127 terms

DAT Bootcamp - Photosynthesis

STUDY
PLAY
_____ are organisms (like humans) that obtain chemical energy from the food they eat
heterotrophs
_____ organisms are capable of making their own food
autotrophic
_____ (like plants) capture solar energy and convert it to chemical energy by photosynthesis
photoautotrophs
_____ is where chemical energy originates
photosynthesis
photosynthesis releases _____, which is crucial for aerobic cellular respiration
oxygen
photosynthesis removes _____ from the atmosphere, working against the _____ effect
carbon dioxide; greenhouse
photosynthesis uses _____ to make _____
photons (light energy); sugars (glucose)
_____ occurs when inorganic carbon is incorporated into an organic molecule
carbon fixation
write the overall chemical equation for photosynthesis:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
what are the 2 stages of photosynthesis?
light dependent reactions; Calvin cycle
_____ use light energy to excite electrons from split water molecules
light dependent reactions
light dependent reactions release _____, synthesize _____, and reduce _____
O2; ATP; NADP+ to NADH
the _____ uses energy stored in ATP and NADPH to fix inorganic carbon dioxide into an organic glucose molecule
Calvin cycle (or light independent reaction)
the Calvin cycle (or light independent reaction) uses energy stored in ATP and NADPH to fix _____ into an _____ molecule
inorganic carbon dioxide; organic glucose
photosynthesis stores solar energy in glucose chemical bonds - how do plants use that energy?
aerobic cellular respiration
photosynthesis has a positive Gibbs free energy (+ ΔG), so it is _____ and _____
non-spontaneous; endergonic
the overall reactions of aerobic cellular respiration and photosynthesis are _____
opposites
solar energy is input to photosynthesis to convert 6 _____ & 6 _____ to 1 _____ and 6 _____
CO2; H2O; Glucose; O2
chemical energy is released as heat and ATP during aerobic cellular respiration, where 1 _____ and 6 _____ convert to 6 _____ & 6 _____
glucose; O2; CO2; H2O
cellular respiration and photosynthesis are similar because they both rely on _____ reactions
redox
photosynthesis and cellular respiration use _____ that create a _____ electrochemical gradient
ETCs; H+
the electrochemical gradients of photosynthesis and cellular respiration allow for _____ by _____
ATP synthesis; chemiosmosis/proton motive force
ATP from the light dependent reactions is not used to _____
power the cell
ATP from the light dependent reactions is consumed to power the _____, which makes glucose
Calvin cycle
Calvin cycle _____ undergoes cellular respiration to produce the ATP that does power the cell
glucose
_____ tissue is found on roots, stems, leaves, flowers, fruits, and seeds - it protects from injury, water loss, and infection
epidermis
_____ mesophyll cells conduct most photosynthesis
palisade
palisade mesophyll cells contain many _____, and are well organized as a single layer below the _____
chloroplasts; upper epidermis
spongy mesophyll cells conduct some photosynthesis, but not as much as the _____
palisade mesophyll
spongy mesophyll cells have few _____, and do not receive _____
chloroplasts; much light
spongy mesophyll cells are found near _____
the lower epidermis
gaps between spongy mesophyll cells facilitate the movement of gases through the _____
stomata
stomata are pores mainly found in the _____ and they are the site of _____
bottoms of leaves; atmospheric gas exchange
_____ surround stomata, and they control whether the stomata are open or closed
guard cells
_____ are dual membrane organelles found in plants and photosynthetic algae
chloroplasts
organisms with chloroplasts for photosynthesis will have _____ for cellular respiration too
mitochondria
like mitochondria, chloroplasts make _____ and have their own _____ & _____
ATP; DNA; ribosomes
chloroplasts contain thylakoids, which capture _____ for the light dependent reactions
photons
the outer/inner membranes of a chloroplast do not absorb photons for the _____
light dependent reactions
both stages of photosynthesis occur within _____
chloroplasts
_____ are photosynthetic organisms that do not have a chloroplast
cyanobacteria
the _____ is the fluid inside the inner membrane of a chloroplast
stroma
the Calvin cycle occurs in the _____ of the chloroplast
stroma
_____ are mini organelles within the stroma of a chloroplast, and the light dependent reactions occur on their membranes
thylakoids
a stack of thylakoids is called a _____
granum
a junction between two grana is called a _____
lamella
H+ ions for chloroplast chemiosmosis accumulate in the _____
thylakoid lumen
ATP synthase is found on the _____ of a chloroplast
thylakoid membrane
ATP synthesis in a chloroplast occurs as H+ flow from the _____ to the _____
thylakoid lumen; stroma
thylakoid membranes have _____ to capture photons
photosystems
photosystems are large _____ that contain special _____, including chlorophylls and carotenoids
proteins; pigments
photosystem _____ are directly responsible for absorbing photons
pigments
what are the 2 important photosystems for photosynthesis?
photosystem I and II
photosystems have a _____ of chlorophyll molecules, known as the _____
special pair; reaction center
what is responsible for making plant leaves green - why?
chlorophyll - reflects green light
the special pair in photosystem I is known as _____ because it absorbs _____ nm wavelengths the best
P700; 700
the special pair in photosystem II is known as _____ because it absorbs _____ nm wavelengths the best
P680; 680
_____ is the splitting of H2O molecules into e-, H+, and O2
photolysis
where does photolysis take place?
photosystem II of the thylakoid lumen
what is the formula for photolysis?
H₂O → 2 e⁻ + 2 H⁺ + ½ O₂
where do electrons travel after photolysis at photosystem II?
the special pair at P680 of photosystem II
as e- travel down the first ETC of the thylakoid membrane, they release energy to be used for _____ into the _____
H+ pumping; thylakoid lumen
after traveling down the primary ETC of the thylakoid membrane, e- will reach _____
photosystem I (P700 special pair)
what happens when e- reach the special pair of P700 at photosystem I?
re-energized using solar energy --> travel down secondary ETC
what is the purpose of the secondary ETC (following PSI) in the light-dependent reactions?
to reduce NADP+ --> NADPH using NADP+ reductase
describe the pathway of non-cyclic photophosphorylation
photolysis --> PSII (P680) --> primary ETC --> PSI (P700) --> secondary ETC --> NADP reductase to make NADPH
non-cyclic photophosphorylation requires light to be absorbed _____, one time at each photosystem
twice
electrons do not travel to _____ in cyclic photophosphorylation, so _____ is not produced
NADP+ reductase; NADPH
describe the general pathway for cyclic photophosphorylation:
photolysis --> PSII (P680) --> primary ETC --> PSI (P700) --> primary ETC --> PSI (P700) --> etc.
this replenishes ATP when the Calvin cycle consumes it
cyclic photophosphorylation
where do the photosynthetic ETCs of the light dependent reactions lie?
thylakoid membrane
what are the products of the light dependent reactions?
ATP and NADPH
the Calvin cycle is sometimes referred to as the _____ because it does not use light energy directly
light independent reactions
the _____ cannot occur without light because it is dependent on the high energy molecules produced from the light reaction (ATP and NADPH)
Calvin cycle
the Calvin cycle fixes _____ into _____
inorganic carbon dioxide; organic glucose
the Calvin cycle repeats 6 times: uses _____ to produce _____
6 CO₂; 1 C₆H₁₂O₆ (glucose)
list the 4 steps of the Calvin cycle
carbon fixation; reduction; regeneration; carbohydrate synthesis
describe the carbon fixation (step 1) of the Calvin cycle
6 CO2 + 6 RuBP → 12 PGA

