Cellular Respiration: Aerobic vs. Anaerobic Processes
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Respiration: The Energy Source of Life
Every living cell needs energy. In humans, our cells need energy for:
- Contracting muscles
- Making proteins
- Making new cells
- Cell division
- Producing heat inside the body
All of this energy comes from the food that we eat. The food is digested (broken down) and absorbed from the intestine into the blood. Then, the blood goes to the body, and the cells take the nutrients.
Aerobic Respiration
Most of the time, our cells release energy from glucose by combining it with oxygen.
Aerobic respiration involves chemical reactions in cells that use oxygen to break down nutrient molecules to release energy.
glucose + oxygen → carbon dioxide + water
Anaerobic Respiration
Anaerobic respiration involves chemical reactions in cells that break down nutrient molecules to release energy without using oxygen.
| Aerobic Respiration | Anaerobic Respiration |
|---|---|
| Uses oxygen | Does not use oxygen |
| No alcohol or lactic acid is made | Alcohol (in yeast and plants) or lactic acid (in animals) is made |
| Large amount of energy released from each molecule of glucose | Much less energy released from each molecule of glucose |
| Carbon dioxide is made | Carbon dioxide is made by yeast and plants, but not by animals |
Gas Exchange in Humans
- Gases go in - gases go out
- Inspire mix of gases
- Lungs - air goes in, air goes out
- Expire: (exhale) some oxygen, carbon dioxide, and some water vapor. 4% Carbon Dioxide. 16% Oxygen. 78% Nitrogen
- Inspire: (inhale) carbon dioxide, oxygen, and some water vapor. 21% Oxygen. 78% Nitrogen. 0.04% Carbon Dioxide
Gas Exchange in the Lungs
The walls of the alveoli are the gas exchange surface
- Tiny capillaries are closely wrapped around the outside of the alveoli
- Oxygen diffuses across the walls of the alveoli into the blood
- Carbon dioxide diffuses the other way
Red blood cells: Deliver carbon dioxide to the lungs and get oxygen. The oxygen is transported to the capillaries, where gas exchange occurs. The blood then takes the oxygen to the lungs again, and the gas exchange process starts again.
The Air Goes:
- Trachea
- Bronchus
- Bronchioles (small ramifications)
- Alveolus
Special Characteristics of Gas Exchange Surfaces
Gas exchange surfaces have special characteristics that help the process to be quick and efficient:
- They are thin to allow gases to diffuse across them quickly
- They are close to an efficient transport system to take gases to and from the exchange surface
- They have a large surface area, so that a lot of gas can diffuse across at the same time
- They have a good supply of oxygen (often brought by breathing movements)