1.9 - Aerobic & Anaerobic Respiration

What respiration is and what it is for

• Respiration is the process that releases energy from glucose. It goes on in every living cell - in animals, plants, and microorganisms - all the time.
• It's not the same as breathing. Respiration is a series of chemical reactions inside cells, each controlled by enzymes, that break glucose down and transfer its energy into a form the cell can use.
• Because it happens continuously in every cell, living things have a constant supply of energy for everything they do.

ATP - The cell's energy currency

• The energy released is carried within the cell by a molecule called ATP.
• The reactions of respiration release energy from glucose and use it to make ATP. The cell then uses ATP to power its activities.

What cells use the energy for

• Contracting muscles - Lets animals move
• Building larger molecules from smaller ones - Such as making proteins from amino acids
• Cell division - Making new cells, and synthesising new substances for growth and repair
• Transmitting nerve impulses
• Active transport - Moving substances across cell membranes
• Keeping body temperature steady - In mammals and birds, when the surroundings are cold

Respiration is exothermic

• Respiration is an exothermic reaction, which means it transfers energy to the surroundings.
• Some of this energy is released as heat.

Aerobic respiration

• Aerobic respiration is respiration that uses oxygen.
• It's the most efficient way to release energy from glucose, transferring far more energy per glucose molecule than respiration without oxygen.
• Because it releases the most energy, it's the form of respiration cells use whenever enough oxygen is available.
• It happens all the time in the cells of plants and animals.

The reaction

• Glucose reacts with oxygen and is fully broken down, releasing energy.
• The waste products are carbon dioxide and water.

The word equation is:

glucose + oxygen → carbon dioxide + water (+ energy released)

Where it happens

• Most of the reactions take place inside the mitochondria - the structures in the cell where aerobic respiration is carried out.
• Cells that need a lot of energy tend to contain large numbers of mitochondria.

Anaerobic respiration

• Anaerobic respiration is the release of energy from glucose without using oxygen. The word "anaerobic" means "without oxygen".
• It happens in muscle cells when they can't get enough oxygen - for example during vigorous exercise.
• In human cells, the glucose is only partially broken down, and lactic acid is produced.

Word equation:

glucose → lactic acid (+ energy released)

Less efficient than aerobic respiration

• Because the glucose isn't fully broken down, anaerobic respiration is less efficient than aerobic respiration.
• It releases less energy and produces less ATP per molecule of glucose than aerobic respiration does.