10. Cellular respiration GapFill

Respiration

Respiration takes place in  leaf cellsciliated cellsall body cellsthe blood plasmasperm cellsmuscle cells, all the time.

Every cell needs energy to stay alive. Respiration is the chemical reaction that releases energy from glucose inside living cells. Energy is measured in kilojoules.

Like all chemical reactions in our cells, respiration is controlled by enzymes.

Respiration happens in little structures in the cytoplasm called the  mitochondriamembranesvacuoleschromosomeschloroplastsplasmids. Cells that need a lot of energy, such as muscle and nerve cells, have more of these than cells like skin cells, which don’t need much energy.

Using energy

Energy released during respiration is used by the organism in several ways:

• Energy may be used to build larger molecules from smaller molecules. For example, plants make amino acids from sugars, nitrates and other minerals. These amino acids are then made into   fatty acidssugarsvitaminsproteinslipidscarbohydrates for growth.
• Animals use energy to enable the muscles to   contractexpandbreatherelaxlengthengrow so that the animals can move.
• Mammals and birds can maintain a steady body temperature. They use energy from respiration to do this when their surroundings are colder than they are.  

Aerobic and anaerobic respiration

Aerobic respiration is the usual form of respiration for animals and plants.

Aerobic respiration uses  oxygennitrogenhydrogenairwatercarbon dioxide to break down the glucose and release all of the energy.

Carbon dioxide and water are waste products of this reaction.

During vigorous exercise, the muscle cells need a lot more energy than usual in order to contract and cause movement.

Therefore, the muscle cells need more   carbon dioxidewaterinsulinethanolglucosecytoplasm and more oxygen for respiration. They also produce more carbon dioxide, which needs to be removed.

When we exercise:

• Our breathing rate increases – we breathe faster and more deeply. This increases the rate of   contractionrespirationdigestiongas exchangeosmosisoxidation in the lungs, so more oxygen enters the blood.
• Our heart beats faster to get blood containing glucose and oxygen to the muscles more quickly and to remove carbon dioxide.

However, if the person goes on exercising, it gets to the point where the muscle cells can’t get enough oxygen to respire aerobically.

So, muscle cells get the extra energy they need by respiring without oxygen.   HormonalNoExcessiveAnaerobicFermentingAerobic respiration happens when oxygen is not available.

In this form of respiration the glucose is only partly broken down, and lactic acid is produced. A much smaller amount of energy is released.

glucose  → lactic acid (+ energy)

Lactic acid is  toxicnutritiousalkalinebeneficialharmlessneutral. When it builds up in the muscle cells it causes muscle fatigue and cramps. To avoid damage to cells, lactic acid has to be broken down to carbon dioxide and water immediately after the exercise has finished. This reaction needs oxygen.

The extra oxygen needed is called an oxygen debt. In order to get the extra oxygen to 'pay back' the debt, the person will   take shallow breathshold their breathkeep on breathing deeplybreathe normallyrespire anaerobicallyslow down their breathing for some time after they have stopped exercising. When all the lactic acid in the muscles is broken down, the oxygen debt has been repaid and normal aerobic respiration carries on.