Video Transcript
Which of the following is not a
stimulus that plants can respond to with some form of movement? (A) A new light source, (B) an
increase in soil moisture, (C) gravity, or (D) changes in atmospheric pressure.
The directional growth or movement
responses of an organism like a plant either toward or away from stimuli are called
tropisms. Let’s take a look through the
answer options and see if they are stimuli that plants can respond to, starting with
option (A), a new light source.
The growth movement of a plant in
response to a light stimulus is called phototropism, which we can remember as the
prefix photo- means light. For example, if a plant stem
receives a light stimulus from only one side, it will grow toward the direction of
light. As light is a stimulus that plants
can respond to with movement, option (A) is incorrect.
Option (B) suggests that an
increase in soil moisture will stimulate the movement of a plant. The roots of many plants tend to
grow toward water, or moisture, in soil through a process called hydrotropism. We can remember this name as the
prefix hydro- means water. As water is a stimulus that plants
can grow toward, option (B) is also incorrect.
Option (C) suggests that plants can
move in response to gravity. Geotropism, or gravitropism,
describes the movement of a plant in response to gravity, which is often observed in
the downward growth of plant roots. So this option can also be
eliminated.
Option (D) suggests that plants
might be able to move in response to changes in atmospheric pressure. Plants don’t require a specific
atmospheric pressure to grow, and a change in atmospheric pressure won’t affect the
movement of plants.
As we are looking for an answer
that is not a stimulus plants can respond to, this means that we have found the
correct answer. The answer choice that is not a
stimulus that plants can respond to with some form of movement is (D), changes in
atmospheric pressure.
