All-in-One Bioenergetics

Photosynthesis

The process where plants synthesise glucose using light energy from the sun.

Chloroplasts

Contain chlorophyll, a pigment, which absorbs light energy.

Photosynthesis Equation (Word)

carbon dioxide + water → glucose + oxygen

Photosynthesis Equation (Symbol)

6CO2 + 6H2O → C6H12O6 + 6O2

Factors Affecting Photosynthesis

• Temperature

• Light intensity

• Carbon dioxide concentration

• Amount of chlorophyll

Temperature Effect on Photosynthesis

Increasing the temperature increases the rate of photosynthesis → kinetic energy of particles is increased

• The rate decreases past a certain temperature as enzymes become denatured.

Light Intensity Effect on Photosynthesis

Increasing the light intensity increases the rate of photosynthesis until another factor becomes limiting.

Carbon Dioxide Concentration Effect

Increasing the carbon dioxide concentration increases the rate of photosynthesis (until another factor becomes limiting) → as CO2 is required to make glucose.

Chlorophyll Amount Effect

Decreasing the amount of chlorophyll (eg. due to a lack of magnesium) decreases the rate of photosynthesis → chlorophyll is required to absorb light energy

Limiting Factor

A factor which can restrict the rate of photosynthesis eg. light intensity.

Calculating Rate of Photosynthesis

Set up bubble potometer apparatus (pondweed in a sealed tube of water, attached to a capillary tube and a gas syringe). Oxygen gas produced causes the bubble in the capillary tube to move. The distance moved by the bubble is used to calculate the volume of oxygen produced.

Farmers and Limiting Factors

They can control temperature, light intensity and CO2 concentration → achieve the fastest possible rate of photosynthesis → leading to a greater yield.

Uses of glucose from photosynthesis

• For respiration

• Converted into insoluble starch for storage

• Produce fat / oil for storage (in seeds)

• Produce cellulose to strengthen cell walls

• Combined with nitrates to form amino acids → proteins

Aerobic respiration

A exothermic reaction where glucose reacts with oxygen to release energy which can be used by cells.

Equations for aerobic respiration (word and symbol)

Glucose + oxygen → carbon dioxide + water (+energy)

• C6H12O6 + 6O2 → 6CO2 + 6H2O (+energy)

Where does aerobic respiration take place?

In the mitochondria

Why do organisms require the energy released by respiration?

• Synthesis of larger molecules

• Muscle contraction

• Maintenance of body temperature

• Active transport

Anaerobic respiration

An exothermic reaction where glucose is broken down to release energy in the absence of oxygen.

Equation for anaerobic respiration

Glucose → lactic acid (+energy)

Why is anaerobic respiration less efficient than aerobic respiration?

Glucose is not completely oxidised, so less energy is transferred.

→ Only used as a last resort.

Why can anaerobic respiration lead to muscle fatigue?

Lactic acid builds up in muscles, preventing efficient contraction.

Oxygen debt

The amount of oxygen needed to convert lactic acid into back into glucose after anaerobic respiration.

Fermentation

A type of anaerobic respiration that occurs in yeast cells.

Equation for fermentation

Glucose → ethanol + carbon dioxide (+energy)

Importance of fermentation reaction

It is used in the production of bread and alcoholic drinks.

Differences between aerobic and anaerobic respiration

• Aerobic requires oxygen → anaerobic does not.

• Aerobic produces CO2 and water; anaerobic produces lactic acid or ethanol + CO2

• Aerobic transfers a greater amount of energy.

How do muscles store glucose?

As glycogen

Changes during increased muscular activity

• Heart rate increases and arteries dilate - increases flow of oxygenated blood to muscles

• Breathing rate increases and breathing volume increases - increases the rate of gaseous exchange.

• Stored glycogen is converted back into glucose.

How is lactic acid transported away from the muscles?

Blood flow through the muscles transports lactic acid to the liver, where it is oxidised back to glucose.

Metabolism

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

How do cells use the energy transferred by respiration?

To continuously carry out enzyme-controlled processes which lead to the synthesis of new molecules.

Examples of metabolic reactions

• Glucose into starch/glycogen/cellulose

• Glycerol and fatty acids into lipids

• Glucose and nitrate ions into amino acids

• Respiration

• Breakdown of excess proteins into urea.