Ch1,2science class 8th Ncert solutions

Ch=1 (crop production and management)

Ques1. 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 _____________.

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

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

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

Sol:

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

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

(c) Damaged seeds would float on top of the water.

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

Ques2. 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 superphosphate
(iii) Chemical fertilisers	(c) Animal excreta, cow dung urine and plant wastes
(iv) Organic manure	(d) Wheat, gram, pea
	(e) Paddy and maize

sol:-

(i) Kharif crops.	(e) Paddy and maize.
(ii) Rabi crops.	(d) Wheat, gram, pea.
(iii) Chemical fertilisers.	(b) Urea and superphosphate.
(iv) Organic manure.	(c) Animal excreta, cow dung urine and plant wastes. 3. Give two examples of each. (a) Kharif crop (b) Rabi crop Soln: Kharif crops- Paddy and maize Rabi crops- Wheat and Pea 4. Write a paragraph in your own words on each of the following. (a) Preparation of soil (b) Sowing (c) Weeding (d) Threshing Sol:- a) Preparation of the soil is the first step in agriculture. Preparation of the soil is done to loosen the soil, which is essential for the root penetration into the soil. This allows the roots to breathe easily. Loosening of the soil allows the growth of earthworms and microorganisms, which will help to keep the soil fertile by adding humus to the soil. Loosening of soil also brings nutrient-rich soil to the top layer, which is essential for the growth of plants. b) Sowing is an important process in crop production. First, healthy seeds are selected before sowing. After selecting healthy seeds sowing is done by either traditional methods or by using equipment’s seed drill. c) Removal of unnecessary plants from the field is called weeding. Weeds compete with crop plants for nutrients and water. This will reduce the yield of the desired crops. Weeds also interfere while harvesting and gets mixed with crops. Some weeds are poisonous to animals and humans. Tilling is a common method which helps removal of weeds before sowing crops, manual methods like physical removal of plants are used to remove weeds. Weedicides are sprayed to get rid of weeds, but this method may affect the health of farmers because of chemicals used as weedicides. d) Process of separating the chaff from the crop is known as threshing. Threshing is carried by a machine called ‘combine’ which is a harvester as well as a thresher. Threshing is also done by winnowing where to blow of wind is used to separate the chaff from crops. 5. Explain how fertilisers are different from manure. Soln: Fertilizers Manure Fertilizer is an inorganic substance. Manure is an organic substance. Fertilizers are prepared artificially. Manure is obtained by decomposition of animal, plant and human waste. Prepared in factories. Prepared in fields. Does not provide Humus to the soil. Provide humus to the soil. Rich in plant nutrients. Relatively less plant nutrients. Long term usage has adverse effects on soil. Long term usage improves soil fertility. 6. What is irrigation? Describe two methods of irrigation which conserve water. Soln: The supply of water to crops at regular intervals is called irrigation. Methods of irrigation which conserve water are a) Drip Irrigation: Here the water goes drop by drop directly into the roots this method is very useful as it conserves the water and also helps in avoiding weeds. b) Sprinkler system: This method is in use in mainly 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. When water is allowed to flow through the main pipe under pressure with the help of a pump, it escapes from the rotating nozzles. It gets sprinkled on the crop as if it is raining. 7. If wheat is sown in the Kharif season, what would happen? Discuss. Soln: Wheat crops may get destroyed if sown in Kharif season because of unfavourable temperature, pests and adaptable conditions for the plants to grow. Kharif come during the rainy season, hence it is not a wise idea to grow wheat in Kharif season. 8. Explain how soil gets affected by the continuous plantation of crops in a field. Soln: Plants require nutrients for their growth. Without optimum nutrients plants will die. Continuous plantation of crops results in depletion of certain nutrients like Nitrogen, Phosphorus, Potassium etc. This results in the decrease of yield due to loss of nutrients hence there should be a gap between crops in order to get a good yield. 9. What are weeds? How can we control them? Soln: In a field many other undesirable plants may grow naturally along with the crop. These undesirable plants are called weeds. Weeds can be controlled by methods called weeding. Tilling before sowing of crops helps in uprooting and killing of weeds, which may then dry up and get mixed with the soil. Weeds are also controlled by using certain chemicals, called weedicides. 10. Arrange the following boxes in proper order to make a flow chart of sugarcane crop production. Soln: 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 chaff. Soln:

