Zoology in NEET is memory heavy but not memory only, because the diagram based and assertion reason questions need understanding. This set runs through human physiology, animal kingdom and classification, structural organisation, genetics and evolution, biotechnology, and ecology. Explanations point to the NCERT line the question came from, so revision stays anchored to the source text.
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.
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.
