Sunday 24 April 2016

CBSE Class 8 - Living Science (CCE Edition) : Crop Production (Text Book Answers)

Living Science (CCE Edition) : Crop Production 

CBSE Class 8 - Living Science (CCE Edition) : Crop Production (Text Book Answers)

Textbook Answers

Multiple Choice Questions (pg 20)

Q: Which of these is not a cereal?...


1: (a) Gram
Explanation: Gram is a legume (pulses) while others are cereals

2: (a) Wheat
Explanation: Wheat is a rabi (winter) crop.

3: (a) organic nutrients
Explanation: Compost is made of dead and decaying organic matter.

4: (a) Wilt
Explanation: Wilt is caused by bacteria while others are fungal infections.

5: (c) it prevents soil erosion.
Explanation: Ploughing loosens soil so that more air can fill up the spaces.

6: (d) All of these

7: (d) ploughing
Explanation: Manuring or Fertilizers or Field Fallowing add nutrients.

8: (b) Combine

VERY SHORT ANSWER QUESTIONS (One word answers) - Pg 20-21

Q1. About how many years ago did agriculture begin?...


1. 10,000 years ago

2. Cereals

3. Loosening and Turning

4. Drill

5. Fallow, organic nutrients.

6. False (Explanation: e.g. Paddy rice needs more water at initial stages. Some ornamentals house plants need very less water.)

7. BHC or gamaxane

8. False (Explanation: Pesticides are harmful to animals and humans. Causes respiratory problems and skin rashes)

9. Rhizobium bacteria

10. Ammonification

11. Milk

12. Apiculture


Q1. Name three natural methods of adding...


1. Field Fallow, Crop Rotation and Mixed Cropping replenish nutrients in soil.

2. Unwanted plants that grow along with crops. Weeds compete with crops for food, water, space and sunlight, thus reducing crop yield.

3. Grains contain moisture which can lead to microbes growth. These microbes will damage the grains.  To remove moisture, grains should be dried before storage.

4. Buffer stocks avoid shortage of grains in crisis situations like natural disaster or war.

5. It is a method to develop a healthy new variety of crop by cross breeding two different varieties of the crop.

6. Nitrogen fixation →  Nitrogen assimilation → Ammonification →  Nitrification → Denitrification

7. Process by which free nitrogen gas is converted into nitrogen compounds (nitrates or nitrites) is called nitrogen fixation. It may occur by lightning or rhizobium bacteria present in legumes.

8. Conversion of inorganic nitrogen compounds into organic nitrogen compounds inside living beings is called nitrogen assimilation.

9. The nitrogen fixing bacterium Rhizobium which live in roots of legume plants. They convert free nitrogen into nitrates.

10. Rearing (breeding, feeding caring etc) of domestic animals for food and other commercial purposes is called animal husbandry.

SHORT ANSWER QUESTIONS (TYPE II) - Answer in 30 words - Pg 21

Q1: Distinguish between kharif and rabi crops?...


1. Kharif crops Rabi crops
   i. Sown in June/July i. Sown in Oct/Dec
   ii. Summer crops ii. Winter Crops
   iii. Harvested in Sep/Oct iii. Harvested in March/April
   iv.  Maize, Paddy, Soyabean, Cotton iv. Wheat, Gram, Pea, Mustard

2. Steps involved in crop production are:
   i. soil preparation
   ii. selection of seed and sowing
   iii. manuring
   iv  irrigation
   v. weeding,
   vi. protection from pests and diseases
   vii. harvesting, threshing and winnowing and
   viii. storage

3. Plants sown at correct distances do not compete for food, nutrients, water and sunlight. Thus they have proper growth.

4. Manures are rich in organic nutrients (Carbon, Hydrogen and Oxygen) and replenish soil. Fertilizers provide mineral nutrients (Nitrogen, Phosphorus, Pottasium) to soil.

5. Drip irrigation is the most suitable method for dry regions. In this method, water is allowed to fall drop by drop from a pipe, just near the roots. It minimizes wastage of water. However its installation cost is high.

6. Excess of water supplied to field is called water logging. It reduces oxygen supply to roots and thus roots gets damaged. Proper drainage and controlled water supply system can prevent water logging.

7. Manual Method: Weeds are pulled out by hand or uprooted by trowel or harrow.
   Biocontrol methods: Insects of particular type that feed on specific weed are used.

8. Insecticides: chemicals that kill insects (eg locusts)
   Rodenticides: chemicals that kills rats/mice or rodents.
   Fungicides : chemicals that kill fungi (blights, rusts, molds).
   All of these are pesticides.

9. One variety of crop is disease resistant while the other variety takes less water. The cross breeding of the two will produce a new variety of crop which will be both disease resistant and consume less water. In this way hybridization is used for developing new variety of crops with desired features.

10. Nitrification is the process of converting ammonia into nitrates. Denitrification is a process in which nitrates are converted into nitrogen gas.


Q2: What precautions must be kept in mind while sowing seeds?

i. Seeds should be healthy and free from diseases.

ii. Seeds should be sown at correct distances and at proper depths.

iii. Sold should be properly aerated and nutrient rich.

Nitrogen Cycle

Nitrogen Cycle
source wikipedia (author: Johann Dréo)

HOTS Questions

Answer 1: (d) using better varieties of crop plants

Answer 2: Drawbacks are:
   i. Seeds sown closer will compete for food, water and sunlight. The germinated plants will have stunted growth.
   ii. Seeds sown distant apart (more than required), it will lead to wastage of field space.

Answer 3: In general plant nurseries provide seeds, saplings or seedlings of various plants. Fully grown plants or trees require more field space, water and food. We hardly find fully grown trees at nurseries.

Answer 4: No crop rotation is used to restore a particular nutrient level to a field. It increases soil fertility. e.g. Growing cereal crops reduces nitrogen from the soil. In next cycle/season legumes are sown which restore the nitrogen level in the soil.

Answer 5: Crop production means planting at large scale for commercial purposes. Growing wheat plants in a garden is just a hobby practice.

Answer 6: In case field has improper drainage system, water logging may occur. Melons will absorb more water and swell. Due to this some may crack.

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