• Occurs in the absence of oxygen. Anaerobic respiration is less efficient and produces lactic acid.

• The splitting of a respiratory substrate, to release carbon dioxide as a waste product. Hydrogen is reunited with atmospheric oxygen with the release of a large amount of energy.

4. The pumping of protons from the mitochondrial matric to the intermembrane space creates a proton gradient. The protons therefore move across the membrane through protein change called a stalked particle. The proton motive force provides energy for ATP synthase to produce ATP.

The site of photosynthesis and are adapted to photosynthesis:

• Contains stacks of thylakoid membranes called grana which provides a large surface area for the attachment of chlorophyll, electrons and enxymes.
• The network of proteins in the grand hold the chlorophyll in a very specific manner to absorb the maximum amount of light.
• The granal membrane had ATP synthase channels embedded allowing ATP to be synthesised as week as being selectively permeable allowing the establishment of a proton gradient.
• Chloroplasts contain DNA and ribosomes allowing them to synthesise proteins needed in the light independent reaction.

1. Photons of light hit chlorophyll molecules in PSII causing the electrons to become excited. This is called photoionization. The charge separation from this drives the process.

   
   

2. Photolysis is the splitting of water with light. One molecule of water requires 4 photons of light to split. When water is split it produces 1 molecule of oxygen, 4 protons and 4 electrons. The oxygen either naturally diffuses out through the stomata or is used in respiration. The 4 electrons replace those lost from chlorophyll, whilst protons move into the stroma, later creating a proton gradient.

3. The excited electron then moves down a series of protein complexes. At one of the complexes the energy from the electron is used to pump 4 protons from the stroma to the thylakoid space.
4. The electron then moves down the chain further to PSI. Here more photons of light are absorbed causing the electron to move back up to a higher energy level.
5. The electron then moves along the chain to another complex where the electron combines with a proton to form a hydrogen atom. This is then used to reduce NADP, forming reduced NADP.
6. The pumping of protons across the membrane means that there is now a greater concentration of protons in the thylakoid space than the stroma. As a result a proton gradient forms with a high concentration in the thylakoid space and a low concentration in the stroma. The protons move across the membrane by diffusion through a protein known as a stalked particle. The movement of these proteins drives the process of photophosphorylation. The enzyme ATP synthase phosphorylates ATP from ADP and Pi.

1. CARBON DIOXIDE FIXATION - carbon dioxide that has diffused in throubh the stomata is fixed with ribulose bisphosphate (RuBP) in a process known as carboxylation. The enzyme Rubisco is needed in order to do this. A 6 carbon sugar is formed first, however this is very unstable and therefore forms 2 molecules of glycerate-3-phosphate.
2. REDUCTION PHASE - The 2 molecules of glucerate-3-phosphate contain a -COOH group and is therefore and acid. The reducing power of reduced NADP therefore reduces the glycerate-3-phosphate, with energy being provided by ATP. This therefore forms 2 molecules of triose phosphate. All of the NADP from the light dependant reaction has now been used with only some of the ATP being used.
3. REGENERATION OR RuBP - 5 molecules of triose phosphate are used in order to regenerate 3 molecules of ribulose bisphosphate. The remaining amount of ATP from the light dependant stage is now used.
4. ORGANIC MOLECULE PRODUCTION - 2 molecules of triose phosphate can combine to form the intermediate hexose sugar fructose 1,6 bisphosphate where after it forms molecules of glucose.

The distribution and abundance of organisms in a habitat is controlled by both BIOTIC factor (living) e.g predators, disease and ABIOTIC factors (non-living) such as light levels and temperature.

Each species has a particular role in it habitat called its niche which consists of its biotic and abiotic interactions with the environment.

Only around 10% of chemical food energy is passed on between organisms in the food chain. With the other 90% being lost to the environment:

• uneaten parts, e.g bones
• decay of dead material e.g bacterial decay
• excretion e.g energy lost in the faeces
• exothermic reactions e.g heat loss in respiration.

Efficiency of energy transfer between trophic levels:
Percentage efficiency = energy available after the transfer/energy available before *100

The chemical energy in dry biomass can be estimated using calorimetry. This is carried out in a bomb calorimeter in which a sample of known mass is burnt in Pure oxygen. The bomb calorimeter is submerged in water and therefore the change in water temperature can be used to calculate the energy in the sample.

• Net primary productivity (NPP) - the rate at which energy is transferred into the organic molecules that make up new plant biomass, that is the chemical energy store in plant biomass after respiratory losses to the environment have been take into account.
• Gross primary productivity (GPP) - the rate at which energy is incorporated into organic molecule in the plants in photosynthesis , that is the chemical energy store in plant biomass, in a given area and time.
• Therefore, NPP=GPP-R.
• The net primary production is available for plant growth and reproduction as well as other trophic levels in the ecosystem such as decomposers and herbivores.
• The net production of consumers(N) such as animals can be calculated by: N=I-(F+R) where I represents the chemical energy stored in ingested food, F represents the chemical energy lost to the environment in faeces and urine and R** represents the respiratory losses to the environment.

Nitrogen is an element used in many biological molecules of which there is a finite amount on the earth. Due to this it must be recycled from dead organisms and waste products. Most of this is carried out by bacteria in the soil. There are four stages of the nitrogen cycle:

• Ammonification where microbes known as saprobiants break down organic matter to ammonia in a two stage process. Firstly, proteins are broken down into amino acids with extracellular protease enzymes. These are subsequently broken down further to remove amino groups with the use of deaminase enzymes. Saprobionts use the products of decomposition for respiration.
• Nitrification where nitrifying bacteria convert ammonia to nitrate ions, NO2-, in an oxidation reaction, with a nitrate ion, NO3-, intermediate. Most plants can take in nitrate ions through their routes.
• Denitrification where nitrate ions, NO3-, are cpmverted to nitrogen gas, N2, by the denitryfying bacteria. This process is wasteful and can be prevented from occurring by soil being well drained and aerated.
• Nitrogen fixation where nitrogen gas is fixed into other compounds by bacteria with nitrogen fixing ability. They do so by reducing nitrogen gas to ammonia which subsequently dissolves to form ammonium ions. Nitrogen fixing bacteria live in root nodules of leguminous plants. The relationship between nitrogen fixing bacteria and the plant is mutualistic, as it is beneficial to both organisms.

Phosphorus like nitrogen is another element found in many biological molecules that needs to be recycled. Plants can take in phosphate ions, PO43-, from soil;. Phosphate is released from sedimentary rocks as a result of weathering, as well as through the decay of bones, shells and the excreta of some birds.
Mycorrhizae are important in facilitating the uptake of water and inorganic ions by plants. These are associations between certain types of fungi and the roots of the vast majority of plants. They increase the surface area and act as a sponge holding water and minerals. As a result a plant can better resist drought and take up inorganic ions more easily.
Natural and artificial fertilisers are used to replace the nitrates and phosphates lost by harvesting plants and removing livestock.
Nitrogen fertilisers greatly increase crop yields and can help deal with the demands of a growing human population. However, they have negative effects on the environment, including reducing biodiversity, leaching and eutrophication.
Leaching is the process by which mineral ions, such as nitrate, dissolve in rainwater and are carried from the soil to end up in rivers and lakes. As a result of this eutrophication occurs. This provides algae in the waterways with enough nitrate ions to grow more rapidly than it otherwise would do. As a result this can block out the light from other plants, causing decay and the use of oxygen in the water way. This eventually leads to the death of the ecosystem.