1. Photosynthesis

2. Photosynthesis summary

3. Heterotrophs – organisms that consume other organisms as good
Heterotrophs – organisms that consume other organisms as good. Heterotrophs cannot make organic molecules from simple inorganic compounds so must ingest them.
Autotrophs – an organism that makes its own food from light or chemical energy without eating.

4. Photosynthesis
Method of converting sun energy into chemical energy usable by cells
Autotrophs: self feeders, organisms capable of making their own food
Photoautotrophs: use sun energy e.g. plants photosynthesis-makes organic compounds (glucose) from light
Chemoautotrophs: use chemical energy e.g. bacteria that use sulfide or methane chemosynthesis-makes organic compounds from chemical energy contained in sulfide or methane

5. Energy Shuttling
Recall ATP: cellular energy-nucleotide based molecule with 3 phosphate groups bonded to it, when removing the third phosphate group, lots of energy liberated= superb molecule for shuttling energy around within cells.
Other energy shuttles-coenzymes (nucleotide based molecules): move electrons and protons around within the cell
NADP+, NADPH NAD+, NADP FAD, FADH2

6. Photosynthesis 12H2O + 6CO2 → 6O2 + C6H12O6 + 6H2O
Water + Carbon dioxide → oxygen + glucose + water

7. Photosynthesis
Photosynthesis takes place in specialized structures inside plant cells called chloroplasts
Light absorbing pigment molecules e.g. chlorophyll

8. Chloroplasts Eukaryotic organelle in which photosynthesis takes place.
Contain their own genetic material and ribosomes.
Endosymbiotic theory: that chloroplasts were once prokaryotic cells that established a symbiotic relationship with a bigger host cell.

9. Chloroplasts
Grana: stacks of thylakoid membranes which are flat saclike structures. Contain the pigment absorbing light.
Stroma: fluid medium of the chloroplast. It is a gel like matrix rich in enzmes

10. Pigments
Light is absorbed by different pigments in the thylakoid membranes
Chlorophylls (green)
Carotenoids (orange)
Xanthophylls (yellow)
Chlorophylls absorb blue and red light wavelengths and reflect green (which is what we see)

11. Overall Reaction 6CO2 + 12 H2O + light energy → C6H12O6 + 6O2+ 6H2O
Carbohydrate made is glucose
Water appears on both sides because 12 H2O molecules are required and 6 new H2O molecules are made
Water is split as a source of electrons from hydrogen atoms releasing O2 as a byproduct
Electrons increase potential energy when moved from water to sugar therefore energy is required

12. There are two stages in photosynthsis:

13. Light dependent phase (in the thylakoid membrane)
The absorbed light energises the electrons within the chlorophyll energised and this is used to split the water molecules.
The electrons pass along the ‘electron transport system’ (ETS) which creates an stepwise transport of electrons that produces energy at every step. The electrons end up at an acceptor (NADP+) which temporarily stores the electrons.
This energy from the ETS pumps protons (H+) into the thylakoid space creating an ion gradient that is used to provide energy to drive the phosphorylation of ADP to ATP
The electrons at the end of the ‘electron transport system’ are accepted by NADP. It also accepts a H+ and becomes NADPH.
The oxygen is a by-product of photosynthesis.

14. Light-dependent Reactions
Photosystem: light capturing unit, contains chlorophyll, the light capturing pigment
Electron transport system: sequence of electron carrier molecules that shuttle electrons, energy released to make ATP
Electrons in chlorophyll must be replaced so that cycle may continue-these electrons come from water molecules, Oxygen is liberated from the light reactions
Light reactions yield ATP and NADPH used to fuel the reactions of the Calvin cycle (light independent or dark reactions)

15. Diagram of light dependent reaction

18. Light independent reaction (calvin-benson cycle)
Carbon dioxide, hydrogen ions (from NADPH) and ATP are used to create sugar molecules.
Note that NADPH and ATP is supplied from the light dependent reaction
Carbon fixation: incorporation of carbon dioxide into ribulose biphosphate, a 5 carbon organic molecules already present in the chloroplast
This is catalysed by the enzyme Rubisco.
This unstable 6 carbon molecule splits into two 3 carbon molecules.
ATP drives the cycle.
NADPH donates a H+ to form 12 3-carbon sugar phosphate molecules.
Two exit the cycle.
The remaining ones generate more ribulose biphosphate to start the cycle again.
The 3-carbon sugar phosphate molecules are the building blocks for the plants main carbohydrates

19. Calvin Cycle (light independent or “dark” reactions)
ATP and NADPH generated in light reactions used to fuel the reactions which take CO2 and break it apart, then reassemble the carbons into glucose.
Called carbon fixation: taking carbon from an inorganic molecule (atmospheric CO2) and making an organic molecule out of it (glucose)
Simplified version of how carbon and energy enter the food chain

21. PGA: phophoglycerate
PGAL: phosphoglyceraldehyde. This is the buidling block for lots of different carbohydrates.

22. Photosynthesis II comes first

25. Text questions to do Chapter 3
1-7 and (should have already done 8-18 with enzymes)
Apply understanding
1, 2, 3, 4,5, 6, 7, 8, 9, 10