Photosynthesis - 13 Flashcards
Basic equation for photosynthesis?
CO2 + H20 –> C6H12O6 + O2
Where does the light dependent reaction occur?
Thylakoid
Where does the light independent reaction occur?
Stroma
Basic equation for light dependent reaction?
Water — Light energy —- O2 released —- ADP +Pi to ATP —> H
Basic equation for Light independent reaction?
H —- CO2 added — ATP to ADP +Pi —-> Glucose
Light-dependent reaction
Comes first
Photolysis: Light energy splits water into H+ (protons) + e-s + O2
Light energy absorbed by photosystems
Light energy excites electrons in the chlorophyll
Chlorophyl has been photoionised
Energy released from electrons used to form ATP when travelling down the ETC and reduce NADP to NADP using e-s + H
ATP transfers energy and reduced NADP transfers hydrogen to the light-independent reaction
H20 is oxidised to O2 which is released into the atmosphere
Use of energy from photoionisation
Making ATP from ADP and inorganic phosphate - photophosphorylation
Making NADPH from NADP
Photolysis
Non-cyclic photophosphorylation
Photosystems are linked by electron carriers
Producing ATP from the ETC
Light energy is absorbed by PSII
Light energy excites electrons in chlorophyll
Electrons move to a higher energy level
High energy electrons released from the chlorophyl and move down the electron transport chain to PSI
As the excited electrons leaves the chlorophyl photolysis occurs
Energy used to transport protons into the thylakoid, causing a higher concentration and therefore producing a proton gradient
Protons move down the their concentration gradient via the enzyme ATP synthase
Forms ATP from ADP and inorganic phosphate
Light energy absorbed by PSI, exciting the electrons further, electrons transferred to NADP along with proton (H+) from the stroma to produce NAPH
Light Independent reaction
Calvin cycle
5C RuBP is carboxylated by CO2 under the addition of the enzyme rubisco
6C molecule is formed which immediately is broken down to 2x3C molecules (GP)
GP is converted to TP using a phosphate from the breakdown the breakdown of ATP–>ADP and H from NADPH –> NADP
TP continues to make 5C RuBP
1C sugar released
Every 3 turns of the Calvin Cycle one molecule of TP is regenerated
6 turns makes 1 molecule of 6C Glucose (Hexose sugar)
Names of all molecules in Calvin Cycle
RuBP = Ribulox Biphosphate GP = Glycerate phosphate TP = Triose Phosphate
Why is ATP a good energy source?
Releases a small, manageable amount of energy at time so no energy is wasted as heat
Small, soluble so is easily transported
Easily broken down
ATP can’t pass out of cell so the cell always has an immediate source of energy
Photosynthesis-limiting factors: light intensity?
Light intensity measured in LUX
Increase in light intensity increases rate of photosynthesis when light intensity is limiting factor
Will level off when temp or CO2 becomes a limiting factor - saturation point
Chlorophyl absorbing light?
Energy needed for light independent reaction
Only certain wavelengths can be absorbed - red and blue light in the sunlight
Green light is reflected - why plants look green
Temperature affecting plants
Photosyntehsis involves enzymes (ATP synthase, Rubisco) - falls below 10 degrees become inactive - more than 45 degrees denatures
High temperatures stomata close - photosynthesis slows down due to less CO2 intakes
Photosynthesis-limiting factors: Temperature?
As temp increases molecules have more kinetic energy
Enzyme and substrate collide more frequently
Increased the rate of photosynthetic reactions
Above optimum temp the enzyme becomes denatured
