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

Solution: All living organisms require food to obtain the necessary energy. This energy is crucial for various life processes such as growth, development, repair of tissues, and overall maintenance of the body's functions. Without food, organisms cannot sustain life.

Solution:

Here is a distinction between a parasite and a saprotroph:

• Parasite: A parasite is an organism that derives its nutrition from the body of another living organism, known as the host. Parasites often harm their host in the process of obtaining nutrients. An example is Cuscuta (Amarbel), which grows on host plants and absorbs nutrients from them.
• Saprotroph: A saprotroph is an organism that obtains its nutrition from dead and decaying organic matter. They secrete digestive juices onto the dead matter, breaking it down externally, and then absorb the nutrients. Examples include mushrooms and many bacteria.

Solution:

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

1. Destarch the plant: Keep a healthy potted plant with variegated leaves (leaves with different colored patches) in a dark room for three days. This ensures that all existing starch in the leaves is used up by the plant.
2. Expose to sunlight: Cover a portion of one or two leaves with black paper strips (using clips to hold them in place) to block sunlight. Then, place the plant in sunlight for about six hours. This allows photosynthesis to occur in the exposed parts of the leaves.
3. Pluck and boil the leaf: Carefully pluck a leaf that was partially covered. Dip the entire leaf in boiling water for a few minutes. This kills the leaf cells and makes them permeable.
4. Remove chlorophyll: Immerse the boiled leaf in a beaker containing alcohol. Place this beaker inside a water bath and heat it gently until the alcohol begins to boil. Caution: Alcohol is flammable, so direct heating should be avoided. This step removes the green chlorophyll from the leaf, making the color changes visible.
5. Test with iodine: Take out the decolorized leaf and rinse it with water. Now, spread the leaf flat and add a few drops of dilute iodine solution over it.
6. Observe the results: Observe the color changes in the leaf. The parts of the leaf that were exposed to sunlight and were not covered by the black paper will turn blue-black, indicating the presence of starch. The parts that were covered by the black paper will remain yellowish-brown (the color of iodine solution), indicating the absence of starch.

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

Solution:

The process of synthesis of food in green plants is called photosynthesis. This vital process primarily occurs in the leaves, which are often referred to as the 'food factories' of the plant. For photosynthesis to take place, 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 vessels.
• Carbon Dioxide: Carbon dioxide gas is taken in from the atmosphere through tiny pores called stomata, which are usually located on the surface of the leaves.
• Sunlight: Sunlight provides the energy required for the process. Leaves contain a green pigment called chlorophyll, located in chloroplasts, which is capable of capturing light energy from the sun.

Using the captured solar energy, plants convert carbon dioxide and water into glucose (a type of sugar), which serves as their food. Oxygen is released as a byproduct of this process. The overall equation for photosynthesis is:

$$6CO\_2\; +\; 6H\_2O\; \backslash xrightarrow\{\backslash text\{Sunlight,\; Chlorophyll\}\}\; C\_6H\_\{12\}O\_6\; +\; 6O\_2$$

The synthesized glucose is then used by the plant for its energy needs and growth, or it can be stored in various parts of the plant for later use.