Class 7 Science - Chapter 1: Nutrition in Plants

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Introduction

All living organisms need food to survive and grow.
Nutrition is the process by which organisms obtain and utilize food.
Plants are autotrophic (self-feeding) and prepare their own food through photosynthesis.

Types of Nutrition

Autotrophic Nutrition
- Organisms make their own food using simple substances like carbon dioxide and water in the presence of sunlight.
- Example: Green plants
Heterotrophic Nutrition
- Organisms depend on other organisms for food.
- Example: Animals, fungi, and some plants

Photosynthesis: The Mode of Nutrition in Plants

What is Photosynthesis?

Photosynthesis is the process by which green plants prepare their own food using carbon dioxide, water, and sunlight in the presence of chlorophyll.
It produces glucose (food) and oxygen (by-product).

Equation for Photosynthesis

Conditions Required for Photosynthesis

Sunlight – Provides energy for the reaction.
Chlorophyll – Green pigment in leaves that traps sunlight.
Carbon Dioxide (CO₂) – Enters through stomata present in leaves.
Water (H₂O) – Absorbed from soil by roots.

Process of Photosynthesis

Absorption of Sunlight by chlorophyll.
Conversion of Solar Energy into Chemical Energy and splitting of water molecules into hydrogen and oxygen.
Formation of Glucose (C₆H₁₂O₆) using hydrogen and carbon dioxide.
Release of Oxygen (O₂) as a by-product.

Importance of Photosynthesis

Provides food for all living beings.
Maintains the balance of oxygen and carbon dioxide in the atmosphere.

How Nutrients are Absorbed in Plants?

Plants absorb minerals and water from the soil through their roots.
Nutrients are transported to different parts of the plant through xylem and phloem.

Other Modes of Nutrition in Plants

Some plants do not have chlorophyll and cannot prepare their own food. They have other modes of nutrition:

1. Parasitic Nutrition

Some plants obtain nutrients from other living plants (hosts).
Example:
- Cuscuta (Amarbel) – It wraps around other plants and absorbs nutrients from them.

2. Saprophytic Nutrition

Some organisms obtain nutrients from dead and decaying matter.
Example:
- Mushrooms and fungi grow on dead and rotting materials.

3. Insectivorous Plants (Carnivorous Plants)

Some plants trap and digest insects to obtain nutrients.
Example:
- Pitcher Plant – It has a modified leaf that traps insects.
- Venus Flytrap – Closes its leaves to capture insects.

4. Symbiotic Relationship (Mutualism)

Some plants live in association with other organisms for mutual benefit.
Example:
- Lichens – A partnership between algae (which makes food) and fungus (which absorbs water and minerals).
- Leguminous Plants (Pea, Beans, Gram, etc.) – Have Rhizobium bacteria in their roots that fix nitrogen from the air.

How Nutrients are Replenished in the Soil?

Continuous cropping reduces the nutrients in the soil.
Nutrients can be replenished by:
1. Adding fertilizers and manures (provides minerals like nitrogen, phosphorus, potassium).
2. Growing leguminous plants (fix nitrogen naturally through Rhizobium bacteria).

Key Terms to Remember

Autotrophs – Organisms that make their own food (e.g., green plants).
Heterotrophs – Organisms that depend on others for food (e.g., animals, fungi).
Photosynthesis – Process by which green plants make food using sunlight, CO₂, and water.
Chlorophyll – Green pigment in leaves that helps in photosynthesis.
Stomata – Tiny pores on leaves for gas exchange.
Parasites – Organisms that obtain nutrients from a living host (e.g., Cuscuta).
Saprophytes – Organisms that feed on dead matter (e.g., fungi).
Insectivorous Plants – Plants that trap and digest insects (e.g., Pitcher Plant).
Symbiotic Plants – Plants that live in mutual association with other organisms (e.g., Lichens).

Conclusion

Plants play a vital role in maintaining the ecosystem.
Photosynthesis is essential for the survival of all living beings.
Different types of plants have different modes of nutrition, including parasitic, saprophytic, and symbiotic relationships.

Class 7 Science Chapter 1 Free Practice Quiz

1. The main mode of nutrition in plants is called:

Correct Answer: B) Autotrophic nutrition
Green plants make their own food, so they are autotrophs.

2. Photosynthesis mainly takes place in which part of the plant?

Correct Answer: C) Leaves
Leaves contain chlorophyll and act as the food factory of the plant.

3. Which of these is NOT a raw material required for photosynthesis?

Correct Answer: D) Oxygen
Oxygen is a product of photosynthesis, not a raw material.

4. The green colour of plants is due to the presence of:

Correct Answer: B) Chlorophyll
Chlorophyll absorbs sunlight energy and gives plants their green colour.

5. Which plant is an example of a parasitic plant that obtains food from another plant?

Correct Answer: A) Cuscuta (Amarbel)
Cuscuta is a parasite that attaches to a host plant and sucks nutrients from it.

6. Organisms that obtain food by decomposing dead plants and animals are called:

Correct Answer: B) Saprophytes
Saprophytes (like some fungi) feed on dead and decaying matter.

7. Insectivorous (carnivorous) plants mainly trap insects to obtain which nutrient lacking in their soil?

Correct Answer: C) Nitrogen
They grow in nitrogen-poor soils and obtain nitrogen by digesting insects.

8. The main products of photosynthesis are:

Correct Answer: A) Glucose and oxygen
Photosynthesis produces glucose as food and releases oxygen.

9. The replenishment of nutrients in the soil mainly occurs through:

Correct Answer: B) Nitrogen fixation and addition of manure/fertilizers
Nitrogen-fixing bacteria and fertilizers help restore nutrients in the soil.

10. The main function of stomata in leaves is to:

Correct Answer: B) Allow exchange of gases (CO₂ in, O₂ out)
Stomata regulate the entry of carbon dioxide and release of oxygen during photosynthesis.