nutrients from the soil. They compete for water and light and thus, affect the growth of crops by reducing the yield. Some weeds even interfere in the harvesting. Weeds can sometimes be poisonous for animals and humans beings.

 

Question 19.What is harvesting?

Answer:

Harvesting is the process of cutting and collecting the matured crop from the fields.

Question 20.What is threshing?

Answer:

The process of separating grains from the harvested crop is called threshing. It may be done manually by striking the harvested crop against a hard surface or by using a machine called a thresher.

Question 21.What does storage mean?

Answer:

Storage means keeping the harvested fruits till they are taken finally to the consumer. Seeds are stored to protect them from birds, insects, rodents, and micro-organisms and also for use during periods of food scarcity.

Question 22.What precautions are taken before storing the grains?

Answer:

Before storing the grains they are sun-dried to reduce the moisture level of grains so that they are saved from pest attacks. Humidity in storage places must also be controlled to prevent the growth of fungus.

 

Question 23.Why are dried neem leaves used for storing food grains at home?

Answer:

Dried neem leaves protect food grains from pests and microorganisms.

Question 24.Name the foods obtained from animals?

Answer:

Milk, eggs, fish, and meat.

Activities:

Activity 1.1Take a beaker and fill half of it with water. Put a handful of wheat seeds and stir well, wait for some time.

Question (i).Are there seeds that float on water?

Answer:

Yes

Question (ii).Would those be lighter or heavier than those which sink?

Answer:

Those would be lighter than those which sink.

Question (iii).Why would they be lighter?

Answer:

They would be lighter because damaged seeds become hollow and are thus, lighter. Therefore, they float on water.

 

Activity 1.2

Take moong or gram seeds and germinate them. Select three equal-sized seedlings out of these. Now take three empty glasses or similar vessels. Mark them A, E, and C. To glass A add a little amount of soil mixed with a little cow dung manure. In the glass, B put the same amount of soil mixed with a little urea. Take the same amount of soil in glass C without adding anything [Fig. 1.3(a)]. Now pour the same amount of water into each glass and plant the seedlings in them. Keep them in a safe place and water them daily. After 7 to 10 days observe their growth [Fig. 1.3(b)]

Question (i).Did all the plants in all the glasses grow at the same pace?

Answer:

No.

Question (ii).Which glass showed better growth of plants?

Answer:

Glass A.

 

Question (iii).In which glass was the growth fastest?

Answer:

Glass B.

Question 3.What is a crop?

Answer:

The plants of the same kind grown at a place are called a crop. Examples are wheat, paddy, etc.

Question 4.What are agricultural practices?

Answer:

The various tasks like preparation of soil, sowing seeds, irrigation, removal of weeds, use of manures and fertilizers, etc carried by farmers to cultivate crops are agricultural practices.

Question 5.Why is soil loosened?

Answer:

Question 6.Why does the loosening of soil allow roots to breathe easily?

Answer:

Air easily enters the loosened soil and thus, allows roots to breathe easily.

Question 7.Name the main tools used for ploughing. Explain their use and structure with the help of a diagram.

Answer:

The main tools used for ploughing are plough, hoe, and cultivator.

(i) Plough. It is used for tilling of the soil, adding fertilizers to the crop, removing the weeds, and scrapping of soil. Plough is made of wood and drawn by a pair of bulls. It contains a strong triangular iron strip called plough share. Its main part is a long log of wood called a plough shaft. There is a handle on one end. The other end is attached to a beam which is hung on the bull’s necks. One pair of bulls and a man operates the plough.

(ii) Hoe is a simple tool used for removing seeds and loosening the soil. Hoe has a long rod of wood or iron. A strong, broad, and bent plate of iron is fixed to one of its ends and works as a blade. The other end of plough shaft is pulled by animals.

(iii) Cultivator. Nowadays ploughing is done by tractor driven cultivator. The use of a cultivator saves labour and time [Fig. (c)].

CHAPTER - 2
Microorganisms: Friend and Foe 
Textbook Questions and Answers

Question 1.Fill in the blanks:

(a) Microorganisms can be seen with the help of a ___________

(b) Blue green algae fix _________ directly from air to enhance fertility of soil.

(c) Alcohol is produced with the help of a microorganism ___________

(d) Cholera is caused by __________

Answer:

(a) Microscope

(b) Nitrogen

(c) Yeast

(d) Bacteria

Question 2.Tick the correct answer:

(a) Yeast is used in the production of

(i) sugar

(ii) alcohol

(iii) hydrochloric acid

(iv) oxygen

Answer:

(ii) Alcohol

(b) Which one of the following is an antibiotic?

(i) Sodium bicarbonate

(ii) Streptomycin

(iii) Alcohol

(iv) Yeast

Answer:

(ii) Streptomycin

(c) Carrier of malaria-causing protozoan is
(i) female Anopheles mosquito
(ii) cockroach
(iii) housefly
(iv) butterfly
Answer:
(i) Female Anopheles Mosquito

(d) The most common carrier of communicable diseases is

(i) ant

(ii) housefly

(iii) dragonfly

(iv) spider

Answer:

(ii) Housefly

(e) The bread or idli dough rises because of

(i) heat

(ii) grinding

(iii) growth of yeast cells

(iv) kneading

Answer:

(iii) growth of yeast cells

(f) The process of conversion of sugar into alcohol is called
(i) nitrogen inflation
(ii) moulding
(iii) fermentation
(iv) infection
Answer:
(iii) fermentation

Question 3.Match the organisms in Column A with their action in Column B.Answer:

Column A Column 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

Answer:

Column A         Column 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

Question 4.Can microorganisms be seen with the naked eye? If not, how can they be seen?

