AOS2 Flashcards
Photosynthesis
Process of capturing light energy to power the production of glucose as energy.
Photosynthesis Inputs
6CO2 + 12H2O + (sunlight)
Photosynthesis Outputs
C6H12O6 + 6O2 + 6H2O
Stages of photosynthesis
Light-Dependent
Light-Independent
Light-Dependent
The first stage of Photosynthesis.
Occurs in the thylakoid membranes
Light-dependent inputs
- 12 H2O
- 12NADP+
- 18ADP + Pi
Light-dependent outputs
- 6 O2
- 12NADPH
- 18ATP
Light-dependent stages
- Light energy energises chlorophyll which pumps H+ and splits water.
- Oxygen is released from the chloroplast via stromata.
- H+ ions generate NADPH and ATP
- ATP and NADPH coenzymes then move onto the light-independent.
Light Independent
2nd stage of photosynthesis.
Occurs in the Stroma
NO LIGHT IS REQUIRED; reactions are energised by ATP and NADPH in coenzymes.
Enzymes in Photosynthesis
Catalyse reactions.
ATP synthase catalyses the reaction ADP + Pi = ATP.
Enzymes regulate each step ensuring reactions are sped up and controlled.
Coenzymes
Assists with reactions by donating energy.
Include: NADPH + ATP. (loaded)
Form unloaded NADP+ and ADP + Pi
Light-Independent Inputs
- 6 CO2
- 12 NADPH
- 18 ATP
Light-Independent Outputs
- Glucose
- 6 H2O
- 12 NADP+
- 18 ADP + Pi
Light-independent steps
- CO2 enters the Calvin cycle and undergoes an initial reaction.
- NADPH donates hydrogen ions + electrons; ATP breaks into ADP + Pi to release energy
- CO2 molecules change and rearrange.
- Leftover O2 combine with Hydrogen ions from NADPH to form water.
Rubisco
The key enzyme of the light-independent stage.
- Binds to CO2 and facilitates further reactions in photosynthesis.
- Binds to O2 to initiate photorespiration.
Role of rubisco in photosynthesis
Calvin Cycle
Responsible for the initial changes to CO2.
High O2, Low CO2 = More photoresp.
Low O2, High CO2 = Less photoresp.
Produce Glucose; 6G3P; 1G3P leaves to make glucose.
Steps of the Calvin Cycle
- Carbon Fixation.
- Reduction.
- Regeneration.
Carbon Fixation
Conversion of CO2 and RuBP into 3-PGA.
- Carbon from inorganic CO2 is fixed into an organic compound (glucose).
- Rubisco takes carbon from inorganic gaseous form (CO2) and incorporates it into an organic compound (3-PGA).
Reduction
NADH donates electrons to an intermediate 3-carbon molecule in the cycle to produce G3P.
Regeneration
The RuBP molecules needed to start the cycle again are reproduced.
Problem with Rubisco
- Sometimes O2 is used as a substrate instead of CO2.
Without RuBisCO CO2 pairing, PHS cannot proceed.
RuBisCO binds to O2 = Photorespiration.
Less PHS = less glucose + wasted energy. This negatively impacts plants’ ability to grow, survive and reproduce.
Factors influencing RuBisCO
Substrate concentration
Temperature
Substrate concentration (RuBisCO)
More substrate = greater chance of binding to an enzyme + undergoing reaction.
When plants need to conserve water…
Stomata will close causing O2 produced to build up inside cells = increased photorespiration.