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Showing posts with label Class VIII Science | Sample Qs. Show all posts

CBSE Guess - 8th NCERT Science, Crop Production and Management – long answer questions

 
Class 8 CBSE NCERT Solutions and Guide >> 8th CBSE Science Solutions


Class 8 NCERT Science - Chapter 1, Crop Production and Management

NCERT Guide - CBSE Guess and Guide

 


Solutions of CBSE Guess Questions (4-5 marks questions)

Question.1: Write a paragraph on the various methods used to replenish the nutrients in the fields.

Solution: When crops are grown in the fields, they use all the nutrients present in the soil. These nutrients have to be replenished for the further cropping. Various methods and products are used for this purpose.

Fertilizers: Fertilizers are the chemicals which replenish the soil with all the nutrients. They are produced in the factories and are inorganic products. Every fertilizer is rich in a particular nutrient. Some examples of fertilizers are urea, ammonia sulphate, potash, NPR etc. They help in getting better and healthy yields. But, excessive use of these chemicals is also harmful.

CBSE Guess - 8th NCERT Science, Crop Production and Management – crop threshingManure: Manures are the organic products, which are obtained by the processing of dead bodies of plants and animals. Dead bodies of plants and animals are dumped in pits. They get decomposed to become manure. Using manure not only improves the texture of the soil but also, improves the water holding capacity of the soil.

Fallowing: Sometimes continuous growing of crops makes the soil barren or infertile. It needs to be left uncultivated so that it can regain its nutrients and fertility. This process of leaving soil uncultivated for one crop season is called fallowing.

Crop Rotation:  If the same crop is grown in the field year after year, it will lead to the deficiency of certain minerals. It is due to this fact that the same crop requires same type of nutrients. To solve this problem farmers are encouraged to grow one pulse crop in – between two cereal crops in the field. So the method of successive cultivation of different crops in an orderly manner on the same fields, in contrast to a one-crop-system or to haphazard crop successions is known as crop rotation. For example, growing legumes as fodder in one season and wheat in the next season. The roots of legumes have so many nodules which contain nitrogen fixing bacteria. These convert free atmospheric nitrogen into nitrates and increase the fertility of the soil. (Replenishing of soil with nitrogen)

Question.2: Write a short note on Threshing & Winnowing.

Solution: When a farmer cut his crops, he has to separate the grain seeds from chaff. This process is called threshing. Mechanically it can be done with the help of threshers and combine. Farmers with small holdings of land do the separation of grain and chaff by winnowing. The grains are thrown from the height in the direction of air. The air carries away the lighter chaff or dried stems and leaves and the heavier grain drop down in the form of a heap. This whole process is called winnowing. 

More Study  
ü  Class 8, Crop Production and Management - Chapter 1, Science - NCERT Answers of Textbook Exercise

ü  Crop Production and Management - 8th NCERT Science - Solutions of CBSE Guess Questions (Objective, Fill in the Blank, MCQ, Short answer types)

ü  CBSE 8th NCERT Science Guide (all chapters)

Coal and Petroleum - CBSE Guess with sample questions answers for Class 8 NCERT Science

 

Coal and Petroleum

Class 8 Science - CBSE Guess and Guide | NCERT Questions Bank

NCERT answers for CBSE Sample Questions - Class 8 Science Chapter 5 Coal and Petroleum

Question.1: What is pure form of carbon?  
Answer: Coke.

Question.2: What are natural resources? How many types of natural resources are available in nature?
Answer: Resources which are obtained from nature are called Natural Resources. On the basis of availability of these resources (materials) can be divided into two types:
1. Inexhaustible Natural Resources - natural resources which cannot be finished by human activities like - sunlight, air
2. Exhaustible Natural Resources - are those resources which are present in limited quantity and may be finished by human activities like - wildlife, coal, petroleum.    

Question.3: What are inexhaustible natural resources? Give two examples of inexhaustible natural resources.   
Answer: See answer of above question.