Answer:

No, we cannot see microorganisms with the naked eye. They can be seen with the help of a microscope.

Question 5.What are the major groups of microorganisms?

Answer:

The major groups of microorganisms are bacteria, fungi, algae, and protozoa.

Question 6.Name the microorganisms which can fix atmospheric nitrogen in the soil.

Answer:

Bacteria e.g., Rhizobium, Azotobactor, and blue-green algae e.g., Anabaena and Nostoc can fix atmospheric nitrogen in the soil.

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

Answer:

The uses of microorganisms are:

1. Microorganisms are utilized in the preparation of wines, pickles, vinegar, cheese, curds, the aroma in tobacco.
2. They are used in the production of antibiotics.
3. They help in sewage disposal.
4. Some soil bacteria like Rhizobium fix atmospheric nitrogen, which is useful for plants.
5. Some microorganisms are used for the large-scale production of alcohol, wine, and acetic acid.
6. Milk is turned into curd by bacteria.
7. Some bacteria help in tanning leather.
8. Some microorganisms are used to produce vaccines.
9. They clean the environment.
10. Some bacteria tenderize meat by breaking down muscle fibers.

Question 8.Write a short paragraph on the harms caused by microorganisms.

Answer:

The harms caused by microorganisms are:

• They cause a number of diseases in men, plants, and animals.
• Some microorganisms spoil milk, pickles, jams, squashes, and other food items.
• They damage the crops and thus, reducing productivity.

Question 9.What are antibiotics? What precautions must be taken while taking antibiotics?
Answer:

Antibiotics are medicines that kill or stop the growth of disease-causing microorganisms. Antibiotics must be taken only on the advice of a qualified doctor. The course of antibiotics prescribed by the doctor must be finished. Antibiotics must not be taken when not needed, because this helps bacteria in our body to develop resistance to them. Next time when we fall ill and need these antibiotics then there would be less effectiveness.

CHAPTER - 2

Microorganisms: Friend and Foe 

Additional Questions and Answers

Question 1.What are microorganisms?

Answer:

Microorganisms are living organisms which cannot be seen with unaided eyes, they can be seen only through the powerful microscope.

Question 2.What happens to moist bread during the rainy season?

Answer:

During the rainy season, moist bread gets spoilt and its surface gets covered with greyish white patches.

Question 3.What are viruses?

Answer:

Viruses are disease-causing agents and are very minute particles visible only under an electron microscope. They are smaller than bacteria.

 Question 4.Name few diseases caused by virsues.
Answer:
Rabies, polio, chickenpox, common cold, influenza (flu), and mosaic of tobacco and potato are the diseases caused by viruses.

Question 5.Where do microorganisms live?

Answer:

Microorganisms live in the soil, mud, water, sea, air, plants, animals, food products, various utensils, etc, and on dead weeds, leaves, clothes, books, jams, pickles, dung, shoes, etc. They also live in man and animals. Amoeba lives alone. Fungi and bacteria live in colonies.

Question 6.State some beneficial effects of bacteria.

Answer:

The beneficial effects of bacteria are:

1. They bring about the decomposition of wastes in the soil and thus, increase the fertility of the soil.
2. Some of the putrifying bacteria decompose the matter of sewage and help in sewage disposal.
3. Some bacteria help in tanning leather.
4. Bacteria tenderize meat by breaking down muscle fibers.
5. Curd, cheese, etc. are formed by the action of bacteria in the milk.
6. The fermentation activity of bacteria is useful in the preparation of vinegar, wine, palm juice, etc.
7. Filamentous bacteria are used in the production of antibiotics.
8. Some bacteria like Rhizobium can fix the nitrogen of the atmosphere, thus, enriching the soil in the nitrogen contents.

 Question 7.Name the bacteria that convert milk into curd.
Answer:
Lactobacillus.

Question 8.Name the bacteria used for the production of acetic acid from alcohol.

Answer:

Acetobacter acetic.

Question 9.What are yeasts? What is their shape? How do they reproduce?

Answer:

Yeasts are (saccharomyces) unicellular and saprophytic fungi. The shape of yeast cells is spherical, elliptical, or cylindrical. Yeast reproduces through asexual mode by budding or by binary fission.

Question 10.Name the gas produced by yeast during respiration.

Answer:

Carbon dioxide.

Question 11.

1. Name the common antibiotic.
2. Name the antibiotics made from bacteria and fungi.

Answer:

1. Penicillin
2. Streptomycin, tetracycline, and erythromycin.

Question 12.Who discovered penicillin?

Answer:

Alexander Fleming discovered penicillin in 1929.

