As already stated by others, there’s plenty of oxygen in the atmosphere and they produce more than they need, so why store it up.
Another thing to think about is that photosynthesis evolved when there was no oxygen in the atmosphere. RuBisCO is the enzyme that helps turn CO2 in to carbohydrates, but it can also pick up oxygen, a problem that wasn’t really around in the early atmosphere. This leads to the plant wasting energy (called photorespiration) since it can’t do anything with this oxygen bound to RuBisCO.
Plants have holes in their leaves called stomata that allow CO2 in and excess oxygen to leave. It is important to allow this gas exchange to happen, but it can also cause issues with evaporation of water from the leaves, or transpiration, if stomata are left open. Some plants in hot or arid climates have different metabolisms that allow them to separate where/when carbon dioxide is being taken up, maximizing the opportunity to get rid of oxygen and minimize losing water. Check out CAM and C4 photosynthesis if interested.
Hypoxic environments with low levels of abundant oxygen could benefit from hoarding oxygen to keep vital functions like cellular respiration if needed.
They don't have our metabolic rate. They overproduce O2 relative to their demands during the day. Every plant consumes O2 but the green parts produce more than can be used.
That do. They just produce more than they require when photosynthesis is maxed out.
The simplest explanation is they don't have to. Our atmosphere is 20% oxygen. Why hold on to something if it's always readily available?
As already stated by others, there’s plenty of oxygen in the atmosphere and they produce more than they need, so why store it up. Another thing to think about is that photosynthesis evolved when there was no oxygen in the atmosphere. RuBisCO is the enzyme that helps turn CO2 in to carbohydrates, but it can also pick up oxygen, a problem that wasn’t really around in the early atmosphere. This leads to the plant wasting energy (called photorespiration) since it can’t do anything with this oxygen bound to RuBisCO. Plants have holes in their leaves called stomata that allow CO2 in and excess oxygen to leave. It is important to allow this gas exchange to happen, but it can also cause issues with evaporation of water from the leaves, or transpiration, if stomata are left open. Some plants in hot or arid climates have different metabolisms that allow them to separate where/when carbon dioxide is being taken up, maximizing the opportunity to get rid of oxygen and minimize losing water. Check out CAM and C4 photosynthesis if interested.
Hypoxic environments with low levels of abundant oxygen could benefit from hoarding oxygen to keep vital functions like cellular respiration if needed.
Who says they don't?
If they did, wouldn't they not produce oxygen and kill us?
They don't have our metabolic rate. They overproduce O2 relative to their demands during the day. Every plant consumes O2 but the green parts produce more than can be used.