Video Transcript
Auxins are a group of hormones
found in plants. Which of the following best defines
hormones? (A) Hormones are chemical
messengers that travel throughout an organism to act on target cells or organs. (B) Hormones are electrical signals
that travel throughout an organism via the nervous system to act on target cells or
organs. (C) Hormones are soluble
carbohydrates that communicate changes in stimuli between the external and internal
environments of an organism. Or (D) hormones are biological
catalysts that speed up the rates of chemical reactions without being used up.
To answer this question, let’s look
at what a hormone is and what it does. And to do this, we’re going to
remove the answer options for now. Hormones are chemical
messengers. And, as the question tells us, they
can be found in plants. Plants, like this one, do not have
nervous systems, so instead they need some kind of chemical messenger to send
signals around the body. These hormones can cause changes in
the organism’s body and can communicate between organs and tissues and allow them to
respond to their external environment.
Let’s take a look at a few of these
responses in plants. Hormones are responsible for
triggering blossoming of flowers, are responsible for pores on the leaves called
stomata to open and close and allow the exchange of gases. Hormones can even promote root
growth and the growth of the other parts of the plant too. In fact, some hormones can have
multiple effects in different areas of the plant. For this reason, hormones need to
be able to travel around the body of an organism to act on target cells where
they’re needed.
Let’s bring back all our answer
options so we can eliminate those that we know are not correct and find our correct
answer. As we now know, plants do not
possess a nervous system, but plants do possess hormones. Therefore, we can eliminate option
(B), as if plants don’t have a nervous system, hormones can’t be electrical signals
that travel via a nervous system in a plant. The term biological catalyst is
used to describe a structure called an enzyme rather than a hormone. So option (D) is also
incorrect.
While option (C) does describe the
fact that hormones can communicate changes between an external and internal
environment of an organism, hormones are usually not carbohydrates. In fact, they’re most often derived
from proteins or lipids. So option (C) is also
incorrect. This leaves us with option (A),
which accurately describes hormones as chemical messengers that travel throughout an
organism to act on target cells or organs.