Question.4: What is coal tar?
Answer: Coal Tar is a black liquid that is produced during destructive distillation of coal. Coal Tar has an unpleasant smell. Earlier coal tar was used for metalling the roads which. Now coal tar is mainly used to produce many types of industrial products, consumables.  

Question.5: What are exhaustible natural resources? Give two examples of exhaustible natural resources.  
Answer: See answer of above question no. 2.

Question.6: What is Petroleum? Write a short note on Petroleum.
Answer: Petroleum is an exhaustible, natural fossil fuel which is extracted from beneath the surface of the earth. Petroleum was formed from the dead bodies of sea organisms which got buried under the sea bed. Over millions of years, in absence of air, under high temperature and pressure these bodies got transformed into petroleum and natural gas.
Petroleum is a dark, oily liquid with some unpleasant odour. It has various useful constituents like - petroleum gas (LPG), petrol, kerosene, diesel, lubricating oil, paraffin wax, bitumen, etc. which are separated from it by the process known as Fractional Distillation.
Due to its high commercial importance petroleum is known as “Black Gold”.   

Question.7: What are fossil fuels?
Answer: Those fuels which got formed by the decomposition of the dead remains of living organisms for a long period of time are called Fossil Fuels. Examples of fossil fuels - coal and petroleum.

Question.9: Define and differentiate between Coal and Coal Gas. [Write short notes on Coal and Coal Gas.]
Answer: Coal is a natural, exhaustible fossil fuel which is found under the surface of the earth. Coal has formed from the dead vegetation over hundreds of millions years through Carbonisation. It is a black, hard solid material. When heated in air it burns and produces mainly carbon dioxide. Coal is mainly used as a fuel in various industries. Several other products like - coke, coal-tar, coal gas etc. obtained after processing coal, are further used for various purposes. In thermal power plants coal is used to produce electricity. In India coal is found mainly in Bihar, Jharkhand, West Bengal and MP.
Coal Gas is a fuel which is obtained during the processing of coal to get coke. Many years ago coal gas was used in America and Britain for street-lighting.     

Question.10: What is Petroleum Refining?
Answer: The extraction process in which different constituents of petroleum are separated, known as Fractional Distillation, is also known as Petroleum Refining.

Question.11: Name three products obtained from Petroleum Refining along with their uses.
Answer: Three products obtained from Petroleum Refining and their uses -
L.P.G: Liquefied Petroleum Gas, used as domestic fuel.
Kerosene: Used as fuel for burning in stoves, lamps, automobiles.
Petrol: As fuel for light vehicles, aviations, dry cleaning of fabrics.   

Question.12: What is carbonization?
Answer: The slow process of conversion of dead vegetation into coal is called Carbonisation.

Question.13: Which gas is mainly released when coal is burnt?
Answer: Carbon dioxide.

Question.14: To which process coal is put to get some useful products?
Answer: Destructive distillation.

Question.15: What is destructive distillation?
Answer: Burning coal in absence of oxygen to get coke and other useful products is called Destructive Distillation.

Question.16: Why cannot we prepare petroleum in our laboratories?  
Answer: Petroleum was formed in hundreds of millions of years by conversion of dead organisms (plants and animals) buried under the surface of the earth under high temperature and pressure conditions.
Such conditions necessary for conversion of dead bodies into fossil fuel cannot be artificially created in laboratories and therefore, we cannot we prepare petroleum in our laboratories.  

More study from Chapter 5, Class 8 NCERT Science

Coal and Petroleum: CBSE Guide NCERT Solutions for Class 8 Science Textbook ExerciseQuestions

Synthetic Fibers and Plastics | Chapter 3, Class 8 NCERT Science - CBSE Sample Questions Answers

 
Class 8 NCERT Solutions CBSE Guide > 8th NCERT Science

Chapter 3, Class 8 NCERT Science - Synthetic Fibers and Plastics

CBSE Sample Questions Answers


Key Terms
Synthetic Fiber Synthetic fibers are made of very large units called ‘polymer’. The synthetic fibers are obtained by chemical processing of petrochemicals. Different types of synthetic fibers are like - rayon, nylon, polyester etc.

