Respiration

The digestive system, lungs and circulation all work to provide cells with glucose and oxygen needed for respiration.

Glucose + oxygen --> carbon dioxide + water + energy.

Mitochondria-tiny rod-shaped organelles found in almost all plant/animal cells, and most aerobic respiration reactions take place here. They have a folded inner membrane, increasing surface area for enzymes.

The number of mitochondria in a cell shows how active the cell is.

Cells that use a lot of oxygen, such as muscle cells, usually have more mitochondria than other types. 

Respiration releases energy from food we eat so our cells can use it.

Cells need energy to carry out basic functions of life:

• They build up larger molecules from smaller molecules to make new cell material. A lot of energy released in respiration is used for this.
• A lot of the energy released is used to make muscles contract.
• Energy is also used to maintain body temperature.

Muscles need energy to be able to contract and expand. Respiration provides this energy.

The rate of respiration increases the harder you exercise, as the harder you exercise the more energy your muscles need. 

Glucose moves into the mitochondria from the blood when you exercise. However, if there isnt enough glucose, your body uses stores of glucose in your muscle and liver cells. This glucose has been stored as glycogen, and is converted back to glucose when needed.

During Excercise:

• Your heart rate increases, because your blood needs to circulate faster so it can supply all the extra oxygen and sugar your cells need and remove all the extra carbon dioxide being produced.
• The rate and depth of your breathing increases, because oxygen and carbon dioxide in the blood need to be exchanged faster with air in the lungs. Increasing depth and rate of breathing increases the volume of air you breathe
• Benifits of exercise-bother you heart and lungs become larger, developing a bigger and more efficient blood supply.

Exercising for a long time causes muscles to fatigue. This means the mucsles stop contracting efficiently. This causes an increasing weakness and pain or cramps.

One cause of fatigue or pain is the build up of lactic acid in the muscles. Blood flowing through the muscles removes lactic acid. Lactic acid builds up becuase of anaerobic respiration.

Not enough oxygen may reach the muscles during exercise. When this happens, they use anaerobic respiration to obtain energy.

Anaerobic respiration involves the incomplete breakdown of glucose and produces lactic acid instead of carbon dioxide and water:

Glucose ---> lactic acid (+energy)

Anaerobic respiration isn't as efficient as aerobic respiration, as glucose isn't broken down properly and far less energy is released.

Oxygen Debt:

Anaerobic respiration produces an oxygen debt. This is the amount of oxygen needed to oxidise lactic acid to carbon dioxide and water. The existence of an oxygen debt explains why we continue to breathe deeply and quickly for a while after exercise.