Respiration 01
Air can enter and leave the lungs because of pressure changes.

Respiration 01

This KS3 Science asks questions on respiration. Breathing is also referred to as respiration. This can be a bit confusing because in schools, we also use the word respiration to describe the release of energy in living cells (it should really be called cellular respiration but that's a bit of a mouthful!).

Breathing is the process by which animals with lungs move air into and out of their respiratory system. This enables their bodies to extract oxygen from the air and to return carbon dioxide to the air. The air is a mixture, mainly nitrogen (78%) and oxygen (21%) with about 1% of other gases including argon, water vapour and carbon dioxide. During respiration, air from outside of the body enters the respiratory system through the nose and mouth (it's better through the nose as it warms and filters the air) and passes down the windpipe (trachea).

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The bottom of the windpipe is split into two bronchi which direct the air into the two lungs. Inside of the lungs, the bronchi are divided into lots of even smaller tubes called bronchioles. These end in air sacs (alveoli) which are covered in blood capillaries. This is where oxygen gets into the bloodstream and the waste carbon dioxide gets out.

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  1. The percentage of oxygen in the air breathed in is .......
    That's about one fifth
  2. The percentage of oxygen in the air breathed out is .......
    It is a common misunderstanding to think that all of the oxygen that goes into the lungs is taken into the body. If it was, mouth to mouth resuscitation would not be possible
  3. The percentage of carbon dioxide in inhaled air is how much?
    There is only a very small percentage of carbon dioxide in the air but it is enough to create a greenhouse effect that keeps the Earth warm enough to support life. Since the middle of the twentieth century, the percentage of carbon dioxide has increased faster than ever before. This increases the greenhouse effect and causes global warming
  4. The percentage of carbon dioxide in exhaled air is about how much?
    That is significantly higher than the amount breathed in. It is a common misunderstanding that we breathe out only carbon dioxide
  5. The percentage of which of these gases of the air breathed in remains unchanged in the air that we breathe out?
    The percentage of water vapour increases in exhaled air
  6. Which is the correct order showing the route that oxygen takes to enter the blood?
    The walls of the alveoli are very thin and covered in blood capillaries. This allows the red blood cells to absorb oxygen as they pass through the lungs
  7. Gas exchange takes place in the alveoli. Which is not true?
    They have a very large surface area which makes the absorption of oxygen and removal of carbon dioxide as efficient as possible. Smoking damages the alveoli and so getting oxygen into the blood is a lot harder
  8. Oxygen passes from the alveoli into the blood. How is it transported?
    Haemoglobin in red blood cells joins with oxygen
  9. Carbon dioxide passes into the alveoli from .......
    The carbon dioxide is released from all living cells during cellular respiration
  10. Air can enter and leave the lungs because .......
    The animal uses its chest muscles to increase the volume of its lungs. The air inside the lungs is therefore more spread out than before, so it has a lower pressure. The higher pressure of the air outside of the lungs forces air into the lungs. The opposite is true of breathing out

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