Video Transcript
Complete the following
statement. The response of a plant to grow in
the direction of gravity is known as blank. (A) Gravitropism, (B) hydrotropism,
(C) thigmotropism, or (D) phototropism.
In order to answer this question
correctly, we first need to understand what tropisms are. Plants are living organisms. And like almost all living
organisms, they need to move. While these movements, which are
usually fairly slow, often go undetected, plants can respond to a wide range of
stimuli, such as light, water, gravity, and even touch.
One of the reasons that plants move
so slowly is that many of their movements require them to grow. The movement of organisms like
plants to grow toward or away from a stimulus is known as a tropism. And there are different types of
tropism depending on what the stimulus is. Tropisms can also be described as
being positive or negative when the plant moves toward or away from a stimulus,
respectively. For example, when a plant’s shoots
and leaves grow toward a light source, they can be described as being positively
phototropic, as phototropism is the word that describes an organism moving in
response to light.
However, we are looking for an
answer that describes the movement of a plant in response to gravity, not to light,
so we can eliminate answer choice (D), phototropism.
When a plant, or a part of the
plant, grows in response to gravity, it is known as gravitropism or sometimes
geotropism. “Gravi” is a shortened version of
gravity, and the prefix geo- refers to the Earth or ground. So gravitropism, or geotropism, is
the growth movement of an organism like a plant in response to the pull of
gravity.
Plants often display both positive
and negative gravitropism. Plant shoots tend to grow upward
against the pull of gravity and so can be described as being negatively gravitropic,
which is important for the parts of the plant that need to seek light for
photosynthesis. In contrast, plant roots can
usually be described as being positively gravitropic. The roots tend to grow down toward
the pull of gravity, which helps them to come into contact with water and minerals
that can usually be found deep in the soil.
Now that we understand what
tropisms are and how gravitropism works we can complete the statement. The response of a plant to grow in
the direction of gravity is known as (A), gravitropism.
