This document is about science biology notes for chapter 12, food sources, It is a complete document for the whole chapter, and it will help you very well
Page 204
Q.1 What do we get from cereals, pulses, fruits and vegetables?
Sol. (i) Cereals provide us with carbohydrates. Also, they are a rich source of energy.
(ii) Pulses give us proteins.
(iii) Fruits and vegetables are a rich source of vitamins and minerals. A small amount
of proteins, carbohydrates, and fats are also present in them.
Page 205
Q.1 How do biotic and abiotic factors affect crop production?
Sol. A variety of biotic factors such as pests, nematodes, diseases, etc. can reduce the net
crop production. A pest causes damage to agriculture by feeding on crops. For example, boll
weevil is a pest on cotton. It attacks the cotton crop, thereby reducing its yield. Weeds also
reduce crop productivity by competing with the main crop for nutrients, light, and space.
Similarly, abiotic factors such as salinity, temperature, etc. affect the net crop production.
Some natural calamities such as droughts and floods are unpredictable. Their occurrence
has a great impact on crops sometimes, destroying the entire crop.
Q.2 What are the desirable agronomic characteristics for crop improvements?
Sol. The desirable agronomic characteristics for crop improvements are:
(i) Tallness and profuse branching in any fodder crop.
(ii) Dwarfness in cereals.
These desirable agronomic characteristic help in increasing crop productivity.
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, Page 206
Q.1 What are macro-nutrients and why are they called macro-nutrients?
Sol. Macro-nutrients are nutrients required in relatively large quantities for growth and
development of plants. They are six in number. Since they are required in large quantities,
they are known as macro-nutrient. The six macro-nutrients required by plants are nitrogen,
phosphorus, potassium, calcium, magnesium, and sulphur.
Q.2 How do plants get nutrients?
Sol. Plants require sixteen essential nutrients from nature for their growth and development.
All these nutrients are obtained from air, water, and soil. Soil is the major source of nutrients.
Thirteen of these nutrients are available from soil. The remaining three nutrients (carbon,
oxygen, and hydrogen) are obtained from air and water.
Page 207
Q.1 Compare the use of manure and fertilizers in maintaining soil fertility.
Sol. Manures increase soil fertility by enriching the soil with organic matter and nutrients
as it is prepared by the decomposition of animal excreta and plant wastes. On the other hand,
fertilizers are mostly inorganic compounds whose excessive use is harmful to the symbiotic
micro-organisms living in soil. Their excessive use also reduces soil fertility. Hence, fertilizers
are considered good for only short term use.
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