- Why do we need oxygen?
- What happens to a fire if it doesn't get enough oxygen?
- Is there the same amount of oxygen everywhere?
Oxygen is needed for burning
Oxygen is a gas in the air that participates in many natural processes.
Do a simple experiment. You'll need a candle, matches, water, a glass bowl, and an empty glass.
- Light a candle and attach it to the bottom of the bowl with melted wax.
- Pour water into a bowl, but do not immerse the candle. To see the effects better, you may add some food colouring or ink into the water.
- Put the glass upside down on the burning candle.
- Watch the changes that happen under the glass closely.
Oxygen is needed for burning. The candle burns until the air under the glass runs out of oxygen. It is said that nature does not tolerate empty space. This is also true here. Instead of the oxygen used up, water is pushed in between the edges of the glass by air pressure. Therefore, the water level under the glass rises higher than outside.
But why did the inner surface of the glass become foggy? Burning releases light, heat, carbon dioxide, and water vapour. Usually, we do not notice the release of carbon dioxide or water vapour, but water vapour accumulated as a mist on the glass in the experiment with a candle. You can also see the release of water vapour if you throw raw wood or wet hay into a fire. They contain more water than dry material, and a smoke column rises from the campfire. The main part of it is water vapour, in which the water particles have joined into water droplets and are therefore visible to the naked eye.
If there is not enough oxygen, toxic carbon monoxide can also be formed during burning. The wood-burning stove must therefore be carefully monitored to allow air to enter throughout the burning. The stove damper must not be closed until the logs have completely burned away! Carbon monoxide causes headaches, fatigue, difficulty breathing and other problems because the body does not get enough oxygen. Large amounts of carbon monoxide can even be life-threatening.
Bonus: Experiment with mice
In science's history, there was once a tragic experiment with two mice. One was placed under a glass dome with a large plant. The glass dome of the second mouse was left empty. After a while, both of the mice died. However, the mouse that was accompanied by a plant lived longer.
The cause of death was the same in both cases: oxygen ran out under the dome. But why did the mouse live longer under the glass dome with the plant? It was concluded that plants could produce oxygen.
This experiment is as cruel as any animal torture. Today, attempts are made not to cause unnecessary suffering to animals. However, some scientific issues are challenging to solve without harming animals. For example, the medicines are tested on animals before humans can use them, and it's difficult to get it right.
Living things need oxygen
Both plants and animals, including humans, need oxygen. They get it from the air. Oxygen is needed by living things to break down nutrients to release energy - this process is called respiration. Energy is used for all activities: movement, growth, digestion, heart function, and more. In addition to releasing energy, respiration produces carbon dioxide and water. Respiration is like burning, though one difference between respiration and burning is that no light is emitted when breathing.
- Energy is released from oxygen.
- Oxygen makes the heart pump.
- Oxygen is needed to break down nutrients.
Oxygen is also needed to decompose dead organisms
When plants and animals die, their bodies begin to decompose at different rates. For example, most of the fallen tree leaves have already disappeared by the following autumn, but it may take decades for the fallen tree trunks to rot. Dead animals decompose much faster than plants. Decomposition is essential in nature: otherwise, the remains of dead organisms would soon cover the whole of the Earth. Many organisms, mainly fungi and bacteria, help with decomposition. They use oxygen for decomposing the dead organisms, and during decomposition, more complex substances become simpler. The end products of decomposition are carbon dioxide and water - just like in combustion and respiration. Decomposition also releases nutrients and other soil components necessary for plants.
Think!
- Why is the decomposition of dead organisms important?
- Who helps the plants to decompose in and on the soil?
Sometimes there is not enough oxygen in the air
Usually, there is enough oxygen in the air around us, but sometimes in specific conditions, there is not enough oxygen in the air– then it is difficult to breathe. Oxygen deficiency can happen at high altitudes in the mountains, as the air is thinner there. Mountaineers must practice in camps at lower altitudes to get used to having less oxygen around before climbing higher. Not all people can cope with such conditions and might become ill– even outstanding mountaineers sometimes get ill in the mountains.
Sometimes if there are many people in a small room (i.e. a classroom!), they might use up a big part of the oxygen. Then they might get sleepy, and their brain does not work as well as it could. That is why it is important to open the windows during the breaks!
- There is less oxygen in the high mountains and not everyone's body adapts to it.
- There is so little oxygen that a fire cannot burn. You can't boil water and cook food and this might lead to hunger.
Bonus: Ozone layer
An oxygen molecule consists of two oxygen atoms. A molecule that consists of three oxygen atoms is called ozone. There is very little ozone in the air near the ground - in large quantities, this substance would be toxic to humans and other organisms. However, ozone plays a critical role in the higher atmosphere: it protects life on Earth from too much solar radiation.
The ozone molecule is easily broken down by several chemicals released into the air by humans. Due to air pollution, the amount of ozone in the atmosphere has decreased. This, in turn, means that being exposed to direct sunlight has become more dangerous than before: it can cause skin cancer.
So-called ozone holes have also been discovered in the ozone layer. These are places where the ozone layer is severely damaged. Ozone holes are mostly located above the poles because the atmosphere is thinner there compared to the equator.
Important terms
- respiration – the process of breaking down nutrients using oxygen
- decomposition – the process of breaking complex substances down into more simple particles
- ozone layer – the layer of ozone in the atmosphere that protects us from the harmful solar radiation
- carbon monoxide – a toxic gas that is produced when there is not enough oxygen for proper combustion
I now know that…
Oxygen is a gas that living organisms need for respiration. Oxygen is also needed for combustion and decomposition. In high mountains, oxygen is more sparse because the air is thinner, making it harder to breathe.