catalyzed by RuBisCo
the most common protein in the world; catalyzes the carbon fixation step in the Calvin cycle
RuBisCo
'normal' photosynthesis can also be called _____ because the carbon fixation step of the Calvin cycle makes three-carbon molecules
C3 photosynthesis
describe the reduction (step 2) of the Calvin cycle
12 ATP + 12 NADPH converts 12 PGA → 12 G-3-P
where do the 12 ADP and 12 NADP+ go after reduction (step 2) of the Calvin cycle?
back to the thylakoid for the light-dependent reactions
describe the regeneration (step 3) of the Calvin cycle
6 ATP converts 10 (of the 12) G-3-P → 6 RuBP

(allows the cycle to repeat)
describe carbohydrate synthesis (step 4) of the Calvin cycle
2 remaining G-3-P (leftover from step 3) are used to build glucose
RuBisCo can bind _____, even though it has a much higher affinity for _____
oxygen; carbon dioxide
RuBisCo is actually called RuBP carboxylase/oxygenase - why?
it has 2 different functions; carboxylation when it binds to CO2 and oxygenase when it binds to O2
RuBisCo's carboxylase function allows for _____
C3 photosynthesis
RuBisCo's oxygenase function results in _____
C₂ photosynthesis (photorespiration)
_____ involves fixation of oxygen by the RuBisCo enzyme, but produces no ATP or sugar
C₂ photosynthesis (photorespiration)
_____ is when water evaporates out of the stomata
transpiration
plants in hot and dry environments close their stomata to minimize _____, which leads to the buildup of _____
transpiration; oxygen

