Coordination & Control MCQs set 3 for Army Medical College (AMC) Entry Test Biology — 20 solved questions.
Q1. While most plant hormones are known to promote growth, one specific hormone induces seed dormancy and prevents germination. Identify this substance.
Answer: Abscisic acid
Explanation: ABA inhibits growth and promotes dormancy, while Gibberellins are the most tempting wrong choice because they specifically break dormancy.
Q2. In myelinated neurons, the nerve impulse exhibits a unique jumping behavior that significantly increases its velocity. Where does this 'jump' occur?
Answer: Nodes of Ranvier
Explanation: Impulse jumps between nodes of Ranvier in saltatory conduction; myelin sheath is tempting but it acts as an insulator, not the jumping site.
Q3. A doctor taps the patellar tendon of a patient, causing an immediate leg extension. This specific reflex arc is unique because it lacks interneurons.
Answer: Monosynaptic reflex
Explanation: The knee-jerk reflex is the only monosynaptic human reflex; polysynaptic is tempting because almost every other reflex involves at least one interneuron.
Q4. Cortisol, a lipid-soluble steroid hormone, regulates metabolism. What is its primary mechanism of action upon reaching a target cell?
Answer: Binding to intracellular receptors
Explanation: Steroids are lipid-soluble and bind intracellularly; peptide hormones are tempting because they require membrane-bound receptors to initiate secondary messenger cascades.
Q5. A 45-year-old patient has a condition affecting both digestive enzyme secretion and blood sugar regulation. Which organ functions as both exocrine and endocrine?
Answer: Pancreas
Explanation: The pancreas is a unique heterocrine gland with both functions; the adrenal gland is tempting because it has two distinct histological regions.
Q6. When blood calcium levels rise above the normal set point, which hormone is secreted by the thyroid gland to lower it?
Answer: Calcitonin
Explanation: Calcitonin reduces blood calcium levels by depositing it in bones; parathyroid hormone is tempting as it performs the exact opposite regulatory function.
Q7. A farmer places a few ripe bananas in a crate of green mangoes to speed up ripening. Which gaseous plant hormone is responsible?
Answer: Ethene
Explanation: Ethene is a gaseous hormone primarily responsible for fruit ripening; cytokinins are tempting because they are liquid hormones that promote cell division.
Q8. During a high fever, the body's internal thermostat attempts to reset. Which part of the brain is primarily responsible for temperature regulation?
Answer: Hypothalamus
Explanation: The hypothalamus serves as the primary thermostat for homeostatic regulation; the thalamus is tempting as it is the major sensory relay station.
Q9. In a 'fight or flight' situation, the adrenal medulla releases adrenaline into the bloodstream. How is this secretion primarily triggered?
Answer: Sympathetic nerve fibers
Explanation: The adrenal medulla is directly innervated by sympathetic fibers; ACTH is tempting because it only regulates the secretion of the adrenal cortex.
Q10. In a laboratory experiment, a high concentration of Indole Acetic Acid (IAA) is applied to root tips. What is the observed effect?
Answer: Inhibition of elongation
Explanation: High auxin concentrations inhibit root elongation while promoting shoot growth; cytokinins are tempting because they generally promote lateral bud growth instead.
Q11. There is a brief interval of time between the arrival of an action potential at a knob and the response. What causes this delay?
Answer: Neurotransmitter diffusion
Explanation: Synaptic delay occurs because chemical neurotransmitters must diffuse across the cleft; electrical synapses are tempting because they lack this significant time delay.
Q12. Following a carbohydrate-rich meal, insulin levels rise to lower blood glucose. Which metabolic process is stimulated by insulin in the liver?
Answer: Glycogenesis
Explanation: Insulin promotes the conversion of glucose into glycogen for storage; glucagon is tempting as it stimulates the breakdown of glycogen during fasting.
Q13. A botanist wants to produce seedless tomatoes by inducing fruit development without the need for pollination. Which hormone should be applied?
Answer: Auxins
Explanation: Auxins can induce fruit development without fertilization, known as parthenocarpy; ethene is tempting because it is associated with the later ripening stage.
Q14. Which chemical substance is unique because it functions as a neurotransmitter when released by neurons and as a hormone when released by glands?
Answer: Norepinephrine
Explanation: Norepinephrine acts as both a hormone and a neurotransmitter in the sympathetic system; acetylcholine is tempting because it is purely a neurotransmitter.
Q15. An individual loses their balance and ability to perform precise muscular movements after a head injury. Which part of the brain is likely damaged?
Answer: Cerebellum
Explanation: The cerebellum coordinates complex voluntary movements and maintains posture; the medulla is tempting because it controls involuntary vital functions like breathing.
Q16. During the human female reproductive cycle, what specific hormonal event is the immediate trigger for ovulation from the Graafian follicle?
Answer: LH surge
Explanation: A sharp surge in Luteinizing Hormone triggers the release of the egg; FSH is tempting because it stimulates follicle maturation before ovulation.
Q17. When the leaves of Mimosa pudica are touched, they fold rapidly. This movement is an anomaly because it is caused by which mechanism?
Answer: Turgor pressure changes
Explanation: Nastic movements like those in Mimosa result from rapid turgor changes; tropic movements are tempting because they involve slower, permanent growth-related changes.
Q18. In regions where the soil is deficient in a certain mineral, many people develop an enlarged thyroid gland. Identify the missing mineral.
Answer: Iodine
Explanation: Thyroxine synthesis requires iodine from the diet to prevent goiter; iron is tempting because it is essential for hemoglobin, not thyroid function.
Q19. Antidiuretic hormone (ADH) is released to prevent dehydration. On which specific part of the nephron does this hormone primarily exert its effect?
Answer: Collecting ducts
Explanation: ADH increases water reabsorption specifically at the collecting ducts; aldosterone is tempting because it primarily regulates sodium and potassium balance instead.
Q20. Nerve impulses are conducted along an axon in only one direction. Which physiological phenomenon is responsible for preventing the backward flow of an impulse?
Answer: Refractory period
Explanation: The refractory period ensures the impulse moves in one direction; myelination is tempting because it increases speed rather than determining the directionality.