Chapter 1: Nutrition in Plants

Bhupendra Rawat -

 Class 7 Science – Chapter 1

Nutrition in Plants

1. Nutrition

Nutrition is the mode of taking food by an organism and its utilisation by the body.

Food provides nutrients that help organisms:

grow and develop,

repair damaged body parts,

maintain the body, and

obtain energy for life processes.

Nutrients

The main components of food are:

Carbohydrates

Proteins

Fats

Vitamins

Minerals

2. Modes of Nutrition

Autotrophic Nutrition

The mode of nutrition in which organisms prepare their own food from simple substances is called autotrophic nutrition.

Green plants are autotrophs.

They use carbon dioxide, water and minerals to prepare food.

Sunlight provides the energy needed.

Heterotrophic Nutrition

Organisms that obtain food from other organisms are called heterotrophs.

Examples: humans, animals and some plants.

3. Photosynthesis

Photosynthesis is the process by which green plants prepare food using carbon dioxide and water in the presence of sunlight and chlorophyll.

Requirements of Photosynthesis

Sunlight

Chlorophyll

Carbon dioxide

Water

Equation

Carbon dioxide + Water

↓ sunlight + chlorophyll

Carbohydrate + Oxygen

The food produced is initially a carbohydrate. Excess carbohydrate is stored as starch. 

Importance of Photosynthesis

Produces food for plants.

Provides food directly or indirectly to almost all organisms.

Releases oxygen into the atmosphere.

Converts solar energy into chemical energy.

4. Leaves – Food Factories of Plants

Leaves are called the food factories of plants.

Stomata

Leaves have tiny pores called stomata.

Stomata allow exchange of gases.

Carbon dioxide enters through stomata.

Stomata are surrounded by guard cells.

Chlorophyll

The green pigment present in leaves is called chlorophyll.

It captures the energy of sunlight needed for photosynthesis.

5. Role of Roots and Vessels

Roots absorb water and minerals from the soil.

Vessels transport water and minerals from roots to leaves.

Carbon dioxide enters the leaves through stomata.

6. Photosynthesis in Coloured Leaves

Some leaves appear red, brown or violet.

They may still contain chlorophyll, but other pigments mask its green colour.

Therefore, such leaves can also carry out photosynthesis. 

7. Nitrogen and Plants

Plants need nitrogen to make:

proteins,

vitamins and

other essential substances.

Although nitrogen is abundant in air, plants cannot directly use atmospheric nitrogen.

Certain soil bacteria convert nitrogen into a usable form.

Rhizobium

Rhizobium bacteria live in the roots of leguminous plants such as:

gram,

peas,

beans,

moong.

Rhizobium converts atmospheric nitrogen into a usable form.

The relationship between Rhizobium and leguminous plants is symbiotic. 

8. Other Modes of Nutrition in Plants

A. Parasitic Nutrition

Some plants cannot prepare their own food and obtain food from another plant.

Example: Cuscuta

Cuscuta (Amarbel) lacks chlorophyll.

It obtains ready-made food from the plant on which it grows.

The plant providing food is called the host.

Cuscuta is called a parasite. 

B. Insectivorous Plants

Some green plants trap and digest insects.

Example: Pitcher Plant

Its modified leaf forms a pitcher-like structure that traps insects.

The insects are digested and their nutrients are absorbed.

Such plants are called insectivorous plants. 

C. Saprotrophic Nutrition

Organisms that obtain nutrients from dead and decaying matter show saprotrophic nutrition.

Examples:

Fungi

Mushrooms

Such organisms are called saprotrophs.

Fungi commonly grow on moist and warm materials.

9. Symbiosis

Symbiosis is a relationship in which two organisms live together and share nutrients and/or shelter.

Example: Lichen

Lichen consists of:

an alga, and

a fungus.

The alga prepares food, while the fungus provides shelter, water and minerals.

10. Replenishment of Nutrients in Soil

Plants continuously absorb minerals from soil, so nutrients may become depleted.

Farmers add:

manure

fertilisers

to replenish nutrients such as:

nitrogen,

phosphorus,

potassium.


 

NCERT Exercise – Answers

1. Why do organisms take food?

Organisms take food because food provides energy for life processes and nutrients required for growth, development, repair and maintenance of the body. 

2. Distinguish between a parasite and a saprotroph.

Parasite

Saprotroph

Obtains food from a living host.

Obtains nutrients from dead and decaying matter.

Usually harms the host.

Feeds on decaying organic material.

Example: Cuscuta

Example: Fungi

3. How would you test the presence of starch in leaves?

The iodine test is used.

Take a leaf.

Treat it appropriately for the iodine test.

Add iodine solution to the leaf.

If starch is present, the leaf or the tested portion turns blue-black.

The presence of starch indicates that photosynthesis has occurred. 

4. Give a brief description of the process of synthesis of food in green plants.

Green plants prepare food by photosynthesis.

Roots absorb water and minerals from the soil.

Carbon dioxide enters leaves through stomata.

Chlorophyll captures sunlight.

Using sunlight as the source of energy, carbon dioxide and water are converted into carbohydrates.

Oxygen is released during the process.

Carbon dioxide + Water → Carbohydrate + Oxygen

(in the presence of sunlight and chlorophyll)

5. Show with the help of a sketch that plants are the ultimate source of food.

A simple food chain can be represented as:

Sun → Green Plants → Herbivores → Carnivores → Humans

Green plants prepare food through photosynthesis. Animals obtain food either directly from plants or indirectly by eating plant-eating animals. Therefore, plants are the ultimate source of food for almost all living organisms.

6. Fill in the blanks

(a) Green plants are called autotrophs since they synthesise their own food.

(b) The food synthesised by plants is stored as starch.

(c) In photosynthesis solar energy is absorbed by the pigment called chlorophyll.

(d) During photosynthesis plants take in carbon dioxide and release oxygen gas. 

7. Name the following

(i) A parasitic plant with yellow, slender and branched stem:

Cuscuta (Amarbel)

(ii) A plant that is partially autotrophic:

Pitcher plant

(iii) The pores through which leaves exchange gases:

Stomata 

8. Tick the correct answer

(a) Cuscuta is an example of:

Answer: (ii) Parasite

(b) The plant which traps and feeds on insects is:

Answer: (iii) Pitcher plant 

9. Match the following

Column I

Column II

Chlorophyll

Leaf

Nitrogen

Rhizobium

Cuscuta

Parasite

Animals

Heterotrophs

Insects

Pitcher plant

Answers:

Chlorophyll → Leaf

Nitrogen → Rhizobium

Cuscuta → Parasite

Animals → Heterotrophs

Insects → Pitcher plant 

10. Mark T or F

(i) Carbon dioxide is released during photosynthesis.

Answer: F

(ii) Plants which synthesise their food are called saprotrophs.

Answer: F

(iii) The product of photosynthesis is not a protein.

Answer: T

(iv) Solar energy is converted into chemical energy during photosynthesis.

Answer: T 

11. Which part of the plant takes in carbon dioxide from the air for photosynthesis?

Answer: (ii) Stomata

Carbon dioxide enters the leaf through the stomata. 

12. Plants take carbon dioxide from the atmosphere mainly through their:

Answer: (iv) Leaves

The gas enters mainly through stomata present on leaves. 

13. Why do farmers grow many fruits and vegetable crops inside large greenhouses? What are the advantages?

Greenhouses provide a controlled environment for growing plants.

Farmers can regulate conditions such as:

light,

water,

temperature, and

carbon dioxide.

This helps provide favourable conditions for plant growth and can improve crop production. 

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