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I am trying to understand if plants and animals use the water that is released in the process of aerobic respiration? I am teaching a class and I want to better understand what happens to the “waste” water.
Question Date: 2019-01-02
Answer 1:

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.

Answer 2:

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.

Answer 3:

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 solvent.

Answer 4:

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 from noaa.gov water cycle

Answer 5:

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.

In 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 water-soluble nutrients from the ground in a process called transpiration.

However, I am not a biologist. This is just what I gathered and 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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