Plant shoots are positively
phototropic. What does this mean? (A) They grow toward a light
stimulus. (B) They grow away from bright
sunlight. (C) They reflect the majority of
the wavelengths of light. Or (D) they grow toward other
brightly colored plants.
When a plant is described as
positively phototropic, it means that it’s displaying a type of tropism called
phototropism, where the prefix photo- means light. A tropism is a growth movement
response. This means that we’re looking for
an answer option that’s describing a plant moving by growing towards or away from
something. So we can eliminate option (C), as
this does not describe a growth movement response.
As the movement response is in
response to a light stimulus, we can also eliminate option (D), as this is not
talking about the plants growing towards or away from light, rather towards or away
from brightly colored plants, which is not a thing that plants usually do. Different parts of a plant can
either be positively phototropic, which means that they grow towards a light
stimulus, or they can be negatively phototropic, which is growth away from a light
stimulus. Plant shoots and leaves contain the
majority of the photosynthesizing cells in a plant, which allows plants to make its
own food, essential for its survival.
Photosynthesis requires light. So it’s beneficial for the shoots
and leaves to grow towards light to access more of it for photosynthesis. Therefore, the shoots could be
described as positively phototropic, as they’re growing towards light. The plant’s roots, however, do not
require light as they don’t photosynthesize. So they’re negatively
phototropic. Therefore, the roots grow downwards
away from the source of light and towards the water and minerals in the soil. We’ve deduced that the shoots are
positively phototropic, as they grow towards a light stimulus.