Bioenergetics

Carbon Dioxide + Water --> Glucose + Oxygen

Energy is required as the reactions are endothermic (take heat in). This energy is supplied by sunlight, which is trapped by the green chemical 'Chlorophyll', which is found in chloroplasts.

There are many factors that affect the rate of photosynthesis, which are: Temperature, co2 concentration, light intensity and chlorophyll concentration. Any factor that stops the reaction going any faster is called the limiting factor.

Temperature increases = rate of photosynthesis increases. This is because more energy is provided for the reaction. However, as the temp approaches 45, the enzymes controlling photosynthesis will be destroyed.

Conc. of co2 increases = Rate of photosynthesis increases, because co2 is needed in the reaction. However, after a certain point an increase in co2 has no further effect, as co2 is no longer the limiting factor.

Light intensity increases = rate of photosynthesis increases, as more energy is provided for the reaction. However, after a certain point an increase in LI has no further effect, as LI is no longer the limiting factor.

Chlorophyll concentration does not vary in the short term but may change if plants are grown in soil without enough minerals to make chlorophyll.

The glucose produced in photosynthesis may be used by the plant during respiration to provide energy.

Glucose may also be changed into other products such as:

- insoluble starch, which is stored in the stem, leaves or roots.

- fat or oil, which is also stored, e.g. in seeds.

- cellulose, to strengthen cell walls.

- proteins, which are used for growth and for enzymes.

To produce proteins from glucose, plants also use nitrate ions, which are absorbed from the soil.

Respiration is an exothermic reaction, meaning it realses energy from glucose molecules for use by the body.

Organisms need this energy:

- for chemical reactions to build larger molecules

- for movement

- to keep warm.

Respiration in cells can be either aerobic or anaerobic.

The equation for aerobic respiration is:

glucose + oxygen --> Carbon dioxide + water.

In anaerobic respiration, the glucose is not completely broken down, meaning that it transfers much less energy than aerobic respiration. The process of anaerobic respiration is different in animals to the process found in plants and yeast.

In animals, lactic acid is produced: Glucose --> Lactic acid.

In plants and yeast, alcohol (ethanol) and carbon dioxide are produced: Glucose ---> ethanol + carbon dioxide.

Anaerobic Respiration in yeast is called fermentation, which is important in the manufacture of bread and alcoholic drinks.

Metabolism is the sum of all the chemical reactions in a cell or in the body. These reactions are controlled by enzymes and many need a transfer of energy. This energy is transferred by respiration and used to make new molecules.

This includes: The conversion of glucose to starch, glycogen and cellulose. The formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids. The use of glucose and nitrate ions to form amino acids, which are used to synthesis proteins. And the breakdown of excess proteins into urea for excretion.

During exercise, the body demands more energy, so the rate of respiration must increase. The heart rate, breathing rate and breath volume all increase to supply the muscles with more oxygem and glucose for the increase in aerobic respiration.

During periods of high activity, the muscles may not be supplied with enough oxygen, so anaerobic respiration starts to take place in the muscle cells.

This causes a build-up of lactic acid and creates oxygen debt. The lactic acid causes the muscles to hurt and stops them contracting efficiently.

Lactic acid is a posion, so needs to be got rid of quickly.

Once exercise is finished, the oxygen debt must be 'repaid'.

After exercise, blood flowing through the muscles transports the lactic acid to the liver where it is broken down.

The oxygen debt is the amount of extra oxygen the body needs after exercise to react with the lactic acid and remove it from the cells.