A fire without flames

About this video

Run up four flights of stairs and you arrive breathing hard, your heart pounding. Your leg muscles have used a lot of energy. Where does it come from, and why do they need oxygen? Food holds energy, much like wood does. When wood burns it combines with oxygen and its energy comes out all at once, as heat and light. Your cells release the energy in food in a similar way, but slowly and gently, with no flames. This is respiration, or cellular respiration.

The fuel is glucose, a sugar that comes from food. The cell combines it with oxygen, and carbon dioxide and water are left over: glucose plus oxygen gives carbon dioxide, water and energy. It happens in many small steps, so the cell can catch the energy instead of losing it as heat, storing it in small packets of a molecule called ATP and spending them wherever work needs doing. Most of it happens in the mitochondria, the cell's power stations; busy cells such as muscle cells have many.

Breathing is not respiration. Breathing moves air in and out of the lungs; respiration is chemistry inside every cell. Breathing brings in the oxygen respiration uses and carries away the carbon dioxide it makes. Plants respire too: photosynthesis stops at night, but every living plant cell respires day and night. What photosynthesis makes, respiration uses, and the other way round. This video goes with the lesson How Cells Release Energy in Biology Level 1 on Knaph.

Transcript

1. 0:00Run up the stairs and you arrive out of breath. Where does that energy come from?
2. 0:09Food holds energy, like wood. Burning wood combines it with oxygen, and the energy comes out all at once.
3. 0:17Your cells do the same with food, but slowly, in many small steps, with no flames.
4. 0:24At each step, energy is caught in small packets called ATP.
5. 0:31The fuel is glucose. Inside the mitochondria it is combined with oxygen.
6. 0:38Carbon dioxide and water are left over.
7. 0:42Glucose and oxygen give carbon dioxide, water and energy.
8. 0:46Busy muscle cells have many mitochondria, so they need lots of oxygen.
9. 0:53Breathing moves air in and out of the lungs. Respiration is chemistry inside every cell.
10. 1:01Breathing brings in the oxygen respiration uses, and takes away its carbon dioxide.
11. 1:11Plants respire too. Photosynthesis needs light, so it stops at night.
12. 1:19But every living plant cell respires all the time, day and night.
13. 1:29Photosynthesis makes glucose and oxygen. Respiration uses them, and gives back carbon dioxide and water.
14. 1:39So the gases of the air go round between living things.