CBSE Class 10 Biology Control and Coordination MCQs Set 22

Answer: (d) Conduction of the nerve impulse

Explanation:
1. The axon is a long fibre that carries the impulse away from the cell body.
2. Dendrites receive impulses.

Teacher's Note:
1. Impulses travel along the axon to its terminal.
2. Receptors, not axons, receive external stimuli.

Answer: (b) Help in the synaptic transmission of nerve impulses

Explanation:
1. Acetylcholine is a neurotransmitter released at the synapse.
2. It carries the signal across the synaptic gap.

Teacher's Note:
1. It is stored in synaptic vesicles.
2. It is broken down by the enzyme acetylcholinesterase.

Answer: (a) Presynaptic neuron

Explanation:
1. Synaptic vesicles store neurotransmitters at the axon end of the presynaptic neuron.
2. They release them into the cleft when an impulse arrives.

Teacher's Note:
1. Receptors for the neurotransmitter are on the postsynaptic membrane.
2. The cleft is only the gap.

Answer: (c) Positively charged

Explanation:
1. Sodium ions rush in on stimulation, so the inside becomes positive (depolarisation).
2. The outside becomes negative.

Teacher's Note:
1. At rest the inside is negative.
2. This reversal travels along the fibre as the impulse.

Answer: (c) -70 mV

Explanation:
1. The inside of a resting neuron is about 70 mV negative compared with the outside.
2. So the value is -70 mV.

Teacher's Note:
1. The sodium-potassium pump helps maintain it.
2. Values differ slightly between cell types.

Answer: (d) Receptor, sensory nerves, CNS, effector

Explanation:
1. A reflex arc starts at the receptor, passes through the sensory nerve to the CNS, then through the motor nerve to the effector.
2. Option (d) gives this order.

Teacher's Note:
1. The stimulus is always detected before the response.
2. The effector is a muscle or gland.

Answer: (a) Duramater, arachnoid, piamater

Explanation:
1. The outermost membrane is the tough duramater, then the arachnoid, and the innermost thin pia mater lies on the brain.
2. Cerebrospinal fluid fills the space between the arachnoid and pia.

Teacher's Note:
1. The three layers protect the brain.
2. Meningitis is their infection.

Answer: (b) Thalamus

Explanation:
1. The hind brain has the cerebellum, pons and medulla oblongata.
2. The thalamus is part of the forebrain.

Teacher's Note:
1. The thalamus relays sensory signals.
2. The hypothalamus lies below it.

Answer: (a) 12

Explanation:
1. Humans have 12 pairs of cranial nerves arising from the brain.
2. There are 31 pairs of spinal nerves.

Teacher's Note:
1. Cranial nerves serve the head and neck.
2. The vagus nerve is the longest.

Answer: (b) Cerebellum

Explanation:
1. Alcohol affects the cerebellum, causing loss of balance and unsteady movements.
2. It also affects judgement.

Teacher's Note:
1. The staggering walk of a drunk person is due to this.
2. Larger amounts also depress the medulla.

Answer: (a) Medulla oblongata

Explanation:
1. The medulla controls involuntary actions like heartbeat, breathing and swallowing.
2. The cerebrum controls voluntary actions.

Teacher's Note:
1. Reflexes like vomiting and sneezing are also centred here.
2. It joins the brain to the spinal cord.

Answer: (b) Hypothalamus

Explanation:
1. The hypothalamus is involved in emotions such as anger, fear and pleasure.
2. It also controls hunger and thirst.

Teacher's Note:
1. It is part of the limbic system.
2. The cerebrum handles thought and voluntary actions.

Answer: (d) All of the above

Explanation:
1. The cerebrospinal fluid cushions the brain and spinal cord from shocks.
2. It also supplies nutrients and removes wastes.

Teacher's Note:
1. It fills the cavities of the brain.
2. It is found between the meninges.

Answer: (d) Thyroxine

Explanation:
1. Thyroxine from the thyroid gland controls the rate of metabolism.
2. It requires iodine for its synthesis.

Teacher's Note:
1. Too little iodine causes goitre.
2. Adrenaline is an emergency hormone.

