|I am trying to understand if plants and animals
use the water that is released in the process of
I am teaching a class and I want to better
understand what happens to the “waste” water. |
|Question Date: 2019-01-02|
Great question. Certainly, metabolic water is
put to use. It's not as if organisms have plumbing
systems to get rid of it. Water is water--the
source is not important. It's interesting to note
that some desert mammals rely almost exclusively
on such water. In other words, they never have
to actually drink water--they manufacture it.
It may be helpful to remember that the water
is made inside the cell. Whether it stays in
the cell or goes into the surroundings (whether
that’s extra-cellular fluid in multicellular
organisms, or the environment in unicellular
organisms) depends mostly on osmosis and
transport mechanisms. For example, a plant’s
roots depend on cellular respiration because
they’re never exposed to light. So they’re making
water. Excess water could be drawn up the plant’s
vascular system and be used by other plant cells,
or evaporate out of the stomata.
Terrestrial animals like us are usually losing
a lot more water than we manufacture, but the
idea is the same. Very active tissues may make
more water than they need. If they have a
circulatory system, the water will be transported
near tissues that are losing water due to
evaporation or other processes. Water can then
diffuse into those cells via osmosis.
Cool trivia—Kangaroo rats can live on metabolic
water and the occasional juicy root.
Thanks for asking. Your efforts to better
understand biology will benefit many students.
Yes - this is why you eat hard candy when in
deserts, because the waste water goes into your
metabolism. More generally, the chemical
reactions of respiration take place in an aqueous
environment, so the water just becomes part of
The water would go into the water cycle,
mostly as water vapor in our out-breaths and
liquid in our urine, with some in sweat and poop.
There, it would join all the other water and water
vapor and go into the water cycle. The picture is
As far as I can tell from the research I did,
any water that the cell
doesn’t need that is produced from aerobic
respiration is expelled.
the case of animals the water diffuses into the
blood stream and
excreted as water vapor in our breathes,
perspiration, or urine. In the
case of plants, the water is released through the
stomata. Although the
water is considered “waste,” it still has a
purpose. For example,
perspiration allows us to cool down, and
the water that is released from
plant’s stomata helps the plant suck up more
from the ground in a process called
However, I am not a biologist. This is just what I
concluded from various sources, so there may be
details which a
scientist who specializes in these topics would be
able to cover better.
Still, I hope I was able to help somewhat.
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