Biology GCSE AQA 4.4 Bioenergetics

Photosynthesis

Occurs in leaves of the plant in the chloroplasts

Inside chloroplasts there is a pigment Chlorophyll which absorbs light

Endothermic Reaction in which energy is transferred from the environment to the chloroplasts by light

Uses energy to convert Co2 and Water to make Glucose and Oxygen

Photosynthesis equation

Carbon Dioxide + Water —Light—→ Glucose and Oxygen

Glucose: C₆H₁₂O₆

Factors effecting Rate of Photosynthesis

Temperature

Light Intensity

Carbon Dioxide Concentration

Chlorophyll amount

Chlorophyll effect on Photosynthesis Rate

Chlorophyll - pigment within chloroplasts that absorbs the light energy for photosynthesis

If plants have less chlorophyll - decreased rate of photosynthesis as less light energy will be absorbed

Levels of chlorophyll can differ in different plants or within individual plants due to disease, environmental stress or lack of nutrients - Damaging chloroplasts

Limiting Factors for Photosynthesis: Light Intensity

As light intensity increases, so does the rate of photosynthesis

When graph plateaus, something else is limiting factor of photosynthesis

Limiting Factors for Photosynthesis: Carbon dioxide concentration

As Co2 Concentration increases, so does the rate of photosynthesis as it is one of the reactants

After a while, rate plateaus, which means something else is the limiting factor of photosynthesis

Limiting Factors for Photosynthesis: Temperature

Initially, as temperature increases, the rate increases as enzymes involved can work quicker and molecules can move faster due to having more kinetic energy.

However after a while, rate drops again as enzymes involved being to denature and by about 45 degrees the enzymes will be fully denatured and the rate falls to 0

Artificial conditions for photosynthesis

• In colder climates - greenhouses are used to trap the sun's heat and increase the temperature 

• Artificial light increases the rate of photosynthesis by mimicking sunlight 

• Co2 can be pumped into area using paraffin heater - provides heat and co2 

• Fertiliser - enough minerals for the plants

• Pesticides - to kill unwanted bugs

Can be expensive - farmers have to look at extra cost vs extra yield

Inverse square law

• The inverse square law states that the intensity of light decreases proportionally to the square of the distance from its source.

• For example, if the distance is doubled, the light intensity decreases to 1/4 of its original value.

Formula: light intensity ∝ 1/distance²

l ∝ 1/d²

Uses of glucose produced from Photosynthesis

Respiration

Converted into insoluble (won’t draw water into cell via osmosis) starch for long term storage - compact so can fit more in a cell. Complex carbohydrate with no particular function. Break it down when photosynthesis isn’t happening (night)

Used to produce fat or oil for storage - stored as future energy sources - particularly for seeds

Used to produce cellulose, which strengthens the cell wall

React with nitrate ions from soil to produce amino acids for protein synthesis - growth

Growth rate of a plant depends on how fast they can photosynthesise

Respiration

Exothermic reaction which transfers energy from glucose and continuously occurs in living cells

Respiration can take place with oxygen (aerobically) or without oxygen (anaerobically) to release energy

Why do Organisms need energy?

Chemical reactions to build larger molecules

Movement - muscular contraction

To keep warm

Aerobic respiration

Glucose + Oxygen —→ Carbon dioxide + water + energy

When there is enough oxygen

Most efficient

Continuous in plants and animals (mitochondria of cell)

Anaerobic respiration in humans

Glucose —→ Lactic acid + energy

As oxidation of glucose is incomplete in anaerobic respiration much less energy is transferred than in aerobic respiration

Not enough oxygen available

Glucose is only partially broken down - inefficient

Lactic acid produced - toxin which has to be removed

Anaerobic respiration in plants and yeast

Glucose —→ ethanol + carbon dioxide + Energy (2 ATP)

Anaerobic respiration in yeast cells is called fermentation and has economic importance in the manufacturing of bread and alcoholic drinks

Respond to exercise

During exercise the human body reacts to the increased demand for energy.
The Heart rate breathing rate and breath volume increase during exercise to supply muscles with more oxygenated blood

During long periods of vigorous activity, muscles become fatigued and stop contracting efficiently (anaerobic respiration)

Investigating the effects of exercise on the body

Breathing rate - how many times chest rises and falls in a given amount of time (for one minute)

Heart rate - measuring pulse - Artery in wrist or neck

Lactic Acid

If insufficient oxygen is supplied, anaerobic respiration takes place in muscles causing a build up of lactic acid

Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose

Oxygen Debt

The incomplete oxidation of glucose causes a build up of lactic acid and creates an oxygen debt

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

Metabolism definition + chemical reactions

Sum of all chemical reactions in a cell or the body

Glucose being used in plants

Glucose in humans stored as glycogen

1 molecule of glycerol + 3 fatty acid molecules - lipid - found in the cell membrane

Excess proteins are broken down into the chemical urea which is then excreted by the kidneys