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.
Temperature (RuBisCO)
Reg temp = RuBisCO affinity for CO2 is greater than O2.
High Temp = Affinity (attraction) for O2 is higher, leading to RuBisCO binding to oxygen more often, leading to photorespiration.
C3 Plants
No Features to fight photorespiration.
“Normal”
Normal photosynthesis.
No evolved adaptations to minimise photorespiration.
eg. Trees, Cereals, nuts, fruit and vegetables.
C4 Plants
Minimise photoresp by separating initial carbon fixation and the remainder of the Calvin cycle over space.
Light Dependent is different for C4 than C3.
Initial carbon fixation occurs in the mesophyll.
Remainder Calvin cycle in specialised cells (bundle sheath cells).
C4 Process (light-independent)
- CO2 enters mesophyll cells and fixed by PEP, creating oxaloacetate. (4-carbon cell)
- Oxaloacetate converts into malate (4-carbon molecule) capable of being transported to bundle-sheath cells.
- Malate breaks down, CO2 is released and enters the Calvin cycle –> glucose production.
- Pyruvate formed (from malate) is transported back to mesophyll cell and converted into PEP (ATP helps).
- PEP –> fixation of CO2 and production of oxaloacetate; cycle repeats.
ALWAYS HIGHER CO2 –> PHOTORESP MINIMISED.
CAM plants
Minimise photoresp by separating initial carbon fixation and the remainder of the Calvin Cycle over time.
HOT ENVIRONMENTS.
Eg. Cactai, Pineapples, Vanilla.
At night in CAM plants
Stomata open; to bring in CO2.
Malate formed from PEP –> (oxaloacetate) (same in c4 plants)
BUT…
Malate is then stored inside the vacuoles within mesophyll cells until day time.
Daytime in CAM plants
Stomata remain closed, preventing water loss.
- Still PHS during the day; malate is cut out of the vacuole and broken down to release CO2; enter Calvin cycle; glucose produced.
Effects on the rate of PHS
- Light.
- Temperature + pH.
- Carbon dioxide.
- Water.
- Enzyme inhibitation.
Light (PHS)
Light increase = PHS increase (to a certain point - plateaus).
Plateaus
No further change can occur; due to:
- Reach maximum possible rate of PHS.
- Other inputs or requirements for PHS is limiting the rate. (Limiting Factor; reactants needed for PHHS which there isn’t enough of).
Temperature + pH (PHS)
PHS rate greatest at optimal temp.
Above optimal temp = denature of enzymes.
Optimal pH = enzymes function best; PHS fastest.
Below Optimal pH = enzymes denature.
Carbon Dioxide (PHS)
High CO2 concentration = Increased PHS (til X (plateaus))
Low CO2 = limit PHS rate.
Water (PHS)
Water stress; casued by droughts or hot weather periods.
Stomata close=limiting exchange of CO2 + O2(more abundant)–> therefore initiate photoresp.
Closed stomata = Low CO2, High O2; decreasing photosynthesis.
Enzyme Inhibition
Influence function of genes; enzyme inhibitor; binds to and prevents an enzyme from functioning.
- Competitive
- Non-competitive
LOWER PHS RATE.
Competitive inhibitor
Hinder enzyme by blocking the active site and preventing the substrate from binding.
Non-competitive inhibitor
Hinders an enzyme by binding to an allosteric site and changing the shape of the active site preventing the substrate from binding.
CRISPR in Agriculture.
- Edit genome of agricultural crops.
Therefore; increasing the amount of crops grown to meet the needs of a growing population.
Gene editing = maximise crop productivity.
How CRIPSR improves PHS rate and crop yields.
Engineer crops that bypass photorespiration,
Improve..
- Target RuBisCO function directly
- Edit the function of chloroplast to become more efficient
- Target stomata to reduce water loss.
Cellular respiration
Cells create usable energy to breakdown large molecules and produce ATP.
Occurs via 2 biochemical pathways:
- Aerobic
- Anaerobic
Aerobic Respiration
Occurs in the presence of oxygen, releasing more energy but slowly.
Consists of 3 stages.
