Video Transcript
Which of the following is correct
about plant shoots? (A) Plant shoots are positively
phototropic and negatively gravitropic. (B) Plant shoots are negatively
phototropic and positively gravitropic. (C) Plant shoots are negatively
hydrotropic and positively gravitropic. Or (D) plant shoots do not display
any major tropisms.
The answer options in this question
provide us with different examples of tropisms that can be carried out by
plants. A tropism is the response of an
organism like a plant to grow toward or away from a stimulus. Remember, a stimulus is any
detectable change in an organism’s internal or external environment that can trigger
an effect in that organism. A tropism can either be positive or
negative. While a positive tropism is the
response of an organism to grow toward a stimulus, a negative tropism is the
response of an organism to grow away from a stimulus.
Let’s take a look at plant shoots
and the different tropisms they can display. Plant shoots and leaves contain the
majority of the photosynthesizing cells in a plant. Photosynthesis is the process by
which plants use light and inorganic materials to make their own food. As this process requires light,
which is usually provided by the Sun, plant shoots tend to grow toward the direction
where most sunlight is available. This is an example of a tropism,
specifically termed phototropism, as the prefix photo- means light. As the plant shoot is growing
toward the light stimulus, it is a positive tropism.
Learning this information allows us
to eliminate answer option (B) that states that plant shoots are negatively
phototropic, which we now know is incorrect. We can also rule out answer option
(D), as we know that the plant shoots do show at least one major tropism, and this
option suggests otherwise.
A gravitropic response is the
movement of an organism in response to a different stimulus, gravity. As the roots of the plants tend to
grow downward toward the pull of gravity to access more water and minerals deeper in
the soil, they can be described as positively gravitropic. However, this question concerns the
plant shoots, not the plant roots. As plant shoots are usually
observed to grow upward against the pull of gravity, plant shoots are actually
negatively gravitropic. This means we can eliminate answer
option (C), suggesting that the shoots are positively gravitropic, which we now know
is incorrect.
This leaves answer option (A),
which appropriately describes two tropisms that are often displayed by plant
shoots. Plant shoots are positively
phototropic and negatively gravitropic.
