1. Sustaining Life on Earth
PHOTOSYNTHESIS
Sustaining Life on Earth

3. Photosynthesis STAGE 1: LIGHT REACTION
In the thylakoid membrane, light energy is captured by pigments which release electrons
Water is broken down,releasing electrons and producing oxygen gas
These free electrons, travel through a series of membrane proteins (electron transport chain) and in the process, ATP and NADPH are produced (reduced form of NADP+)
STAGE 2: DARK REACTION (Calvin Cycle)
In the stroma, NADPH, CO2, and the energy from ATP are used to make glucose
All of these stages occur in the chloroplasts of palisade cells.

4. Both xylem and phloem are vascular tissues found in a plant.
Xylem is a tubular structure which is responsible for water transport from the roots towards all of the parts of the plant.
Phloem is also a tubular structure but is responsible for the transportation of food and other nutrients needed by plant.
Xylem imports water and minerals while Phloem transports water and food. Xylem exists as non-living tissue at maturity, but phloem is living cells.

5. Photosynthesis Overview

6. The Light Reaction
In this stage, plants use Photosystems I and II to make ATP and NADPH which will be used in the dark reaction to produce glucose.
This stage involves a series of steps that all occur in the thylakoid membrane of the chloroplast.

7. What is a Photosystem?
A multisubunit complex found mainly in the thylakoid membranes.
It is primarily involved in capturing light to cause a series of redox reactions.

9. Photosystems I and II

10. A photon strikes photosystem II and exites one electron of chlorophyll P680. The electron is passed on to the electron acceptor pheophytin, then to plastoquinone, then through an electron transport chain.
Pheophytin is the primary electron acceptor from chlorophyll 680 in photosystem II.

11. Z protein breaks water into O2 gas (leaves the cell by diffusion), H+ ions (build up in the thylakoid lumen) and 2 electrons which replace those lost by PSII.

12. As electrons pass through the Q cycle, H+ ions are transported from the stroma into the thylakoid lumen. 4 H+ ions move in for every 2 electrons passed through the cycle. These electrons are used to replace the electrons lost by PSI.

13. Excited electrons from photosystem I are passed to ferredoxin, then to the enzyme NADP reductase which helps to reduce NADP+ to NADPH.

14. H+ that has built up in the thylakoid lumen moves through the ATP synthase protein, and one ATP is made for every 4H+ that pass through. This is called photophosphorylation

15. An Overview
A photon strikes photosystem II and exites one electron of chlorophyll P680. The electron is passed on to the electron acceptor pheophytin, then to plastoquinone, then through an electron transport chain.
Z protein breaks water into O2 gas (leaves the cell by diffusion), H+ ions (build up in the thylakoid lumen) and 2 electrons which replace those lost by PSII.
As electrons pass through the Q cycle, H+ ions are transported from the stroma into the thylakoid lumen. 4 H+ ions move in for every 2 electrons passed through the cycle. These electrons are used to replace the electrons lost by PSI.
Excited electrons from photosystem I are passed to ferredoxin, then to the enzyme NADP reductase which helps to reduce NADP+ to NADPH.
H+ that has built up in the thylakoid lumen moves through the ATP synthase protein, and one ATP is made for every 4H+ that pass through. This is called photophosphorylation.

16. The Light Reaction

17. End Result of Light Reaction:
H2O is broken down, O2 gas produced
Proton gradient created by H+ ions is used to create ATP molecules
The electrons make it to the final electron acceptor, NADP+, reducing it to NADPH
ATP and NADPH are only generated when the sun’s light energy is harnessed  they both go on to the dark reaction where they are used to create glucose

18. www. unitedstreaming.com
REFERENCES:
www. unitedstreaming.com
Nelson Biology 12. Thompson Canada Ltd Pages 157, 158, 160.
Nelson Biology 12 Student CD
© R. Scarth