Polymer The word ‘Polymer’ comes from two Greek words: ‘poly’ means many and ‘mer’ means part or unit. When smaller units of as chemical substance are combined to form a large single unit then it is called polymer. Example - cellulose, polythene etc.

Biodegradable Materials A material which gets decomposed through natural processes such as, action by bacteria are called ‘biodegradable’ materials. Examples - paper, wood, vegetables etc.

Short answer type CBSE sample questions answers

Question.1: Why rayon is completely synthetic fiber?

Answer: Rayon is not completely synthetic fiber because it is not completely made of synthetic materials. It uses tree pulp as the raw material.

Question.2: What is PET?

Answer: PET is a form of polyester. It is synthetic material. It is mainly used to make bottles, utensils, films, wires and many other useful products. The most common and visible usage being PET jars in our kitchens.

 
Long answer type CBSE sample questions answers

Question.1: Name different artificial fibers and write their uses.

Answer: Following are the main synthetic fibers:
  • Rayon - It’s also called the artificial silk as it has great luster and is light in weight. It is obtained by chemical treatment of wood pulp. It can be woven like silk and dyed in different colours. It’s used as dress material. Mixed with cotton, it is used to make curtains, bed-sheets etc. It’s used with wool to make beautiful carpets.
  • Nylon - It’s the strongest, 100% manmade fiber. It’s made by coal, water and air. It’s elastic in nature and light in weight. It is lustrous and thus ideal for making dresses. Nylon is also used to make stockings, seat-belts, ropes, tents, toothbrushes, sleeping bags, curtains, parachutes etc.
  • Polyester - It is made up of multiple units of ‘esters’. The clothing made of this fiber does not get wrinkled easily. It’s always crisp and easily washable. PET is also derived from polyester which in turn is used to make containers, utensils, films, wires etc.
  • Acrylic - Acrylic is like wool and is used to make sweaters and suit lengths. 

Question.2: Explain uses of Melamine and Bakelite.

Answer:
Uses of Melamine - Melamine is a kind of thermosetting plastic which has great capacity to tolerate heat. It does not allow the heat to pass through easily. Melamine being a fire-resistant material has many other uses like in making kitchenware and handles of the cooking ware so that they do not heat up and remain easy to handle while cooking. It is also used in preparing fire resistant fabrics.

Uses of Bakelite - Bakelite is a poor conductor of electricity and does not allow the electric current to pass through it. Therefore, it’s used to make electric plugs and switches. Because of its heat resistant character it is used to make handles of utensils.

Question.3: Write advantages of disadvantages of synthetic fibers.
Answer:
Advantages of synthetic fibers:

1)     Synthetic fibers are generally wrinkle resistant. So it is convenient to wash and wear.
2)     Synthetic fibers are strong so they can take up heavy loads easily. They have got high tensile strength, which enables them to carry weights.
3)     They have great elasticity and so can be easily stretched.
4)     Synthetic fibers are generally soft, because of which they used to make variety of clothes and clothing materials.

Disadvantages of synthetic fibers:

1)     Synthetic fibers can’t absorb moisture. This makes them unsuitable during summer. When our body sweats this make body sticky and skin irritating.
2)     They are dangerous to be worn near fire or heat, as they can easily catch fire.
3)     They are difficult to iron (press) as they melt very easily.

Question.4: How disposal of plastic is a problem? Explain. or Why the wastage of plastics is considered against eco-friendly?
Answer: There are several reasons for which the wastage of plastics is considered not eco-friendly (environment friendly). First of all, the plastics are non-biodegradable in nature and take several years to degenerate. Some plastics which cannot be recycled are a great problem to finally dispose them off. The burning of plastics is also a very slow process during which they release a lot of poisonous gases to the environment causing air-pollution. Such plastic items thrown carelessly in an eating garbage they may cause death for some animals like - cows, dogs etc. The poly-bags, plastic wrappers etc carelessly thrown here and there are responsible for clogging of drains. Being non-degradable, such disposed plastic wastes get buried into the soil resulting soil pollution and decreasing soil fertility. Because of all these reasons the disposal of plastic remains a genuine problem and wastage of plastics is also considered as against environment friendly.       

