UNIT 3 - AOS 2 - Photosynthesis Flashcards
How does light availability/intensity effect the rate of photosynthesis?
- The photosynthetic rate ^ as light intensity ^ until light saturation point (maximal point)
- The rate then plateaus because there is only so much light the plant can take in.
- At this point if there was a impact/limitation on the rate pf photosynthesis it would be due to a different factor. (CO2, Water, temp)
- chlorophyll pigments absorb violet, blue and red lights best
How does water availability effect the rate of photosynthesis?
WATER DEFICIT
= Limited water = stomata close to prevent water loss
- No gas exchange
- CO2 cant enter the plant -> photosynthesis stops
- prolonged = plant death
WATER LOGGING
= To much water in soil = decreased air spaces = depleted O2 in soil.
- Plant root cells can’t respire -> do not have energy to uptake water.
- Water is input for light dependent stage of photosynthesis
How does temperature effect the rate of photosynthesis?
Low temp = low amount of collisions = decreased photosynthesis rate
- As temp increases = collisions ^ = ^ photosynthesis rate
- When optimum is exceeded = enzymes begin to denature
How does carbon dioxide concentration effect the rate of photosynthesis?
If concentration of CO2 ^ = increased rate of photosynthesis until it plateaus
Plateaus due to:
1. enzymes involved in carbon fixation (rubisco) being saturated with substrate.
2. Not enough availability of co-enzymes ; NADH & ATP
Light Dependent stage - C3 plants
LOCATION: Thylakoid (chloroplasts)
INPUTS: H2O, ADP+Pi, NADP+, Solar energy
OUTPUTS: O2, ATP, NADPH
- water is the supplier of hydrogen atom that makes NADP+ –> NADPH = loaded coenzyme.
- oxygen is the by-product of splitting water
Light- Independent stage (CALVIN CYCLE) - C3 plants
LOCATION: Stroma
INPUTS: ATP, NADPH, CO2
OUTPUTS: ADP+Pi, NADP+, Glucose
*Rubisco is the acceptor of Carbon molecules & enzyme which helps fix the inorganic carbon dioxide to RUBP.
*NADPH is the donor of hydrogen to make the glucose molecule
- 1. Rubisco accepts the CO2 molecules and sends it into carbon cycle after creating a unstabel 6 carbon molecule where they become 3-PGA (= 3 carbon molecule)
2. ATP and NADPH unload to transform the 3-PGA to G3P–> 2 G3P then go off to create Glucose (2xG3P = 6 carbons)
3. The rest of the G3P then uses ATP to create RuBP = more rubisco (6 carbon molecules)
C3 Plants -> characteristics of photosynthesis
- 85% of plants
- cool, moist areas
- e.g. wheat, rice, oat
- All photosynthesis occurs in mesophyll cells
Photorespiration
When rubisco binds with oxygen instead of CO2
-> the active site of rubisco can accommodate for oxygen and carbon dioxide.
-> Glucose isn’t produced = less efficient
How does and increase in temperature ^ rate of photorespiration (C3 plants)
- Leaves are exposed to ^ temps
- Ability of Rubisco to distinguish between CO2 and O2 decreases
- Rubisco binds to O2
- Rate of respiration ^
How does dried out conditions ^ photorespiration (C3 plants)
(decrease in water availability = stomata close to retain water within leaves = less gas exchange)
- Conditions dry out
- Stomata close
- CO2 cant enter and O2 can’t leave the leaves
- ^ O2 concentrations within the leaf
- ^ rate of photorespiration.
C4 plant characteristics
- 3% of plants
- warm & tropical environments
- e.g. sugar cane, mullet
- Photosynthesis occurs in mesophyll cells (carbon fixation) and bundle sheath cells (glucose production)
Describe photosynthesis in a C4 plant
STAGE 1: CARBON FIXATION
(carbon dioxide -> malic acid.)
- Occurs in mesophyll cells
- PEP carboxylase is use to join carbon dioxide to a carrier molecule.
- PEP carboxylase enzyme can only bind to CO2 at its active site = decreases photorespiration.
- The carbon dioxide is then fixed into Oxaloacetic acid to then become malic acid
STAGE 2: GLUCOSE PRODUCTION
- Occurs in bundle-sheath cells
- Glucose production via the Calvin cycle.
- C4 produce a steady supply of carbon dioxide from the breakdown of malic acid. = ^ CO2 in leaves.
- Malic acid is constantly converted to pyruvate and carbon dioxide.
Photosynthesis in CAM plants
STAGE 1 - CARBON FIXATION
- Mesophyll cells -> at Night
- Stomata are open allowing free passage of CO2 into leaves
- CO2 is fixed into oxaloacetic acid and then malic acid.
- Malic acid is stored in vacuoles in the plant cells until after sunrise.
STAGE 2 - GLUCOSE PRODUCTION
- Mesophyll cells -> daylight
- Stomata are closed
- The stored malic acid is transported from vacuoles into the stroma of chloroplasts. and is broken down into CO2
- The steady release of CO2 increases the amount in leaves helping rubisco enzyme bind to CO2 -> then Calvin cycle occurs.
