Topic 5 - On the Wild Side Flashcards
(20 cards)
Features of the photosynthesis reaction
- photosynthesis require energy from light to split apart bonds in water molecules
- the hydrogen from the water molecules reacts with CO2 to form glucose (a fuel)
- oxygen is released into the atmosphere
Photolysis
the splitting of water by light
Phosphorylation of ADP
ADP + Pi + energy -> ATP
- condensation reaction
- catalysed by ATP synthase
Hydrolysis of ATP
ATP + H2O -> ADP + Pi + energy
- third phosphate group is removed and energy stored within this bond is released
- catalysed by ATPase
LDR step 1
Light needs to be harvested
Energy from a photon is used to do two things:
- excites two electrons in the chlorophyll molecule, causing them to leave
- allows an enzyme in PSII to split water (photolysis)
LDR step 2
Electrons from PSII are excited
- energy from light raises two electrons to a higher energy level
- they leave the chlorophyll molecule and pass through a series of electron carrier molecules
LDR step 3
The Electron Transport Chain
- the electrons that were captured by the first electron carrier now pass down the ETC, releasing energy as they pass from one electron carrier to the next
- this energy is used to pump H+ ions into the thylakoid space
LDR step 4
Photophosphorylation
- hydrogen ions have accumulated in the thylakoid space, creating a concentration gradient
- they diffuse out via a channel in an ATP synthase enzyme
- this enzyme makes ATP from ADP and inorganic phosphate
LDR step 5
Electrons from PSI
- excited electrons from PSI will enter another ETC, eventually combining with and reducing NADP
- two electrons and two hydrogen ions will react with NADP for form reduced NADP
LDR step 6
Photolysis of water
- produces protons and electrons
- allows for replacement of electrons lost from reaction centre in photosystem II
LIR 1st stage
Carbon fixation
- in the stroma, carbon dioxide combines with a 5C compound - RuBP
- this reaction is catalysed by an enzyme called RuBISCO
- this forms an unstable 6C compound (other C comes from carbon) which immediately breaks down into two 3C molecules called GP
LIR 2nd stage
Reduction
- GP is reduced into GALP (also 3C)
- this requires the ATP and NADPH from light-dependent reactions
- reduced NADP provides the hydrogen for the reduction of GP
- ATP provides the energy needed for this endothermic reaction
GALP -> glucose
2 out of every 12 GALP molecules formed are involved in the formation of glucose (6C)
LIR 3rd stage
Regeneration
- 10 out of every 12 GALP molecules formed are involved in the recreation of RuBP
- The 10 GALP molecules rearrange to form 6 5C compounds, then phosphorylation using ATP forms RuBP
- this requires energy from the hydrolysis of ATP
How glucose from the Calvin Cycle is used
synthesis of:
- polysaccharides (starch for storage, cellulose for cell wall)
- lipids (waterproofing and energy storage)
- amino acids (to make proteins)
- nucleic acids (DNA and RNA)
used in respiration to produce carbon dioxide and water and release energy
Stroma
the fluid surrounding the thylakoid membranes that contains all enzymes needed to carry out the light-independent reactions of photosynthesis
Thylakoid
a system of interconnected flattened, fluid-filled sacs, where the light-dependent reactions take place
- provides large SA
- contains: photosynthetic (pigments e.g. chlorophyll), electron carriers, ATP synthase
Granum
a stack of thylakoids joined to one another
Starch grain
stores the product of photosynthesis
Photosystem
a protein complex consisting of a light-harvesting system and reaction centre that is involved in the absorption of light and transfer of electrons in photosynthesis
