B9

Aerobic respiration takes place all the time in plant and animal cells. Aerobic respiration is an exothermic reaction using glucose and oxygen to transfer energy. The energy transferred is needed for all living processes. Carbon dioxide and water are produced as wate products. Most of the chemical reactions of aerobic respiration take place in the mitochondria and are controlled by enzymes.

The equation for aerobic respiration is:

• Glucose + oxygen ----------> carbon dioxide + water (energy transferred to the environment)

The transferred energy may be used by the organism to:

• build larger molecules from smaller ones.
• enable muscle contraction in animals.
• Maintain a constant body temperature in colder surrounds in mammals and birds.
• Move materials such as mineral ions into cells against a concentration gradient (active transport)
• build sugars, nitrates, and other nutrients into amino acids and then proteins in plants.

Limewater turns milky in the presence of carbon dioxide. It can be used to show that exhaled air contains more carbon dioxide than inhaled air.

Carbon dioxide dissolves in water to form a weakly acidicsolution. Hydrogencarbonate indicator is used to show the presence of carbon dioxide in solution.

It is:

• red at neutral pH(no carbon dioxide)
• yellow at low pH (carbon dioxide present)

• When you exercise, your muscles need more energy so that they can contract.
• You need to increase the rate at which oxygen and glucose reach the muscle cells for aerobic respiration. You also need to remove the extra waste carbon dioxide produced, more quickly.
  • Glucose + Oxygen -----> carbon dioxide + water (energy transferred to the environment)
• The heart rate increases and the blood vessels supplying the muscles dilate (widen). This allows more blood containing oxygen and glucose to reach the muscles.
• Your breathing rate and the depth of each breath also increase. This allows a greater uptake of oxygen and release of carbon dioxide at the lungs.
• Muscles store glucose as glycogen. The glycogen can be converted back to glucose for use during exercise.

• If you use muscles over a long period then they will get tired (fatigued) and stop contracting efficiently. For example, this might happen when you lift a weight repeatedly for a few minutes or when you go jogging.
• When your muscles cannot get enough oxygen for aerobic respiration, they start to respire anaerobicallu (without oxygen)
• In aerobic respiration the glucose is not completely broken down and lactic acid is produced.
  • Glucose -----> lactic acid (energy transferred to the environment)
• Less energy is transferred from the glucose in anaerobic respiration.
• One cause of muscle fatigue is the build-up of lactic acid. This creates an oxgyen debt.
• Blood flowing through the muscles removes the lactic acid.

Plants and microorganisms also respire anaerobically.

• Plant cells and yeast cells produce ethanol and carbon dioxide
  • glucose -----> ethanol + carbon dioxide (energy transferred to the environment)
  • C6H12O6 -----> 2C2H5OH+2C02
• Anaerobic respiration in yeast cells is called fermentation.

The metabolism of an organism is the sum of all the reactions that take place in a cell or in the body.

Some of the most common metabolic reactions include the conversion of small molecules into larger molecules.

• Glucose to starch, glycogen, or cellulose.
• Fatty acids and glycerol to lipids.
• Glucose and nitrate ions to amino acids.
• Amino acids to protein.

Other common metabloic reactions are:

• The reactions of respiration and photosynthesis.
• The breakdown of excess proteins in the liver to form urea.

Some of the energy transferred by respiration is used to bring about movement. Some is used to build up or break down molecules.

Mammals and birds also use energy from respiration to maintain a constant body temperature.