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Topic 5: Energy transfers in and between organisms - Coggle Diagram

- - - - 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.
        
        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.
        
        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.
        
        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.
        
        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.
        
        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.
- - - - 2. Link reaction - the 2 molecules of pyruvate are actively transported into the mitochondria. The enzyme decarboxylase then removes a molecule of CO2 with a hydrogen being lost, going on to reduce NAD. The acetate formed then combines with coenzyme A to form a molecule of Acetyl Coenzyme A. Per molecule of glucose 2 molecules acetyl coenzyme A are formed and 0 ATP.
        
        Krebs cycle - The Krebs cycle occurs in the matrix of the mitochondria. Being with the acetyl coenzyme A gives the 2-carbon acetate to a 4-carbon molecule already present. The 6 carbon molecule that is formed then undergoes a series of reactions. Eventually, the starting 4-carbon molecule is regenerated to accept another acetate molecule. The Krebs cycle turns 2 times per molecule of glucose and therefore per molecule of glucose 2 ATP molecules, 6 NADH molecules, 2 FADH molecules and 4 CO2 molecules are produced.
        
        Oxidation phosphorylation - the process of oxidative phosphorylation occurs as follows:
        
        The reduced NAD (NADH) from the Krebs cycle binds to Protein complex I, releasing it hydrogen atoms as protons and electrons. The NAD hydrogen carrier then goes back to the Krebs cycle to be used again. Reduced FAD (FADH) binds to complex II. It also releases it hydrogen atoms as protons and electrons. The protons move into the mitochondrial matrix whilst the electrons released go into the electron chain.
        
        The electrons are then passed down a chain of protein complexes (complex I to IV) each having a higher affinity than the previous. In complexes, I, III and IV the energy from the electron is used to pump across protons. For each hydrogen released by NADH 4 protons are pumped across. The protons are pumped into the intermembrane space.
        
        After the electrons have pumped across the protons they are accepted by the final acceptor oxygen. The electrons combine with a proton to form a hydrogen atom, which the combines with oxygen to form water.
        
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- - - - 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.