Question 13.Draw a diagram to show blue-green algae.
Answer:
Question 14.Describe the role of blue-green algae in the fertility of the soil.
Answer:
Blue-green algae have the ability to fix atmospheric nitrogen into usable compounds. It increases the humus content of the soil. This improves the water-holding capacity of the soil. Due to these reasons, the fertility of the soil is increased and hence, crop growth is also increased.
 Question 15.What are pathogens?
Answer:
Microorganisms causing diseases in human beings, plants, and animals are called pathogens.
Question 16.How do disease-causing microorganisms enter our bodies?
Answer:
Disease-causing microorganisms enter our body through the air we breathe, the water we drink, or the food we eat; or transmitted by direct contact with an infected person or through an animal carrier.
Question 17.What are communicable diseases?
Answer:
Communicable diseases are those microbial diseases which are spread from an infected person to a healthy person through the air, water, food, or physical contact e.g., malaria, T.B, AIDS, cholera, common cold, chickenpox, etc.Question 18.How is the plasmodium parasite causing malaria transmission?
Answer:
Plasmodium parasite is transmitted by the bite of the female anopheles mosquito. Anopheles mosquito merely acts as a carrier of malaria-causing parasites. It takes them alongwith the blood sucked from an infected person and transmits them to a healthy person.

Question 19.What is a causative microorganism of chickenpox and polio?
Answer:
Disease – Causative microorganism
Chicken Pox – Virus
Polio – Virus

Question 20.What is a mode of transmission of causative microorganisms chickenpox and polio?
Answer:
Chicken Pox – Air, contact
Polio – Air, water.

Question 21.What is a causative microorganism of cholera and typhoid?
Answer:
Bacteria.

Question 22.What is anthrax?
Answer:
Anthrax is a dangerous human and cattle disease caused by a bacterium.

Question 23.Name a disease of cattle caused by a virus.
Answer:
Foot and mouth disease of cattle is caused by a virus.

Question 24.Name the bacteria which causes anthrax disease.
Answer:
Bacillus anthracis.

Question 25.Who discovered the bacterium which causes anthrax disease?
Answer:
Robert Koch (1876).

Question 26.Name a disease in plants caused by bacteria. What is its mode of transmission?
Answer:
Citrus canker. Its mode of transmission is air.

Question 27.Name a disease in plants caused by fungi. What is its mode of transmission?
Answer:
Rust of wheat. Its mode of transmission is insects and seeds.

Question 28.Name a disease in plants caused by viruses. What is its mode of transmission?
Answer:
Yellow vein mosaic of bhindi. Its mode of transmission is insect.

Question 29.How food can become a ‘poison’?
Answer:
Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death.

Question 30.What is food poisoning?
Answer:
Food poisoning is due to the consumption of food spoilt by some microorganisms.
 
Question 31.Is spoiling food a chemical reaction?
Answer:
Yes.

Question 32.What happens when food gets spoiled?
Answer:
Spoiled food emits a bad smell and has a bad taste and changed colour.

Question 33.What is the role of nodules in the biological fixation of nitrogen?
Answer:
The role of nodules in the biological fixation of nitrogen is to fix atmospheric nitrogen into nitrates.

Question 34.Name the bacteria which can fix nitrogen present in the air.
Answer:
Rhizobium, Clostridium, and Azotobacter.

Question 35.Name the most abundant gas present in the air. What is its percentage in our atmosphere?
Answer:
Nitrogen. Our atmosphere consists of 78% nitrogen gas.
 
Question 36.In which form is nitrogen present in all living organisms?
Answer:
Proteins, chlorophyll, nucleic acids, and vitamins.

Question 37.With the help of a labelled diagram explain the various stages of the nitrogen cycle.
Answer:
The various stages of the nitrogen cycle are:
In the soil nitrogen is present in the form of nitrates by the following processes:
Nitrogen and oxygen combine to form nitric acid at the time of lightning in the atmosphere. This nitric acid forms nitrates which reach the earth with rainwater.
Nitrates are formed in the soil from the decay of dead plants and animals.
Nitrogen-fixing bacteria present in soil and root nodules of some leguminous plants convert the nitrogen in the air directly into nitrates.
The plants absorb nitrates from the soil and convert them into plant proteins and plant protoplasm.
The animals eat plants and convert plant proteins into animal proteins.
The plant proteins and animal proteins of dead plants and animals are converted into ammonia in the soil by bacterial decomposition.
Nitrifying bacteria convert ammonia into nitrites and these nitrates are converted into nitrates in the soil.
Some of the nitrates formed in the soil are converted back into free nitrogen gas by
denitrifying bacteria. This free nitrogen gas goes back into the atmosphere and the nitrogen cycle is repeated again and again.

Activities

Activity 1
Collect some moist soil from the field in a beaker and add water to it. After the soil particles have settled down, observe a drop of water from the beaker under a microscope.
Question (i).What do you sec?
Answer:
We see tiny organisms under a microscope.
 
Activity 2
Take a few drops of water from a pond. Spread on a glass slide and observe through a microscope.
Question (i).Do you find tiny organisms moving around?
Answer:
Yes.

