| What is the light-dependent reaction | - Needs light energy
- Takes place in the thylakoid membranes of the chloroplasts
- Includes two types of photophosphorylation |
| hOverview of the light-dependent reaction | - Light energy is absorbed by chlorophyll in the photosystems
- It excites electrons in the chlorophyll, releasing them from mol.
- Chlorophyll has been photoionised
- Some energy released by electrons used to add a phosphate to ADP to form ATP
- Some used to form reduced NADP
- ATP transfers energy, reduced NADP transfers H to the light-independent reaction
- During process H2O is oxidised to O2 |
| Structure of a chloroplast (photosytems) | - Have photosynthetic pigments
- Coloured substances, absorb light energy for photosyn.
- Pigments found in thylakoid membranes, attached to proteins
- Protein + pigment = photosystem
- There are 2 photosystems |
| The 2 photosystems | - PSI absorbs light best at longer wavelengths
- PSII absorbs light best at shorter wavelengths |
| How is the energy captured from the light in the light-dependent reaction used | - Making ATP from ADP + inorganic phosphate (photophosphorylation)
- Making reduced NADP from NADP
- Splitting water into protons (H+ ions), electrons + O2 (photolysis) |
| Oxidation | - Loss of electrons or loss of hydrogen or gain of oxygen |
| Reduction | - Gain of electrons or gain of hydrogen or loss of oxygen |
| What are the two types of photophosphorylation in the light-dependent reaction | - Non-cyclic (produces ATP, reduced NADP, O2)
- Cyclic (only produces ATP) |
| Non-cyclic photophosphorylation key steps (all happening together btw) | - Light energy excites electrons in chlorophyll
- Photolysis of water produces protons (H+ ions), electrons, O2
- Energy from the excited electrons makes ATP (chemiosmosis)
- Energy from the excited electrons generates reduced NADP |
| Light energy excites electrons in chlorophyll | - Light energy is absorbed by PSII
- It excites electrons in chlorophyll
- Electrons move to a higher energy level (they have more energy)
- These high energy electrons are released, move down ETC to PSI |
| Photolysis of water produces protons (H+ ions), electrons, O2 | - As electrons leave PSII to move down ETC, they must be replaced
- Light energy splits water into protons (H+ ions), electrons, O2 by photolysis |
| Equation for the photolysis of water | 2H20 ---------> 4H+ + 4e- + O2
water ----------> protons + electrons + oxygen |
| Chemiosmosis meaning | - Electrons flowing down ETC, creating proton gradient across membrane
- To drive ATP synthesis |
| Energy from the excited electrons makes ATP (chemiosmosis) | - Excited electrons lose energy as they move down ETC
- Energy used to transport protons into thylakoid via protein pumps
- Thylakoid has a higher conc. of protons than the stroma
- Protons move down their conc. gradient, into stroma, via ATP synthase channel proteins
- As the protons move, they change structure of the enzyme |
| Energy from the excited electrons generates reduced NADP | - Light energy is absorbed by PSI, which excites the electrons again to an even higher energy level
- Electrons are transferred to NADP, along with a proton (H+ ion) from the stroma, to form reduced NADP |
| Cyclic photophosphorylation | - Only uses PSI
- Electrons from chlorophyll aren't transferred to NADP, but are transferred to PSI via electron carriers
- So electrons are recycled + can repeatedly flow through PSI |
| How are chloroplasts adapted to carry out light-dependent reactions | - LSA of thylakoid membranes for attachment of chlorophyll
- Granal membranes have ATP synthase, catalyse production of ATP
- GM selectively permeable, allows formation of proton gradient
- Contain DNA + ribosomes, quickly + easily make proteins involved in reaction |
