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Photosynthesis

Terms in this set (29)

Photosynthesis equation
6CO2 + 6H2O + light energy --> C6H12O6 + 6O2
ATP
- releases small amount of energy (none lost through heat)
- easily broken down (released instantly)
-small & soluble (easily transported)
- quickly remade
- causes phosphorylation to make other molecules more reactive
-can't pass out of cell
Metabolic Pathway
A series of small reactions controlled by enzymes
Phosphorylation
adding a phosphate to a molecule
Photophosphorylation
Adding phosphate to a molecule using light
Photolysis
The splitting of a molecule using light energy
Photoionisation
When light energy 'excites' electrons in an atom or molecule, giving them more energy and causing them to be released.
The release of electrons causes the atom or molecule to become a positively-charged ion.
Hydrolysis
The splitting of a molecule using water
Decarboxylation
The removal of carbon dioxide from a molecule
Dehydrogenation
The removal of hydrogen from a molecule
Redox Reactions
Reactions that involve oxidation and reduction
Coenzymes
Molecule that aids function of an enzyme
- work by transferring a chemical group from one molecule to another
Chloroplast
-flattened organelle surrounded by double membrane
-thylakoids are stacked up (grana) and linked together by lamellae
-contain photosynthetic pigments to absorb light energy needed for photosynthesis
-pigments are attached to proteins which form photo systems
-stroma is held within inner membrane surrounding thylakoids, it contains enzymes, sugars and organic acids
-carbs not used straight away are stored in starch grains in stroma
Light-Dependant Reaction
1) Occurs in thylakoid membranes
2) Light energy absorbed by chlorophyll in photosystems. Electrons become excited which leads to their release from molecule (photoionisation of chlorophyll)
3) Energy from released electrons to add to phosphate group to ADP to produce ATP, and some is used to reduce NADP to produce rNADP.
4) ATP transfers energy and rNADP transfers hydrogen to light-independent reaction
5) H20 is oxidised to O2
Production of ATP (LDR)
1) electrons pass down electron transfer chain from PSII to PSI via redox reactions, losing energy at each step
2) energy used to actively transport protons from stroma into thylakoid
3) creating electrochemical (proton) gradient across thylakoid membrane
4) protons move via facilitated diffusion down electrochemical gradient into stroma via ATP synthase embedded in thylakoid membrane
5) energy from this allows ADP+Pi-> ATP
Production of rNADP (LDR)
In PSI electrons are excited and transferred to NADP (with proton from photolysis) to reduce NADP, forming rNADP
Products of LDR
-ATP, light independent reaction
- rNADP, light independent reaction
- oxygen, leaves cell as by-product or used in respiration
Light-Independent Reaction
Also known as Calvin Cycle
- occurs in stroma
- ATP and rNADP supply energy and hydrogen to make simple sugars from CO2
Non-Cyclic Photophosphorylation I
1) light energy absorbed by PSII
2) electrons excited in chlorophyll
3) electrons move to higher energy level
4) high-energy electrons are released from chlorophyll and move down electron transfer chain to PSI
Non-Cyclic Photophosphorylation II
1) electrons that leave must be replaced
2) Light energy splits water into protons (H+ ions), electrons and O2 (photolysis)
H2O-> 2H+ + 0.5O2
Non-Cyclic Photophosphorylation III
1) electrons lose energy as they move down transport chain
2) energy is used to transport protons into thylakoid so there is a higher concentration of protons; creating proton gradient across thylakoid membrane
3) protons move down concentration gradient into stroma via enzyme ATP synthase which is embedded in thylakoid membrane. Energy combines ADP + Pi-> ATP
Non-Cyclic Photophosphorylation IV
1) light energy is absorbed by PSI which excited electrons to even higher energy level
2) electrons are transferred to NADP along with H+ ion from stroma to form rNADP
cyclic photophosphorylation
-only uses PSI
-electrons from chlorophyll aren't passed onto NADP, and instead passed back via electron carriers
-electrons are recycled and repeatedly flow through PSI
-only produces small amounts of ATP
Calvin Cycle I
-CO2 enters leaf through stomata and diffuses into stroma
-combines with ribulouse biphosphate (RuBP, 5C) (reaction catalysed by rubisco)
-produces unstable-6C molecule which breaks down into 2x3C molecule: glyeracte 3-phosphate (GP)
Calvin Cycle II
-hydrolysis of ATP (from LDR) provides energy to turn GP into triose phosphate (TP, 3C)
-reaction requires H+ ions which come from rNADP
-rNADP recycled to NADP
- some TP is converted to useful organic compounds (glucose, etc) and some continues in Calvin cycle
Calvin Cycle III
-5/6 molecules of TP produced in cycle regenerate RuBP
-this uses rest of ATP produced by LDR
Useful Organic Substances
- TP & GP are converted into useful organic substances, such as glucose
- Carbs (hexose sugars) are made by joining 2 TP molecules (larger ones made by joining hexose sugars in different ways)
- Lipids made using glycerol that is synthesised from TP, and fatty acids which are synthesised from GP
-Amino acids, some are made from GP
Limiting factor- light intensity
- rate of photosynthesis increases with factor
- if factor was dramatically reduced:
> levels of ATP and rNADP would fall because LDR limited due to less photoionisation of chlorophyll
> leading to LIR to stop, then GP can't be reduced to TP meaning TP can't regenerate RuBP as these all require ATP &/ rNADP
Limiting factor- CO2 concentration
- rate of photosynthesis increases with factor
- if factor was dramatically reduced:
> LIR limited
>less ... to combine with RuBP to form GP
> Less GP reduced to TP
> less TP converted to organic substances
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