Activity 3
Take 1/2 kg flour (atta or mauia), add some sugar, and mix with warm water. Add a small amount of yeast powder and knead to make a soft dough.
Question (i).What do you observe after two hours? Did you find the dough rising?
Answer:
After two hours we find the dough rising.

Activity 4
Take a 500 mL beaker filled upto 3/4 with water. Dissolve 2-3 teaspoons of sugar in it. Add half a spoon of yeast powder to the sugar solution. Keep it covered in a warm place for 4-5 hours. Now smell the solution.
Question (i).Could you get a smell?
Answer:
Yes, I can smell alcohol.

Activity 5
Take two pots and fill each pot half with soil. Mark them A and B. Put plant waste in pot A and things like polythene bags, empty glass bottles, and broken plastic toys in pot B. Put the pots aside. Observe them after 3-4 weeks.
 
Question (i)Do you find any difference in the contents of the two pots?
Answer:
Yes.

Question (ii).What is the difference in the contents of the two pots?
Answer:
Plant waste in pot A gets decomposed whereas there is no change in contents of pot B.

Question (iii).How has plant waste in pot A decomposed?

Answer:
The plant waste gets converted into manure by the action of microbes.

Question (iv).Why do the contents of pot B (polythene bags, empty glasses, bottles, and broken toys) did not undergo any change?

Answer:
Contents of pot B (polythene bags, empty glasses, bottles, and broken toys) did not undergo any change because microbes could not ‘act’ on them and convert them into manure.

Chapter 3 

Synthetic Fibres and Plastics

Textbook Questions and Answers

Question 1.Why are some fibers called synthetic?
Answer:
Some fibers are called synthetic because they are made by human beings, e.g., polyester, acrylic etc.

Question 2.Mark (✓) the correct answer:
Rayon is different from synthetic fibers because:
(i) It has a silk-like appearance.
(ii) It is obtained from wood pulp.
(iii) Its fibres can also be woven like those of natural fibres.
Answer:
(ii) It is obtained from wood pulp.
 
Question 3.Fill in the blanks with appropriate words:
Synthetic fibres are also called _____ or _____ fibres.
Synthetic fibres are synthesised from raw material called _____
Like synthetic fibres, plastic is also a _____
Answer:
artificial or man-made
petrochemicals
polymer.

Question 4.Give examples which indicate that nylon fibers are very strong.
Answer:
Parachutes and ropes for rock climbing.

Question 5.Explain why plastic containers are favoured for storing food?
Answer:
The three main advantages of using plastic containers for storing food are:
Plastic is nonreactive.
Plastic is light, strong, and durable.
Plastic is cheap.
 
Question 6.Explain the difference between thermoplastic and thermosetting plastics.
Answer:
The difference between thermoplastic and thermosetting plastics is:

Thermoplastics soften on heating and then can be moulded into various shapes. They can be melted and shaped any number of times, e.g. polythene, PVC. BUT
Thermosets are plastics which once set, do not soften on heating. They retain the shape in which they were originally moulded. They are harder and stiffer than thermoplastics, e.g. bakelite, melamine.

Question 7.Explain why the following are made of thermosetting plastics.
Saucepan handles.
Electric plugs/switches/plugboards.
Answer:
Saucepan handles are made of thermosetting plastics (bakelite) because it is a poor conductor of heat.
Electric plugs/switches/plug boards are made of thermosetting plastics (bakelite) because it is a poor conductor of electricity.

Question 8.Categorize the materials of the following products into ‘can be recycled and ‘cannot be recycled’:
Telephone instruments, toys, cooker handles, carry bags, ballpoint pens, plastic bowls, electric wire covering, plastic chairs, electrical switches.
Answer:
Can be recycled: Telephone instruments, plastic toys, ballpoint pens, plastic bowls.
(As these are thermoplastics, so these can be recycled).
Cannot be recycled: Cooker handles, carry bags, plastic covering on an electric wire, plastic chairs, etc.
(As these are thermosetting plastics, these cannot be recycled).

Question 9.Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Answer:
We would advise Rana to buy cotton shirts because cotton clothes absorb sweat in summers whereas synthetic fibers do not absorb sweat and stick to the body making one feel uncomfortable.
 
Question 10.Give examples to show that plastics are non-corrosive in nature.
Answer:
Examples to show that plastics are non-corrosive in nature:
A wide range of chemicals is stored in plastic containers.
Food items are stored in plastic containers.
(Different buckets and mugs are made of plastics.

Question 11.Should the handle and bristles of a toothbrush be made of the same material? Explain your answer.
Answer:
No, the handle and bristles of a toothbrush should not be made of the same materials because the handle of the toothbrush must be hard and thus is made of thermosetting plastic whereas bristles of a toothbrush are made up of nylon which is soft, flexible, and strong.

Question 12.“Avoid plastics as far as possible.” Comment on this advice.
Answer:
Plastic takes several years to decompose. It is not environment friendly. It causes environmental pollution. Besides, the burning process in the synthetic material is quite slow and it does not get completely burnt easily. In the process, it releases lots of poisonous fumes into the atmosphere causing air pollution. Therefore, avoid the use of plastics as far as possible. The plastics garbage should be recycled.

Question 13.
Match the terms of column A correctly with the phrases given in column B.
Column A             Column 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 cookware.
(iv) Nylon         (d) Fabrics do not wrinkle easily.

