photosynthesis part 1

who converts light to chemical energy

photosynthetic organisms

what do non photosynthetic organisms rely on photosynthetic organisms for

for energy and biomass

what  is the source of the sugars that most organisms use to fuel cellular respiration and make ATP. 

photosynthesis

what are the inputs and outputs of photosynthesis

inputs: light energy, carbon dioxide, and water

outputs: sugar and oxygen

where does the oxygen that gets released come from

from water

where does the carbon from CO2 go during photosynthesis

to sugar

at its core what is photosynthesis

another redox process that is based on changes in electron position, and that results in changes in potential energy

what absorbs wavelengths of light

molecules called pigments

what does the absorption of energy result in

electrons being excited to a high energy state

what happens after the electrons get excited

 In one of the photosynthesis machines called photosystem II (PSII), excited electrons are passed to a molecule called PQ—reducing it. Light energy then becomes chemical energy PQ then carries the high-energy electron out of PSII and passes it to an electron transport chain (ETC). Energy transfer during a series of redox reactions allows the ETC to pump protons across a membrane, driving production of ATP by ATP synthase.

what step accomplishes the transformation of light energy to chemical energy

when PQ reduces the excited electrons

what happens during stage 2 of photosynthesis

in pigment molecules associated with a different machine called photosystem I excited electrons are passed through a series of carriers until they reach an enzyme called NADP reductase. NADP reductase (NADPR) uses the energy to catalyze the reduction of a molecule called NADP⁺. The reduced form of NADP⁺, NADPH, is an electron carrier very similar to NADH in cellular respiration.

what are the ATP and NADPH produced from the energy harvested in PSII and PSI used in

they are used in a series of reactions called the Calvin cycle that results in the reduction of CO₂ to produce sugars.

what does the Calvin cycle do

it reduces CO2 to produce sugars

what is produced during stage 1 of photosynthesis

ATP

what is produced during stage 2 of photosynthesis

NADPH

what is produced during stage 3 of photosynthesis

Sugar

Photosynthesis involves multiple energy transfers and transformations. At the end of stage 2, what form is most of the energy in?

chemical energy

what contains more energy shorter light wavelengths or longer ones

shorter ones

what color are the shorter wavelengths and what color are the longer wavelengths

purple and blue are shorter

orange and read are longer

why is long-term exposure of skin to UV light more dangerous than long-term exposure of skin to IR light?

UV light contains much more energy than IR light — enough to damage proteins and nucleic acids.

what are chlorophyll a and chlorophyll b

the two major photosynthetic pigments in plants

do plants absorb all light? why?

no because the chlorophylls can only absorb wavelengths in specific parts of the spectrum

Why do leaves and other plant parts that have chlorophyll-containing cells appear green?

The chlorophylls absorb most of the violet-blue and orange-red wavelengths, but reflect green and yellow wavelengths, which is what we see.

What happens when a photon of the appropriate wavelength strikes a chlorophyll molecule? and what are the three possibilities that can happen afterwards?

The short answer is that the energy passes to an electron in the pigment, exciting it to a higher energy state. Within a few trillionths of a second, one of three things will happen:
 

1. The electron drops back down to a lower energy state and releases the excess energy as heat and/or light.
    

2. The energy passes to a nearby pigment, exciting one of its electrons.
    

3. The electron is transferred to a different, non-pigment molecule, reducing it.

explain the path electrons take to eventually get to the PQ

• Electrons are passed in a direct line from the water oxidation site, where water is "split", to the site where they are excited to a higher energy state and then to molecules that transfer them to PQ.

explain the structure of PSII

• PSII is a large, multi-protein, multi-pigment complex where different parts interact in precise orientations. It is also found as a dimer, meaning that two copies of the machine are joined side-by-side

are their chlorophyll in PSII? why?

yes. so many pigment molecules can absorb photons and pass the energy to the electron excitation site.

what happens to electrons that reach the end of the photosynthetic electron transport chain

they are at low energy and are taken up by an electron acceptor and carried to PSI

what carries electrons from PSII to the ETC

PQ

what happens to the low energy electrons when they reach pSI

they are boosted to high energy electrons again when chlorophyll molecules in PSI absorb photons and transfer the energy to these electrons

what is NADPH

a molecule that is essential for reducing the carbon atoms in CO2 and producing sugars

what do PSI and PSII have in common common

• They both have chlorophyll molecules that are embedded throughout the machine.

  • They are both embedded in a membrane inside chloroplast

how does PSII obtain electrons

by oxidizing or “splitting” water

How does PSI get electrons

from an electron carrier from the ETC

explain the path electrons take in PSI

Electrons enter the complex at the bottom middle at a site where the electron carrier from the ETC binds. Once the electrons reach an excited state, they are passed up and out of the complex to another electron carrier, which binds to the complex at the top middle. In most cases, the electron carrier passes these excited electrons to an enzyme that reduces NADP⁺ to NADPH.

does PSI contribute to the production of ATP?

yes it contributes to the production of both ATP and NADPH

do the electrons emerging from PSI always get passed to NADP reductase?

no sometimes they get passed back to the ETC where they lead to proton pumping and production of ATP by ATP synthase

When electrons from PSI feed the ETC, they come back to PSI at the end of the ETC. Which description most accurately describes this process?

Cyclic electron flow, because electrons flow in a loop into and out of PSI.

where are all the machines needed for photosynthesis found

in chloroplast specifically in its thylakoid membrane

what are the flattened sack like inner membranes of chloroplasts called

thylakoids

thylakoid lumen

the inside of the thylakoid

stroma

the space between the thylakoid membranes and the inner chloroplast membrane

Why do chloroplasts have such an extensive system of internal membranes?

The extensive membranes provide a large surface area for many copies of the photosynthetic machinery (PSII, PSI, the ETC, and ATP synthase) to reside, meaning that a lot of ATP and NADPH production can occur in a small space.