A patient develops Cushing's syndrome due to excessive cortisol. Which feedback mechanism is disrupted?
Answer: B
In Cushing's syndrome, elevated cortisol fails to inhibit CRH and ACTH secretion, disrupting the normal negative feedback loop of the HPA axis.
Q.42Hard
Which of the following best explains oxygen-hemoglobin dissociation curve shift to the RIGHT?
Answer: B
Right shift (Bohr effect) occurs with decreased pH, increased CO2, increased temperature, and elevated 2,3-DPG, facilitating oxygen release to tissues.
Q.43Hard
A person injures their spinal cord at the cervical level. Which of the following would NOT be affected?
Answer: D
Taste is mediated by cranial nerves (VII, IX, X) which are not affected by cervical spinal cord injury. Cervical injury affects arms, legs, and potentially breathing.
Q.44Hard
A researcher observes that blocking acetylcholinesterase leads to prolonged muscle contraction. This demonstrates that acetylcholinesterase's role is to:
Answer: C
Acetylcholinesterase breaks down acetylcholine in the synaptic cleft, terminating signal transmission; its inhibition causes acetylcholine accumulation and sustained contraction.
Q.45Hard
In a diabetic patient with hyperglycemia, which of the following best explains why glucose appears in urine?
Answer: B
Glucose is normally filtered and reabsorbed via active transport. When blood glucose exceeds ~180 mg/dL, the reabsorptive capacity is saturated, causing glycosuria.
Advertisement
Q.46Hard
Which neural pathway transmits pain and temperature sensation from the body to the brain?
Answer: B
The spinothalamic tract carries pain and temperature information from the spinal cord to the thalamus and sensory cortex via crossed fibers.
Q.47Hard
A marathon runner experiences muscle cramps after 2 hours of intense exercise despite adequate hydration. Analysis shows normal blood glucose and electrolyte levels. Which physiological mechanism most likely explains this condition?
Answer: A
Despite normal glucose and electrolytes, prolonged high-intensity exercise causes lactate accumulation and acidosis beyond the muscle buffer system's capacity, leading to involuntary muscle cramps through disrupted calcium regulation in muscle fibers.
Q.48Hard
A population of beetles shows variation in shell color. After a pesticide treatment, dark-colored beetles survive better. This is an example of:
Answer: B
Directional selection occurs when one extreme phenotype has higher fitness. Dark beetles have selective advantage, shifting population toward darker phenotype.
Q.49Hard
In a gene pool of 500 individuals with allele frequencies p = 0.7 and q = 0.3, how many heterozygous individuals are expected according to Hardy-Weinberg principle?
Which of the following mutations would most likely be lethal?
Answer: C
Loss of an entire chromosome causes imbalance in gene dosage affecting multiple essential genes, making it almost always lethal.
Q.51Hard
Which of the following best explains why antibiotic-resistant bacteria increase in a population after antibiotic exposure?
Answer: C
Pre-existing resistant bacteria survive antibiotic exposure while susceptible ones die, increasing resistant population frequency—natural selection.
Q.52Hard
If a woman with normal vision (but carrier for color blindness) has children with a color-blind man, what percentage of their daughters are expected to have normal vision?
Answer: B
Carrier mother (XBXb) × Color-blind father (XbY) produces: XBXb (carrier daughter), XbXb (color-blind daughter), XBY (normal son), XbY (color-blind son). 50% of daughters (1 out of 2) have normal vision.
Q.53Hard
Gene flow between two populations can prevent genetic drift from causing fixation of alleles because:
Answer: A
Gene flow (migration) introduces alleles from one population to another, counteracting genetic drift and maintaining genetic variation.
Q.54Hard
A three-point testcross in Drosophila yields recombinant classes with lower frequencies than parental classes. This demonstrates:
Answer: B
Lower recombinant frequencies indicate genes are linked but can undergo crossing over, producing recombinants at lower frequencies than parentals.
Q.55Hard
A lethal allele that causes embryonic death in homozygous condition would alter the expected dihybrid ratio from 9:3:3:1 to:
Answer: A
If one dominant homozygous class (AABB, AABb, or AAbb) is lethal, the 9:3:3:1 ratio adjusts accordingly. Common outcome is 9:3:4 when one class is removed.
Q.56Hard
In humans, if both parents are heterozygous carriers of sickle cell anemia (HbAS), what is the probability of their child being completely unaffected?
Answer: C
Cross: AS × AS produces AA (unaffected, 41), AS (carrier, 21), SS (affected, 41). Probability of unaffected = 41 + 21 = 43 = 0.75
Q.57Hard
The concept of 'adaptive radiation' is best exemplified by:
Answer: A
Darwin's finches underwent adaptive radiation, diverging from a common ancestor into multiple species with different beak morphologies adapted to different food sources.
Q.58Hard
A population experiences a bottleneck reducing its size from 10,000 to 100 individuals. Which evolutionary consequence is MOST likely?
Answer: C
Bottlenecks drastically reduce population size, increasing genetic drift. Random allele loss occurs, reducing genetic variation and increasing chance of fixation.
Q.59Hard
In a X-linked trait, if the allele frequency of the recessive allele in males is 0.1, what is the allele frequency of the recessive allele in females at Hardy-Weinberg equilibrium?
Answer: B
For X-linked traits in males (hemizygous), allele frequency equals phenotype frequency. In females at equilibrium, the allele frequency is the same as in males: 0.1
Q.60Hard
A mutation changes a GC base pair to AT in a non-coding region of DNA. This mutation's evolutionary significance depends primarily on:
Answer: A
Mutations in non-coding regions vary in importance. Those in regulatory elements (promoters, enhancers) can be significant; most others are neutral.
