bisc exam 2-photosynthesis Flashcards
What is Photosynthesis, and why do plant cells do it?
process by which plants utilize light energy from the sun, CO2 from the atmosphere and H2O from the Earth to produce glucose.
Plants ( are autotrophs, meaning they can synthesize their own food.
What other organisms are photosynthetic?
Cyanobacteria
Various types of algae
what are the two phases of photosynthesis? and where do they take place
- light reactions in the thylakoid membrane of the chloroplast
- calvin cycle in the stroma (think cytoplasm) of the chloroplast
what is a photopigment?
chemical that absorbs energy in the form of photons (from sun)
what is the primary photopigment in plants? and what light frequencies does it absorb?
chlorophyll - all forms of chlorophyll absorb high frequency light like 400-500 nm (purple blue light) and absorbs some low frequency light like 600-700nm (yellow orange light), but reflects 500-600nm (green light)
what would happen if a plant with green leaves (chlorophyll present) was exposed to green light
would not be able to perform light dependant reactions of phtosythesis - In these reactions, photons, or “packets” of light energy from the sun, as well as water are used to power the transport of electrons (and the subsequent generation of a proton gradient) so that oxygen can be synthesized and some ATP can be produced. Additionally, a new electron carrier NADPH is formed in this phase, and will be used in the Calvin Cycle (or dark reactions).
what happens during light reaction phase?
photons, or “packets” of light energy from the sun, as well as water are used to power the transport of electrons (and the subsequent generation of a proton gradient) so that oxygen can be synthesized and some ATP can be produced. Additionally, a new electron carrier NADPH is formed in this phase, and will be used in the Calvin Cycle (or dark reactions).
tldr: mainly acts as an electron transport chain and (limited) ATP synthesis and the end products are ATP and NADPH for the calvin cycle
what are some similarities between cellular respiration and photosynthesis?
-produce a form of energy (cell respiration=ATP, Photosynthesis=glucose)
-consist of a series of redox reactions
what are some differences between cellular respiration and photosynthesis?
-photosynthesis is largely anabolic (ie. reducing (gain electron) CO2 to make glucose), while cellular respiration is largely catabolic (ie. oxidizing(losing electron) glucose to make ATP)
-photosynthesis relies on light energy to catalyze, while cell respiration relies on metabolic energy (glucose and carbs) to catalyze
do cellular respiration and photosynthesis ever occur at the same time?
the two processes are cyclical in some plant cells (ie. the water and CO2 produced from cell respiration is used by chloroplast in photosynthesis which produces O2 and glucose that mitochondria can use for cellular respiration again)
what is a photosystem?
membrane-bound protein complexes embedded within thylakoid membrane within the chloroplast. they are involved in light reactions of photosynthesis
Which of the following membranes/ regions in the chloroplast is functionally equivalent to the cristae membrane in mitochondria?
Thylakoid membrane
what processes happen during the light reaction phase?
light enters P ll –> H20 oxidized to O2 (also referred to as water splitting)1` –> light enter P l and the electrons from oxidizing in P ll enter too which contribute to reducing NADP+ to NADPH
-simultaineously protons (H+) are bing pushed against concentration gradient (stroma into thylakoid lumen)
-WHY?
what happens at P700 under P l?
For every 2 photons, 2 electrons are transferred from:
Plastocyanin (Pc), to
Chlorophyll a, to
Ferredoxin (Fd), to
NADP+ (to become NADPH)
Water is split into oxygen at which of the following protein complexes?
