Photosynthesis
- Created by: kira.watson
- Created on: 15-12-15 09:59
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- Photosynthesis
- Cholorplasts
- small, flattened organelles
- double membrane = chloroplast envelope
- thylakoids (fluid filled sacs) stack = grana
- grana = linked by (lamellae) thylakoid membrane
- Pigments
- chlorophyll a chlorophyll b carotene
- coloured substances that absorb light energy
- found in thylakois membranes - attached to proteins forming a photosystem
- PSI absorbs light best at 700nm, PSII absorbs light best at 680nm
- stroma = gel-like substance containing enzymes, sugars, organic acids and oil droplets
- Adaptations
- chloroplast envelope = keeps reactants for photosynthesis close to reaction sites
- thylakoids = large surface area to allow as much light energy as possible to be absorbed
- thylakoids = lots of ATP synthase present to produce ATP in the LDR
- stroma = contains enzymes, sugars and organic acids for LDR to take place
- Light Dependent Reaction
- LDR
- requires light energy
- takes place in thylakoid membrane of chloroplasts
- light energy = absorbed by pigments and converted to chemical energy
- light energy is used to add a phosphate group to ADP (forming ATP) and reduce NADP
- ATP transfers energy + reduced NADP transfers hydrogen to the LDR
- H20 is oxidised to O2
- Non-Cyclic Phosphorylation
- 1
- light energy = absorbed by PSII which excites electrons in chlorophyll
- electrons move to a higher energy level and move along electron transport chain to PSI
- 2
- the electrons that have left PSII need to be replaced
- light energy splits water into protons (H+ ions) and electrons and oxygen
- 2H2O -> 4H+ and O2
- 3
- excited electrons lose energy as they move along the electron transport chain
- energy is used to transport protons into thylakoid membrane
- thylakoid now has a higher concentration of protons
- protons move down concentration gradient into stroma via ATP synthase (energy from this forms ATP)
- 4
- light energy = absorbed by PSI - excites electrons to an evn higher level
- protons and electrons = transferred to NADP from stroma, forming reduced NADP
- 1
- Cyclic Phosphorylation
- only uses PSI
- electrons from the chlorophyll are passed back to PSI via electron carriers
- electrons are recycled and can repeatedly flow through PSI
- only produces small amounts of ATP
- LDR
- Light Independent Reaction
- Info
- involves reduction of CO2 (it's combined with hydrogen during a series of reactions
- triose phosphate is formed - it's used to make gluose + other useful organic substances
- energy and H+ ions provided by ATP and reduced NADP from the LDR are needed to keep the cycle going
- the starting component (ribulose biphosphate) is regenerated
- involves reduction of CO2 (it's combined with hydrogen during a series of reactions
- The Calvin Cycle
- takes place in stroma of chloroplasts
- reduces CO2 (it's combined with hydrogen during reactions)
- produces triose phosphate (used to make glucose)
- needs energy and H+ ions to keep it going (provided by ATP and reduced NADP from LDR)
- 3
- 5 out of every 6 molecules of TP produced aren't used to make hexose sugars, but to regenerate RuBP
- regenerating RuBP uses rest of ATP produced by LDR
- 5 out of every 6 molecules of TP produced aren't used to make hexose sugars, but to regenerate RuBP
- 2
- ATP from LDR provides energy to reduce GP to triose phosphate (TP)
- reduction reaction requires H+ ions from reduced NADP (and LDR) -> reduced NADP = recycled to NADP
- TP = converted to organic compounds e.g. glucose
- reduction reaction requires H+ ions from reduced NADP (and LDR) -> reduced NADP = recycled to NADP
- ATP from LDR provides energy to reduce GP to triose phosphate (TP)
- 1
- CO2 enters leaf through stomata, then diffuses into stroma pf chloroplast
- CO2 = combined with ribulose phosphate (RuBP) - a 5-carbon compound
- produces unstable 6-carbon compound -> breaks down into 2 molecules of 3-carbon compound: glycerate 3-phosphate (GP)
- ribose biphosphate carboxylase (rubisco) catalyses reaction between CO2 and RuBP
- produces unstable 6-carbon compound -> breaks down into 2 molecules of 3-carbon compound: glycerate 3-phosphate (GP)
- CO2 = combined with ribulose phosphate (RuBP) - a 5-carbon compound
- CO2 enters leaf through stomata, then diffuses into stroma pf chloroplast
- Organic Substances
- Carbohydrates: simple sugars (glucose) made my joining 2 TP molecules, and polysaccharides (starch/cellulose) made by joining 2 hexose sugars in different ways
- Amino acids: some = made from GP
- Nucleic acids: sugar in RNA = made using TP
- Lipids: made using glycerol synthesised from TP, and fatty acids synthesised from GP
- 6 turns = 1 glucose
- 6 turns requires 18 ATP and 12 reduced NADP from the LDR
- 5 out of 6 TP are used to regenerate RuBP
- Info
- Cholorplasts
- glucose has 6 carbons so 2 TP molecules are needed to form 1 glucose molecule
- cycle must turn 6 times to produce 2 molecules of TP that can be used to make 1 glucose
- 3 turns of calvin cycle = 1 TP produced (used to make glucose)
- 6 turns = 1 glucose
- 6 turns requires 18 ATP and 12 reduced NADP from the LDR
- 5 out of 6 TP are used to regenerate RuBP
- 6 turns = 1 glucose
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