Class 7 Science
NCERT Solution Part 1
Question 1: Why do organisms need to take food?
Answer: Organisms need to take food so that they can get raw material for growth and repair and can get energy for carrying out various activities.
Question 2: Distinguish between a parasite and a saprotroph.
Answer: A parasite lives on or inside the body of another organism; to get shelter and food. A parasite lives on a live host. On the other hand, a saprotroph feeds on dead and decaying remains of animals and plants.
Question 3: How would you test the presence of starch in leaves?
Answer: Steps to test the presence of starch in leaves:
- Boil the leaf in water for about 10 minutes.
- After that, boil the leaf in alcohol; over water bath.
- Wash the boiled leaf with cold water and spread on a flat surface.
- Pour a few drops of iodine on the leaf.
If the iodine turns into dark blue colour, it shows the presence of starch in the leaf.
Question 4: Give a brief description of the process of synthesis of food in green plants.
Answer: Photosynthesis is the process by which green plants make food. Green plants trap solar energy with the help of chlorophyll. Water and carbon dioxide are the raw materials, which are converted into carbohydrates; during the process. Oxygen is the byproduct of photosynthesis. This can be shown by the following equation:
6CO2 + 6H2O → C6H12O6 + 6O2
Question 5: Show with the help of a sketch that the plants are the ultimate source of food.
The following figure shows a food chain, which shows that the plants are the ultimate source of food.
Question 6: Fill in the blanks:
(a) Green plants are called ___________since they synthesise their own food.
(b) The food synthesised by the plants is stored as _________________.
(c) In photosynthesis solar energy is captured by the pigment called ___________.
(d) During photosynthesis plants take in ______________________ and release __________________.
Answer: (a) autotrophs, (b) starch, (c) chlorophyll, (d) carbon dioxide, oxygen