Class 10 Biology — Important Questions with Answers

What it is

Oxygen rides on haemoglobin in red blood cells from the lungs to every tissue.

Answer

Oxygen diffuses from the air sacs (alveoli) of the lungs into the blood, where it binds to the red pigment haemoglobin in red blood cells to form oxyhaemoglobin. The blood carries it to the tissues, where oxygen is released for respiration. Haemoglobin makes this transport efficient because it has a high affinity for oxygen.

What it is

Arteries carry blood away from the heart under high pressure; veins bring it back and have valves.

Answer

Arteries carry blood away from the heart, usually oxygenated (except the pulmonary artery), have thick elastic walls and no valves because blood flows under high pressure. Veins carry blood towards the heart, usually deoxygenated (except the pulmonary vein), have thinner walls and contain valves to prevent the backflow of low-pressure blood.

What it is

Photosynthesis is how green plants make their own food (glucose) from CO2 and water using sunlight.

Answer

Photosynthesis is the process by which green plants make their own food (glucose) from carbon dioxide and water using sunlight, releasing oxygen. The balanced equation is: 6CO2 + 6H2O -> C6H12O6 + 6O2. It requires chlorophyll (the green pigment), sunlight, carbon dioxide and water.

What it is

A reflex arc gives an instant, automatic response through the spinal cord - no thinking needed.

Answer

A reflex arc is the pathway followed by a nerve impulse during a reflex action, allowing a quick automatic response without conscious thought. When you touch a hot object, receptors in the skin send an impulse along a sensory neuron to the spinal cord; there a relay neuron passes it to a motor neuron, which carries the impulse to the muscles of the hand, causing you to pull your hand away instantly.

What it is

Sexual reproduction mixes two parents' genes to create variety; asexual makes identical copies.

Answer

In sexual reproduction two parents contribute genes, and the mixing of DNA during the formation of gametes and their random combination at fertilisation creates new gene combinations in the offspring. In asexual reproduction a single parent produces genetically identical copies, so there is little variation. Greater variation gives species a better chance of surviving changes in the environment.

What it is

Crossing two hybrids (Tt x Tt) gives a 3:1 tall-to-short ratio because T is dominant over t.

Answer

The F1 generation is all Tt (tall), because T is dominant over t. When F1 plants (Tt x Tt) are crossed, the F2 offspring are TT, Tt, Tt, tt. TT, Tt and Tt appear tall while tt is short, giving a phenotypic ratio of 3 tall : 1 short. The genotypic ratio is 1 TT : 2 Tt : 1 tt.

What it is

A food chain shows who eats whom, and only about 10 percent of energy passes to the next level.

Answer

A food chain is a series of organisms through which energy and nutrients pass as one organism eats another, for example grass -> deer -> lion. The ten percent law states that only about 10 percent of the energy at one trophic level is passed on to the next level; the rest is lost mainly as heat. This is why food chains usually have only three or four links.