WJEC A-level Biology Photosynthesis

• Photosynthesis equation

  6CO2 + 6H2O --> light energy --> C6H12O6 + 6O2
• What is point where the rates of reaction of respiration and photosynthesis are the same?

  Compensation point
• Leaves are lost when

  Sunlight is low and they'd loose too much energy
• Where does photosynthesis occur?

  Chloroplast
• Which layer are the photosynthesis takes place?

  Mainly palisade mesophyll cells/guard cells of green leaves
• What is cytoplasmic streaming?

  The movement of cytoplast to the best position for light absorption and photosynthesis.
• Why are chloroplasts transducers?

  They convert the energy of light photons into chemical energy of ATP.
• What are the two main types of pigments?

  Chlorophylls and carotenoids.
• Chlorophylls absorb what colour light?

  Red and blue-violet regions. Green reflected
• Carotenoids absorb what colour light?

  Blue-violet. Orange/yellow are reflected.
• What absorbs light energy and converts it to chemical?

  Photosynthetic pigments
• What is the absorption spectrum?


  A graph plotting a pigment's light absorption versus wavelengths of light
• What is the action spectrum?

  The rate of photosynthesis versus wavelengths of light
• Why does each pigment absorb at a different wavelengths?

  Helps the plant carry out photosynthesis at a wider range of wavelengths and increase the rate of photosynthesis.
• What is chromatography for?

  To separate mixtures of substances into their components.
• What is the stationary phase?

  Where the molecules can't move. It is a solid or a really thick liquid
• What is the mobile phase?

  Where the molecules can move. This is always a liquid or a gas
• What is the Rf value?

  distance moved by substance/distance moved by solvent
• What is used to show up colourless amino acids in chromatography?

  Ninhydrin
• What happens to the leaf if there are more chloroplasts?

  The leaves become greener or darker.
• What does cyclic photophosphorylation produce?

  ATP and NADPH2
• What does non-cyclic photophosphorylation produce?

  ATP
• Where are chlorophylls and carotenoids found?

  Thylakoid membranes.
• What are antenna complexes?

  Groups of pigments like chlorophylls and accessory pigments.
• What pigment is the primary pigment?

  Chlorophyll a-in the reaction centre.
• Where are the accessory pigments found?

  Antenna complex.
• Where does light dependent photosynthesis take place?

  Thylakoid membrane.
• What are the absorption peaks of PSI and PSII?

  PSI-700. PSII-680
• What is the splitting of water called?

  Photolysis
• Explain non-cyclic photophosphorylation

  Light strikes PSII exciting electrons passing onto electron acceptor. Water split, electrons replace those in chlorophyll a. Go down electron transport chain, loose energy to proton pumps pumping into thylakoid space. Creates gradient where protons go through ATP synthase creating ATP. Excited electrons in PSI (same thing with chlorophyll a) replaces electrons from PSII, electron acceptor reduces NADP, creates NADPH2.
• What is the final electron acceptor in non-cyclic photophosphorylation?

  Reduced NADP
• What is the source of electrons in non-cyclic photophosphorylation?

  Water and PSII
• Explain cyclic photophosphorylation.

  Light is absorbed in PSI excited electrons go back down electron transport chain to produce ATP.
• Where does the light independent stage occur?

  Stroma
• Explain the Calvin Cycle

  RuBP combines with CO2 using the enzyme Rubisco forming an unstable 6 carbon compound that immediately splits into 2x3-carbon compound called GP. GP is then phosphorylated by ATP and reduced by NADPH2 to a triose phosphate TP. 10/12 molecules of TP stay in the cycle and get reused. 2 go off and form glucose. (Glucose needs 2xTP to form 1x glucose due to number of carbons.) The rest of the TP uses ATP to reform RuBP to carry on the cycle.
• Explain Calvins experiment.

  Radioactive CO2 is given to algae. After different set amounts of time it is dropped into alcohol. Then chromatography is used to separate the molecules.
• What is autoradiographs?

  X-rays places next to the chromatogram to see where there are radioactive substances. The darker and bigger the spots the more of a molecule there is.
• What is the law of limiting factors?

  When a chemical process is affected by more than one factor its rate is limited by that factor which is nearest its minimum.
• How do you find the limiting factor?

  Keep increasing the factors to work out which is the limiting one.
• What is chorosis?

  A condition where leaves don't produce enough chlorophyll causing leaves to be pale, yellow or yellow/white