Topic 5

• describe the structure of cholorypast

  A small, flattened structure found in plant and algal cells. It's surrounded by a double membrane, and also has membranes inside called thylakoid membranes. These membranes are stacked up in some parts of the chloroplast to form grana. Grana are linked together by lamellae — thin, flat pieces of thylakoid membrane.
• what is the stoma ?

  -fluid centre which contains enzymes involved in the lIR
• What is chlorophyll?


  -chlorophyll is group of 5 key closely related pigments

  -each pigment absorbs a different wavelength of light

  -the light absorbed leads to the photoionisation of chlorophyll(LDR)
• what are the advantages of multiple pigments?

  -a wider range of wavelength of light is absorbed.

  -therefore more light energy is absorbed for the LDR (more photoionisation of chlorophyll)
• where does the LDR and LIR occur?

  LDR occurs in thylakoid membrane

  LIR occurs in the stroma
• what is needed in the LDR?

  ATP and reduced NADP which are created by light energy and water
• what are the four stages of LDR?

  1. photoionisation of chlorophyll

  2. production of atp and reduced nadp

  3. chemiosmosis

  4. photolysis
• what is photolysis?


  The splitting of water using light energy into protons and electrons. the h+ is picked up the NADP and is used in the LIR

  the electrons are passed along a chain of carrier proteins.

  the oxygen is either used for respiration or it diffuses out of the leaf through the stomata.
• describe the process of photoionisation

  light energy is absorbed by chlorophyll and the energy results in electrons becoming excited and raising up and energy level to leave the chlorophyll

  some of the energy from the released electrons is used to make atp and reduced nadp in chemiosmosis
• describe the process of chemiosmosis

  1. the electrons that gained energy and left the chlorophyll move along a series of proteins embedded with the thylakoid membrane

  2.as they move they release energy and some of the energy is used to pump the protons across the chloroplast membrane

  3. an electrochemical gradient is created, the protons pass through ATP synthase which results in the production of ATP

  4. the protons 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
• the whole process of LDR

  Light energy is absorbed by PSII. The light energy excites electrons in chlorophyll. The electrons move to a higher energy level (i.e . they have more energy). These high-energy electrons are released from the chlorophyll and move down the electron transport chain to PSI.

  As the excited electrons from chlorophyll leave PSII to move down the electron transport chain, they must be replaced. Light energy splits water into protons, electrons and oxygen — photolysis.

  The excited electrons lose energy as they move down the electron transport chain. This energy is used to transport protons into the thylakoid. so that the thylakoid has a higher concentration of protons than the stroma. This forms a proton gradient across the thylakoid membrane. Protons move down their concentration gradient, into the stroma, via the enzyme ATP synthase, which is embedded in the thylakoid membrane. The energy from this movement combines ADP and inorganic phosphate to form ATP.

  Light energy is absorbed by PSI, which excites the electrons again to an even higher energy level. Finally, the electrons are transferred to NADP, along with a proton (H + ion) from the stroma, to form reduced NADP.
• (exam question model answer)

  In the light-dependent reaction of photosynthesis, light energy generates ATP. Describe how.

  1. Chlorophyll absorbs light energy;

  2. Excites electrons / electrons removed (from chlorophyll);

  3. Electrons move along carriers/electron transport chain releasing energy;

  4. Energy used to join ADP and Pi to form ATP;

  5. Photolysis of water produces protons, electrons and oxygen;

  6. NADP reduced by electrons / electrons and protons / hydrogen;
• what is the energy resulting from the photoionisation of chlorophyll

  used in?

  1) Making ATP from ADP and in organic phosphate. This reaction is called photo phosphorylation.

  2) Making reduced NADP from NADP.

  3) Splitting water into protons (H + ions), electrons and oxygen. This is called photolysis
• key molecules of the LIR

  ATP is hydrolysed to provide energy to this reaction and reduce NADP donates the hydrogen to reduce GP
• describe the process of the LIR

  1. CO2 reacts with ribulose bisphosphate to form two molecules of GP and the reaction is catalysed by the enzyme rubisco

  2. GP is reduced to 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

  4. the rest of the molecule is used to regenerate RUBP with energy from ATP

  5. products are glucose, but the glucose can join to form sucrose and cellulose and starch. it can also be converted into glycerol and therefore combine with fatty acids to make lipids for the plant
• process of LIR

  (exam style answer)

  1. Carbon dioxide combines with ribulose bisphosphate/RuBP;

  2. To produce two molecules of glycerate 3-phosphate/GP;

  3. Reduced to triose phosphate/TP;

  4. Requires reduced NADP;

  5. Energy from ATP;
• Why does The Calvin Cycle Needs to Turn Six Times to Make One Hexose Sugar?


  1) Three turns of the cycle produces six molecules of triose phosphate , because two molecules of TP are made for every one C02 molecule used.

  2) Five out of six of these TP molecules are used to regenerate ribulose bisphosphate.

