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Photosynthesis converts solar energy into...
chemical energy
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Autotrophs...
- are the producers of the biosphere
- plants are photo autotrophs using sunlight to make organic molecules from H2O and O2
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Heterotrophs are...
the consumers of the biosphere, they obtain their organic material from other organisms
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Chloroplasts are structurally similar to and likely evolved from
photosynthetic bacteria
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What is the major location of photosynthesis?
leaves
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where do plants get their green colour?
from chlorophyll, the green pigment within chloroplasts
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Light energy absorbed by chlorophyll drives the synthesis of what?
of organic molecules in chloroplasts
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CO2 enters and O2 exits the leaf through microscopic pores called...
stomata
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Where are chloroplasts mainly found?
In the mesophyll, interior tissue of the leaf
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How many chloroplasts does the typical mesophyll have?
30-40 chloroplasts
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Chlorophyll is in a membrane of...
thylakoids
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What are the stacks thylakoids are in called?
grana
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Photosynthesis consists of two stages...
light reactions (photo) and the calvin cycle (synthesis)
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What does the light reaction (in the thylakoids) look like?
- -split H2O
- -Release O2
- -Reduce NADP+ to NADPH
- -Generate ATP from ADP by photophosphorylation
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The Calvin cycle (in the stroma) forms sugar from?
CO2, using ATP and NADPH
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What does the Calvin cycle begin with?
carbon fixation, incorporating CO2 into organic molecules
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What are the reactants and products of photosynthesis?
- Reactants: 6CO2 12H20
- Products: C6H12O6 6H2O 6O2
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Chloroplasts are chemical...
factories
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What do thylakoids transform light energy into?
chemical energy of ATP and NADPH
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Light behaves as though it consists of discrete partials called....
photons
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what is the electromagnetic spectrum?
the entire range of electromagnetic energy, or radiation
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What are pigments and what do they do?
pigments are substances that absorb visible light. Different pigments absorb different wavelengths
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What are chlorophyll a, chlorophyll b, and carotenoids and what do they do?
- Chlorophyll a--is the main photosynthetic pigment
- Chlorophyll b--broadens the spectrum used for photosynthesis
- Carotenoids--absorb excessive light that would damage chlorophyll
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What does a photosystem consist of?
a reaction center complex surrounded by light harvesting complexes
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What does the primary electron acceptor do?
in the reaction centers accepts an excited electron from chlorophyll a
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What is the first step of the light reactions?
Solar powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor
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What are the two types of photosystems in the thylakoid membrane?
Photosystem I (PSI) and photosystem II (PSII)
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Explain photosystem II (PSII)
PSII functions first and is best at absorbing a wavelength of 680nm
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What is the reaction center chlorophyll a of PSII called?
P680
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What wavelength is photosystem I (PSI) best at absorbing?
700nm
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The reaction center chlorophyll a of PSI is called...
P700
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What are the two possible routes for electron flow during light reactions?
linear and cyclic
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Explain the linear electron flow
the primary pathway, involves both photosystems and produces ATP and NADPH using light energy
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Explain the Cyclic flow of electrons
flow uses only photosystem I and produces ATP but not NADPH, it generates surplus ATP satisfying the higher demand in the Calvin cycle
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When P680 is missing an electron what does it become/do?
it becomes P680+ and is a very strong oxidizing agent
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How is H2O split and what does it do?
H2O is split by enzymes and the electrons are transfered from the hydrogen atoms to P680+, thus reducing it to P680
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Explain the ETC (electron transfer chain)
each electron falls down an ETC from the primary electron acceptor of PSII to PSI, energy released from the fall drives the reaction of proton gradient across the thylakoid membrane, diffusion of H+ (protons) across the membrane drives ATP synthesis
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What happens in PSI?
- transferred light energy excites P700+ (P700 that is missing an electron) accepts an electron passed down from PSII via the electron transfer chain
- the electrons are then transferred to NADP+ and reduce it to NADPH
The electrons of NADPH are available for the reactions of the calvin cycle
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How many ATP and NADPH are produced in the Calvin Cycle?
18 ATP and 12 NADPH
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How does carbon enter and leave the Calvin Cycle?
enters as CO2 and leaves as a sugar called glyceraldehyde-3-phosphate (G3P) which makes glucose
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For the net synthesis of 1 G3P the Calvin Cycle must take place how many times?
three times, fixing 3 molecules of CO2
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How do plants protect themselves from dehydration on hot days?
- they close the stomata which conserves H2O but limits photosynthesis
- it reduces access to CO2 and causes O2 to build up
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What does photorespiration do?
How is it different from photosynthesis?
in most plants (C3) initial fixation of CO2 via rubisco, forms a three-carbon compound, in photorespiration, rubisco adds O2 instead of CO2 in the Calvin Cycle
Photorespiration consumes O2 and organic fuel and releases CO2 without producing ATP or sugar
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Explain C4 plants
they minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells, this step requires the enzyme PEP carboxylase
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Eplain PEP carboxylase
it has a higher affinity for CO2 than rubisco does; it can fix CO2 even when CO2 concentrations are low (some plants use CAM to fix carbon)
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What are the two distinct reactions of photosynthesis?
- light reactions-absorb light and produce O2
- dark reactions-fix CO2
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Explain the three stages of photosynthesis
- stage 1: capturing solar energy and transferring it to electrons
- stage 2: using captured solar energy to make ATP and to transfer high energy electrons to NADP+ yielding NADPH which is a high energy electron carrier molecule
- stage 3: using energy stored in ATP and high energy electron carried by NADPH to form energy rich organic molecules such as C6H12O6 for CO2
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