eutrophication

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1) Remember, aerobic respiration ( Kreb cycle + electron transport chain) is not only limited to animal cells, it occurs with plants as well. O2 is reactant

2) However, like you stated, plants can also fix CO2 and H20 to produce carbohydrates via (photophosphorlyation + calvin's cycle). O2 is product

Thus, these two O2 consuming and producing biochemical pathways are always occurring in the plant cells. However, the balance between the two is dependent on the availability of certain precursors and the overall homeostatic state of the plant.

For example, plants are constantly respiring because that's their main way to produce ATP. However, they are not always producing carbohydrates to grow!

This imbalance, leads to step 1 occuring more often than step 2 and thus net O2 concentration will decrease and lead to hypoxia in the general vicinity.

The key to understanding this is that, all biochemical pathways are dynamic and are never completely off. There is always a shift in preference and this is due to many different types of regulations. E.g allosteric and covalent modification of key enzymes
 
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Wait so theyre using and creating O2, but theyre using more than theyre creating? What makes you say that?
 
How do you think plants get energy, ATP ?

They're constantly using and making O2. However, at night, carbohydrate production is limited due to less light being able to activate photosynthesis. This decreases the production of O2 and therefore you see a net decrease in O2 concentration.

In the case of algae blooms, they are using more O2 than they are producing. It all depends on the given concentration of certain metabolites and the homeostatic condition of the plants!

Nothing in living systems is black and white. Everything is dynamic and a balance between different biochemical pathways is paramount to the survival of an organism. That is why metabolic regulation is so important!
 
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How do you think plants get energy, ATP ?

They're constantly using and making O2. However, at night, carbohydrate production is limited due to less light being able to activate photosynthesis. This decreases the production of O2 and therefore you see a net decrease in O2 concentration.

In the case of algae blooms, they are using more O2 than they are producing. It all depends on the given concentration of certain metabolites and the homeostatic condition of the plants!

Nothing in living systems is black and white. Everything is dynamic and a balance between different biochemical pathways is paramount to the survival of an organism. That is why metabolic regulation is so important!
Great response thanks. 👍
 
I also have something to add. I just took a test on this a week ago, and another reason is that those algae proliferate, but then they also die and their corpse sink down. The bacteria in the sea feast on these algae corpses and proliferate, taking up O2 and releasing CO2. I'm talking about LARGE quantity of bacteria that suck up all available O2 in that region.
 
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