Nutrition In Plants: Class 7 Science Chapter 1 Notes

Key Terms and Definitions

Nutrition

The process of taking food by an organism and its utilisation by the body.

Autotrophs

Organisms that make their own food from simple substances. Example: Green plants.

Heterotrophs

Organisms that depend on other organisms for their food. Example: Animals, non-green plants.

Photosynthesis

The process by which green plants make their own food using carbon dioxide, water, and sunlight in the presence of chlorophyll.

Stomata

Tiny pores present on the surface of leaves, which are responsible for the exchange of gases (CO2 and O2).

Chlorophyll

The green pigment in leaves that traps sunlight for photosynthesis.

Parasite

An organism that lives on or inside another organism (the host) and derives its food from it. Example: Cuscuta (Amarbel).

Saprotroph

An organism that gets its nutrition from dead and decaying matter. Example: Fungi, Mushrooms.

Symbiosis

A relationship where two different organisms live together and share shelter and nutrients, mutually benefiting each other. Example: Lichens (algae and fungus).

Insectivorous Plants

Plants that feed on insects to fulfill their nitrogen requirements. Example: Pitcher plant.

The Process of Photosynthesis Explained

Photosynthesis is the cornerstone of life on Earth, and it's the process through which green plants act as the planet's primary producers. The name itself comes from 'photo' (light) and 'synthesis' (to put together). Plants require three key raw materials for this process: water, carbon dioxide, and sunlight. Water is absorbed from the soil through the roots and transported to the leaves via pipe-like vessels. Carbon dioxide from the atmosphere enters the leaves through tiny pores called stomata. The magic ingredient is chlorophyll, the green pigment found in organelles called chloroplasts within the leaf cells. Chlorophyll has the unique ability to trap energy from sunlight. This trapped solar energy is then used to convert water and carbon dioxide into chemical energy in the form of glucose (a type of sugar), which is the plant's food. A vital byproduct of this process is oxygen, which is released back into the atmosphere through the stomata. This entire food-making factory is primarily located in the leaves, which is why they are often called the 'kitchen' of the plant.

Key Points to Remember

• All living organisms require food for energy, growth, and repair of body parts.
• Green plants are autotrophs because they prepare their own food.
• The process of food synthesis in plants is called photosynthesis.
• The chemical equation for photosynthesis is: 6CO₂ (Carbon Dioxide) + 6H₂O (Water) → C₆H₁₂O₆ (Glucose) + 6O₂ (Oxygen) in the presence of Sunlight and Chlorophyll.
• Chlorophyll is the green pigment that traps sunlight.
• Stomata are tiny pores on leaves for gas exchange.
• Some plants are heterotrophs, like the parasitic Cuscuta (Amarbel) or insectivorous Pitcher Plant.
• Saprotrophs like fungi get nutrients from dead and decaying matter.
• Lichens are a classic example of symbiosis between an alga and a fungus.
• Rhizobium bacteria in the roots of leguminous plants fix atmospheric nitrogen into a usable form for the plant, showing another symbiotic relationship.

Autotrophic vs. Heterotrophic Nutrition

Steps of Photosynthesis

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Examples of Heterotrophic Nutrition in Plants

• {"title":"Parasitic Nutrition","bodyMarkdown":"Example: Cuscuta (Amarbel)\nCuscuta is a yellow, wire-like plant that lacks chlorophyll. It climbs onto a host plant and uses special structures called haustoria to absorb ready-made food directly from the host, harming it in the process."}
• {"title":"Insectivorous Nutrition","bodyMarkdown":"Example: Pitcher Plant\nThe pitcher plant grows in nitrogen-deficient soil. Though it has chlorophyll and can photosynthesize, it traps and digests insects to supplement its nitrogen needs. The leaf is modified into a pitcher-like structure with a lid. Insects are attracted by nectar, slip inside, and are digested by enzymes."}
• {"title":"Saprotrophic Nutrition","bodyMarkdown":"Example: Fungi (Mushrooms, Bread Mould)\nFungi secrete digestive juices onto dead and decaying organic matter. These juices convert the solid matter into a liquid solution, which is then absorbed by the fungi as nutrients."}

Exam Tip

In exams, questions about Photosynthesis are very common. Always write the full, balanced chemical equation and mention the necessary conditions (Sunlight and Chlorophyll) above and below the arrow. When asked about special modes of nutrition (parasitic, insectivorous), always give a specific example and explain why the plant needs that mode of nutrition (e.g., lack of chlorophyll for Cuscuta, nitrogen deficiency for Pitcher Plant).

Quick Revision Check

• What are the four things required for photosynthesis? Sunlight, Water, Carbon Dioxide, and Chlorophyll.
• Why is Cuscuta (Amarbel) called a parasite? Because it lives on a host plant and takes ready-made food from it, causing harm to the host.
• What is the function of stomata in leaves? Stomata are pores that allow for the exchange of gases, mainly taking in carbon dioxide and releasing oxygen.
• What is the relationship between an alga and a fungus in a lichen? It is a symbiotic relationship. The fungus provides shelter and absorbs water/minerals, while the alga, being an autotroph, prepares food for both.

Frequently Asked Questions

Frequently Asked Questions