  3) This means that for three turns of the cycle only one TP is produced that's used to make a hexose sugar.

  4) A hexose sugar has six carbons though, so two TP molecules are needed to form one hexose sugar.

  5) This means the cycle must turn six times to produce two molecules of TP that can be used to make one hexose sugar. 6) Six turns of the cycle need 18 ATP and 12 reduced NADP from the light-dependent reaction.
• What are the optimum conditions for photosynthesis?

  1. High light intensity of a certain wavelength

  Light is needed to provide the energy for the light dependent reaction — the higher the intensity of the light, the more energy it provides. Only certain wavelengths of light are used for photosynthesis. The photosynthetic pigments chlorophyll a, chlorophyll b and carotene only absorb the red and blue light in sunlight. (Green light is reflected, which is why plants look green.)

  2. Temperature around 25 °C

  Photosynthesis involves enzymes (e.g. ATP synthase, rubisco). If the temperature falls below 10 °C the enzymes become inactive, but if the temperature is more than 45 °C they may start to denature. Also, at high temperatures stomata close to avoid losing too much water. This causes photosynthesis to slow down because less C02 enters the leaf when the stomata are closed.

  3. Carbon dioxide at 0 .4%

  • Carbon dioxide makes up 0.04% of the gases in the atmosphere.

  • Increasing this to 0.4% gives a higher rate of photosynthesis, but any higher and the stomata start to close.
• what is a limting factor?

  any factor that reduces the rate of photosynthesis

  which could be temperature, light intensity and co2.
• what are the methods used by agriculture practises?

  1)Carbon dioxide concentration

  C02 is added to the air, e.g. by burnin g a small amount of propane in a C O , generator.

  2)Light

  light can get in through the glass

  lamps provide light at night time

  3) temperature

  Glasshouses trap heat energy from sunlight, which warms the air. Heaters and cooling systems can also be used to keep a constant optimum temperature , and air circulation systems make sure the temperature is even throughout the glass hous.e
• what are the 4 key stages of aerobic respiration?

  1. Glycolysis (cytoplasm)

  2. Link reaction (mitochondrial matrix)

  3. Krebs cycle (mitochondrial matrix)

  4. oxidative phosphorylation (mitochodrial inner- membrane cistae)
• what is glycolysis and describe the process?

  Respiration produces ATP.

  Glycolysis is the first stage of anaerobic and aerobic respiration. It occurs in the cytoplasm and is an anaerobic process.

  phosphorylation of glucose to glucose phosphate, using ATP

  production of triose phosphate

  oxidation of triose phosphate to pyruvate with a net gain of ATP and reduced NAD.
• what happens if respiration is only anaerobic?

  If respiration is only anaerobic, pyruvate can be converted to ethanol or lactate using reduced NAD. The oxidised NAD produced in this way can be used in further glycolysis.
• what happens if respiration is aerobic?

  If respiration is aerobic, pyruvate from glycolysis enters the mitochondrial matrix by active transport
• describe the process of the links reaction?

  Pyruvate and NADH are actively transported from the cytoplasm into the mitochondrial matrix

  1. pyruvate is oxidised to acetate.

  2. NAD picks up the hydrogen and becomes reduced NAD

  3. Acetate combines with coenzyme A to produce to acetylcoenzyme A

  products of link reaction which occurs twice for everyturn

  2-acetylCoA

  2-co2 released

  2-reduced nad
• describe the process of the krebs cycle

  Acetyl CoA from the link reaction combines with a four-carbon molecule (oxaloacetate) to form a six-carbon molecule (citrate).

  • Coenzyme A goes back to the link reaction to be used again.

  The 6C citrate molecule is converted to a 5C molecule. •Decarboxylation occurs, where CO2 , is removed. • Dehydrogenation also occurs, where hydrogen is removed. • The hydrogen is used to produce reduced NAD from NAD.

  The 5C molecule is then converted to a 4C molecule.

  • D e c arboxylatio n and dehydrogenation occur, producing one molecule of reduced FAD and two of reduced N A D.

  • ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ADP. When a phosphate group is directly transferred from one molecule to another it's called substrate-level phosphorylation. Citrate has now been converted into oxaloacetate.
• what are the products of the krebs cycle?

  per cycle

  3-reduced NAD

  1-reduced FAD

  1-ATP

  2-co2

  per glucose molecule

  6-reduced NAD

  2-reduced FAD

  2-ATP

  4-CO2
• how are the products of the krebs cycle used in oxidative phosphorylation?

  1 coenzyme A - reused in the next link reaction

  Oxaloacetate- regenerated for use in the next krebs cycle

  2 CO2 - released as a waste product

  1 ATP- used for energy

  3 reduced NAD- to oxidative phosphorylation

  1 reduced FAD- to oxidative phosphorylation
• describe the process of oxidative phosphorylation?

