AQA GCSE Respiration (Biology)

Respiration

Respiration is a chemical reaction that occurs in every living cell

Cellular respiration is an exothermic reaction which is continuously occurring in living cells.

Using the energy released from respiration

Cellular respiration releases energy from glucose. This energy is used for living processes both within the cell and the organism as a whole.

Organisms use this energy for:

1.Chemical reactions to build larger molecules

2.Movement

3.Keeping warm.

Chemical reactions to build larger molecules.

Energy is needed to build large molecules from smaller ones during chemical reactions.

There are several examples of this:

Glucose → starch (plants store energy)

Glucose → cellulose (plant cell walls)

Glucose + nitrates → amino acids → proteins (growth & repair)

Below is a diagram showing how glucose molecules are combined together to make starch, this process needs energy.

Movement

In order for us to move, our muscles need to contract. Muscle contraction needs energy.

Below is a table giving examples of types of movement and which muscles contract.

Type of movement	Name of muscles that contracts
Breathing in	Diaphragm muscle and intercostal muscles
Walking	Leg muscles

Plants can also move in growth movements, which needs energy. An example of this is how a shoot grows towards the light.

Keeping Warm

Mammals and birds use energy to maintain a constant internal body temperature.

Organisms have enzymes to speed up chemical reactions, these enzymes have optimum temperatures where they work best.

Energy released in respiration helps to maintain core body temperature.

Types of Respiration

There are two types of respiration:

Aerobic (using oxygen)

Anaerobic (without oxygen)

In both cases energy is transferred from the chemical energy store in glucose to another energy store.

If a person is walking, then the energy is transferred mechanically from the chemical energy store in glucose into kinetic energy store for movement of the person.

Aerobic Respiration.

Aerobic respiration occurs within the mitochondria of cells and uses oxygen to release energy from glucose.

Aerobic respiration is the complete oxidation of glucose.

Anaerobic Respiration

Anaerobic respiration releases energy from glucose in the absence of oxygen.

Anaerobic respiration is the incomplete oxidation of glucose.

There are two types of anaerobic respiration:

1.Anaerobic respiration in animals

2.Anaerobic respiration in plants and yeast.

Anaerobic respiration in animals.

During intense exercise, oxygen cannot be delivered to muscle cells fast enough to allow aerobic respiration to occur. As a result the muscle cells will start to respire anaerobically in order to release some energy.

Equation for anaerobic respiration in animals is shown below.

Problems with anaerobic respiration in animals:

1. The glucose is not completely oxidised, so its only partially broken down. This means that only some of the energy is released from the glucose.

Anaerobic respiration will release approximately 10% of the energy compared to aerobic respiration.

2. Lactic acid is produced during anaerobic respiration, this acts as a mild poison causing muscle fatigue in animals. When oxygen becomes available again, the lactic acid is broken down. The amount of oxygen needed to break down the lactic acid is known as the oxygen debt.

Anaerobic respiration in plants & yeast.

Both plants and yeast (type of fungus) can release energy from glucose in the absence of oxygen.

Plant roots in water logged soil will be oxygen deficient, so they need to be able to respire anaerobically.

When yeast cells carry out anaerobic respiration it is often called fermentation. This process is used in the production of alcoholic drinks and bread.

The equation for anaerobic respiration in plants and yeast is shown below.

Feature	Aerobic Respiration	Anaerobic Respiration
Oxygen needed	Yes	No
Location	In mitochondria	In cytoplasm
Word equation	Glucose + oxygen → carbon dioxide + water	Animals:Glucose → lactic acid Plants & yeast: Glucose → ethanol + carbon dioxide
Products	Carbon dioxide and water	Lactic acid (animals) Ethanol and carbon dioxide (plants and yeast)
Energy transferred	Large amount of energy	Small amount of energy
Breakdown of glucose	Complete breakdown	Incomplete breakdown
When it happens	Normal conditions when oxygen is present	When oxygen supply is limited e.g. during intense exercise
Effect on muscles	No oxygen debt	Oxygen debt builds up