BIO 1210 LECTURE 7: Energy from Sunlight Photosynthesis

what is the chemical formula for photosynthesis?

6CO2 + 6H2O → C6H12O6 + 6O2

does carbon dioxide or water gain hydrogens and electrons?

carbon dioxide gains hydrogens and electrons and is reduced while water loses hydrogens and electrons is oxidized

what does the xylem transport?

water

what does the phloem transport?

glucose

what part of the plant are the sites of photosynthesis?

leaves

Through where does CO2 enter a leaf and O2 exit a leaf?

stomata

What type of cells within leaves contain abundant chloroplasts?

mesophiles

The ____ the wavelength, the ___ the energy?

shorter; greater

How is the color of an object determined?

the wavelength of visible light reflected by the object

Which wavelength is not absorbed (which wavelength does photosynthesis not use)?

green because green is reflected, so chlorophyll, chloroplasts, and leaves appear green

what are carotenoids?

pigment molecules that absorb violet/blue/green wavelength; red/orange/yellow wavelength are refelcted

does chlorophyll a, b or carotenoid have the greatest relative absorption? Which one has the lowest?

chlorophyll b; carotenoid has the lowest

what happens when a discrete quantity of light energy (called a photon) contacts a chlorophyll molecule?

one of the chlorophyll’s electron absorbs this light energy and the absorbed energy “boosts” the electron from a low-energy ground state to a high energy excised state

If the electron is “captured” in its high-energy excited state?

the energy can be used to produce ATP and NADPH

what is NADPH during photosynthesis?

coenzyme that accepts and carries electrons during photosynthesis

what are photosystems?

protein complexes embedded in the thylakoid membranes of chloroplasts

where does light reactions occur?

on the thylakoid membrane of chloroplasts

what is required for light reactions?

sunlight and water

what is produce during light reactions?

oxygen, ATP, and NADPH (no glucose is produced during this stage yet just the energy needed to make glucose)

where does the calvin cycle occur in?

the stroma (fluid) of chloroplasts

what is required during the calvin cycle?

carbon dioxide and the ATP and NADPH produced during the light reactions

what does the calvin cycle produce?

glucose

does the calvin cycle require sunlight?

no, but it cannot proceed without the ATP and NADPH from the light reactions

When is ATP made by light reaction consumed during photosynthesis?

during the Calvin cycle and is therefore not available for other cellular work

what is photosystem II?

• the water-splitting photosystem

• sunlight is absorbed by a chlorophyll molecule, causing its exited electron to “jump” from one chlorophyll molecule to another

• electron that reach the reaction center chlorophylls called P680, it is transferred tot he primary electron acceptor and “trapped” in its high-energy state

what replaces the lost electron of photosystem II?

the oxidation of water; electron is added back to chlorophyll and oxygen is released

During light reactions electron transport chain what does the potential energy of the excited electron convert into?

kinetic energy as it “falls” down the chain

what is chemiosmosis in light reactions?

• a large concentration gradient of H+ on one side of the membrane results in high potential energy

• H+ move back down heir concentration gradient through an ATP synthase enzyme in the thylakoid membrane

what is photophosphorylation?

when the kinetic energy spins the ATP synthase enzyme, synthesizing ATP by oxidative phosphorylation

what is photosystem I?

NADH producing photosystem

• sunlight is absorbed by a chlorophyll molecule causing its excited electron to “jump” from one chlorophyll molecule to another

• when the electron reaches the reaction center chlorophylls called P700, it is transferred to the primary electron acceptor and “trapped” in its high-energy state

what does NADP+ reduced to?

NADP+ is reduced to NADPH

How does carbon enter the calvin cycle?

as three molecules of CO2

what enzyme catalyzes the binding between each carbon in the calvin cycle?

rubisco

What does each carbon bind to in the Calvin cycle?

to a 5-carbon acceptor molecule called RuBP to form a 6-carbon molecule (3 total)

what does the 6-carbon molecule split into?

two 3-carbon molecules called 3-PGA (6 total)

what does the ATP and NADPH produced during the light reaction reduce each 3-carbon 3-PGA molecule?

into a 3-carbon G3P molecule (6 total)

what happens after one G3P molecule leaves the cycle?

one G3P molecule leaves the cycle and 5 remains for a total of 15 total carbons and additional ATP converts the five G3P molecules into 3 RuBP molecules

what happens after two “turns” of he calvin cycle?

two 3-carbon G3P molecules have left the cycle to form a 6-carbon glucose molecule

what is the glucose produced by photosynthesis used for?

fuel during cellular respiration, stored as starch, formed into cellulose to build cell walls and consumed by heterotrophs

what does a high water use efficiency (WUE) mean?

high WUE means much CO2 is taken in with minimal H2O lost

what is the enzyme that first binds to CO2 to bring it into the Calvin cycle?

rubisco (could also bind to O2)

what if rubisco binds to O2 instead of CO2?

yields no photosynthetic output and wastes the CO2 present because the Calvin cycle is “occupied” by O2 (WUE is lowered)

what problems do most C3 plants deal with?

photorespiration

In C4 plants, what enzymes does CO2 first bound to?

PEP carboxylase

where is CO2 transported to in C4 plants?

to the bundle sheath cells (only cells in which the calvin cell occurs) and undergoes calvin cycle but it is so concentrated that any effect of O2 is “swamped out”

How does C4 increase WUE?

by efficiently utilizing all the CO2 taken into the plant

when do CAM plants open their stomata

only open heir stomata at nigh where there is less H2O lost

where is CO2 stored in CAM plants when PEPcase binds to it?

in the cell’s central vacuole overnight

How does the CAM strategy increase WUE?

by minimizing the amount of H2O lost from the plant

what are most plants C3 plants? why haven’t all plants evolved a C4 or CAM strategy?

• more energy is required

• the benefits outweigh the costs for plants in dry, hot environments

Which of the following statements regarding water use efficiency (WUE) and alternative photosynthetic pathways is correct?

when rubisco binds to oxygen in C3 plants photorespiration results, lowering WUE

During cellular respiration ____ is ____ into _____.

glucose; oxidized; carbon dioxide

which of the following statement regarding glycosides is correct?

two molecules of NAD+ are reduced to two molecules of NADH during glycolysis

The light reactions of photosynthesis ___while the calvin cycle of photosynthesis _____

produce ATP; requires ATP

Which of the following statements regarding fermentation is correct?

all of the above