Nutrition in Plants: Class 7 Science Chapter 1 Guide

What are the Modes of Nutrition in Plants?

Just like we need food to live, grow, and get energy, plants do too! The process of taking in food and using it is called nutrition. In the plant kingdom, there are two main ways of getting this nutrition.

1. Autotrophic Nutrition: The word 'auto' means self, and 'trophos' means nourishment. So, autotrophic plants are 'self-nourishers'. They are like master chefs who prepare their own food. They use simple substances from their surroundings—carbon dioxide from the air, water from the soil, and energy from sunlight—to create their own food. This process is famously known as photosynthesis. All green plants are examples of autotrophs. They form the foundation of most food chains on Earth.

1. Heterotrophic Nutrition: The word 'hetero' means other. Heterotrophic plants cannot make their own food. They depend on other plants or animals for their nutrition, much like we do. These are less common but very interesting. This group includes parasitic plants that steal food, insectivorous plants that trap and eat insects, and saprotrophs that feed on dead and decaying matter.

How Photosynthesis Works: The Plant's Food Factory

1. Step 1: Gathering the Raw Materials — The plant needs two main ingredients: carbon dioxide (CO₂) and water (H₂O). The leaves have tiny pores on their surface called stomata, which act like little mouths to take in carbon dioxide from the air. The roots absorb water and minerals from the soil, which are then transported up to the leaves through pipe-like vessels.
2. Step 2: The Role of Sunlight and Chlorophyll — The leaves contain a green pigment called chlorophyll. This pigment is what gives leaves their green color. Chlorophyll's special job is to trap energy from sunlight. Think of it as the 'stove' that provides the heat to cook the food. This is why photosynthesis only happens during the day.
3. Step 3: The 'Cooking' Process — Inside the leaf cells, the captured sunlight energy is used to combine carbon dioxide and water. This chemical reaction converts the raw materials into food for the plant. The food is a type of sugar called glucose.
4. Step 4: The Products - Food and Oxygen — The final products of photosynthesis are glucose (food) and oxygen. The glucose is used by the plant for its growth and energy needs. Any extra glucose is stored as starch. The oxygen (O₂) is a by-product that is released back into the air through the stomata. This is the very oxygen that we and other animals breathe to live! The overall equation for photosynthesis is: Carbon Dioxide + Water --(in the presence of Sunlight and Chlorophyll)--> Glucose + Oxygen

Beyond Photosynthesis: Other Ways Plants Get Nutrients

While most plants are autotrophs, some have evolved different strategies to survive. These are the heterotrophs.

• Parasitic Plants: These plants live on other living plants (called the host) and steal nutrients from them. A common example is Cuscuta (Amarbel). It has a yellow, wiry stem that twines around the host plant. It lacks chlorophyll and cannot make its own food, so it uses special structures to absorb ready-made food directly from the host plant, often harming it in the process.

• Insectivorous Plants: These are the 'carnivores' of the plant world! They grow in soil that is poor in certain nutrients, like nitrogen. To supplement their diet, they have developed clever traps to catch and digest insects. The Pitcher Plant is a great example. Its leaf is modified into a pitcher-like structure with a lid. When an insect enters, the lid closes, and the insect is trapped and digested by juices inside the pitcher.

• Saprotrophs: These organisms get their nutrition from dead and decaying organic matter. Fungi, like mushrooms and bread mould, are classic examples. They release digestive juices onto the dead matter, which breaks it down into a liquid form. They then absorb the nutrients from this liquid. This mode of nutrition is called saprotrophic nutrition.

Key Concepts to Remember

• Chlorophyll is essential: Only plants with chlorophyll can perform photosynthesis and make their own food.
• Stomata are crucial: These tiny pores on leaves are the gateways for carbon dioxide to enter the plant for photosynthesis.
• Sunlight is the ultimate energy source: Photosynthesis converts light energy from the sun into chemical energy (food), which then fuels almost all life on Earth.
• Parasites vs. Saprotrophs: A parasite feeds on a living host, while a saprotroph feeds on dead and decaying matter.
• Storage of food: Plants store the extra food they make in the form of starch in various parts like leaves, stems, roots, and fruits.

Practice Questions with Solutions

• Q: Define photosynthesis. Name the raw materials required and the products formed during this process. A: Step 1: Photosynthesis is the process by which green plants synthesize their own food (carbohydrates) from carbon dioxide and water in the presence of sunlight. Step 2: The raw materials required are carbon dioxide (from air), water (from soil), and sunlight. Chlorophyll is also essential. Step 3: The products formed are carbohydrates (food) and oxygen. Final answer: Photosynthesis is the food-making process in green plants using CO2, water, and sunlight, producing carbohydrates and oxygen.
• Q: Differentiate between autotrophic and heterotrophic nutrition in plants, giving one example for each. A: Step 1: Autotrophic nutrition is a mode of nutrition where organisms synthesize their own food from simple inorganic substances. Example: Green plants. Step 2: Heterotrophic nutrition is a mode of nutrition where organisms obtain food from other organisms. Example: Cuscuta (parasitic plant) or pitcher plant (insectivorous). Final answer: Autotrophs make their own food (e.g., green plants), while heterotrophs obtain food from others (e.g., Cuscuta).
• Q: Why do insectivorous plants, like the pitcher plant, trap insects even though they are green and can perform photosynthesis? A: Step 1: Insectivorous plants are green and perform photosynthesis to produce carbohydrates. Step 2: However, they typically grow in soil that is deficient in certain nutrients, particularly nitrogen. Step 3: They trap and digest insects to obtain the necessary nitrogen compounds that they cannot get from the soil. Final answer: Insectivorous plants trap insects to fulfill their nitrogen requirements, as they grow in nitrogen-deficient soil.
• Q: What is the primary role of chlorophyll in the process of photosynthesis? Where is it mainly found in a plant? A: Step 1: Chlorophyll is a green pigment present in plants. Step 2: Its primary role in photosynthesis is to absorb sunlight energy, which is essential for converting carbon dioxide and water into food. Step 3: Chlorophyll is mainly found in the chloroplasts, which are located in the leaves of the plant. Final answer: Chlorophyll absorbs sunlight energy for photosynthesis and is mainly found in the leaves' chloroplasts.

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