The Light Dependent Reaction

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The Light Dependent Reaction
2010-04-06 08:02:39
biology photosynthesis light dependent

A test based on the light-dependent stage of photosynthesis. Aimed at A2 level biologists.
Show Answers:

  1. The light energy captured in the light-dependent stage of photosynthesis is used for 2 purposes. What are they?
    • 1) to add an inorganic phosphate (Pi) molecule to ADP, thereby making ATP
    • 2) to split water into H+ ions (protons) and OH- ions. As the splitting is caused by light, it is known as photolysis
  2. In terms of photosynthesis it is okay to think of oxidation as what?
    The combination of a substance with oxygen
  3. In terms of photosynthesis it is okay to think of reduction as what?
    The loss of oxygen from a substance
  4. Oxidation results in energy being (1) (2). Reduction results in energy being (3) (4).
    (1) given (2) out

    (3) taken (4) in
  5. Oxidation and reduction always...........
    occur together
  6. When a chlorophyll molecule absorbs light energy, it boosts the energy of a pair of electrons to a.......
    higher energy level.
  7. The electrons that leave the chlorophyll molecule after becoming excited are taken up by what?
    A molecule called an electron carrier
  8. Having lost a pair of electrons the chlorophyll molecule has been....(1)... Having gained a pair of electrons the electron carrier has been....(2)....
    • (1) oxidised
    • (2) reduced
  9. The electrons are now passed along a number of electron carriers in a series of what?
    oxidation-reduction reactions
  10. The electron transport chain is located in what?
    The membranes of the thylakoids.
  11. Each new carrier is at a (3 words) level than the previous one in the chain, and so the electrons lose energy at each stage. This energy is used to combine an inorganic phosphate molecule with an ADP molecule in order to make ATP.
    slightly lower energy
  12. Photolysis of water:
    The loss of electrons when light strikes a chlorophyll molecule leaves it short of electrons. If the chlorophyll molecule is to continue absorbing light energy, these electrons must be replaced. The replacement electrons are provided from water molecules that are split using light energy. This photolysis of water also yields hydrogen ions (protons). The equation for this process is:
    2H2O >>>>> 4H+ + 4e- + O2
    What is the word equation for this process?
    water goes to protons + electrons + oxygen
  13. These hydrogen ions (protons) are taken up by an electron carrier called?
  14. On taking up the hydrogen ions (protons) the NADP becomes?
  15. The reduced NADP then enters the light-independent reaction along with the electrons from the chlorophyll molecules. The reduced NADP is important because it is a further potential source of?
    chemical energy to the plant
  16. The oxygen by-product from the photolysis of water is either?
    used in respiration or diffuses out of the leaf as a waste product of photosynthesis
  17. The light-dependent reaction of photosynthesis takes place in the thylakoids of chloroplasts. The thylakoids are disc-like structures that are stacked together in groups called?
  18. Chloroplasts are structurally adapted to their function of capturing sunlight and carrying out the light-dependent reaction of photosynthesis in what 4 ways?
    1) The thylakoid membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the light-dependent reactions.

    2) A network of proteins in the grana hold the chlorophyll in a very precise manner that allows the maximum absorption of light.

    3) The granal membranes have enzymes attached to them, which help manufacture ATP.

    4)Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for the light-dependent reaction.