  1) Hydrogen atoms are released from reduced NAD and reduced FAD as they're oxidised to NAD and FAD, The H atoms split into protons (H +) and electrons (e-).

  2) The electrons move down the electron transport chain (made up of electron carriers), losing energy at each carrier. 3) This energy is used by the electron carriers to pump protons from the mitochondrial matrix into the intermembrane space (the space between the inner and outer mitochondrial membranes).

  4) The concentration of protons is now higher in the intermembrane space than in the mitochondrial matrix — this forms an electrochemical gradient (a concentration gradient of ions).

  5) Protons then move down the electrochemical gradient, back across the inner mitochondrial membrane and into the mitochondrial matrix, via ATP synthase (which is embedded in the inner mitochondrial membrane). This movement drives the synthesis of ATP from ADP and in organic phosphate (Pj). 6) This process of ATP production driven by the movement of H + ions across a membrane (due to electrons moving d own an electron transport ch a in) is called chemiosmosis .

  7) In the mitochondrial matrix, at the end of the transport chain, the protons, electrons and O2 (from the blood) combine to form water. Oxygen is said to be the final electron acceptor.
• Describe how ATP is made in mitochondria. (6)

  - Substrate level phosphorylation / ATP produced in Krebs cycle;

  - Krebs cycle and link reaction produces reduced NAD and reduced FAD;

  - Electrons released from reduced coenzymes NADH and FADH;

  - Electrons pass along carriers through electron transport chain;

  - Energy released;

  - Protons move into intermembrane space;

  - ADP + Pi converted to ATP;

  - Catalysed ATP synthase;
• How can ATP production be affected by mitochondrial diseases?

  1) Mitochondrial diseases affect the functioning of mitochondria. They can affect how proteins involved in oxidative phosphorylation or the Krebs cycle function, reducing ATP production.

  2) This may cause anaerobic respiration to increase, to try and make up some of the ATP shortage.

  3) This results in lots of lactate being produced, which can cause muscle fatigue and weakness.

  4) Some lactate will also diffuse into the bloodstream, leading to high lactate concentrations in the blood.
• How do plants use the sugars from photosynthesis?

  Most of the sugars synthesised by plants are used by the plant as respiratory substrates. The rest are used to make other groups of biological molecules. These biological molecules form the biomass of the plants.
• plants photosyntheses and produce biomass

  1) An ecosystem includes all the organisms living in a particular area and all the non-living (abiotic) conditions.

  2) In all ecosystems, there are producers — organisms that make their own food

  3) During photosynthesis plants use energy and carbon dioxide to make glucose and other sugars

  4) Some of the sugars produced during photosynthesis are used in respiration, to release energy for growth.

  5) The rest of the glucose is used to make other biological molecules, such as cellulose .These biological molecules make up the plant's biomass — the mass of living material.

  6) Biomass can also be thought of as the chemical energy stored in the plant.

  7) Energy is transferred through the living organisms of an ecosystem when organisms eat other organisms.
• what is biomass?


  Biomass can be measured in terms of mass of carbon or dry mass of tissue per given area. The chemical energy store in dry biomass can be estimated using calorimetry.
• how can biomass be determined?

  1) Dry mass is the mass of the organism with the wa ter removed.

  2) To measure the dry mass, a sample of the organism is dried, often in an oven set to a low temperature. The sample is then weighed at regular intervals (e.g. every day). Once the mass becomes constant you know that all the water has been removed.
• how can the chemical store of biomass be determined?

  1) A sample of dry biomass is burnt and the energy released is used to heat a known volume of water.

  2) The change in temperature of the water is used to calculate the chemical energy of the dry biomass.
• what is Gross primary production (GPP)?


  Gross primary production (GPP) is the chemical energy store in plant biomass, in a given area or volume.

  its the total energy resulting in photosynthesis
• What is net primary production?

  Net primary production (NPP) is the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account

  This net primary production is available for plant growth and reproduction. It is also available to other trophic levels in the ecosystem, such as herbivores and decomposers.

  its the energy left over that is available to create new biomass.
• how does intensive rearing of domestic livestock increase energy conversion?

  -movement is restricted and so less energy is used in muscle contraction

  -the environment can be kept warm in order to reduce heat loss from the body (most intensively reared species are homeothermic)

  -feeding can be controlled so that the animals receive the optimum amount and type of food for maximum growth with no wastage

  -predators are excluded so that there is no loss to other organisms in the food web.
• how can NPP be reduced in relation to animals?

  (exam question model answer)

  1 Slaughtered when still growing/before maturity/while young so more energy transferred to biomass/tissue/production;

  2 Fed on concentrate /controlled diet /controlled conditions/so higher proportion of (digested) food absorbed/lower proportion lost in faeces / valid reason for addition;

  3 Movement restricted so less respiratory loss / less energy used;

  4 Kept inside/heating/shelter / confined so less heat loss / no predators; 5 Genetically selected for high productivity;