CBSE Class 7 Science Chapter 1: Nutrition in Plants NCERT Solutions

All living organisms require food to sustain life. Food serves as the primary source of energy needed for various life processes such as growth, development, repair of tissues, and overall maintenance of the body's functions. Without adequate food, an organism cannot perform these essential activities and would eventually cease to survive.

Here is a distinction between a parasite and a saprotroph:

To test for the presence of starch in leaves, follow these steps:

1. Destarching: Place a healthy, potted plant with green leaves in a dark room for about three days. This ensures that all the stored starch in the leaves is used up by the plant for its metabolic activities.
2. Partial Covering: Select a leaf from the plant and cover a portion of it completely with a strip of black paper, securing it with paper clips. This prevents sunlight from reaching the covered area.
3. Exposure to Sunlight: Keep the plant in bright sunlight for about six hours. This allows photosynthesis to occur in the parts of the leaves exposed to light.
4. Plucking the Leaf: Carefully pluck the selected leaf from the plant. Remove the black paper strip and trace the outline of the covered and uncovered areas onto a sheet of paper for reference.
5. Boiling in Water: Dip the leaf in boiling water for a few minutes. This process kills the leaf cells and makes the cell membranes permeable.
6. Boiling in Alcohol: Immerse the leaf in a beaker containing alcohol. Place this beaker inside a larger water bath and heat it gently until the alcohol begins to boil. Caution: Alcohol is highly flammable, so this step must be done carefully over a water bath, not directly over a flame. This step removes the chlorophyll from the leaf, decolorizing it.
7. Rinsing and Iodine Test: Take out the decolorized leaf and rinse it thoroughly with water to remove any residual alcohol. Now, spread the leaf flat and pour a few drops of dilute iodine solution over it.
8. Observation: Observe the changes in the leaf. The parts of the leaf that were exposed to sunlight (and thus performed photosynthesis) will turn blue-black, indicating the presence of starch. The parts that were covered with black paper will remain yellowish-brown (the color of the iodine solution), indicating the absence of starch.

This experiment demonstrates that sunlight is necessary for photosynthesis, which produces starch in the leaves.

Green plants synthesize their own food through a process called photosynthesis, which primarily occurs in their leaves. The leaves act as the 'food factories' of the plant. For this process to happen, several raw materials must be available:

• Water: Water is absorbed by the roots from the soil and transported upwards through the stem and branches to the leaves via specialized vascular tissues called xylem.
• Carbon Dioxide: Carbon dioxide gas is taken in from the atmosphere through tiny pores on the surface of the leaves called stomata.
• Sunlight: Sunlight provides the energy required for photosynthesis. This light energy is captured by a green pigment called chlorophyll, which is present in the chloroplasts within the leaf cells.

Using the captured sunlight energy, chlorophyll helps to convert carbon dioxide and water into glucose (a type of sugar), which is the plant's food. This process can be summarized by the following equation:

$$Carbon\; Dioxide\; +\; Water\; \to \; (in\; the\; presence\; of\; Chlorophyll\; and\; Sunlight)\; \to \; Glucose\; +\; Oxygen$$

Oxygen, a byproduct of photosynthesis, is released into the atmosphere through the stomata. The glucose produced is either used immediately by the plant for energy or stored in various parts of the plant as starch for later use.