Class 7 Nutrition in Plants Notes for exams

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This Class 7 Science exam notes page covers Chapter 1 Nutrition in Plants: the meaning of nutrition, autotrophic nutrition in green plants, and the heterotrophic modes of nutrition, which are parasitic, saprophytic, carnivorous and symbiotic. It includes examples such as cuscuta, pitcher plant, Drosera, Rhizobium and lichen, for quick revision before the exam.

Chapter 1: NUTRITION IN PLANTS

Nutrition

Nutrition is the process of manufacturing or taking in and utilising food for various life processes.

TYPES OF NUTRITION

1. Autotrophic Nutrition

In autotrophic nutrition, green plants take in inorganic substances like water, carbon dioxide, sunlight and chlorophyll, and convert them into organic substances like glucose. Oxygen is given out in this reaction.

Requirements of a green plant for autotrophic nutrition:
1. Plants need soil and atmosphere to grow.
2. They get water and minerals from the soil in raw form.
3. They get carbon dioxide from the atmosphere.
4. They get light and temperature from the sun.
5. They have a green pigment called chlorophyll, which is present in abundance in their leaves.
6. Plants collect the raw materials and cook their food in the leaves.

2. Heterotrophic Nutrition

In heterotrophic nutrition, non-green plants and animals depend on green plants for their food. Heterotrophic nutrition can be seen in four forms:
1. Parasitic mode
2. Saprophytic mode
3. Carnivorous mode
4. Symbiotic mode

PARASITIC MODE OF NUTRITION

Some plants, like cuscuta (dodder), depend on other plants for their nutrition. These parasitic plants do not have chlorophyll, so they are pale yellow in colour. They have special structures called haustoria that help them to extract nutrition from other plants.

In parasitic mode of nutrition, the organism which derives nutrients is called a parasite. The organism on which the parasite depends is called a host.

Did you know?
Rafflesia, the world's largest flower, is also a parasitic plant.

SAPROPHYTIC MODE OF NUTRITION

Some plants grow on dead organic matter and obtain their food only from it. Such mode of nutrition is called saprophytic nutrition, and such plants are called saprophytes. Saprophytes release enzymes outside their body, digest the organic matter and then absorb it. This is called extracellular digestion.

Saprophytes (sapros meaning rotten, and phyte meaning plant) are decomposers. Dead organisms are broken down into simple substances by them. In exchange, they release vital chemicals into the soil. These chemicals are absorbed and used by autotrophs. Saprophytes help to reuse and recycle organic material.

CARNIVOROUS PLANTS

In some areas the soil is deficient in certain nutrients, especially nitrogen. Plants growing in such areas need to obtain these nutrients from other sources.

Carnivorous plants are plants that derive some of their nutrients by trapping and consuming animals, mainly insects. Therefore, such plants are also called insectivorous plants.

Some common examples are the pitcher plant, Drosera (sundew), bladderwort and the Venus flytrap.

The nitrogen requirement of these plants is supplied by the digested insects. Unlike parasitic plants like cuscuta, the pitcher plant has chlorophyll.

SYMBIOTIC PLANTS

Some symbiotic organisms show a win-win kind of interdependence. This interdependence can be between a plant and a bacterium, or a plant and a fungus.

A symbiotic relationship is a close association between individuals of different species. The relationship is based on the nutritional benefits they derive from each other.

Example: Rhizobium and leguminous plants
Gram and pea plants are common examples of legumes. Legumes growing in soil develop nodules in their roots, which harbour bacteria called Rhizobium. The bacterium can convert nitrogen from the air into a form that the plant can absorb. The bacteria provide usable nitrogen to the plant, and in return, they get a suitable condition for their survival in the root nodule.

Example: Lichen (fungus and algae)
The fungus component of a lichen is called the mycobiont, and the algal component is called the phycobiont. The algal partner makes food and provides it to the fungus. In return, the fungus provides water, minerals and shelter to the alga.