3 Stages of Aerobic Respiration
- Glycolysis
- Krebs Cycle
- Electron transport chain (ETC)
Glycolysis
Occurs in the cytosol
Inputs:
- Glucose
- 2 ADP + 2 Pi
- 2 NAD+ and 2 H+
Outputs:
- 2 pyruvate
- 2 ATP
- 2 NADH
Energy is released to be used by the cell.
Role of the Krebs Cycle
To generate high-energy electrons and proton carriers (NADH and FADH2) that can be used in ETC.
Linking Glycolysis and Krebs
- Pyruvate is transported to mitochondria and combines with coenzyme A to create acetyl-CoA
Krebs cycle
Occurs in the mitochondrial matrix
Inputs:
- 2 acetyl-CoA (derived from 2 pyruvate).
- 2 ADP + 2 Pi
- 6 NAD+ and 6 H+
- 2 FAD + 4 H+
Outputs:
- 4 CO2
- 2 ATP
- 6 NADH
- 2 FADH2
Electron Transport chain
Occurs in the inner membrane of the mitochondria (cristae).
Inputs:
- 6 O2 + 12H+
- 26/28 ADP + 26/28 Pi
- 10 NADH
- 2 FADH2
Outputs:
- 6 H2O
- 26/28 ATP
- 10 NAD+ and 10H+
- 2 FAD + 4H+
Enzymes + co-enzymes in cellular respiration
Catalyse reactions of cellular respiration and allow them to proceed at higher rates.
Unloaded enzymes
ADP, NAD+ and FAD
Loaded enzymes
ATP, NADH and FADH2
Anaerobic Fermentation
Occurs in the absence of oxygen and releases less energy but quickly.
Stages:
- Glycolysis
- Lactic acid fermentation (animals) or ethanol fermentation (yeast).
Anaerobic Fermentation in animals
Undertake this due to insufficient oxygen availability.
- Glycolysis
glucose -> 2pyruvate ->2lactic acids.
|. |
2ADP+Pi ->2ATP.
2NAD+ -> 2NADH —- >2NADH ->2NAD+
Ethanol fermentation (yeast)
Also, involves glycolysis but instead pyruvate —> ethanol + CO2.
glucose -> 2pyruvate -> 2 ethanol + CO2
|. |
2ADP+Pi ->2ATP.
2NAD+ -> 2NADH —-> 2NADH ->2NAD+
Factors influencing the rate of cellular respiration
- Glucose
- Temperature
- O2 Concentration.
Factors influencing the rate of cellular respiration
GLUCOSE
Increase glucose = increase rate of cell resp.
Decrease glucose = decrease rate of cell resp.
Factors influencing the rate of cellular respiration
OXYGEN
High O2 = increased rate of aerobic respiration.
Low O2 = switch to anaerobic respiration.
No O2 = no cell resp.
1/2 O2 + 2e- + 2H+ —-> H2O
Factors influencing the rate of cellular respiration
TEMPERATURE
cooler temp = less enzyme substrate collisions lowering cell resp rate.
Optimal temp = enzyme activity and cell resp will increase til max.
Above temp = denatured enzymes; negative impact on cell resp rate.
Biomass
Organic material from living things
Biofuel
Fuel derived from bio-mass (organic material)
Biofuel production steps
- Deconstruction
- Digestion
- Anaerobic or ethanol fermentation.
- Purification + Hydration.
Deconstruction (Biofuel)
Enzymes, acid and heat are used to crush the biomass.
Digestion (Biofuel)
Simple enzymes are added to break down cell walls and starch into simple sugars such as glucose.
Anaerobic or ethanol fermentation. (Biofuel)
Microorganisms (yeast + bacteria) produce ethanol + CO2.
Purification + Dehydration (Biofuel)
Of Ethanol so that it is useable, as a liquid fuel.
Benefits of Biofuel
Renewable
Many materials can be used, eg:
- Corn.
- Garbage.
- Sewage.
- Landfill
Drawbacks of Biofuel
- High-sugar products (many foods) are easier to make biofuels from.
- Low sugar options are costly to process into biofuel.
- Land requirements to allow biomass time to ferment.
- Efficiency is low. (Transportation of biomass is energy expensive).