(O2 can't leave and CO2 can't enter the leaf)
RuBisCo is encouraged to bind oxygen and photorespiration starts to occur when it is _____ and plants _____
hot and dry; close their stomata
where does photorespiration/C2 photosynthesis occur?
chloroplast stroma
what are the 2 products of after RuBP is oxygenated in C2 photosynthesis/photorespiration?
PGA (3 carbon) and phosphoglycolate (2 carbon - hence C2 photosynthesis)
the byproducts of photorespiration are metabolized by _____ & _____
peroxisomes; mitochondria
2 2 carbon phosphoglycolate molecules regenerate _____, with the loss of 1 carbon at the _____
1 3 carbon PGA

mitochondria
if RuBisCo were to bind 6 _____ molecules to carboxylate RuBP, there would be a net gain of _____ fixed carbon atoms as 1 _____ molecule
CO2; 6; glucose
if iRuBisCo were to bind 6 _____ molecules to oxygenate RuBP, there would be a _____ fixed carbon atoms and no _____ would be made
O2; net loss of 3; glucose
what are 2 mechanisms plants have evolved to minimize photorespiration?
C4 and CAM photosynthesis
C4 photosynthesis uses an enzyme called _____, to combine CO2 and PEP at the mesophyll cell
PEP carboxylase
in C4 photosynthesis, CO2 + PEP in the presence of PEP carboxylase makes _____ at the mesophyll cell
oxaloacetate
in C4 photosynthesis, oxaloacetate converts to malate at the _____
mesophyll cell
C4 photosynthesis is called C4 because..?
both oxaloacetate and malate are 4 carbon compounds
in C4 photosynthesis, malate is transported from _____ cells to _____ cells, via _____
mesophyll; bundle sheath; plasmodesmata
in C4 photosynthesis, malate is decarboxylated at the _____ cells to release _____ and 3 carbon pyruvate
bundle sheath; 1 carbon CO2
the CO2 released at the bundle sheath cell of C4 photosynthesis can undergo fixation using _____
RuBisCo
what is the advantage of bundle sheath cells in C4 photosynthesis?
they do not contain as much O2, so photorespiration is less likely
what happens to the 3 carbon pyruvate at the bundle sheath cell of C4 photosynthesis?
it is shuttled back to the mesophyll cell alongside the hydrolysis of ATP --> AMP
what does pyruvate convert into when back at the mesophyll cell of C4 photosynthesis?
PEP for more C4 cycles
C4 photosynthesis occurs in a small percentage of plants living in _____ environments
hot
C4 photosynthesis prevents photorespiration through the _____ of carbon dioxide
spatial isolation
_____ means that inorganic carbon is transported to a different location to prevent photorespiration
spatial isolation
CAM plants use _____, which prevents photorespiration through timing
temporal isolation
CAM plants close their stomata to prevent transpiration during the _____
day
_____, CAM plants have their stomata open, allowing carbon dioxide to enter the leaf
at night
after CO2 diffuses into the mesophyll of CAM plants (at night), what happens?
PEP carboxylase takes CO2 (1 carbon) + PEP (3 carbon) --> oxaloacetate (4 carbon) --> malate (4 carbon)
what happens to the 4 carbon malate molecule produced in CAM photosynthesis?
it is stored in the mesophyll vacuole for later use
in CAM photosynthesis, malate will leave the mesophyll vacuole and convert back into oxaloacetate during..?
the next day - when stomata are closed and ATP + NADPH are being produced in abundance by the light-dependent reactions
daytime oxaloacetate (4 carbon) of CAM photosynthesis will hydrolyze _____ to produce _____ and _____
ATP --> ADP; CO2 (1 carbon); PEP (3 carbon)
CAM daytime CO2 combines with RuBP in the presence of RuBisCo to enter the _____
Calvin cycle
the overall advantage is that _____ photosynthesis can proceed during the day while stomata are closed (reducing _____ loss)
CAM; H₂O
most photosynthetic organisms utilize _____ photosynthesis
oxygenic
oxygenic photosynthesis releases oxygen into the atmosphere via the _____ at _____ of the light dependent reactions
photolysis of water; photosystem II
_____ does not use water as an initial electron source for the light dependent reactions
anoxygenic photosynthesis
anoxygenic photosynthesizers consume (and fix) _____, but they do not release _____ into the environment
inorganic carbon dioxide; oxygen
some common anoxygenic photosynthesizers include..?
green and purple sulfur bacteria
green and purple sulfur bacteria use _____ as their source of protons and electrons for the light dependent reactions
hydrogen sulfide (H2S)
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