Answer:
Column A             Column B
(i) Polyester     (d) Fabrics do not wrinkle easily.
(ii) Teflon             (c) Used for making non-stick cookware.
(iii) Rayon             (a) Prepared by using wood pulp.
(iv) Nylon             (b) Used for making parachutes and stockings.

Question 14.“Manufacturing synthetic fibers is actually helping conservation of forests”. Comment.
Answer:
Synthetic fibers are obtained by chemical processing of petrochemicals and not from fibres obtained from plant and animal sources. Hence we do not have to cut trees for manufacturing synthetic fibres and thus forests are conserved.
 
Question 15.Describe an activity to show that thermoplastic is a poor conductor of electricity.
Answer:
Take a dry cell to connect conducting wires and electric bulb with it, keeping a gap of 5 cm between two ends (A and B) of conducting wares in the circuit. Place an object of thermoplastic in the gap making sure that it touches the ends of the wires and thus the circuit is completed.

The bulb does not light up. However, if the thermoplastic object is removed from the circuit and ends A and B are joined then the bulb glows up. This shows that thermoplastic is a poor conductor of electricity.

CHAPTER 3 

Synthetic Fibres and Plastics

Additional Questions and Answers

Question 1.How are fabrics made?
Answer:
Fabrics are made using fibres obtained from natural or artificial sources.

Question 2.Name few natural fibers.
Answer:
Jute, cotton, silk, and wool.

Question 3.Name few artificial fibers.
Answer:
Rayon, terylene, nylon, polythene, Teflon, etc.

Question 4.What is a polymer?
Answer:
Polymer (poly means many, mers means parts) is a large molecule comprised of repeating structural units (monomers) joined together. There may be hundreds or even thousands of structural units in a polymer.
 
Question 5.What is rayon?
Answer:
The artificial silk prepared from cellulose is called rayon.

Question 6.Write the uses of rayon?
Answer:
The uses of rayon are:
Rayon mixed with cotton is used for making nurses’ dresses. Rayon makes them easier to wash and more hygienic.
Rayon mixed with wool is used for making carpets. Rayon makes them lighter and more durable.
Rayon gauze is used in bandaging. Rayon gauze can absorb over 90% of its own weight of water. Rayon gauze does not adhere to wounds.

Question 7.How is nylon prepared?
Answer:
Nylon is prepared from coal, water, and air.

Question 8.Write the properties of nylon.
Answer:
The properties of nylon are:
It is strong, elastic, and light.
It is lustrous and easy to wash.

Question 9.Why is polyester suitable for making dress material?
Answer:
Polyester is suitable for making dress material because this fabric does not get wrinkled easily. It remains crisp and easy to wash.
 
Question 10.What is PET? What are its uses?
Answer:
PET is a very familiar form of polyester. PET is used for making bottles, utensils, films, wires, and many other useful products.

Question 11.Why we should never wear polyester clothes while working in the kitchen or in a laboratory?
Answer:
We should never wear polyester clothes while working in the kitchen or in a laboratory because in case of fire the polyester fabric melts and sticks to the body of the person wearing it.

Question 12.How are all synthetic fibres prepared?
Answer:
All synthetic fibres are prepared by a number of processes using raw materials of petroleum origin called petrochemicals.

Question 13.Write unique characteristics of synthetic fibers} which make them popular dress materials.
Answer:
The unique characteristics of synthetics fibers are:
They dry up soon
Are durable
Less expensive
Readily available
Easy to maintain
 
Question 14.What are plastics?
Answer:
Plastics are polymers of very high molecular masses. They are generally not affected by acids or alkalis. They can be moulded to any desired shape.

Question 15.Why storing any food item, water, milk, pickles, dry food, etc. Plastic containers seem most convenient?
Answer:
Storing any food item, water, milk, pickles, dry food, etc. plastic containers seem most convenient because of their lightweight, lower price, good strength, and easy handling.

Question 16.Which property of plastic makes it useful in cars, aircraft, and spacecraft?
Answer:
Plastics are lighter compared to metals, therefore, they are useful in cars, aircraft, and spacecraft.

Question 17.Which material is called biodegradable?
Answer:
A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable.

Question 18.Which material is called non-biodegradable?
Answer:
A material which is not easily decomposed by natural processes is termed non-biodegradable.
 
Question 19.The disposal of plastic is a major problem. Why?
Answer:
Disposal of plastic is a major problem because:
It takes several years to decompose.
If burnt that it takes a long time to get completely burnt and in the process, it releases a lot of poisonous fumes into the atmosphere causing air pollution.

Activities
Activity 1
Make a list of some common articles made from fibers. Try to separate them into those made from natural fibers and those made from artificial fibers. Make entries in Table (a).
Table (a): Natural and Artificial Fibres
Name of Article Type of Fibre (Natural/artificial)
1. Acrylic sweater    Artificial
2. Woollen sweater    Natural
3. Cotton shirt            Natural
4. Nylon saree            Artificial
5. Nylon tents            Artificial

Question (i).Why did you label some fibers as artificial?
Answer:
We have labelled some fibres as artificial because they are man-made fabrics.

