Thanks for the A2A.
I'll start by saying that there is no "optimal" percentage of oxygen in air. At least, not for air in open spaces.
The sentence you refer to says: "So, as long as there is any oxygen (more than 0.1%), it is treated equally." This implies that the human body doesn't care how much oxygen there is when it's breathing at sea-level pressures. It neither needs more nor benefits from more. This is true of healthy people under normal conditions. Underwater divers need more than 21% oxygen, because water pressure makes it difficult to get enough oxygen into your lungs when you only breathe normal air.
Thanks for the A2A. I'll start by saying that there is no "optimal" percentage of oxygen in air—at least, not for air in open space. Oxygen content can be measured by taking a sample of air and measuring how much oxygen it contains, but this isn't really useful unless you're trying to measure how much gas you've got left in your tank or something like that (which makes more sense if you're thinking about diving).
What's more important than the ratio of oxygen to other gases is whether or not there's enough time between breaths for all those other gases to dissolve into your blood before you exhale again and let them out again. The answer is generally yes—if you keep breathing deeply enough so that all your blood circulates through your lungs every few seconds or so, then even if the atmosphere has very little oxygen compared with nitrogen or carbon dioxide (or whatever else), those other things will still get dissolved into your bloodstream at a rate equal to their flow rate through your alveoli on each breath-in cycle (this happens because gas exchange occurs across membranes).
The first thing you should know is that there's no such thing as an "optimal" percentage of oxygen in air. This is because the human body requires a certain amount of oxygen at all times, and it won't do you any good if your room is two percent full of pure O2 and 98 percent nitrogen. The level needed to sustain life changes depending on what you're doing: if you're sleeping or sitting still, then less oxygen suffices; but if you're exercising vigorously (or running from an approaching bear), then more may be required.
There are many processes we can think about when considering how much O2 our bodies need:
The recommended minimum safe partial pressure of oxygen in air for humans is 21%. Lower than that, and you're likely to experience hypoxia—a condition where the body does not get enough oxygen to function properly. If you've ever been at altitude, this is what happens when your body cannot adapt quickly enough to the decreased amount of oxygen around it.
If you're exposed to hypoxia, you may feel dizzy or confused, but those symptoms don't necessarily mean that your body isn't getting enough oxygen—your heart rate may be low and slow because all systems are going through a "slow down" period while they figure out how much energy they need to expend on each task at hand (i.e., walking). You'll also notice that it feels harder for your brain or muscles to think or move as fast as normal (especially if they're used regularly).
Oxygen is a basic requirement for life. The human body needs oxygen to survive and cannot survive without it. Oxygen is a gas that makes up about 21% of the air we breathe, and it is used in our bodies by cells to release energy from food and generate heat and chemical reactions necessary for life. Oxygen helps us breathe, digest food, fight disease, grow hair, produce energy inside cells (ATP), move muscles around your body, think clearly and stay active.
The sentence you refer to says "So, as long as there is any oxygen (more than 0.1%), it is treated equally." This implies that the human body doesn't care how much oxygen there is when it's breathing at sea-level pressures; only how much oxygen there is if you go higher than sea level.
So, as long as there is any oxygen (more than 0.1%), it is treated equally. You can see this in the following graph:
(source: https://www.quora.com/How-does-oxygen-affect-the-human-body)
Your body is more sensitive to oxygen levels at high altitudes. It needs higher oxygen levels at high altitudes, and lower oxygen levels at low altitudes. The amount of oxygen your body needs does not change as you move from one altitude to another.
The body does not need more than 21% oxygen. It is just fine with the amount of oxygen in its environment, and that is why it does not benefit from more oxygen.
In fact, your body will not function properly if it is exposed to an excess of 100% pure oxygen for too long. This can lead to a condition called hyperoxia, which includes symptoms such as dizziness or fainting. The reason behind this is that hyperoxia causes changes in the blood vessels and tissues of your body, resulting in reduced blood flow through these vessels and tissues. And since there’s less blood flowing through them when you have hyperoxia because there’s so much extra oxygen around to dilute the normal amount of air (which contains only around 21% oxygen), they become engorged with fluid – leading to swelling and discomfort or even pain!
The amount of oxygen in the air is about 20%. This is true of healthy people under normal conditions. When you are awake, your body uses up the oxygen that is delivered to it and so your blood has a lower than normal concentration of oxygen (it becomes hypoxic). To compensate for this, your body releases adrenaline which causes increased breathing rate and deeper breaths. As a result, more CO2 is expelled from the lungs and less O2 absorbed into them. So overall there's more CO2 within you than before (around 10-15% higher) but there's still not too much since our bodies have adapted to these new levels by changing their biochemical reaction rates accordingly; i.e., faster metabolic processes produce more CO2 per unit time than slower ones do so we're still close enough to homeostasis here even though things look different biologically speaking on paper!
Oxygen is needed to support life. It's a gas that we breathe in to fuel our bodies and brains. Oxygen is required for the body to burn carbohydrates—that means, it helps us move around and think clearly. It's also what keeps your lungs working properly so you can breathe on land or underwater without any trouble.
Oxygen is also used by the nervous system, which controls all of your body's functions; without it, you wouldn't be able to feel anything! And lastly but not leastly (I just made up a word), oxygen plays an important role in the immune system: without this gas running through your veins like blood does, bacteria would have no problem taking over your body and making it their home for eternity.
As a chemical element, oxygen is a colourless and odourless gas. It's the third most abundant element in the universe, only behind hydrogen and helium. It makes up 20% of Earth's atmosphere by volume, but is not as abundant on land as it is in seawater.
Oxygen is necessary for life to exist, but it can be dangerous when too much oxygen comes into contact with human skin or lungs. The reason for this is because too much free (uncombined) oxygen will react with other elements within your body's cells which can result in organ damage if exposed long enough!
The main takeaway from this is that the body needs oxygen to live, but it doesn't need much. The human body can get by with as little as 0.1% of oxygen in air, and some people have been recorded living for several minutes after being placed in an environment with no oxygen at all (this was during experiments).