Respiration
In this topic you will:
- find out how every living cell gets the energy it needs to stay alive
- do an experiment to investigate how, in respiration, some energy is released as heat
- think about the difference between breathing and respiration.
Key words
- glucose
- mitochondria
Using energy to stay alive
Our bodies need energy for many different reasons. For example:
All of our energy comes from the food that we eat. Carbohydrates are especially good for giving us energy.
When we eat food containing carbohydrates, our digestive system breaks the carbohydrates down to a kind of sugar called glucose. The glucose goes into our blood. The blood delivers glucose to every cell in the body. The cells use the glucose to get the energy that they need.
Quick Fact
Your body doesn't use food directly for energy. First, it breaks down carbohydrates into a sugar called glucose. This glucose is carried in the blood to cells, where it's used to release the energy your body needs.
Common Mistake
Many students think we get energy directly from food as soon as we eat it. In reality, our body must first break down the carbohydrates into glucose, which is then transported by the blood and used by cells to release energy.
Releasing energy from glucose
Energy must be changed from one type to another, or be transferred, in order to do something.
The energy in glucose is locked up inside it. Glucose is an energy store. Before your cells can use the energy, it has to be released from the glucose.
This is done by tiny structures called mitochondria that are found inside cells. Most cells have many mitochondria inside them. Mitochondria release energy from glucose, so that the cells can use the energy.
The mitochondria carry out a chemical reaction called aerobic respiration. Aerobic means that it uses oxygen, from the air. Here is the word equation for aerobic respiration:
glucose + oxygen → carbon dioxide + water
In this reaction, some of the energy inside the glucose is released. This is done in a very controlled way. Just a little bit of energy is released at a time – just enough for the cell’s needs.
Quick Fact
Cells release energy from glucose through a process called aerobic respiration. This happens inside structures called mitochondria, which use oxygen to break down glucose and release energy in small, controlled amounts.
Common Mistake
It’s easy to assume that glucose itself is the energy the body uses. In reality, energy must be released from glucose inside mitochondria through a process called aerobic respiration. This controlled release provides usable energy for cells.
Questions
Show Answer
Neurones require more energy to transmit electrical impulses, so they contain more mitochondria to release energy through aerobic respiration.
Show Answer
Glucose and oxygen
Show Answer
Carbon dioxide and water
Show Answer
During aerobic respiration, glucose reacts with oxygen to produce carbon dioxide as a waste product. This extra carbon dioxide is removed from the body when we breathe out.
Respiration and heat production
In Stage 7, you learned that every time energy is transferred or transformed, some of it is changed to heat energy.
In respiration, chemical energy stored in glucose is transferred to other substances, so that cells can use it. In this process, some of the energy is changed to heat energy. So respiring cells get a little bit warmer than their surroundings.
Quick Fact
During respiration, not all of the energy from glucose is used for work. Some of it is transferred as heat energy, which slightly raises the temperature of respiring cells compared to their surroundings.
Common Mistake
Some students think heat is added from outside the body during respiration. In fact, heat is produced as a by-product when cells convert glucose into usable energy. That’s why respiring cells get warmer on their own.