Answer: (a) Testosterone

Explanation:
1. Testosterone from the testes causes the male features, such as a beard and a deep voice.
2. Oestrogen does the same for females.

Teacher's Note:
1. It is secreted from puberty.
2. Its release is stimulated by pituitary hormones.

Answer: (a) Iron is essential for the synthesis of thyroxine

Explanation:
1. Iodine, not iron, is needed to make thyroxine.
2. The other statements are true.

Teacher's Note:
1. Iodised salt prevents goitre.
2. Thyroxine controls the overall metabolism.

Answer: (c) Adrenal medulla

Explanation:
1. The pituitary controls the thyroid, adrenal cortex and gonads through tropic hormones.
2. The adrenal medulla is under nervous control.

Teacher's Note:
1. The pituitary is the master gland.
2. The adrenal medulla responds to the sympathetic nerves.

Answer: (c) Secretin

Explanation:
1. Secretin, discovered by Bayliss and Starling (1902), was the first hormone found.
2. It is released from the duodenum.

Teacher's Note:
1. It stimulates pancreatic juice.
2. Insulin was isolated later, in 1921.

Answer: (c) Increases

Explanation:
1. ADH helps reabsorb water in the kidney.
2. With less ADH, more water is lost, so urine volume and the frequency of micturition increase.

Teacher's Note:
1. Lack of ADH causes diabetes insipidus.
2. ADH is made in the hypothalamus.

Answer: (d) All of the above

Explanation:
1. Oxytocin causes contraction of the uterus during birth (parturition) and the ejection of milk (let-down).
2. So all the options are correct.

Teacher's Note:
1. It is released by the posterior pituitary.
2. It is called the birth hormone.

Answer: (d) All of the above

Explanation:
1. Auxins promote fruit development, rooting of cuttings and prevent early fall of leaves and fruits.
2. All three are used in agriculture.

Teacher's Note:
1. Auxins also cause phototropism.
2. Synthetic auxins are used as weedkillers.

Answer: (b) Suppression of growth of axillary buds by the presence of the apical bud

Explanation:
1. The apical bud makes auxin that stops the side buds from growing.
2. This is apical dominance.

Teacher's Note:
1. Removing the tip lets lateral buds grow, as in hedge trimming.
2. Cytokinins oppose this effect.

Answer: (a) Is a hormone whose main function is to induce cell division

Explanation:
1. Cytokinins promote cell division and delay ageing of leaves.
2. They are made in actively dividing tissues like root tips.

Teacher's Note:
1. Abscisic acid causes dormancy.
2. Cytokinins are also used in tissue culture.

Answer: (d) Leaf fall and dormancy

Explanation:
1. Abscisic acid is a growth inhibitor.
2. It promotes leaf fall, seed and bud dormancy and closing of stomata.

Teacher's Note:
1. It is called the stress hormone.
2. It acts opposite to gibberellins.

Answer: (d) Abscisic acid

Explanation:
1. Abscisic acid inhibits growth and causes dormancy.
2. The others promote growth.

Teacher's Note:
1. Ethylene is another inhibitor.
2. Auxins, gibberellins and cytokinins are promoters.

Answer: (d) Auxin accumulates on the shaded side

Explanation:
1. Light makes auxin move to the shaded side of the shoot.
2. The shaded cells elongate more, bending the shoot towards light.

Teacher's Note:
1. This was shown by experiments with coleoptiles.
2. The lighted side grows less, not more.

Answer: (c) Gibberellin

Explanation:
1. Gibberellins cause stem elongation, as in dwarf plants and rosette plants.
2. They stimulate the internodes to grow longer.

Teacher's Note:
1. Gibberellins also break seed dormancy.
2. They are used to make grapes larger.

Answer: (d) a-(ii), b-(iii), c-(iv), d-(v), e-(i)

Explanation:
1. Auxin causes phototropism, cytokinins cell division, gibberellins stem elongation.
2. Abscisic acid closes stomata and ethylene ripens fruits.

Teacher's Note:
1. Ethylene is the only gaseous plant hormone.
2. Learn one function for each hormone.