Last Important Revision@CBSE TOPPER
1. Why leaves become yellow in the absence of light?
Ans: Presence of light is quite necessary for plants because in presence of light plants by the process of photosynthesis synthesizes their food.
In the absence of light the process of photosynthesis is not possible.
For synthesis of food presence of a pigment called chlorophyll is also necessary which absorbs the sunlight and helps in photosynthesis process.
The colour of this pigment is green and therefore most of the plants exhibit green colour.
But when there will be no sunlight, no photosynthesis takes place and as plant will not get energy there will be no chlorophyll in the plant after some time and thus plant start becoming yellow in the absence of light.
2. Which raw materials are responsible for the release of O2, in photosynthesis?
Ans: Water and carbon-dioxide are the two raw materials responsible for the release of oxygen during photosynthesis. Water is absorbed from soil through the roots and CO2 diffuses from the air into the plant through stomata. These raw materials are then converted into energy-yielding glucose molecules.
3. What happens to extra glucose or carbohydrate in an animal body?
Ans: In an animal body, extra glucose or carbohydrate is stored in the liver as well as in skeletal muscles in the form of glycogen.
Glucose is converted to glycogen (starch-like carbohydrate) in liver. When the body is in need of energy, glycogen is converted back into glucose.
4. Name an energy rich carbohydrate stored in large quantities in liver and muscle cells.
Ans: Glycogen is an energy rich carbohydrate that is stored in large quantities in the liver and skeletal muscles of the body. It is a branched-chain polymer of glucose. It serves as a reserve source of energy.
5. What is mainly digested by stomach of man?
Ans: The digestion of proteins occurs in the stomach. It is facilitated by digestive enzymes (pepsin, hydrochloric acid). HCl provides acidic medium while pepsin acts on proteins and breaks them into smaller peptides.
6. How does most CO2, reach the photosynthesizing cells of a green leaf?
Ans: Most CO2 reach the photosynthesizing cells of green leaves through diffusion. Stomata (tiny pores) present of leaf surface and stem facilitates gaseous exchange between the plant cells and the surrounding. CO2 move into the cells through these small pores.
7. Name two molecules produced by the digestion of starch and fat respectively.
Ans: The digestion of starch (complex carbohydrate) produces glucose and maltose (simple sugars).Fats are broken down to produce molecules of glycerol and fatty acids.
8. What will happen if the liver of a person gets damaged?
Ans: If the liver of a person get damaged, fat digestion would be affected. As a result, liver will not produce bile efficiently and the emulsification of fats will stop.
9. Stomata of desert plants remain closed during the day. Explain how and when they take up CO2 to perform photosynthesis?
Ans: Desert plants close their stomata during the day to prevent transpiration and loss of water. To perform photosynthesis, CO2 is necessary. They take up CO2 during the night through stomata and store it in their photosynthesizing cells in the form of an intermediate until the day. And when sunlight is available, they perform photosynthesis to make their food.
10. Where does aerobic respiration occur? How many molecules of ATP are released during it?
Ans: Respiration on the basis of presence or absence of oxygen can be of two types: aerobic respiration and anaerobic respiration. Aerobic respiration occurs in the presence of oxygen while anaerobic occurs in the absence of oxygen. Site of aerobic respiration is mitochondria. During aerobic respiration 38 ATP molecules released.
Read this too: Important Biology Q/A Life process
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