Objective type CBSE Questions with their Answers

Question.1: Fill in the blanks:
a. The fiber we get from plants and animals `is called _______.
b. The fiber we obtain from chemicals is called _______.
c. The chemicals of petroleum origin used to form synthetic fiber are called _______.
d. Synthetic substances apart from fibers are _______.
e. Plastics which can be bent and moulded are called _______.
f. ______ is used to make the handles of cookware because it is _______ to heat.
g. Switch board and electric plugs are made of _______.
h. ______ is the most expensive natural fiber.
i. Cotton is the polymer of _____.
j. We should avoid using ________ carry bags.
  
Answer: a - natural fiber, b - artificial / synthetic fiber, c - petrochemicals, d - plastics, e - thermoplastics, f - melamine, resistant, g - Bakelite, h - silk, i - cellulose, j - polythene.

Related Study

Crop Production and Management - Class 8 NCERT Science - Solutions of CBSE Guess Questions

 

CBSE Class VIII - Chapter 1, NCERT Science

Crop Production and Management


Solutions of CBSE Guess Questions (1 – 2 Marks Questions)

Question.1: Why does every living organism need food?

Answer: Every living organism needs food to grow and perform various other activities and body functions.

Question.2: Where do we get our food from?

Answer: We get our food from plants and animals.

Question.3: What is crop?

Answer: When same types of plants are grown at a large scale, it is called crop.

Question.4: Name the factors controlling crop production.

Answer: Soil, water, sunlight and air.

Question.5: Based on factors required to grow plants, how many crop seasons are observed in India?

Answer: Broadly two crop seasons: Rabi & Kharif.

Question.6: What are crumbs?

Answer: Crumbs are big pieces of soil present in fields, which require tilling.

Question.7: Which agricultural tools are used for tilling?

Answer: Plough, Hoe & Cultivators.

Question.8: Who supplies mineral nutrients to plants?

Answer: Soil.

Question.9: Which manure is called Organic manure?

Answer: Manure obtained from the dead bodies of plants and animals.

Question.10: Name any two important fertilizers.

Answer: Urea, NPK (Nitrogen, Phosphorus, Potassium).

Question.11: What is a fallow?

Answer: An uncultivated field between two cropping is called a fallow.

Question.12: Which bacteria are present in the legumes of leguminous plants?

Answer: Rhizobium.

Question.13: What is harvesting?

Answer: Cutting of the crop after it is mature is called harvesting.

Question.14: How does reduction in moisture of newly harvested grains help in storage?

Answer: It prevents pests, insects, bacteria etc from attacking the grains.

Question.15: Name the places where grains are stored at large scale.

Answer: Granaries and silos.


Solutions of CBSE Guess Questions (2 – 3 Marks Questions)

Question.16: Write the names of various agricultural practices undertaken to produce a crop.

Answer: Following agricultural practices are performed to produce the crop:

1.       Soil preparation,
2.       Sowing,
3.       Adding manure and fertilizers,
4.       Irrigation,
5.       Protection from weeds,
6.       Harvesting &
7.       Storage.

Question.17: Why is the soil turned and loosened before seeds are sown?

Answer: The soil is turned and loosened during the process of ploughing. The ploughing loosens the soil particles and turn the soil of upper surface. This allows the nutrients from the dead organism to be released back in the soil and better penetration and absorption of nutrients by plant roots. 

Question.18: What is the role of water in production of crops?

Answer: Water is essential for all plants. Crops should get enough water at different stages of their growth. Different crops require different amount of water in the field. The wheat crop requires moderate amount of water at the time sowing, flowering, and ripening of crop. Therefore, crops should be irrigated properly according to their needs.  

Question.19: What are the different methods of irrigation?

