All Free Biology MCQs with Answers

871. Acetylcholine is broken down by

• A. Acetylcholinesterase
• B. Monoamine oxidase
• C. COMT
• D. Peptidase

Explanation: Acetylcholinesterase in the synaptic cleft rapidly breaks down acetylcholine to terminate the signal.

872. The sympathetic nervous system

• A. Decreases heart rate
• B. Causes fight-or-flight response
• C. Stimulates digestion
• D. Constricts pupils

Explanation: The sympathetic division mediates fight-or-flight responses: increased heart rate, dilated pupils, inhibited digestion.

873. Which neurotransmitter is inhibitory in the CNS?

• A. Glutamate
• B. GABA
• C. Dopamine
• D. Serotonin

Explanation: GABA (gamma-aminobutyric acid) is the main inhibitory neurotransmitter in the CNS, causing Cl- influx and hyperpolarization.

874. The cerebellum controls

• A. Memory
• B. Balance and coordination
• C. Heart rate
• D. Vision

Explanation: The cerebellum coordinates voluntary movements, balance, posture, and motor learning.

875. A reflex arc involves

• A. Only the brain
• B. Only the spinal cord
• C. Spinal cord and brain
• D. Receptor, spinal cord, effector

Explanation: A simple reflex arc involves receptor → sensory neuron → spinal cord integration → motor neuron → effector, without brain involvement.

876. Parkinson's disease involves deficiency of

• A. Serotonin
• B. Dopamine
• C. GABA
• D. Acetylcholine

Explanation: Parkinson's disease results from degeneration of dopaminergic neurons in the substantia nigra, causing tremors and rigidity.

877. The master endocrine gland is the

• A. Thyroid
• B. Adrenal
• C. Pituitary
• D. Pancreas

Explanation: The pituitary gland is called the master gland because its hormones regulate other endocrine glands.

878. Insulin is produced by

• A. Alpha cells
• B. Beta cells
• C. Delta cells
• D. Acinar cells

Explanation: Beta cells of the pancreatic islets produce insulin in response to high blood glucose.

879. Thyroid hormones regulate

• A. Only growth
• B. Basal metabolic rate
• C. Only blood pressure
• D. Only digestion

Explanation: T3 and T4 regulate basal metabolic rate (BMR), growth, development, and body temperature.

880. Cortisol is produced by

• A. Adrenal medulla
• B. Adrenal cortex
• C. Anterior pituitary
• D. Thyroid

Explanation: Cortisol (a glucocorticoid) is produced by the adrenal cortex, especially in response to stress.