CBSE Class 10 Science Biology Questions Assignment Set 04

Answer: Fats are digested in the small intestine. Bile from the liver breaks large fat globules into small droplets (emulsification), and pancreatic lipase then breaks them into fatty acids and glycerol. Intestinal juice completes the digestion.

Teacher's Note:
1. Bile is not an enzyme; it only emulsifies fats.
2. Lipase does the chemical breakdown.

Answer: Autotrophic nutrition needs chlorophyll, sunlight, carbon dioxide and water. The products are carbohydrates, and oxygen is released as a by-product.

Teacher's Note:
1. These are the requirements of photosynthesis.
2. Oxygen is the by-product.

Answer: Xylem carries water and minerals from the roots upward only, through dead cells, mainly by transpiration pull. Phloem carries food made in the leaves to all parts of the plant in both directions, through living cells, and uses energy (ATP).

Teacher's Note:
1. Compare substance, direction, cell type and energy use.
2. A short table-like answer scores well.

Answer: Oxygen is carried by haemoglobin in red blood cells as oxyhaemoglobin. Carbon dioxide is more soluble in water, so most of it is carried dissolved in blood plasma.

Teacher's Note:
1. Haemoglobin has a high affinity for oxygen.
2. Carbon dioxide travels mainly in dissolved form.

Answer: A neuron has a cell body with a nucleus, short branched dendrites, and a long axon ending in nerve endings. The dendrites receive information, which travels as an electrical impulse along the axon. At the nerve endings a chemical is released that passes the signal across the synapse to the next neuron.

Teacher's Note:
1. A neuron conducts impulses in one direction.
2. Name the parts in order of the impulse path.

Answer: The hormone auxin is made at the shoot tip. When light falls from one side, auxin diffuses to the shaded side and makes those cells grow longer, so the shoot bends towards light.

Teacher's Note:
1. Phototropism is the growth movement in response to light.
2. Auxin concentration is higher on the shaded side.

Answer: Endocrine glands release hormones directly into the blood, which carries them to target organs. Examples are insulin controlling blood sugar and adrenaline preparing the body for emergencies. Feedback mechanisms regulate the amount of hormone released.

Teacher's Note:
1. Hormones act slowly but have long-lasting effects.
2. Mention at least one gland and one hormone.

Answer: Organisms must respond to changes in the environment and keep their internal activities working together. Control and coordination lets the body detect stimuli, take decisions and act through nerves and hormones in animals and hormones in plants.

Teacher's Note:
1. Without coordination the parts of the body would not work as a whole.
2. Give both response and integration.

Answer: Sexual reproduction combines DNA from two parents, so offspring show variation. Variation helps a species adapt to changing conditions and survive, and it provides the raw material for evolution.

Teacher's Note:
1. Variation is the key advantage.
2. Asexual reproduction gives nearly identical copies.

Answer: Barrier methods such as condoms and diaphragms; chemical methods such as oral contraceptive pills; intrauterine devices such as copper-T; and surgical methods such as vasectomy in males and tubectomy in females.

Teacher's Note:
1. Group the methods into four types.
2. Each prevents fertilisation or implantation.

Answer: They add their secretions to the sperms to form semen. These fluids provide nutrition to the sperms and make their movement through the male reproductive tract easier.

Teacher's Note:
1. The sperms are carried in the secretions of these glands.
2. Nutrition and easier transport are the two functions.

Answer: DNA carries the information for making proteins and hence the body design. Copying it ensures that the offspring inherit the same body design as the parent. The copying is not perfectly accurate, so small variations arise, and these help the species survive.

Teacher's Note:
1. Reproduction needs a copy of the blueprint.
2. Slight errors create variation.

Answer: It is the progressive increase in the concentration of harmful, non-biodegradable chemicals such as pesticides as they pass along the food chain. Yes, the levels differ: they are lowest in producers and highest in the top consumers, including human beings.

Teacher's Note:
1. Pesticides are absorbed by plants and then stored in the bodies of consumers.
2. Concentration rises at each higher trophic level.

Answer: Non-biodegradable wastes remain in the environment for long periods, pollute soil and water, and block drains. Their harmful chemicals enter food chains and get magnified, harming living organisms and the ecosystem.

Teacher's Note:
1. Such wastes cannot be broken down by decomposers.
2. Link the answer to food chains.

Answer: The ozone layer absorbs harmful ultraviolet radiation from the sun. Its depletion lets more UV reach the earth and can cause skin cancer, cataract and damage to crops and marine life. Chemicals called CFCs cause the damage, so an international agreement under UNEP in 1987 froze and then reduced CFC production, and CFC-free refrigerators are used.

Teacher's Note:
1. Name the chemical responsible and the global agreement.
2. Mention at least two harmful effects.