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Monday, July 24, 2017

CROP PRODUCTIION AND MANAGEMENT



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 ___Crop__.
(b)   The first step before growing crops is __prepration __ of the soil.
(c)    Damaged seeds would __float_ on top of water.
(d)   For growing a crop, sufficient sunlight and ____Water___ and __nutrients__ from the soil are essential.

2.      Match items in column A with those in column B.
A                                                                                       B
(i) Kharif crops                                                (a) Food for cattle
ii) Rabi crops                                                   (b) Urea and super phosphate
(iii) Chemical fertilisers                                 (c) Animal excreta, cow dung urine and plant waste
(iv) Organic manure                                       d) Wheat, gram, pea
(e) Paddy and maize
Answer: (i)-(e) , (ii)-(d) , (iii)-(b) , (iv)-(c)
3.      Give two examples of each.
(a) Kharif crop
(b) Rabi crop
Ans: (a) Kharif crop- Paddy and maize       (b) Rabi crop- Wheat, gram, pea

4.      Write a paragraph in your own words on each of the following.
(a)    Preparation of soil : The preparation of soil is the first step before growing a crop. One of the most important tasks in agriculture is to turn the soil and loosen it. 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 process of loosening and turning of the soil is called tilling or ploughing. This is done by using a plough. Ploughsare made of wood or iron.
(b)   Sowing: Sowing is the most important part of crop production. Before sowing, good quality seeds are selected. Good quality seeds are clean and healthy seeds of a good variety. Farmers prefer to use seeds which give a high yield.
(c)    Weeding: The removal of weeds is called weeding. Weeding is necessary since weeds compete with the crop plants for water, nutrients, space and light. Thus, they affect the growth of the crop. Some weeds interfere even in harvesting and may be poisonous for animals and human beings. Farmers adopt many ways to remove weeds and control their growth. Tilling before sowing of crops helps in uprooting and killing of weeds, which may then dry up.
(d)   Threshing: Harvesting in our country is either done manually by sickle or by a machine called harvester. In the harvested crop, the grain seeds need to be separated from the chaff. This process is called threshing. This is carried out with the help of a machine called ‘combine’ which is in fact a combined harvester and thresher.
5.      Explain how fertilisers are different from manure.
Ans: Differences between Fertiliser and Manure
S. No.
Fertiliser
Manure

1
A fertiliser is an inorganic salt.
Manure is a natural substance obtained
by the decomposition of cattle dung, human waste and plant residues.
2
Prepared in factories
Prepared in fields
3
Does not provide humus to soil
Provides humus to soil
4
Very rich in plant nutrients like Nitrogen, phosphorus and potassium
Manure is relatively less rich in plant nutrients

6.      What is irrigation? Describe two methods of irrigation which conserve water.
Ans: The supply of water to crops at different intervals is called irrigation.
                 i.   Sprinkler System: This system is more useful on the uneven land where sufficient water is not available. The perpendicular pipes, having rotating nozzles on top, are joined to the main pipeline at regular intervals.
                ii.   In this system, the water falls drop by drop just at the position of the roots. So it is called drip system. It is the best technique for watering fruit plants, gardens and trees. The system provides water to plants drop by drop
7.      If wheat is sown in the  kharif  season, what would happen? Discuss.
Answer : Wheat is a rabi crop, hence it requires cold climatic conditions to be grown properly. If it  is sown in the kharif season, it will not grow or may get destroyed due to excessive rains in the  kharif season.
8.       Explain how soil gets affected by the continuous plantation of crops in a field.
Answer:Soil supplies mineral nutrients to the crop. These nutrients are essential for the growth of plants. Continuous growing of crops in the same field makes the soil poorer in certain nutrients. This makes the soil in fertile. And then, to replenish the soil with nutrients  farmers need to add manures to the soil



9.      What are weeds? How can we control them?
Answer: The undesirable plants may grow naturally along with the crop are called weeds. There are many ways to remove weeds and control their growth. Weeds can be removed by uprooting or cutting them close to the ground, from time to time. This is done with the help of a khurpi. Weeds are also controlled by using certain chemicals, called weedicides, like 2,4–D. These are sprayed in the fields to kill the weeds.

