Science M.C.Q

(B) Sensory neuron
Explanation: Sensory neuron carries electrical impulses from receptor to brain while motor neuron carries electrical impulses from the brain to effectors.

(D) (i) and (iv)
Explanation: The respiration process can be aerobic or anaerobic. Aerobic respiration occurs in the presence of oxygen in mitochondria whereas, anaerobic respiration occurs in the absence of oxygen in the cytoplasm. Alcoholic fermentation, which is carried out by unicellular organisms like yeast. Yeast breaks down pyruvic acid anaerobically into ethanol and carbon dioxide in the cytoplasm.
Hence option (ii) and (iii) are wrong.

(D) Unidirectional
Explanation: The flow of energy in an ecosystem is always unidirectional. As the energy moves progressively through one trophic level to another, it is no longer available to the previous level. The energy that is captured by the autotrophs (producers) does not revert back to solar radiation. The energy which passes on to the herbivores (primary consumers) from the autotrophs does not come back to the autotrophs.

(A) (i) - (a), (ii) - (c), (iii) - (b), (iv) - (d)
Explanation:
- Phototropism refers to the movement of a plant toward a light source.
- Geotropism the growth of the parts of plants in response to the force of gravity.
- Hydrotropism the growth or turning of plant roots towards or away from moisture.
- Chemotropism may be defined as the movement or the growth of the organism in response to a chemical stimulus.

(C) The population of tiger will decreases and the population of grass will increase.
Explanation: If deer are missing from the given food chain, the population of the tiger will decrease and the growth of the grass will increase. A missing link in a food chain will create an imbalance in the ecosystem.

(D) Hydrogen bond
Explanation: Each DNA molecule consists of two twisted strands of bases that form a shape called a double helix. The two strands are held together by hydrogen bonds between pairs of bases.

(D) Oxygen is used during germination
Explanation: In the given experimental set-up, germinating peas will undergo aerobic respiration, in which they will use up oxygen and release carbon dioxide. Carbon dioxide released will be absorbed by sodium hydroxide present in this test tube. As germinating peas will consume oxygen present in test tube, a suction force will be developed. Due to pressure difference, the coloured oil drop will move towards the test tube. Thus, this experiment will help to investigate the amount of oxygen used during germination.