topic 5 - energy transfer in organism

• structure of a chloroplast

  1. thylakoid membrane - folded membranes that contain cholorphyll and electron carrier proteins which are embedded in the membrane which are both involved in the LDR
  2. stroma - fluid centre which contains enzymes involved with LIR
  3. inner and outer membrane - controls what can leave and enter the organelle
• what are the two stages of photosythnesis

  1. light independent reaction
  2. light dependent reaction
• where does the LDR take place

  • thylakoid membrane or grana
• where does the LIR take place

  • stroma
• what are the key 4 stages of LDR

  • photolysis
  • photoionisation of cholorphyll
  • cheimosmosis
  • production of ATP and reduced NADP
• • photolysis light energy is absorbed by chlorophyll and splits water into oxygen, H+ and e-
  • h20 -> 1/2 o2 + 2e- + 2H+
  • the H+ is picked by NADP to form reduced NADPH and is used in the LIR
  • the e- are passed along a chain of electron carrier proteins
  • the oxygen is either used for respiration or it diffuses out of the leaf through the stomata
• photoionisation of chlorophyll - step 2 LDR

  • light energy is absorbed by the chlorophyll and the energy results in electrons becoming excited and raising up an energy level to leave chlorophyll
  • therefore the chlorophyll has been ionised by light
  • some of the energy from the released electrons is used to make ATP and reduced NADP in chemiosmosis
• LDR - step 3 chemiosmosis

  • the electrons that gained energy and left chlorophyll move along a series of proteins embedded within the thylakoid membrane
  • as they move along they release energy and some of that energy from the electrons is used to pump/active transport the h+ ions across chloroplast membrane
  • an electrochemical gradient is created. the h+ ions pass through the enzyme ATP synthase which result in the production of ATP
  • the h+ ions combine with the co-enzyme NADP to become reduced NADP
  • because the protons move from a high to low concentration gradient this is known as chemiosmosis
• LIR - Calvin cycle

  • the LIR is a cycle
  • the Calvin cycle occurs in the stroma and the fluid contains the enzyme RuBisCo which catalyses the reaction. this stage is temperature sensitive due to the fact it involves enzymes
  • uses carbon dioxide, reduced NADP and ATP to form a hexose sugar
  • the ATP Is hydrolysed to provide energy for this reaction and the reduced NADP donates the hydrogen to reduce molecules GP in this cycle
• process of the Calvin cycle

  1. carbon dioxide reacts with ribulose bisphosphate to form GP which is split into two as it is unstable which are 3 carbon compound, this reaction is catalysed by the enzyme rubisco
  2. GP is reduced to triose phosphate (TP) using energy from ATP and by accepting a H from reduced NADP
  3. some of the carbon from TP leaves the cycle each turn to be converted into useful organic substances such as hexose sugar
  4. the rest of the molecule is used to regenerate RuBP with the energy from ATP
  5. whilst glucose is the product this monosaccharide can make,disaccharides.polysaccharides
• limiting factors of photosynthesis 


  light
• limiting factor of photosynthesis 


  carbon dioxide concentration
• limiting factor of photosynthesis

  temperature
• word equations for photosynthesis

  • 6CO2 + 6H2O → C6H12O6 + 6O2
  • carbon dioxide + water → glucose + oxygen
• aerobic respiration

  • glucose + oxygen → carbon dioxide + water + energy
• 4 key stages of aerobic respiration

  • glycolysis which occurs in the cytoplasm
  • links reaction that occurs in the matrix
  • Krebs cycle that occurs in the matrix
  • oxidative phosphorylation which occurs in the inner-membrane Cristae
• process of glycolysis

  • phosphorylating glucose to glucose phosphate using ATP
  • production of triode phosphate 3C
  • oxidation of triose phosphate to produce 2 pyruvate 3c x2 with a net gain of 4 ATP and reduced NAD
• products of glycolysis

  1. 2 pyruvate
  2. net gain of 2 ATP
  3. 2 NADH
• links reaction process

  • the pyruvate made in glycolysis is oxidised to acetate 2c
  • NAD picks up the hydrogen and becomes reduced NAD
  • acetate then combines with coenzyme A in to produce acetyl coenzyme A
• products of links reaction

