All Free Biology MCQs with Answers

961. Synovial joints are characterized by

• A. No movement
• B. Presence of synovial fluid
• C. Cartilage only
• D. Fibrous capsule only

Explanation: Synovial joints (freely movable) contain synovial fluid for lubrication and nutrition of articular cartilage.

962. Osteoblasts are

• A. Bone-destroying cells
• B. Bone-forming cells
• C. Mature bone cells
• D. Fat cells in bone

Explanation: Osteoblasts are bone-forming cells that secrete collagen and matrix, later becoming osteocytes.

963. Ligaments connect

• A. Muscle to bone
• B. Bone to bone
• C. Muscle to muscle
• D. Cartilage to cartilage

Explanation: Ligaments connect bone to bone, providing joint stability. Tendons connect muscle to bone.

964. Rigor mortis occurs due to

• A. Excess ATP
• B. Lack of ATP
• C. Excess calcium
• D. Lack of calcium

Explanation: Without ATP, myosin heads cannot detach from actin, causing persistent muscle contraction (rigor mortis).

965. The A-band contains

• A. Only actin
• B. Only myosin
• C. Both actin and myosin
• D. Neither

Explanation: The A-band (dark) contains the entire length of myosin filaments and overlapping actin filaments.

966. Kidneys perform their osmoregulatory role under the effect of Antidiuretic Hormone, which type of urine is produced in this situation?

• A. Hypotonic urine with decreased volume
• B. Hypotonic urine with increased volume
• C. Hypertonic urine with decreased volume
• D. Hypertonic urine with increased volume

Explanation: ADH makes the distal tubule and collecting duct permeable to water, so water is reabsorbed into the salty medulla and a small volume of concentrated urine leaves. Concentrated means hypertonic, and reabsorbing water necessarily reduces the volume, so the two halves of the answer must move together. Hypotonic urine of large volume is what appears when ADH is absent, as in diabetes insipidus.

967. Which part of brain controls transition between sleeping and wakefulness?

• A. Medulla oblongata
• B. Cerebellum
• C. Cerebrum
• D. Pons

Explanation: The pons contains the centres that switch the brain between sleep and wakefulness and it also regulates the rhythm of breathing alongside the medulla. The medulla is the tempting answer because it too is part of the brain stem, but its role is the automatic control of heart rate, breathing and blood vessel diameter. The cerebellum handles balance and coordination and takes no part in the sleep cycle.

968. Which part of the brain contains central chemoreceptors that monitor CO2 levels in blood?

• A. Pons
• B. Midbrain
• C. Hypothalamus
• D. Medulla oblongata

Explanation: The respiratory centre of the medulla carries chemoreceptors that detect the fall in pH caused by rising carbon dioxide and increase the rate and depth of breathing until the excess is blown off. Oxygen level is monitored elsewhere, by peripheral receptors in the aorta and carotid arteries, and acts only as a weak backup stimulus. This is why holding the breath becomes unbearable from carbon dioxide build up rather than from lack of oxygen.

969. Which component of a reflex arc connects the sensory neuron to the motor neuron within the spinal cord?

• A. Receptor
• B. Effector
• C. Muscle fiber
• D. Associative neuron

Explanation: The associative or relay neurone sits in the grey matter of the spinal cord and passes the impulse straight from the sensory to the motor neurone, which is what allows the response to happen before the brain is even informed. The receptor detects the stimulus at the start of the arc and the effector, usually a muscle or gland, produces the response at the end. A muscle fibre is part of the effector rather than a link in the pathway.

970. The 9:3:3:1 ratio of law of independent assortment can be affected by

• A. Genetic drift
• B. Small population
• C. Gene linkage
• D. Gene duplication

Explanation: Independent assortment requires the two genes to be on different chromosomes, so genes linked on the same chromosome travel together and the dihybrid ratio departs from 9:3:3:1, with parental combinations over represented. Genetic drift and small population size shift allele frequencies across generations rather than distorting the ratio within a single cross. Crossing over partly restores the expected ratio by separating linked genes.