Maharashtra Board Class 7 Science Chapter 4 Nutrition in Living Organisms PDF Download

Nutrition In Living Organisms

Let's Recall

1. What is malnutrition?

2. Which are the ways to prevent malnutrition?

Nutrition

Some life-processes go on continuously in living organisms. Substances which are digested and assimilated for obtaining energy and for the growth and health of our body are called foodstuffs.

We get several types of nutrients from foodstuffs. Nutrients can be classified into two types, namely, macro-nutrients and micro-nutrients.

Nutrients like carbohydrates, proteins and fats are required in large quantity. These are macro-nutrients. Minerals and vitamins are required in very small quantity. They are called micro-nutrients.

Teacher's Note

Nutrition means eating food to stay healthy. Just like we need rice, vegetables and milk to grow strong, plants also need water and minerals from soil.

Exam Trick

Remember: Macro = big amount. Micro = small amount. Carbs and proteins are macro. Vitamins are micro - you need only a little bit!

Points to Remember

Nutrition is taking food into the body and using it for energy and growth.
Macro-nutrients are needed in large amounts like carbohydrates and proteins.
Micro-nutrients are needed in small amounts like vitamins and minerals.
Foodstuffs are substances we eat for health and energy.

Autotrophic Nutrition

Some organisms can produce their own food and thus nourish themselves. This is called autotrophic nutrition.

Heterotrophic Nutrition

Some organisms depend on other organisms, plants or animals, for their food. This is called heterotrophic nutrition.

Autotrophic Plants

Can You Tell?

How do plants produce their own food?

Plants also need food for their growth. They can produce their own food. With the help of sunlight and chlorophyll, plants make their food in their leaves, using water and nutrients from the soil and carbon dioxide from the air. This process is called as photosynthesis.

\[6 \text{ CO}_2 + 6 \text{ H}_2\text{O} \xrightarrow{\text{Sunlight}} \text{Food (glucose)} + 6 \text{ O}_2 \xrightarrow{\text{Chlorophyll}} \text{ C}_6 \text{ H}_{12} \text{ O}_6 + 6 \text{ O}_2\]

Teacher's Note

Photosynthesis is how plants make food using sunlight. Think of it like a kitchen where plants cook their own food with sun, water and air.

Exam Trick

Remember: Photo = light, Synthesis = making. So photosynthesis = making food with light. Plants need sunlight, water and CO2 to make glucose and oxygen.

Points to Remember

Autotrophic plants make their own food using sunlight.
Photosynthesis happens in the leaves where chlorophyll is present.
Plants use water, minerals, carbon dioxide and sunlight to make food.
Oxygen is released during photosynthesis as a waste product.

Plants convert light energy into chemical energy and store it in the form of food.

Water, minerals and salts are absorbed by roots from the soil. The stem transports them up to the leaves. The leaves have microscopic openings called stomata through which they take in the CO2 from the air. The chloroplasts present in the leaves contain chlorophyll, which absorbs sunlight, helping to convert carbon dioxide and water into food. Oxygen is given out in this process.

Besides leaves, photosynthesis takes place in some other parts like green stems, too, as they contain chlorophyll.

Teacher's Note

The green colour in leaves comes from chlorophyll. Chlorophyll catches sunlight and helps the plant make its own food, like a cooking fuel.

Exam Trick

Remember: Stomata = tiny holes in leaves. Like the pores in your skin, stomata let the plant breathe and take in CO2 for photosynthesis.

Points to Remember

Chlorophyll is the green pigment in leaves that captures sunlight.
Stomata are tiny openings in leaves that allow carbon dioxide to enter.
The xylem transports water and minerals up from roots to leaves.
Oxygen is released through stomata as a waste product of photosynthesis.

Transport System In Plants

Take a pumpkin stem having 2-3 leaves. Cut it under water with a sharp blade. Take some water in a conical flask and add 7-8 drops of ink to it. Put the pumpkin stem vertically in that flask. Observe the changes that take place in it and discuss them in the classroom.

The transport system of plants consists of the xylem and the phloem. The xylem transports minerals and water from the root to all aerial parts of the plant. The phloem transports the food (glucose, etc.) from the leaves to other parts of the plant where it is either consumed or stored. Though the plants have a transport system, they do not have a separate digestive or excretory system.

Find Out

What is chemosynthesis? Which plants produce their food by chemosynthesis?

Let's Recall

Which are the different substances excreted by plants? Why?

Teacher's Note

The xylem and phloem work together like blood vessels in our body. Xylem carries water up and phloem carries food down to all parts of the plant.

Exam Trick

Remember: Xylem = water carrier (X for upward flow). Phloem = food carrier (P for plant food). Xylem always goes up, phloem can go up or down!

Points to Remember

Xylem transports water and minerals from roots to leaves and other parts.
Phloem transports food made by leaves to all parts of the plant.
Plants do not have a separate digestive system like animals do.
Plants also do not have an excretory system for removing waste.

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