Class 7 Science Nutrition in Plants Exam Notes

Class 7 Science Nutrition in Plants Exam Notes. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Covers following topics:

1.Mechanism of Photosynthesis

Class 7 Science: Nutrition in Plants (Exam Notes)

Covers the following topics: Mechanism of photosynthesis, site of photosynthesis, and nutrition in non-green plants.

Plants are the producers in nature. They produce food for all living organisms. They utilise the sun's radiant energy and convert it into chemical energy, so they also act as converters. Plants use sunlight in photosynthesis. During photosynthesis, in the presence of sunlight, CO₂ and H₂O are converted into carbohydrate and O₂ molecules.

MECHANISM OF PHOTOSYNTHESIS

\[ 6CO_2 + 6H_2O \xrightarrow[\text{Chlorophyll}]{\text{Light}} C_6H_{12}O_6 + 6O_2 \]

Steps of photosynthesis

1. Chlorophyll traps the sunlight.
2. CO₂ and water molecules are used as raw material.
3. The chlorophyll converts the raw material into carbohydrate.
4. Oxygen is released as a by-product in this process.

REQUIREMENT OF PHOTOSYNTHESIS

Green plants need the following things to prepare their own food:

1. Carbon dioxide: Plants take up carbon dioxide from the atmospheric air through the stomata present on the undersurface of the leaves. Guard cells around the stomata regulate their opening and closing.
2. Chlorophyll: It is the green pigment present in the leaf. The green colour of leaves is due to the presence of chlorophyll. It is usually present in a special cell organelle called the chloroplast. Chlorophyll captures solar energy during photosynthesis.
3. Sunlight: Sunlight comes from the Sun. It is essential, as it provides the energy required for the reaction.
4. Water and minerals: The roots of the plants absorb water along with minerals from the soil and transport them to the leaves for photosynthesis.

SITE OF PHOTOSYNTHESIS

Photosynthesis occurs in the chlorophyll of leaves and sometimes in the stems which are green in colour.

Importance of photosynthesis

1. It is the primary source of food production for all other living organisms.
2. It maintains the balance of oxygen and CO₂ in the atmosphere.

NUTRITION IN NON-GREEN PLANTS

Non-green organisms like bacteria and fungi do not contain chlorophyll, so they cannot prepare their food by photosynthesis. These are heterotrophic organisms.

1. Parasites: Plants which depend on other living organisms for their nutritional requirement are known as parasitic plants. Dodder (Amarbel) is a plant parasite which produces special sucking roots called haustoria for the absorption of food from the host plant.
2. Saprophytes: Organisms which depend on dead organic matter for their nutrition are known as saprophytes. For example, bacteria and fungi.
3. Carnivorous and insectivorous plants: Some plants also take food just like animals. Their food consists of small insects. For example, the pitcher plant. In a pitcher plant, the leaf is modified into a pitcher-like structure. When an insect sits on it, the lid is closed and the insect is trapped in the pitcher. It is then digested by the secretion of enzymes.
   
4. Symbiosis: It is a partnership between two organisms in which both partners benefit from each other. For example, lichen. Lichen is a combination of an alga and a fungus, in which the fungus provides water and minerals to the alga, whereas the alga supplies organic food to the fungus.
   

HETEROTROPHIC NUTRITION IN ANIMALS

Animals and non-green organisms like fungi cannot manufacture their own food. For their food, they depend upon green plants, directly or indirectly. Therefore, they are called heterotrophs and their mode of nutrition is known as heterotrophic nutrition.

All animals are divided into three categories on the basis of their eating habits:

1. Herbivorous animals: Animals which feed directly on plants are called herbivorous animals or herbivores. Examples are cow, buffalo, goat, etc.
2. Carnivorous animals: Animals which eat the flesh of other animals are called carnivorous animals or carnivores. Examples are lion, tiger, etc.
3. Omnivorous animals: Animals which eat both plants and the flesh of other animals are called omnivorous animals or omnivores. Examples are human beings, pig, crow, cockroach, etc.

2.CO₂ & water molecule used as raw material.

3.Now the chlorophyll convert the raw material into carbohydrate.

4.Oxygen is generated as a by product in this process.