10.   Arrange the following boxes in proper order to make a flow chart of sugarcane crop production.
The correct order is 5à6-à4à7à2à3à1
11.   Complete the following word puzzle with the help of clues given below.
Answer: Down
1.Irrigation
2.Storage
5. Crop
Across
3. Harvester
4. Gram
6. Winnowing


Thursday, July 20, 2017

CLASS VIII SCIENCE SYNTHETIC FIBERS AND PLASTIC

Synthetic Fibres and Plastics
10. Give examples to show that plastics are non-corrosive in nature.
Ans. Plastics are not corroded Example-the cleansing chemicals that we use at home are stored in plastic bottles, instead of metal containers.
11. Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.
 Ans. No. The handle of a toothbrush should be hard and strong, while the bristles should be soft and flexible.
12. ‘Avoid plastics as far as possible’. Comment on this advice.
Ans.
·         Plastics are non-biodegradable they take several years to decompose.
·         Plastics add to the environmental pollution. They cannot be burnt as when burnt,
·         Plastic bags thrown in the garbage dump are swallowed by animals like cows and choke their respiratory system.
·         We should avoid plastics as far as possible.
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 cookware
(iv) Nylon
(d) Fabrics do not wrinkle easily
 Answer
A
B
(i) Polyester
(d) Fabrics do not wrinkle easily
(ii) Teflon
(c) Used to make non-stick cookware
(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.
Ans. Raw materials for natural fibres are mainly derived from plants and this means cutting a lot of trees. This leads to deforestation. But raw materials of synthetic materials are mainly petrochemicals. Hence, manufacturing synthetic fibres helps in the conservation of forests.
15. Describe an activity to show that thermoplastic is a poor conductor of electricity.
Ans.


Saturday, July 15, 2017

CLASS VIII SCIENCE COMBUSTION AND FLAME



1. List conditions under which combustion can take place.
Ans. Conditions under which combustion can take place are as follows:
a. Air
b. The ignition temperature
c. Inflammable substance.

2. Fill in the blanks.
(a) Burning of wood and coal causes ______________ of air.
(b) A liquid fuel, used in home is ____________.
(c) Fuel must be heated to its ________________ before it starts burning.
(d) Fire produced by oil cannot be controlled by ____________.
Ans. Fill in the blanks.
(a) Burning of wood and coal causes pollution of air.
(b) A liquid fuel, used in home is LPG.
(c) Fuel must be heated to its ignition temperature before it starts burning.
(d) Fire produced by oil cannot be controlled by water.

3. Explain how the use of CNG in automobiles has reduced pollution in our cities.
Ans. The use of CNG in automobiles has reduced pollution in our cities because CNG does not produce any poisonous gas on burning. That is why pollution in our cities is reduced.

4. Compare LPG and wood as fuels.
Ans. LPG burns easily and produces more heat in comparison to wood. Besides, it is a clean fuel, it does not produce fume and ashes as wood do. LPG can be stored and transported easily and conveniently.

5. Give reasons.
(a) Water is not used to control fires involving electrical equipment.
(b) LPG is a better domestic fuel than wood.
(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.
Ans. (a) Water is not used to control fire produced by electrical equipment because water is conductor of electricity and may result in electric shock.
(b) LPG is a substance which is cheaper and burns easily. It produces large amount of heat and does not leave behind any undesirable substance.
(c) Paper catches fire easily, but when it is wrapped around an aluminium pipe,  the ignition temperature does not meet as heat is transferred to aluminium to lower the temperature of paper.

6. Make a labelled diagram of candle flame.
Ans.

7. Name the unit in which the calorific value of a fuel is expressed.
Ans. The calorific value of a fuel is expressed in kilojoules per kg (kj/kg).

8. Explain how CO2 is able to control fires.
Ans. Carbon dioxide being heavier than oxygen covers the fire like a blanket. Since the contact between fuel and oxygen is cut off, the fire is controlled. The added advantage of carbon dioxide is that in most cases it does not harm the electrical appliances.

9. It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Ans. Green leaves contain water it cools the combustible materials, its temperature is brought below its ignition temperature.
In dry leaves, water is absent so burning process start as the temperature is raised above the ignition temperature and the leaves catch fire easily.

10. Which zone of a flame does a goldsmith use for melting gold and silver and why?
Ans. The outermost zone of a flame , because it has the highest temperature to melt the gold and silver.

11. In an experiment 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180,000 kj. Calculate the calorific value of the fuel.
Ans. Calorific value of a fuel = Total heat produced/total mass burnt.
mass of fuel = 4.5 kg.
Heat produced = 180,000 kj.
Therefore, calorific value of fuel = 180,000/4.5kg = 40,000 kj/kg.

12. Can the process of rusting be called combustion? Discuss.
Ans. Yes, process of rusting can be called combustion, slow combustion, because rusting also takes place in presence of air in the atmosphere.

13. Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?
Ans. The water of Ramesh’s beaker will get heated in a shorter time because the outermost part of the flame is the hottest.



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