Answer: Supply of water to crops at appropriate intervals is called irrigation. Various sources of irrigations are- wells, tube wells, ponds, lakes, rivers, canals etc. Different methods of irrigation are adopted on the basis of the soil types, size of the field, requirement of water by the crop and of course, the availability of water. Some of the traditional methods of irrigation include water supply through moat (Pulley-system), chain pump, dhekli and rahat (lever-system).
Modern methods of irrigation help us to use water most economically. Two such methods are- Sprinkler system and Drip system.

Question.20: What is humus? How is it formed?   

Answer: Humus is a kind of soil rich in nutrients. It is formed by the microbial action on dead decaying bodies of plants and animals. It’s generally formed on those spots where – there are dense layers of trees. The soil below it becomes dark having more number of pathogenic bacteria.

Question.21: Why does a farmer rotate crops in the field? (Crop-rotation)

Answer: If the same crop is grown in the field year after year, it will lead to the deficiency of certain minerals. It is due to this fact that the same crop requires same type of nutrients.
To solve this problem farmers are encouraged to grow one pulse crop in – between two cereal crops in the field. So the method of successive cultivation of different crops in an orderly manner on the same fields, in contrast to a one-crop-system or to haphazard crop successions is known as crop rotation. For example, growing legumes as fodder in one season and wheat in the next season. The roots of legumes have so many nodules which contain nitrogen fixing bacteria. These convert free atmospheric nitrogen into nitrates and increase the fertility of the soil. (Replenishing of soil with nitrogen)

Question.22: What safety measures are to be taken in handling pesticides and weedicides?    

Answer: Weedicides and pesticides are highly poisonous chemicals. They kill the pests. They can harm the human also. So, certain precautionary measures should be taken while spraying pesticides and weedicides.

·   They should be kept away from the reach of children.
·   They should not be inhaled while spraying. Gloves and mouth covers should be used while spraying them.
·   Hands should be washed properly after their use.

Question.23: Distinguish between pesticides and weedicides.

Answer: Weeds are controlled by using certain chemicals called weedicides. These chemicals don’t cause any damage to the crop.
Pesticides are the chemicals which are used to kill the pests growing on the crops. They kill the eggs and larvae of the insects.

Question.24: Why should the harvested grains is protected from moisture?

Answer: The harvested grains should be protected from moisture because of the following reasons:
a)       It promotes the growth of insects.
b)       Moisture helps in germination of seed.
c)       It promotes the growth of fungi.

d)       It speedily spoils the quantity and quality of grains.

Solutions of CBSE Questions (Objective type / Multiple Choice / True-False)

Question.1: Fill in the blanks:
a.         ____ is used for sowing of seeds.
b.         Loosening the soil is also called _____.
c.          ____ is the second agricultural practice.
d.         _____ and ____ are used to add nutrients in the soil.
e.         Manures are the ___ substances.
f.          ____ is a weedicides.
g.         ____ is the economical method of irrigation.
h.         Leaving field uncultivated is called ______.
i.           _____ is used to separate seed from the chaff.
j.          Crops sown in the rainy season are called ______.
Solution: a. seed drill, b. tilling, c. sowing, d. manures and fertilizers, e. organic, f. metachlor, g. drip irrigation, h. fallow, i. thresher, j. rabi crops.
Question.2: Write ‘True/False’ for the following statements:
a.         Many plants are first grown in kindergartens and then sown in fields.
b.         Seeds can only be sown by using seed drills.
c.          Earth worms are farmer friendly.
d.         Substances that kill pests are called weedicides.
e.         Cutting and gathering of mature crops is called harvesting.
f.   Process of beating grains to separate them crop plants is called winnowing.
g.         Excess use of fertilization is not good for crops & soil.
h.         Animals which provide us with eggs and flesh are called milch animals.
Solution: a-false, b-false, c-true, d-false, e-true, f-false, g-true, h-false

 Further study - 
Class 8, Crop Production and Management - Chapter 1, Science - NCERT Answers of Textbook Exercise [Read] 

 CBSE Guess - 8th NCERT Science, Crop Production and Management – long answer questions [Read]