IMO Practice Test — Control and Coordination
6 Questions • 15 min • Olympiad level
15:00
Question 1 of 6
In a reflex like pulling away from a pin-prick, the brain learns about the event only AFTER the hand is withdrawn because:
The spinal cord handles the reflex quickly, then informs the brain
The brain is switched off
There are no nerves to the brain
Reflexes never reach the brain
Explanation: Reflexes are processed by the spinal cord for speed; the brain is informed afterwards.
Question 2 of 6
Auxin causes a shoot to bend towards light because it:
Collects on the shaded side and makes those cells grow longer
Stops all growth
Is made only in roots
Destroys the lit side
Explanation: Auxin gathers on the shaded side, lengthening those cells, so the shoot bends towards light.
Question 3 of 6
Just before an exam, a student's heart races and palms sweat. This is mainly due to:
Adrenaline preparing the body for 'fight or flight'
Insulin lowering blood sugar
Auxin
Thyroxine deficiency
Explanation: Adrenaline from the adrenal gland prepares the body for stress (fight-or-flight).
Question 4 of 6
A person with very low thyroxine may feel tired and gain weight because thyroxine controls the body's:
Rate of metabolism
Reflexes
Reproduction only
Blood clotting
Explanation: Thyroxine controls metabolic rate; too little slows metabolism, causing tiredness and weight gain.
Question 5 of 6
Why do plants rely on hormones rather than a nervous system for coordination?
They have no nerves or muscles; chemical signals diffuse to cause growth responses
Hormones are faster than nerves
Plants do not respond to stimuli
Plants have a brain
Explanation: Lacking nerves and muscles, plants coordinate through slow chemical (hormonal) signals that alter growth.
Question 6 of 6
Both the nervous system and hormones coordinate the body, which shows that the two systems:
Work together, each suited to fast or long-lasting control
Never interact
Do the same job identically
Are both very slow
Explanation: Fast nervous control and slower, lasting hormonal control complement each other to coordinate the body.