  • 2 acetyl coA
  • 2 co2 released
  • 2 reduced NAD
• Krebs cycle

  • acetyl-coA reacts with a 4 carbon molecule, releasing coenzyme A and producing a 6 carbon molecule that enters the Krebs cycle
  • then goes through a series of redox reactions, the Krebs cycle generates reduced coenzymes, 3 reduced NAD and a reduced FAD and ATP by substrate-level phosphorylation and carbon dioxide is lost
• products per cycle are

  • 3 reduced NAD
  • 1 reduced FAD
  • 1 ATP
  • 2 co2
• produce per glucose molecule are

  • 6 reduced NAD
  • 2 reduced FAD
  • 2 ATP
  • 4 CO2
• oxidative phosphorylation

  • involves the electron transport chain, where electrons are transported across it this releases energy
  • the energy actively transports the h+ ions from the inner mitochondrial membrane into the intermembrane space to create a electrochemical gradient
  • h+ ions can move down the concentration gradient through facilitated diffusion with the help of ATP synthase
  • it'll phosphorylate ADP into ATP
  • 34 ATP molecules created
  • oxygen is final electron accepted and creates water
• anaerobic respiration

  • occurs in the absence of oxygen
  • occurs in the cytoplasm only
  • the pyruvate produced in glycolysis is reduced to form ethanol and carbon dioxide in plants and microbes
  • or lactase in animals by gaining the hydrogen from reduced NAD, the oxidises NAD so that it can be reused in glycolysis and ensure ATP is being continuously produced
• energy transfer

  • in any ecosystem, plants are the producers in a food web as they are able to produce their own carbohydrates using carbon dioxide in the atmosphere or water
  • between each trophic level in a food web the majority of energy is lost due to respiration and excretion
  • the remaining energy is used to form the biomass
• decomposers 


  an organism that breaks down dead organic matter in the environment

  e.g bacteria, fungi
• detritvore


  decomposers which eats dead organic matter and digests it internally to gain nutrients

  e.g earthworm, millipede
• Biomass

  the total mass of living material in a specific area at a given time.
• why is using dry biomass better?

  Fresh mass is quite easy to assess but the presence of varying quantities of water makes it highly unreliable
• issues with measuring biomass

  • biomass always involves taking small samples which may not always be representative This is a significant limitation of measuring biomass.
  • biomass changes over time - e.g deciduous trees loose their leaves in Winter - more useful to give biomass over a period of time
• calorimetry

  • method to measure the chemical energy store in the dry mass of the sample being tested
  • use an incubator or an oven to heat the sample to remove all the water from it
  • the burnt sample is then place in pure o2 within a sealed chamber called a bomb
  • the bomb is surrounded by a water bath with a stirrer and thermometer that regulates and monitors the temperature
  • measure the energy release through this equation
  • Heat energy = mass of water (g) x specific heat capacity of water (J/g°C) x temperature change (°C)
• pyramid of numbers 


  shows the total number of individual organisms at each level in the food chain of an ecosystem
• pyramid of biomass


  the representation of total living biomass or organic matter present at different trophic levels in an ecosystem.
• pyramid of energy 


  that compares the energy used by organisms at each trophic level. The energy in an energy pyramid is measured in units of kilocalories (kcal).
• List five reasons why not all of the solar energy can be used in photosynthesis. (5)

  • light missed plant / leaf / chloroplast so it passes straight through
  • wrong wavelength of light/not all the λ isabsorbed
  • some light reflected / not absorbed /refracted back into atmosphere
  • energy lost as heat by respiration / metabolic processes

  CO2 / temperature or other limiting factors
• Why is energy transfer so inefficient?

  • each organism in the food chain utilises some of energy at each trophic level
  • therefore only a small fraction is passed on at each successive stage in the chain
  • main loss is from respiration
  • the remainder is made available to the next trophic level

  in reality, the relative inefficiency of energy

  transfer between trophic levels mean that

  most food chains only have 4-5 trophic levels
• GPP: Gross Primary Production

  • the total quantity of chemical energy store in a plant biomass in a given area or volume, and in a given time
• NPP: Net Primary Production

  the chemical energy store when energy losses from respiration have been taken into account
• Inefficient energy transfer due to the following:

  1. Not all parts of an organism is consumed eg.bones
  2. Some parts are consumed but not digested therefore lost in faeces/waste
  3. Some also lost as excretory products eg. urine
  4. Some energy losses to the environment by virtue of existing/living eg: