Chapter 8: Photosynthesis Flashcards
photosynthesis
energy within light is captured and used to synthesize carbohydrates
biosphere
regions on the surface of the Earth and atmosphere where living organisms exist
energy cycle
cells use organic molecules for energy and plants replenish those molecules using photosynthesis
heterotroph
must eat food (organic molecules from their environment) to sustain life
autotroph
makes organic molecules from inorganic ones
photoautotroph
use light as a source of energy
chloroplast
organelle in plants and algae that carries out photosynthesis
stomata
carbon dioxide enters and oxygen exits leaf through here
inter-membrane space
separates inner and outer membrane
thylakoid membrane
contains pigment molecules, encloses thylakoid lumen
granum
stack of thylakoids
stoma
fluid filled region between thylakoid membrane and inner membrane
two stages of photosynthesis
light reactions in thylakoid membrane
calvin cycle in stoma
absorption spectrum
wavelengths that are absorbed by different pigments
action spectrum
rate of photosynthesis by whole plat at specific wavelengths
photosystem 1
primary role to make NADPH
addition of H+ to NADP+ contributes to H+ gradient by depleting H+ from stroma
photosystem 2
first step in photosynthesis, excite ground state electrons
light excites pigment molecules in PS 2 and PS 1
photophosphorylation
chemiosmotic mechanism that causes ATP synthesis, driven by the flow of H+ from thylakoid lumen into stroma
three chemical products from photosynthesis
oxygen
NADPH
ATP
noncyclic
electrons begin at PS 2 and eventually transfer to NADPH, linear process
produces ATP and NADPH in equal amounts
cyclic photophosphorylation (electron flow)
electron cycling releases energy to transport H+ into lumen driving ATP synthesis
homologous genes
similar because they are derived from a common ancestral gene
photosystem 2 steps
1 - light harvesting complex
2 - reaction center
light harvesting complex
directly absorbs photons, energy transferred via resonance energy transfer
reaction center
electron transfers to primary electron acceptor and captured
z scheme
zig-zag shape of the energy curve; photosynthesis involves increases and decreases in the energy of an electron as it moves from PS 2 through PS 1 to NADPH
Calvin cycle (Calvin-Benson cycle)
requires massive input of energy (18 ATP + 12 NADPH) product is G3P
Calvin cycle phases
carbon fixation
reduction and carbohydrate reduction
regeneration of RuBP
carbon fixation
CO2 incorporated into RuBP using rubisco enzyme; product is a six-carbon intermediate that splits into two 3-phosphoglycerate molecules (3PG)
reduction and carbohydrate reduction
6CO2 –> 12 G3P, ATP used to convert 3PG into 1,3 biphosphoglycerate (1,3 BPG), NADPH electrons reduce it to G3P
regeneration of RuBP
10 G3P are converted into 6 RuBP using 6 ATP
variations in photosynthesis
environmental conditions can influence both the efficiency and the way the Calvin cycle works (light intensity, temperature, water availability, CO2 availability)
photorespiration
O2 added to RuBP and releases CO2, likely in hot and dry environments, essentially Calvin cycle but the sugar is recycled and not created, happens to C3 plants
carboxylase
bonds to CO2
oxygenase
bonds to O2
C3 plants
make 3PG and cannot survive in deserts due to performing photorespiration and wasting energy
C4 plants
evolved a mechanism to minimize photorespiration
mesophyll cells
CO2 enters via stomata and 4 carbon compound formed (PEP carboxylase doesn’t perform photorespiration)
bundle-sheath cells
4 carbon molecule transferred that releases steady supply of CO2, minimizing photorespiration
