NIOS Class 12 Environmental Science Chapter 21
INTEXT QUESTIONS 21.1
1. Define sustainable agriculture.
Ans: Sustainable agriculture and farming systems are those that are least toxic and least energy intensive and yet maintain productivity and profitability.
2. Mention three advantages of sustainable agriculture.
Ans: Sustainable agriculture is helpful to the environment because
- (i) It protects environment quality
- (ii) Uses natural resources efficiently
- (iii) Decreases dependency on non-renewable resources.
INTEXT QUESTIONS 21.2
1. How does crop rotation practice improve soil quality?
Ans: Crop rotation practice increases soil fertility by growing legumes as a rotational crop, decreases soil erosion, and controls pests and diseases.
2. What is the difference between polyculture and multiple cropping?
Ans:
- Polyculture is the practice of growing plants simultaneously on a piece of land which matures at various times.
- Multiple cropping is growing two or sometimes three different crops in succession on the same land within a year.
3. Define biofertilizers and give two important advantages of using it.
Ans: Biofertilizers are plant nutrients of biological origin, like algae, bacteria, fungi, which have no harmful effect on soil and environment.
Advantages: A large amount of money can be saved by reducing the purchase and production of chemical fertilizers, and human health can be saved from the harmful effects of chemical fertilizers.
4. What roles do Rhizobium and blue-green algae play in agriculture?
Ans: Rhizobium, a symbiotic bacterium, lives in the root nodules of legume plants and fixes atmospheric nitrogen and ultimately makes the soil rich in nitrogen, which is essential for plant growth. Blue-green algae (BGA) fix atmospheric nitrogen in their special cells called heterocysts and ultimately provide nitrogen to the soil. Both Rhizobium and BGA act as biofertilizers.
INTEXT QUESTIONS 21.4
1. Mention two important agricultural inputs which are avoided in organic farming.
Ans: Two important agricultural inputs which are avoided in organic farming are Chemical fertilizers and pesticides.
2. What is IPM, and what is its aim?
Ans: IPM is Integrated Pest Management, which avoids harmful chemical pesticides and uses biological methods and agricultural practices to get rid of the pests. Its aim is not to eradicate the pests but to keep them at an economically tolerable level.
3. What types of improved crop varieties can be produced by gene transfer technology?
Ans: Gene transfer technology can produce crops:
- Resistant to herbicides and pesticides.
- Resistant to insects and diseases.
- Tolerant of high salt in the soil.
- With improved nutritional quality.
- Prolonging shelf life.
4. What is “Golden Rice”?
Ans: “Golden Rice” is a transgenic rice with enhanced vitamin A content.
TERMINAL EXERCISE
1. Define sustainable agriculture and justify its need.
Ans: Sustainable agriculture is that form of agriculture which attempts to produce sufficient food to meet the needs of the present-day population without exhausting soil fertility and irreversibly damaging the environment. Sustainable farming systems are those that are least toxic and least energy intensive and yet maintain productivity and profitability, i.e. low-input agriculture or organic farming.
Sustainable agriculture is required because it.
- Supports profitable production;
- Protects environmental quality;
- Uses natural resources efficiently;
- Provides consumers with affordable, high-quality products;
- Decreases dependency on non-renewable resources;
- Enhances the quality of life for farmers and rural communities.
- It will last for generations to come.
2. What are the two most important effects of an increase in population in the cities?
Ans: The proportion of the global population living in urban areas is increasing, and the urban population is increasing rapidly in developing countries. Poverty is becoming one of the major problems in urban areas as more poor people migrate to cities from villages.
3. Why do you need to improve the existing varieties of plants (give any three reasons)?
Ans:
- (i) Development of high-yielding varieties of crop plants.
- (ii) Food crops developed for better and higher nutritional quality, like protein quality in pulses, baking quality in wheat, preserving quality in fruits and vegetables, and oil quality in oilseed-producing plants.
- (iii) Development of crop varieties resistant to diseases and pests.
- (iv) Improving varieties for resistance against heat, cold, frost, drought and waterlogging.
4. Mention any four types of crops that one can produce by applying gene transfer technology.
Ans: Cotton – Bt Cotton, Rice- Golden Rice, tomato, and potato.
5. Explain the aim and objectives of the process of IPM.
Ans: IPM aims to keep the crop damage to an economically tolerable level. The most sustainable way to control pests is a carefully designed integrated pest management (IPM) program. In this approach, each crop and its pests are evaluated as parts of an ecological system. Then farmers develop a control program that includes cultivation, biological and chemical methods applied in proper sequence and with the proper timing.
6. What are GMOs? Explain briefly, giving any two examples.
Ans: The crop plants produced by genetic techniques are called “transgenics” or genetically modified (GM) plants or genetically modified organisms (GMOs).
7. What is biological control of pests?
Ans: Biological control of pests is to use other biological organisms.
- Pest on the cucumber plants is controlled by using a predatory mite that feeds on red spider mite.
- Citrus fruit damage by scale insects is controlled by an Australian ladybird, which eats away the insects.
- Mealy bug pests of the Cassava plant were controlled by a parasitoid wasp, which was its natural enemy.
- Hormones are used that disrupt the insect’s normal life cycle, thereby preventing it from reaching maturity and reproducing and multiplying.
8. Which are the two most important items which are applied generously in normal agriculture but are avoided in organic farming?
Ans: Chemical fertilisers and chemical pesticides.
9. How do blue-green algae help in agriculture?
Ans: Blue-green algae (BGA or cyanobacteria) like Nostoc and Anabaena are free-living photosynthetic organisms also capable of fixing atmospheric nitrogen. In the flooded rice fields blue blue-green algae serves as a nitrogen biofertilizer.
10. Define biofertilizer and its uses in agriculture.
Ans: Biofertilizers are plant nutrients of biological origin, like algae, bacteria, fungi, which have no harmful effect on soil and the environment. When they are applied in the soil, they enhance the growth and yield of crops, improve soil fertility and reduce pollution.
- Rhizobium biofertilizer: Rhizobium is a symbiotic bacterium that forms root nodules in legume plants. These nodules act as miniature nitrogen production factories in the fields. The nodule bacteria fix more nitrogen (N2) than is needed by the legume plant and the bacteria. The surplus fixed nitrogen is then secreted and fertilises the soil.
- Azotobacter biofertilizer: Azotobacter are aerobic, free-living nitrogen fixers growing in the rhizosphere (around the roots) and fix atmospheric nitrogen non-symbiotically and make it available to the particular cereals. These bacteria produce growth-promoting hormones which help enhance the growth and yield of the plant.
- Azospirillium biofertilizer: These are aerobic, free-living nitrogen fixers which live in associative symbiosis on the root surface of the host plant. It increases crop yield, supplying growth hormones and vitamins to the host plant.
- Blue green algae: Blue green algae (BGA or cyanobacteria) like Nostoc and Anabaena are free-living photosynthetic organisms also capable of fixing atmospheric nitrogen. In the flooded rice fields, blue-green algae serve as a nitrogen biofertilizer.
- Azolla biofertilizers: Azolla is a water fern in which the nitrogen-fixing blue-green algae Anabaena grow. It contains 2-3% nitrogen when wet and also produces organic matter in the soil. The Azolla-Anabaena combination type biofertilizer is used all over the world.
- Phosphorus solubilising biofertilizer: Some microorganisms are capable of solubilising immobilised phosphorus, making it available to plants for absorption.
- Mycorrhizal fungi, which act as a biofertilizer, are known to occur naturally on the roots of forest trees and crop plants. The fungus has the ability to dissolve and absorb phosphorus that plant roots can not readily absorb.
