Video Transcript
The graph provided shows how the
shaded and illuminated sides of the tip of a plant stem change over time. How will this affect the growth of
the plant? (A) The plant will grow toward the
light source. (B) The plant will grow away from
the light source. (C) The plant will grow
irregularly, which will stunt its development. Or (D) there will be multiple side
shoots.
Let’s start by taking a careful
look at this graph so we can answer the question. The 𝑥-axis represents time,
measured in minutes, and the 𝑦-axis represents a length increase in the cells in
the stem tip, measured in millimeters. Therefore, the graph shows the
growth over a short space of time of the two different sides of the tip of a plant
stem: one that is illuminated by light and one that is not. We can see pretty clearly that the
side of the stem that is shaded and not illuminated by light grows a lot more than
the side that is illuminated.
What happens if one side of a plant
stem is growing faster than the other side? If cells on one side of the stem
elongate while the cells on the other side do not grow as fast, the stem begins to
bend away from the direction of the elongating cells. This is because upward growth is
restricted by the cells that are not elongating so much. As the cells on the shaded side of
the stem are lengthening comparatively more than the cells on the illuminated side,
the stem bends toward the source of illumination. This is how plants are able to grow
toward light, through a process called phototropism. We can deduce that the differences
in growth between the shaded and illuminated sides of a plant stem, which have been
illustrated in the graph, cause it to grow toward a source of light.
So, the correct answer to this
question is (A). The plant will grow toward the
light source.
