Science [2 Mark Questions]

Leaves shows following adaptations for photosynthesis:

1. Leaves serve to provide large surface area to facilitate maximum light absorption.
2. The extensive network of veins helps quick transport of substances to and from the mesophyll cells.
3. Leaves contain chloroplasts, the site for photosynthesis. Since upper surface of leaves are directly illuminated, number of chloroplast is higher in the upper surface.
4. Presence of tiny pores called as stomata on leaf's surface facilitate gaseous exchange and transpiration.

The availability of oxygen is much less in aquatic environment than in terrestrial environment. Due to this, aquatic organisms need to work harder to obtain oxygen. Hence, rate of breathing in aquatic organisms is much faster than in terrestrial organisms.

Gastric glands produce the following substances:

1. Mucus: Moistening the food and protecting the wall of the stomach from corroding action of HCl and pepsin.
2. HCl: It makes the food soft, sterilised and acidified for pepsin to act upon food.
3. Gastric Lipase: It is active only in infants. It partially breaks down fat into its components.
4. Rennin: It is active in infants where it helps in curdling of milk (casein to paracasein) for action of pepsin.
5. Pepsin: It is secreted in inactive state of pepsinogen. Pepsin hydrolyses proteins into soluble fragments of peptones and proteoses.

1. Trypsin: Proteins, peptones and proteoses.
2. Amylase: Starch, dextrins.
3. Pepsin: Proteins.
4. Lipase: Fats.

Respiration and photosynthesis are the two vital processes for plant life. The plant kept in light would be able to produce oxygen, required for respiration, by the process of photosynthesis and would live longer. The one kept in dark would die as soon as the container becomes filled with carbon dioxide gas produced by respiration.

Human heart has four completely separated chambers which allow two completely separated circuits of oxygenated and deoxygenated blood i.e. double circulation.

1. It ensures complete separation of oxygenated and deoxygenated blood.
2. It allows rapid pumping of oxygenated blood under high pressure which is required by active endothermic animals to maintain the constant body temperature.

If leaves of a healthy potted plant are coated with Vaseline, it will clog the stomatal pores on leaves. Blockage of stomata will stop transpiration and exchange of gases from leaves. Transpiration plays an important role in ascent of sap in plants. Hence, lack of transpiration will stop ascent of sap. Moreover, stoppage of exchange of gases would also stop respiration and photosynthesis in leaves. This will result in death of leaves and finally the plant would die due to lack of food.

If plant is releasing carbon dioxide and taking in oxygen during the day, it means that respiration is happening in plant. But it does not mean that photosynthesis is not happening. Carbon dioxide released after respiration comes out of stomata. Respiration is independent of photosynthesis.

Importance of soil for plant growth:

1. Soil provides the base on which a plant can grow.
2. Soil serves as reservoir of water for plants.
3. Soil serves as reservoir of different minerals which are essential for growth of plants.
4. Soil contains many organic materials which provide nutrients to plants.

The food of herbivores contains a huge amount of cellulose. The animals need the assistance of certain bacteria to digest cellulose and this process takes time. Due to this, herbivores have longer small intestine than carnivores. Meat is easier to digest and hence carnivores have small intestine which is much smaller than in herbivores.

1. Digestion of food is completed only in small intestine.
2. Wall of the intestine bears a number of finger-like projections called villi. Villi provide a large surface area to the lining layer for absorption.
3. The epithelium, lining the villi, is made of cells having a number of very fine projections known as microvilli. Microvilli are specialised for absorption.
4. Wall of the intestine, especially the interior of villi, has lymph and blood vessels for carrying the absorbed food to different parts of the body.