Video Transcript
Which plant tropism does
indoleacetic acid, IAA, play a major role in controlling? (A) Hydrotropism, (B) phototropism,
(C) aerotropism, or (D) neurotropism.
Indoleacetic acid, which is often
shortened to simply IAA, belongs to a group of chemical messengers, or hormones,
called auxins that play various roles in plants. IAA is produced mainly in the cells
of the apical bud, which is the top bud of the plant. Some of the numerous functions of
IAA are controlling growth by regulating cell division and elongation, sometimes in
response to certain stimuli such as light.
The directional growth response of
parts of an organism like a plant in response to light is called phototropism. IAA produced in the shoot tip
diffuses down the plant from cell to cell, stimulating cell elongation in the cells
below the apical bud and resulting in growth of the shoot in the direction of a
light source. You might have seen the prefix
photo-, which means light, in other words that are relevant to plants, such as
photosynthesis. This is because plants require
light for photosynthesis, which is the process by which many plants make their own
food in the form of sugars like glucose.
The photosynthesizing parts of the
plant, like its shoot and any leaves that might be attached to it, will therefore
benefit from growing toward areas where more light is available through phototropism
so that they can capture more light and therefore synthesize sugars more
efficiently.
Now we know the correct answer to
this question. The plant tropism that IAA plays a
major role in controlling is (B) phototropism.