Question 1.
Fill in the blanks.
(a) Microorganisms can be seen with the help of a _____
(b) Blue-green algae fix ______ directly from the air to enhance the fertility of soil.
(c) Alcohol is produced with the help of _____
(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) 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 fixation
(ii) moulding
(iii) fermentation
(iv) infection
Answer:
(iii) fermentation

Question 3.
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

Answer:
(i) (e)
(ii) (a)
(iii) (b)
(iv) (c)
(v) (d)
(vi) (f)

Question 4.
Can microorganisms be seen with the naked eye? If not, how can they be seen?
Answer:
The microorganisms cannot be seen with our naked eyes because they are very small in size. Some of these, such as fungus growing on bread, can be seen with a magnifying glass. Others cannot be seen without the help of a microscope.

Question 5.

What are the major groups of microorganisms?
Answer:
Microorganisms are classified on the basis of their size into four major groups. These groups are:
(a) Bacteria
(b) Fungi
(c) Protozoa
(d) Some algae

Question 6.
Name the microorganisms which can fix atmospheric nitrogen in the soil.
Answer:
Rhizobium, Clostridium and Azotobacter.

Question 7.
Write 10 lines on the usefulness of microorganisms in our lives.
Answer:
Microorganisms are useful to us in many ways. For example,

• Bacteria like Lactobacillus convert milk into curd.
• Bacteria are also involved in the making of cheese.
• Acetobacter aceti is used for producing acetic acid from alcohol.
• Yeast is used in the commercial production of alcohol, wine and bakery products.
• Some specific microorganisms are helpful in manufacturing of antibiotics.
• Microorganisms act as cleansing agents and decompose the waste products into manure.
• Dead or weakened microbes are used in the preparation of vaccines.
• Some bacteria fix atmospheric nitrogen and increase soil fertility.
• Algae, yeast, fungi or bacteria may be used as an ingredient or a substitute for protein-rich foods that are suitable for human or animal consumption.
• Some microorganisms are taken as probiotics, that are believed to provide health benefits when consumed.

Question 8.
Write a short paragraph on the harms caused by microorganisms.
Answer:
Microorganisms are harmful to us in many ways. For example, microorganisms, called pathogens cause disease in humans, plants and animals. Pathogens or germs enter a healthy body through air, water, contaminated food and infected person by direct or indirect contact or by the carrier. Common ailments like cold, influenza (flu), cough, polio, chicken pox are caused by viruses. Foot and mouth diseases in the cattle are also caused by viruses. Typhoid, tuberculosis (TB) are caused by bacteria. Anthrax a dangerous human and cattle diseases is also caused by bacteria.

Diseases like dysentery and malaria are caused by protozoa. Ringworm is caused by fungi. Several microbes causes diseases in plants and thus reduces the yield. Citrus canker, a bacterial disease, affects trees of citrus fruit and is spread by air. Bhendi yellow vein mosaic disease is caused by a virus and is spread by insects in lady fingers. Rust of wheat is a fungal disease spread through air. Microorganisms that grow on our food sometimes produce toxic substances. These make the food poisonous causing serious illness and even death. This food-borne illness is called food poisoning.

Question 9.

What are antibiotics? What precautions must be taken while taking antibiotics?
Answer:
Antibiotics are the medicines which kill or stop the growth of the disease-causing microbes. They are manufactured by growing specific microorganisms. They are used to cure a variety of diseases.

It is important to take antibiotic only on the advice of a qualified doctor. One must finish the course prescribed by the doctor to make the drug more effective. Antibiotics must not be taken unnecessarily because it may kill beneficial bacteria also. Antibiotics are, however, not effective against cold and flu as they are caused by viruses.