photosynthesis. -the transfer of energy from sunlight to organic molecules -occurs in green plants,...
TRANSCRIPT
Photosynthesis
- the transfer of energy from sunlight to organic molecules
- occurs in green plants, algae and some bacteria
- involves a complex series of chemical reactions
Chloroplasts
- the organelle in plants where photosynthesis takes place
- double outer membrane- stroma (solution)- thylakoids (interconnected stacks of grana)
Sunlight
- electromagnetic spectrum
Pigment - compound that absorbs light
Chloroplast pigments:- chlorophylls (mostly a and b)- carotenoids (yellow, orange, brown)
Accessory pigments (chlorophyll b, carotenoids)
Electron Transport
The energy from sunlight is transferred from one molecule to another through electrons
Photosystem - clusters of pigment molecules
Step 1: light is absorbed by chlorophyll a in photosystem II, which causes the electrons to be “excited”
Step 2: excited electrons move to primary electron acceptor
Step 3: excited electrons move through electron transport chain
Step 4: light is absorbed by chlorophyll in photosystem I, and excited electrons move through etc
Step 5: excited electrons combine with NADP+ to form NADPH (will be used in next step
Chemiosmosis
ATP is produced
NADPH and ATP is used in the next part of photosynthesis - the Calvin Cycle
The Calvin Cycle
Produces organic compounds using the energy from ATP and NADPH formed during the light reactions.
The Calvin cycle “fixes” carbon from CO2.
Step 1: CO2 diffuses into the stroma. An enzyme combines a CO2 molecule with a 5-carbon molecule (RuBP). The 6-carbon molecule splits into a pair of 3-carbon molecules (PGA)
Step 2: PGA is converted into PGAL using ATP and NADPH.
Step 3: Some PGAL molecules can be used to make organic compounds
Equation for Photosynthesis
6CO2 + 6H2O + light energy -->
C6H12O6 + 6O2
Three turns of the Calvin cycle require nine ATP and six NADPH.
Mr. Durand Photosynthesis Song
Photosynthesis Song
Alternative Pathways
C3 plants - plant species that fix carbon exclusively through the Calvin cycle.
C4 plants - plant species that fix CO2 into four-carbon compounds- plants that partially close their stomata during the hottest part of the day-examples - corn, sugar cane, crabgrass
CAM plants - plant species that fix CO2 at night when their stomata are open-grow fairly slowly-lose less water than C3 or C4 plants-examples - cactuses, pineapples
Rate of Photosynthesis
Affected by:- light intensity - rate increases then levels off to a plateau- CO2 levels - rate increases then levels off to a plateau- temperature - rate increases, peaks at a certain temp, then decreases