Activity 2
Take an iron stand with a clamp. Take a cotton thread of about 60 cm in length. Tie it to the clamp so that it hangs freely from it as shown in Fig. 1. At the free end suspend a pan so that weight can be placed in it. Add weight one by one till the thread breaks. Note down the total weight required to break the thread. This weight indicates the strength of the fiber. Repeat the same activity with threads of wool, polyester, silk, and nylon. Tabulate the data as shown in Table. Arrange the threads in order of their increasing strength.

CHAPTER 4 

Materials: Metals and Non-Metals

Textbook Questions and Answers

 

Question 1.Which of the following can be beaten into thin sheets:
(a) Zinc
(b) Phosphorus
(c) Sulphur
(d) Oxygen
Answer:
(a) Zinc

Question 2.Which of the following statement is correct?
(a) All metals are ductile.
(b) All non-metals are ductile.
(c) Generally, metals are ductile.
(d) Some non-metals are ductile.
Answer:
(d) Generally, metals are ductile.

 Question 3.Fill in the blanks:

1.   1 Phosphorus is a very _______ non-metal.
2.Metals are _______ conductors of heat and __________
3.Iron is _______ reactive than copper.
4.Metals react with acid to produce __________ gas.

 

Answer:

1.      reactive

2.      good, electricity

3.      more

4.      hydrogen

 

Question 4.Mark ‘T’ if the statement is true and ‘F’ if it is false.

1.      Generally, non-metals react with acids.

2.      Sodium is a very reactive metal.

3.      Copper displaces zinc from zinc sulphate solution.

4.      Carbon can be drawn into wires.

 

Answer:

1.      False

2.      True

3.      False

4.      False

Question 5.Some properties are listed in the following table. Distinguish between metals and non-metals on the basis of these properties:

Properties	Metals	Non-metals
1. Appearance
2. Hardness
3. Malleability
4. Ductility
5. Heat conduction
6. Conduction of electricity

Answer:

Properties	Metals	Non-metals
1. Appearance	Lustrous (shiny)	Non-lustrous (dull)
2. Hardness	Very hard	Soft
3. Malleability	Malleable	Not malleable
4. Ductility	Ductile	Not ductile
5. Heat conduction	Good conductors	Bad conductors of heat
6. Conduction of electricity	Good conductor of electricity	Bad conductors of electricity

Question 6.Give reasons for the following:

1.      Aluminium foils are used to wrap food items.

2.      Immersion rods for heating liquids are made up of metallic substances.

3.      Copper cannot displace zinc from its salt solution.

4.      Sodium and potassium are stored in kerosene.

 

Answer:

1.      Aluminium is non-toxic and malleable and hence thin sheets of aluminium can be formed.

2.      Metallic substances are good conductors of electricity therefore immersion rods are made up of metallic substances.

3.      Copper is less reactive than zinc and hence it cannot displace zinc from its salt solution.

4.      Sodium and potassium are stored in kerosene because it vigorously reacts with oxygen and water.

 

Question 7.Can you store the lemon pickle in an aluminium utensil? Explain.
Answer:
No, we can not store the lemon pickle in an aluminium utensil because aluminium is metal and thus will react with lemon and produce toxic substances.

Question 8.
Match the substance given in Column A with uses given in Column B.

A	B
(i) Gold	(a) Thermometers
(ii) Iron	(b) Electric wire
(iii) Aluminium	(c) Wrapping food
(iv) Carbon	(d) Jewellery
(v) Copper	(e) Machinery
(vi) Mercury	(f) Fuel

Answer:

A	B
(i) Gold	(d) Jewellery
(ii) Iron	(e) Machinery
(iii) Aluminium	(c) Wrapping food
(iv) Carbon	(f) Fuel
(v) Copper	(b) Electric wire
(vi) Mercury	(a) Thermometers

 

Question 9.What happens when:
(i) Dilute sulphuric acid is poured on a copper plate.
(ii) Iron nails are placed in a copper sulphate solution. Write word equations of the reactions involved.
Answer:
(i) Copper reacts with sulphuric acid and forms copper sulphate and hydrogen (gas).
Copper + Sulphuric acid → Copper sulphate + Hydrogen gas.
Cu + H₂SO₄ → CuSO₄ + H₂ ↑

(ii) Iron displaces copper from copper sulphate solution hence a reddish-brown copper is formed on the iron nails and the blue colour of copper sulphate solution slowly becomes light green.
Iron + Copper sulphate → Copper + Iron sulphate.
Fe + CuSO₄ → Cu + FeSO₄

 

Question 10. Saloni took a piece of burning charcoal and collected the gas evolved in a test tube:
(i) How will she find the nature of the gas?
(ii) Write down word equations of all the reactions taking place in this process.
Answer:
(i) To find the nature of the gas, she will dissolve it in the water and test it with litmus paper.
(ii) (a) Charcoal (c) + Oxygen (O₂) → Carbon dioxide (CO₂)
(b) Carbon dioxide (CO₂) + Water (H₂O) → Carbonic acid (H₂CO₃)
The nature of this gas is acidic because it turns red litmus blue.

