Introduction to the Topic

Welcome to another exciting journey into the world of science! Have you ever wondered how plants get their food? Unlike humans and animals, who depend on plants and other animals for food, plants can make their own food. In NCERT Class VII Science, Chapter 1 - Nutrition in Plants, we explore the fascinating ways in which plants obtain the nutrients they need to grow, survive, and thrive. Let us dive deep into the mechanism of plant nutrition and understand the wonders of green leaves!

Key Concepts Explained

To understand how plants nourish themselves, we must first look at what nutrition means and the different modes of nutrition found in the plant kingdom.

1. What is Nutrition?

Nutrition is the mode of taking food by an organism and its utilization by the body. Living organisms require food to get energy, build their bodies, and repair damaged parts. The components of food that are necessary for our body are called nutrients (such as carbohydrates, proteins, fats, vitamins, and minerals).

2. Modes of Nutrition in Plants

There are primarily two modes of nutrition in plants:

  • Autotrophic Nutrition: Plants that can make food themselves from simple substances are called autotrophs (auto = self, trophos = nourishment). Therefore, plants are called autotrophs.
  • Heterotrophic Nutrition: Some plants cannot make their own food and depend on the food produced by other plants. They are called heterotrophs (heteros = other).

3. Photosynthesis: Food Making Process in Plants

Leaves are the food factories of plants. Therefore, all the raw materials must reach the leaf. Water and minerals absorbed by the roots are transported to the leaves by vessels that run like pipes throughout the root, stem, branches, and leaves.

The leaves have a green pigment called chlorophyll. It helps leaves capture the energy of the sunlight. This energy is used to synthesize (prepare) food from carbon dioxide and water. Since the synthesis of food occurs in the presence of sunlight, it is called photosynthesis (photo = light, synthesis = to combine). The process can be represented in an equation format:

\text{Carbon dioxide} + \text{Water} \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} \text{Carbohydrate} + \text{Oxygen}

During this process, oxygen is released. The presence of starch in leaves indicates the occurrence of photosynthesis. Starch is also a carbohydrate.

4. Other Modes of Nutrition in Plants

Not all plants are autotrophic. Some plants rely on alternative methods for survival:

  • Parasitic Plants: Some plants do not have chlorophyll and cannot synthesize their own food. They use the heterotrophic mode of nutrition. For example, Cuscuta (Amarbel) takes food from the host plant on which it climbs.
  • Insectivorous Plants: There are a few plants which can trap insects and digest them. These are insectivorous plants, such as the pitcher plant. They usually grow in nitrogen-deficient soil.
  • Saprotrophs: Organisms that take in nutrients in solution form from dead and decaying matter are called saprotrophs. Fungi (like mushrooms and bread molds) secrete digestive juices on dead matter and convert it into a solution to absorb nutrients.
  • Symbiotic Relationship: Some organisms live together and share shelter and nutrients. This is a symbiotic relationship. For example, certain fungi live inside the roots of trees, and the tree provides nutrients to the fungus, while in return, the fungus provides water and certain nutrients. Lichens are another great example where an alga and a fungus live together.

5. Replenishment of Nutrients in the Soil

Plants absorb minerals and nutrients from the soil. Therefore, the amount of nutrients in the soil keeps declining. Fertilizers and manures containing plant nutrients like nitrogen, potassium, and phosphorus are added to the soil to enrich it. Additionally, the bacterium Rhizobium can take atmospheric nitrogen and convert it into a soluble form for leguminous plants like gram, peas, and beans.

Summary & Key Takeaways

  • All animals and humans are dependent on plants for their food, either directly or indirectly.
  • Plants are autotrophs and synthesize their own food by the process of photosynthesis.
  • Green plants use chlorophyll, sunlight, carbon dioxide, and water to make carbohydrates.
  • Parasites, insectivorous plants, and saprotrophs are examples of non-autotrophic modes of plant nutrition.
  • Symbiosis allows certain organisms to share a mutually beneficial relationship for survival.
  • Soil nutrients are replenished naturally through manure, fertilizers, and nitrogen-fixing bacteria like Rhizobium.