What is a plastid
organelle found in plants and algae
Plastid function
- storage
- photosynthesis
- color
different types have different function
structure of plastid
- double membrane (like mitochondria)
- membranes split by intermembrane space
- contains flattened and interconnected Saks (thylakoids)
- contains circular DNA
- divide by binary fission
Thylakoids
flattened and interconnected sacs (imagine stack of pita breads) site of photo system 2
somata
cells on epidermis (skin) that open and close to allow gas into the cell
mesophyll cell
where photosynthesis takes places, contains chloroplasts
photosynthesis equation
6CO2 + 12 HO2 = C6H12O + 6H2O + 6O2
2 photosynthesis routes
- linear flow
- cyclic
linear flow
primary pathway, uses PS1 and PS2
- produced NADPH + ATP with light energy
- O2 released
- electron in dimer gets hit with light energy and leaves photosynthesis leaving a gap
- gap is filled by electron from water splitting
- proton pumped from storm to thylakoid
- proton gradient –> ATP synthase for ATP production
cyclic oxygen flow
ATP produced, only photosystem 1 used
- no O2 released
- produces more ATP
Calvin Cycle
uses Rubisco (key enzyme) to produce glucose
- if high temps: somata closes
- prevents water loss
- CO2 concentration in cell drops
- photorespiration favored
photorespiration
rubisco fixes O2 instead of Co2
- wasteful –> no incorporation of C into sugar
- plants evolved to deal with this
Rubisco
key enzyme in Calvin Cycle
- does not fix cycle
instead…
- separates locations
- allows somata to stay open at night
- reduces efficiency
