All Free Biology MCQs with Answers

651. Compared with blood in the renal artery, blood leaving the kidney in the renal vein contains

• A. less urea and less oxygen
• B. more urea
• C. more glucose than normal
• D. no red blood cells

Explanation: The kidney removes urea into urine and consumes oxygen for its active transport, so both fall in the outflowing blood. Glucose is conserved, and red cells never leave the vessels.

652. Urine is stored before elimination in the

• A. kidney
• B. urinary bladder
• C. ureter
• D. gall bladder

Explanation: The bladder is a muscular bag that stretches to hold several hundred millilitres until micturition. The gall bladder stores bile, a similarly named but unrelated job.

653. The normal body temperature of a healthy human is maintained at about

• A. 25 degrees Celsius
• B. 30 degrees Celsius
• C. 37 degrees Celsius
• D. 42 degrees Celsius

Explanation: Enzymes of the body work best near 37 degrees, and the hypothalamus holds temperature within a degree of this set point. Sustained values several degrees away in either direction are dangerous.

654. Animals such as fish and reptiles, whose body temperature changes with the environment, are called

• A. endotherms
• B. homeotherms
• C. warm blooded animals
• D. ectotherms

Explanation: Ectotherms gain heat from outside sources and so track ambient temperature, whereas endotherms generate their own heat metabolically. Cold blooded is the older term for the same idea.

655. On a cold day, the arterioles supplying the capillaries of the skin

• A. constrict, reducing heat loss from the surface
• B. dilate widely to warm the skin
• C. burst under pressure
• D. stop carrying blood altogether

Explanation: Vasoconstriction keeps warm blood in the core, which is why skin looks pale in the cold. Dilation happens in heat to dump warmth, the opposite response to the opposite stimulus.

656. A lizard basking on a rock in the morning sun is demonstrating

• A. shivering thermogenesis
• B. behavioural thermoregulation
• C. chemical heat production
• D. evaporative cooling

Explanation: Since reptiles cannot raise temperature metabolically, they move between sun and shade to manage it. Behaviour is their thermostat, whereas mammals mostly adjust internally.

657. The layer of fat beneath the skin of mammals helps control temperature by

• A. producing heat through metabolism
• B. increasing blood flow to the surface
• C. insulating the body against heat loss
• D. absorbing sunlight

Explanation: Subcutaneous fat conducts heat poorly, so it keeps core warmth in, which is why marine mammals carry thick blubber. Generating heat is the job of metabolism in liver and muscle, not of fat.

658. A dog cools itself by panting because

• A. panting draws cold air into the lungs
• B. dogs sweat heavily from the skin
• C. panting raises the metabolic rate
• D. evaporation from the tongue and airways removes heat

Explanation: With few sweat glands, dogs rely on evaporating water from the moist surfaces of the mouth and lungs. Rapid shallow breathing maximises this evaporation without disturbing blood gases.

659. The control of body temperature by the hypothalamus is an example of

• A. negative feedback
• B. positive feedback
• C. hormonal rhythm
• D. conditioned reflex

Explanation: Any deviation from the set point triggers responses that reverse it, the defining feature of negative feedback. Positive feedback amplifies change, as in childbirth, and would be useless for stability.

660. At rest, most of the heat of the human body is produced by the

• A. brain
• B. liver and other metabolically active organs
• C. skin
• D. bones

Explanation: The liver's constant metabolism releases enough heat at rest to dominate body warmth, while during hard exercise skeletal muscle takes over as the main source. The skin loses heat rather than making it.