Photosystem II only
what is noncyclic Photophosphorylation also referred to as
Z scheme
where does cyclic Photophosphorylation take place
(the cyclic form) typically occurs in cyanobacteria or other photosynthetic prokaryotes.
can also occur in plant cells like we have been discussing with non-cyclic
differences between cyclic and noncyclic Photophosphorylation
cyclic: non-clyic:
Only PSI PSI and PSII
H2O not used H2O used
No O2 made O2 made
No NADPH made NADPH made
ATP for cell energy ATP for Calvin Cycle
where does non-cyclic Photophosphorylation take place
in plants with more accessto water (ie. to have H2O split at PS ll)
what is the calvin cycle?
the light-independent reactions or darkness reactions after the light dependant reactions. there are 5 reactions total split into 3 phases
what are the 3 phases of the calvin cycle and how many reactions are in each?
- carbon fixation- 1 reaction
- reduction- 2 reactions
- regneration of RuBp- 2 reactions
what is the net reaction of the calvin cycle
3CO2 + 6NADPH + 5H2O + 9ATP → Glyceraldehyde-3-Phosphate (G3P) + 2H+ + 6NADP+ + 9ADP + 8Pi
what happens during carbon fixation phase in the calvin cycle?
Ribulose-1,5,-bisphosphate (RuBP) combines with CO2 to produce an unstable six-carbon intermediate that ultimately splits into two 3-phosphoglycerate (3-PG) molecules.
This reaction must take place at a minimum of 3 times to accumulate enough 3-PG to:
Produce enough G3P at the end of the cycle to be transformed into glucose.
Produce enough G3P at the end of the cycle to regenerate RuBP.
what happens during reduction phase in the calvin cycle?
Two chemical reactions that produce glyceraldehyde-3-phosphate (G3P).
result in the reduction of 3-phosphoglycerate to glyceraldehyde-3-phosphate (G3P). In the process, one ATP molecule is used for each 3-phosphoglycerate that is reduced, and one NADPH is oxidized to NADP+ in the process. A minimum of 2 G3P molecules are required to ultimately produce glucose (which again, does not happen during the Calvin Cycle itself), but typically more G3P molecules are produced in order to synthesize glucose and regenerate RuBP in the final phase of the Calvin Cycle.
what happens during regneration phase in the calvin cycle?
utilize some of the G3P produced to reproduce RuBP (other G3P molecules are used outside of the Calvin Cycle to produce glucose).
A minimum of 2 G3P molecules are necessary to resynthesize a single RuBP molecule. ATP is also used in this process.
what are Mycorrhizae?
class of fungi that are often (physically) associated with the roots of a plant, and thus exist within the soil. these fungi are good at sequestering carbon (in the form of CO2) from the atmosphere, and provide some of this CO2 to their plant hosts. The mycorrhizae also benefit from the CO2, as they undergo their own form of (non-photosynthetic) carbon fixation.
what is photorespiration?
when [O2] > [CO2], RuBisCo binds oxygen instead of CO2 and catalyzes the process known as photorespiration.
This process is wasteful, as it uses energy produced from the light-dependent reactions of photosynthesis but does not result in the synthesis of a useful intermediate for the Calvin Cycle.
what is transpiration?
the process of plants releasing water through small pore located on the underside of their leaves called stomata(plural of stoma)
what circumstances will make C3 plants open their stomata?
high humidity, heat from direct sunlight and/or low CO2 concentration
why do plants avoid photorespiration/ try to mitigate it?
the process is wasteful bc it uses ATP but doesn’t do anything
how do C3 plants mitigate photorespiration?
3 Plants have no mechanism for mitigating photorespiration
where does the calvin cycle happen in C3 plants
mesophyll cells
examples of C3 plants
wheat and soybean
how do C4 plants mitigate photorespiration?
spatial mechanism- initial CO2 fixation occurs in mesophyll cells, and the subsequent Calvin cycle takes place in specialized bundle sheath cells, maximizing CO2 concentration and minimizing photorespiration.
examples of C4 plants
corn and sugarcane
how do CAM plants mitigate photorespiration?
temporal-close their stomata during the day and take up CO2 at night, when the air temperature is lower, still have increased CO2 in mesophyll cells like C4 plants
examples of CAM plants
desert or tropical plants-pineapple