 

Question 11.One day Reeta went to a jeweler’s shop with her mother. Her mother gave old gold jewellery to the goldsmith to polish. The next day when they brought the jewellery back they found that there was a loss in its weight. Can you suggest a reason for the loss of weight?
Answer:
The jeweller must have cleared the jewellery in aqua regia solution. This solution is a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3 : 1. This acid solution dissolves some gold in it, due to which there is a loss in the weight of jewellery.

CHAPTER 4 

Materials: Metals and Non-Metals

Additional Questions and Answers

 

Question 1.Give examples of metals.
Answer:
Examples of metals are gold, silver, sodium tungsten, cadmium, nickel, uranium, and mercury.

 

Question 2.Give examples of non-metals?
Answer:
Examples of non-metals are chlorine, helium, oxygen, carbon, fluorine, sulphur, iodine, and bromine.

Question 3.Name the metal which is liquid at room temperature.
Answer:
Mercury

 Question 4.Write the physical properties of metals.
Answer:
The physical properties of metals are:

·         Metals are solid at room temperature except for mercury.

·         Metals generally have high melting points.

·         The surface of most metals has a shiny appearance.

·         Metals are malleable, i.e., they can be beaten into sheets.

·         Metals are ductile, i.e., they can be stretched into wires.

·         Metals are good conductors of electricity.

·         Metals are good conductors of heat.

·         Metals are sonorous, i.e., they produce sound when they are struck by themselves or by any other object.

 

Question 5.
(i) What do you observe when magnesium ribbon is heated over a flame?
(ii) What change do you observe in the colour of red and blue litmus papers when they are dipped into solution obtained by mixing solid residue from (i) in water? What do you conclude?
(iii) Write chemical equations for the above two reactions.
Answer:
(i) When magnesium ribbon is heated over the flame then it burns with brilliant light and gets converted into a white solid residue.

(ii) The solution obtained by mixing white solid residue produced above with water turns red litmus into blue colour and blue litmus remains unaffected. This shows that the solution is alkaline hence oxide formed is basic in nature.

(iii) 2Mg + O₂ → 2MgO
MgO + H₂O → Mg(OH)₂

 

Question 6.What happens when a small piece of sodium metal is dried and kept in water?
Answer:
When a small piece of sodium metal is dried and kept in the water we observe that the sodium piece starts moving in water with a hissing sound and sodium catches fire.
2Na + 2H₂O → 2NaOH + H₂ ↑

 

Question 7.Does magnesium react with cold water? What happens when the water is heated?
Answer:
Magnesium does not react or mildly react with cold water. When water is heated then magnesium reacts with hot water or steam vigorously and produces magnesium hydroxide and hydrogen.
Mg + 2H₂O → Mg(OH)₂ + H₂
(Magnesium) + Water → Magnesium Hydroxide + Hydrogen

 

Question 8.How do metals react with dilute acids?
Answer:
Metals usually displace hydrogen from dilute acids and salt is formed. Only the less reactive metals like copper, silver, and gold do not displace hydrogen from dilute acids.
Metal + Hydrochloric acid → Metal chloride + Hydrogen (gas)
Metal + Sulphuric acid → Metal sulphate + Hydrogen (gas)

Question 9.Write the word equation for the reaction of magnesium with dil. hydrochloric acid.
Answer:
Magnesium reacts with dil. hydrochloric acid to form magnesium chloride and hydrogen gas is evolved.
Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

 

Question 10.What happens when iron nails are added to copper sulphate solution?
Answer:
When iron nails are added to copper sulphate solution the blue colour of copper sulphate starts fading and iron sulphate is formed. Iron displaces copper from copper sulphate and copper gets deposited on the iron nails.
Fe + CuSO₄ → FeSO₄ + Cu

 

Question 11.What happens when strips of magnesium are added to iron sulphate solution?
Answer:
When strips of magnesium are added to iron sulphate solution then magnesium displaces iron from iron sulphate solution and forms magnesium sulphate. Iron gets deposited on the magnesium strips.
Mg + FeSO₄ → MgSO₄ + Fe

 

Question 12.What would you observe when a strip of zinc is dipped in the solution of copper sulphate?
Answer:
When a strip of zinc is dipped in the solution of copper sulphate solution then zinc displaces copper from copper sulphate solution. A red-brown coating of copper forms on the strips of zinc.

 Question 13.Write the uses of metals.
Answer:
The metals are used for:

·         making machines

·         making buildings

·         making automobiles, aeroplanes, trains, satellites, industrial gadgets

·         making cooking utensils and water boilers

·         making electric gadgets

·         making electric cables

·         fine electric contacts in computers and solar cells

·         for making jewellery, mirrors

·         making foils for wrapping of food items, medicines, chocolates, cigarettes, etc.

 

Question 14.Why is iron used for making machines, automobiles, and buildings?
Answer:
Iron is very strong, hard, and rigid therefore, it is used for making machines, automobiles, and buildings.

Activities

Activity 1
Take a small iron nail, a coal piece, a piece of thick aluminium wire, and a pencil lead. Beat the iron nail with a hammer (Fig.). Try to hit hard. Hit hard the aluminium wire also. Then repeat the same kind of treatment on the coal piece and pencil lead. Record your observations in the table.

