Video Transcript
Which of the following best
explains how legumes, a type of plant, use movements to utilize light–dark
cycles? (A) Legumes will move their leaves
to ensure that they always grow toward the Sun. (B) Legumes will move their leaves
to close them at night and open them during the day. Or (C) legumes will actively move
their roots to find areas with more sunlight.
Legumes are a family of plants,
commonly referred to as pulses, that produce important agricultural products, such
as beans, lentils, and peas. These plants exhibit a variety of
interesting movements. Let’s explore the movements that
legumes can exhibit in response to light–dark cycles in order to answer our
question.
Legumes, and some other plants,
have photoreceptors that can sense changes in light intensity. During the day, their leaves are
open and upright. As night approaches and the
photoreceptors detect a decrease in light intensity, their leaves may close up and
their stems may droop. When light intensity increases
again as daylight approaches, the leaves tend to return to their normal upright
position. This movement response of legumes
to light-dark cycles is called nyctinasty. The prefix nyct- refers to night,
and the suffix -nasty refers to a nondirectional movement response.
We call these kinds of responses
nondirectional, as they are independent of the direction of the stimulus. This means that regardless of where
the light stimulus arrives from, the leaves always open or close up, and the stems
rise or droop in the same manner.
Now, we can explain how legumes use
movements to utilize light–dark cycles and therefore answer this question. The correct answer is (B). Legumes will move their leaves to
close them at night and open them during the day.
