Page 12 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

directly from it. Such plants can weaken their hosts, reduce their growth and

sometimes may kill them.
8. Why do farmers grow leguminous and non-leguminous crops alternately in their

fields?
Ans. Farmers grow leguminous and non-leguminous crops alternately to improve soil

fertility and maintain their fields. Leguminous crops like peas and beans, fix nitrogen
in the soil, enriching it for non-leguminous crops like wheat and maize. This rotation

helps manage soil nutrients, reduce pests and diseases and improve soil structure,
ensuring better crop yields.

G. Long-answer questions :
1. Farmers spread manure or fertilisers in the field. Why are these added to the soil?

Ans. The main reasons farmers spread manure or fertilizers in their field are:
• Plants need nutrients such as nitrogen, phosphorus and potassium to grow.

Manures and fertilizers contain all of these. These help plants to grow faster
and give more yield.

• Since manure is an organic material made from animal waste, it helps improving
soil structure. It increases the water and air retention capacity of the soil. This

makes easier for the roots to grow and access the nutrients they need.
• Manure adds organic matter that helps bind soil particles together, reducing

soil erosion.

• By using appropriate fertilizers, farmers can balance the nutrient levels in the
soil, preventing any one nutrient from becoming depleted.

• Usage of manures and fertilizers help improve crop quality. This leads to diseases
and pest resistant crops which further yields to crop yield.

2. Explain different modes of nutrition with examples.

Ans. Different modes of nutrition are:
• Autotrophic Nutrition: In this type if nutrition, organisms make their own food

using carbon dioxide and water.

For example, Green plants and algae.
• Heterotrophic Nutrition: In this type of nutrition, organisms depend on other

organisms for their food.

For example, animals, humans, non-green plants, decomposers, etc.
The types of heterotrophic nutrition are:

(a) Saprotrophic Nutrition: In this mode of nutrition, organisms obtain their food
from dead and decaying organic matter. For example, fungi and certain bacteria.

12