IMO Practice Test — Plant Growth and Development
6 Questions • 15 min • Olympiad level
15:00
Question 1 of 6
Removing the shoot tip of a plant makes the side branches grow more. This is because the tip normally supplies:
Auxin, which causes apical dominance
Ethylene, which ripens fruit
ABA, which closes stomata
Cytokinin only
Explanation: The tip's auxin suppresses lateral buds; removing it releases the side branches to grow.
Question 2 of 6
Storing unripe bananas with a ripe apple speeds up their ripening because the apple releases:
Ethylene gas
Auxin
Abscisic acid
Gibberellin
Explanation: Ripe fruit releases ethylene, a gaseous hormone that triggers ripening in nearby fruit.
Question 3 of 6
During a drought, a plant's stomata close mainly due to a rise in:
Abscisic acid
Auxin
Gibberellin
Cytokinin
Explanation: ABA, the stress hormone, accumulates in water stress and closes stomata to conserve water.
Question 4 of 6
A short-day plant kept under long days will most likely:
Fail to flower
Flower earlier
Die immediately
Grow no leaves
Explanation: Short-day plants need short days (long nights) to flower; long days prevent flowering.
Question 5 of 6
Winter wheat sown in spring without a cold spell does not flower well. This shows the need for:
Vernalisation
More auxin
Less light
Higher temperature
Explanation: Such varieties require a cold period (vernalisation) before they can flower.
Question 6 of 6
The fact that a single plant can grow differently shaped leaves underwater and in air illustrates:
Plasticity
Apical dominance
Vernalisation
Senescence
Explanation: Changing form in response to the environment is plasticity (heterophylly is one example).