Video Transcript
Plant roots are positively
gravitropic; what does this mean? (A) They are positively attracted
to soil. (B) They grow away from other plant
roots. (C) They grow toward the direction
of gravity. Or (D) they grow in the opposite
direction to sunlight.
To answer this question, we need to
investigate what it means for plant roots to be positively gravitropic. While some people might think that
plants are fairly immobile organisms, many of them can actually move in response to
a wide range of different stimuli: water, light, touch, and even the pull of
gravity.
Gravitropism, which is sometimes
called geotropism, contains the prefix gravi-, indicating that this word describes a
response to gravity. The suffix -tropism describes a
growth movement response of an organism like a plant either toward or away from a
particular stimulus. Using this information, we can work
out that gravitropism is the movement of an organism in response to gravity. While positive gravitropism is
growth toward the pull of gravity, negative gravitropism is growth away from the
pull of gravity.
This question specifically asks us
about gravitropic responses in a plant’s roots. Do you think that plant roots will
grow toward the pull of gravity or away from the pull of gravity? The main function of a plant root
is usually to absorb water and minerals, which tend to be found deeper in the
soil. This is why plant roots tend to
grow downward into soil toward the direction of gravity through positive
gravitropism, a response which is so strong that this will happen even when the
plant is turned on its side.
We can see that the answer choice
that correctly describes the meaning of plant roots being positively gravitropic is
(C). They grow toward the direction of
gravity.
