Respiration (AQA GCSE Biology): Revision Notes
Respiration
What is respiration?
Respiration is a process that happens in all living cells. It can work in two ways:
There are two main types of respiration that cells can use depending on the availability of oxygen:
- Aerobic respiration - uses oxygen
- Anaerobic respiration - happens without oxygen
Comparing aerobic and anaerobic respiration
Aerobic respiration
This type of respiration needs oxygen to work properly and is the most efficient way for cells to release energy.
The equation:
Key features of aerobic respiration:
- Uses oxygen from the air
- Completely breaks down glucose
- Releases lots of energy
- Is an exothermic reaction (gives out heat)
Anaerobic respiration (in muscles)
This happens when there's not enough oxygen available, such as during intense exercise.
The equation:
Key features of anaerobic respiration:
- Works without oxygen
- Only partly breaks down glucose
- Releases much less energy than aerobic respiration
- Also an exothermic reaction
What do we use the energy for?
Cellular respiration gives us energy for many important jobs in living things:
- Building molecules - making larger chemicals from smaller ones
- Movement - helping muscles contract
- Active transport - moving substances around cells
- Keeping warm - maintaining body temperature
All of these processes require energy input, which is why respiration is so essential for life. Without the energy from respiration, these vital cellular processes cannot occur.
Fermentation
Anaerobic respiration also happens in plant cells and yeast. This process is called fermentation.
The equation:
Useful applications:
- Making bread - the carbon dioxide gas makes dough rise
- Making alcoholic drinks - like wine and beer
Remember: Anaerobic respiration works differently in muscles compared to plants and yeast. In muscles it produces lactic acid, but in plants and yeast it produces ethanol and carbon dioxide.
Respiration vs photosynthesis
These two processes are opposites of each other and work together to maintain the balance of gases in our atmosphere:
| Aerobic respiration | Photosynthesis |
|---|---|
| Gives out energy | Takes in light energy |
| Uses oxygen | Makes oxygen |
| Makes carbon dioxide | Uses carbon dioxide |
| Exothermic reaction | Endothermic reaction |
| Happens in mitochondria | Happens in chloroplasts |
| Happens in all living cells | Only happens in plant cells |
Worked Example: Comparing Respiration Types
Question: Compare aerobic respiration with anaerobic respiration in muscles.
Answer: Both processes use glucose as fuel. Aerobic respiration needs oxygen but anaerobic respiration doesn't.
Glucose gets completely broken down during aerobic respiration, so it releases much more energy. Anaerobic respiration only partly breaks down glucose.
Aerobic respiration makes two products - carbon dioxide and water. Anaerobic respiration in muscles only makes one product - lactic acid.
Key Points to Remember:
- Aerobic respiration needs oxygen and releases lots of energy
- Anaerobic respiration works without oxygen but gives less energy
- Fermentation is anaerobic respiration in yeast and plants
- Energy from respiration is used for movement, building molecules, and keeping warm
- Respiration is the opposite of photosynthesis