How does earth maintain a constant level of oxygen?

It doesn’t! the oxygen level of the planet has varied quite dramatically in the last 500 million years ago; as the climate cooled and the land plants died off, oxygen level fell to as low as 12 percent by the beginning of the triassic. Back then, the air at sea level would have felt thinner than at the top of the Alps today.

Burning fossil fuels has reduced oxygen levels very slightly  - about 0.057 percent over the last 30 years. Deforestation only has a small effect because when rainforest is cut down, other plants are usually grown in its place. But it’s marine plankton, rather than trees, that produces about 70 percent of atmospheric oxygen. Global warming will have a significant impact on plankton, which is a much more serious threat to oxygen levels.

DOES  PHOTOSYNTHESIS  OCCURS WHEN  MOONLIGHT  SHINES  ON  A PLANT?

Photosynthesis uses the energy from sunlight to convert carbon dioxide (CO2) and water into glucose and oxygen. Some of this glucose is used to build plant cells and some is converted back into CO2 and water to provide energy for the plant’s metabolism. The light from a full Moon on a clear night is only about one sixthousandth the brightness of an overcast day, but photosynthesis reactions will still occur, just 6,000 times more slowly. This is too slow to be useful to the plant because it will actually gain less CO2 from photosynthesis than it loses from the respiration of its cells. As the Sun rises each day, photosynthesis becomes more and more effective until the plant absorbs just enough CO2 to keep up with the amount burned for energy. This is called the ‘compensation point’ and it occurs in the early morning and then again in the late evening as the light levels drop again. Outside of these times, photosynthesis isn’t useful to the plant and many plants close their leaves at night so it doesn’t disrupt the circadian rhythms that control flowering.

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WHY  DOES  LACTIC  ACID  BUILD  UP  IN  MUSCLE?

During aerobic exercise our muscle ‘burn’ glucose with oxygen to produce carbon dioxide, water and energy. But when we are exercising hard, the lungs can’t keep up with the muscles’ demand for oxygen. Rather than just giving up, our muscle switch to an anaerobic chemical chemical reaction that doesn’t need oxygen.

This is less efficient because it doesn’t produce as much as enegy per molecule of glucose burned, but it’s better than nothing. Unfortunately, instead of water and carbon dioxide, anaerobic respiration produces lactic acid as one of it’s waste products. If you exercise hard, this will be produced faster than your bloodstream can transport it away to your liver where it is processed and broken down.

As the level of acid builds up in your muscles, you feel a burning sensation that acts as a warning that your muscle are almost out of energy. Like other sorts of pain, the ‘purpose’ is to signal that your body needs to rest. So, next time you go for a run bear your overworked body a thought and maybe catch your breath.