Photosynthesis. Introduction. Autotrophs : any organism that can make their own food. Photoautotrophs : use light energy Chemoautotrophs change inorganic chemicals such as hydrogen sulfate into chemical energy. Important structures.
two outer membranes
thylakoid membrane system
Organelle of photosynthesis in plants and algae
b One of the photosynthetic cells inside leaf
leaf’s upper epidermis
photosynthetic cell in leaf
leaf’s lower epidermis
6H2O + 6CO2
6O2 + C6H12O6
Where the two stages of photosynthesis occur inside the chloroplast
Electron returns to resting, unexcited state.
Excited electrons are passed to other atoms.
Chief way energy moves through cells
Molecules that gain electrons always carry greater energy than before receiving them
Can view this as passing of potential energy from molecule to molecule
ADP + Pi
end products (e.g., sucrose, starch, cellulose)
Pores for gas exchange
C4 plants produce an enzyme that is better at attracting carbon (in addition to RUBISCO) called PEP Carboxylase
allows CO2to be taken into the plant very quickly
"delivers" the CO2 directly to RUBISCO
Called C4 because the CO2is first incorporated into a 4-carbon compound
Stomata are open during the day
photosynthesizes faster than C3 plants under high light intensity and high temperatures
better water use efficiency because PEP Carboxylase brings in CO2faster doesn’t need to keep stomata open as much
C4 plants include several thousand species in at least 19 plant families, including corn & sugarcane
C4 photosynthesis also adds additional energy expense; outcompeted in mild climates by C3 plants.
CAM = CrassulaceanAcid Metabolism
after plant family in which it was first found (Crassulaceae)
because CO2is stored as an acid before use in photosynthesis
Stomata open at night (evaporation rates usually lower), closed during day
CO2 converted to acid, stored @ night
acid broken down
CO2 released to RUBISCO for photosynthesis
better water use efficiency than C3s under arid conditions
open stomata @ night when transpiration rates are lower
no sunlight, lower temperatures, lower wind speeds, etc.
May CAM-idleunder extremely arid conditions
leave stomata closed night and day
O2 given off in photosynthesis is used for respiration
CO2given off in respiration is used for photosynthesis
kind of like a perpetual energy machine, but plant cannot CAM-idle forever
allows plant to survive dry spells, recover very quickly when water is available again (unlike plants that drop their leaves and twigs and go dormant during dry spells)
C4 and CAM photosynthesis originally evolved as successful adaptations to hot/dry regions
Researchers are now using these adaptations to fight world hunger.
several genes that code for the C4 photosynthesis enzymes have been introduced from corn into rice
once in rice, genes increase rice plant’s ability to photosynthesize higher growth rates and food yields