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Life Processes in Animals

What a body cannot use has to leave

Not everything that goes in stays. Two things leave by different routes.

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The idea

Blood carries carbon dioxide to the lungs. Carbon dioxide leaves into the air when we breathe out.

The gut is the long food tube. The anus is the way out for what the gut cannot digest. On the way, the large intestine takes back water and some salts. What remains is a semi-solid stool, which is thick but not hard. It waits in the rectum. The rectum is the last part of the large intestine. Then the stool leaves. That leaving is egestion.

Two routes out: the breath and the anus.

Carbon dioxide leaves with the breath. Undigested food leaves through the anus. Only the second is egestion.

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This track

  1. 0 Start here
  2. 1 Digestion, absorption and egestion
  3. 2 One path, and a job at every stop
  4. 3 Saliva and starch
  5. 4 Ruminants and birds
  6. 5 Checkpoint: what a body does with food
  7. 6 Breathing is not respiration
  8. 7 Lungs, gills and moist skin
  9. 8 Getting food and oxygen around
  10. 9 What a body cannot use has to leave
  11. 10 The path of air
  12. 11 How the chest moves
  13. 12 Gases swap at the alveoli
  14. 13 Villi give food a way in
  15. 14 Checkpoint: the breathing path, the chest and villi
  16. 15 The big picture
  17. 16 Track quiz

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