Practice Coordination & Control MCQs for NUMS MDCAT (Military Medical) Biology — topic-wise sets with solved answers.
Q1. A patient experiences a loss of tactile sensitivity in their fingertips, specifically for light touch. Which specialized receptor is primarily responsible for this sensation?
Answer: Meissner's corpuscles
Explanation: Meissner's corpuscles are specialized for light touch; Pacinian corpuscles fail here as they are receptors for deep pressure and vibration.
Q2. During the resting membrane potential of a neuron, which ion's high permeability and outward leakage primarily maintain the internal negative charge?
Answer: Potassium ions
Explanation: Potassium ions leak out through non-gated channels to maintain negativity; sodium ions fail because their influx would cause depolarization instead.
Q3. A neurotransmitter is released into the synaptic cleft to propagate a signal. Which enzyme specifically inactivates acetylcholine to prevent continuous stimulation?
Answer: Acetylcholinesterase
Explanation: Acetylcholinesterase hydrolyzes acetylcholine to terminate the signal; Adrenaline is a different neurotransmitter and does not break down acetylcholine in synapses.
Q4. A clinical examination reveals that a patient can perceive sensations but cannot relay sensory information to the correct cerebral cortex area. Which structure is damaged?
Answer: Thalamus
Explanation: The thalamus acts as the main relay station for sensory input; the hypothalamus fails as it primarily regulates homeostasis and hormones.
Q5. In a laboratory experiment, the dorsal root of a spinal nerve in a frog is surgically severed. What is the most likely physiological outcome?
Answer: Loss of sensory perception
Explanation: The dorsal root carries sensory fibers only; the ventral root is incorrect because it carries motor fibers responsible for muscle contraction.
Q6. Which cranial nerve is distinct for extending beyond the head and neck to innervate thoracic and abdominal viscera like the heart?
Answer: Vagus nerve
Explanation: The vagus nerve is the tenth cranial nerve; the facial nerve is incorrect as it is the seventh cranial nerve.
Q7. A student suddenly encounters a predator while hiking. Which physiological change is triggered by the activation of the sympathetic nervous system?
Answer: Dilation of pupils
Explanation: The sympathetic system dilates pupils for better vision; the parasympathetic system fails because it causes pupillary constriction and promotes digestion.
Q8. A child presents with stunted physical growth, mental retardation, and dry skin due to congenital thyroid hormone deficiency. What is this condition?
Answer: Cretinism
Explanation: Cretinism results from congenital thyroid deficiency; Myxoedema fails as it refers to thyroid deficiency occurring specifically in adult life.
Q9. After consuming a large volume of water, a person produces dilute urine. Which hormone's secretion is suppressed to allow this homeostatic adjustment?
Answer: Antidiuretic hormone
Explanation: Low ADH reduces water reabsorption in collecting ducts; Aldosterone fails because it primarily regulates sodium and potassium balance, not pure water.
Q10. A patient with Addison's disease shows low blood pressure and high serum potassium. Which adrenal cortex hormone is specifically lacking in this case?
Answer: Aldosterone
Explanation: Aldosterone promotes sodium reabsorption and potassium excretion; Cortisol fails as it primarily regulates glucose metabolism rather than electrolyte balance.
Q11. Immediately following a carbohydrate-rich meal, which specific cells in the Islets of Langerhans increase their secretory activity to maintain glucose homeostasis?
Answer: Beta cells
Explanation: Beta cells produce insulin to lower blood glucose; Alpha cells fail because they secrete glucagon which increases blood glucose levels.
Q12. During the follicular phase of the menstrual cycle, rising estrogen levels eventually suppress the release of FSH. This is an example of:
Answer: Negative feedback
Explanation: High estrogen levels inhibit FSH via negative feedback; positive feedback fails because it would amplify the signal rather than suppressing it.
Q13. In the process of phototropism, a plant stem bends towards light. On which part of the stem does auxin accumulate to facilitate elongation?
Answer: Shaded side
Explanation: Auxin accumulates on the shaded side, causing cell elongation; the lighted side fails because auxin is sensitive to light and migrates.
Q14. A farmer wishes to induce 'bolting' or rapid stem elongation in a rosette plant like cabbage. Which hormone should be applied commercially?
Answer: Gibberellins
Explanation: Gibberellins induce bolting and stem elongation; Abscisic acid fails because it is a growth inhibitor that promotes dormancy and abscission.
Q15. During a period of severe drought, a plant prevents excessive transpiration by closing its stomata. Which hormone acts as the primary stress signal?
Answer: Abscisic acid
Explanation: Abscisic acid promotes stomatal closure during water stress; Cytokinins fail as they generally promote cell division and delay leaf senescence.
Q16. Which type of neuron is characterized by having a single long dendron and a relatively short axon, carrying impulses toward the CNS?
Answer: Sensory neuron
Explanation: Sensory neurons have long dendrons and short axons; motor neurons fail because they have many short dendrites and one long axon.
Q17. When a person accidentally touches a hot object, they withdraw their hand before feeling pain. Which structure serves as the primary coordinator here?
Answer: Spinal cord
Explanation: The spinal cord coordinates the reflex arc directly; the medulla oblongata fails because it controls involuntary autonomic functions like breathing.
Q18. An athlete suffers a head injury and subsequently struggles with maintaining balance and performing smooth, coordinated muscular movements. Which brain region is likely affected?
Answer: Cerebellum
Explanation: The cerebellum coordinates precise voluntary movements and balance; the cerebrum fails as it is responsible for conscious thought and sensory processing.
Q19. A patient is diagnosed with hypocalcemia. Which hormone is released by the body to increase blood calcium levels by stimulating bone resorption?
Answer: Parathormone
Explanation: Parathormone increases blood calcium by mobilizing it from bone; Calcitonin fails because it lowers blood calcium by promoting bone deposition.
Q20. In myelinated neurons, the nerve impulse travels significantly faster by jumping from one non-myelinated gap to the next. What are these gaps called?
Answer: Nodes of Ranvier
Explanation: Nodes of Ranvier are the gaps where saltatory conduction occurs; Schwan cells fail because they are the cells that form the myelin.
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