 

Table: Malleability of Materials

Object/Material	Change in shape (Flattens/Breaks into pieces)
Iron nail	Flattens
Coal piece	Breaks into pieces
Aluminium	Wire Flattens
Pencil lead	Breaks into pieces

Activity 2
Recall how to make an electric circuit to test whether electricity can pass through an object or not (Fig.).






Now, repeat the activity with the materials mentioned in the table. Observe and group these materials into good conductors and poor conductors.

Table: Electrical Conductivity of Materials

Materials	Good Conductor/Poor Conductor
1. Iron rod/nail	Good Conductor
2. Sulphur	Poor Conductor
3. Coal piece	Poor Conductor
4. Copper wire	Good Conductor

Activity 3
Let us check the nature of rust formed as a result of the reaction between iron, oxygen, and water. Collect a spoonful of rust and dissolve it in a very little amount of water. You will find that the rust remains suspended in water. Shake the suspension well. Test the solution with red and blue litmus papers (Fig.).








What do you observe? Is the solution acidic or basic?
Answer:
We observe that red litmus turns blue. The solution is basic.

 

Activity 4
Take a small amount of powdered sulphur in a deflagrating spoon and heat it. If the deflagrating spoon is not available, you may take a metallic cap of any bottle and wrap a metallic wire around it and give it the shape shown in Fig. (a).
As soon as sulphur starts burning, introduce the spoon into a gas jar/glass tumbler [Fig.(a)]. Cover the tumbler with a lid to ensure that the gas produced does not escape. Remove the spoon after some time. Add a small quantity of water into the tumbler and quickly replace the lid. Shake the tumbler well. Check the solution with red and blue litmus papers [Fig. (b)].

 

Question (i) What do you observe?
Answer:
We observe that blue litmus turns red. Therefore, this solution is acidic.

Activity 5
Take a 250 ml beaker/glass tumbler. Fill half of it with water. Now carefully cut a small piece of sodium metal. Dry it using filter paper and wrap it in a small piece of cotton. Put the sodium piece wrapped in cotton into the beaker. Observe carefully. When the reaction stops touch the beaker. What do you feel? Has the beaker become hot? Test the solution with red and blue litmus papers. Is the solution acidic or basic?

Question (i).What do you feel? Has the beaker become hot?
Test the solution with red and blue litmus papers. Is the solution acidic or basic?
Answer:
Yes. The beaker becomes very hot. The solution is basic because it turns red litmus blue.

 

Activity 6
Take samples of metals and non-metals listed in the table in separate test tubes and label them as A, B, C, D, E, and F. With the help of a dropper add 5 ml of dilute hydrochloric acid to each test tube one by one. Observe the reactions carefully. If no reaction occurs in the cold solution, warm the test tube gently. Bring a burning matchstick near the mouth of each test tube. Repeat the same activity using dilute sulphuric acid instead of dilute hydrochloric acid. Record your observation in the table.

Table 5: Reaction of Metals and Non-metals with Acids

Test tube Label	Metal/Non-metal	Reaction with Dilute Hydrochloric Acid Room Warm Temperature	Reaction with Dilute sulphuric Acid Room Warm Temperature
A	Magnesium (ribbon)	Hydrogen gas is liberated
B	Aluminium (foil)	Hydrogen gas is liberated
C	Iron (filings)	Hydrogen gas is liberated
D	Copper (peeled flexible wire)	No reaction takes place	Hydrogen gas is liberated
E	Charcoal (powder)	No reaction takes place	No reaction takes place
F	Sulphur (powder)	No reaction takes place	No reaction takes place

Activity 7
Prepare a fresh solution of sodium hydroxide in a test tube by dissolving 3-4 pellets of it in 5 ml of water. Drop a piece of aluminium foil into it. Bring a burning matchstick near the mouth of the test tube. Observe carefully.
Answer:
We observe that a gas is produced which burns with a pop sound. This gas is hydrogen gas.

Activity 8
Take five 100 ml beakers and label them A, B, C, D, and E. Take about 50 ml of water in each beaker. Dissolve in each beaker a teaspoonful of each substance as indicated in Fig. (a).
Keep the beakers undisturbed for some time. Record your observations in your notebook.

Beaker A: Copper sulphate (CuSO₄) + Zinc granule (Zn)
Beaker B: Copper sulphate (CuSO₄) + Iron nail (Fe)
Beaker C: Zinc sulphate (ZnSO₄) + Copper turnings (Cu)
Beaker D: Iron sulphate (FeSO₄) + Copper turnings (Cu)
Beaker E: Zinc sulphate (ZnSO₄) + Iron nail (Fe)
Fig. (a) and (b) Displacement reactions.

 

Question (i).
What changes do you observe in the various beakers?
Answer:
In beaker A, zinc displaces copper from copper sulphate (CuSO₄). The blue colour of copper sulphate disappears and a powdery red mass of copper is deposited at the bottom of the beaker.
Copper sulphate + Zinc → Zinc sulphate + Copper
In beaker B, iron displaces copper from copper sulphate solution. The blue colour of copper sulphate disappears and it becomes light green. A red coloured powder of copper is deposited on the copper.
In beaker C, D, E, there is no change.