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What happens in the light reaction of photosynthesis?

converts light energy to chemical and produces O2 in thylakoid membranes 1. water is split to make O2 and H+
2. Light energy is used to reduce NADP+ to NADPH
(also makes ATP from ADP and P)

How is the Calvin Cycle linked to the light reactions?

The calvin cycle needs NADPH and ATP made from the light reaction while the light reactions need NADP+ and ADP+P from the calvin cycle

What kind of light do plants NOT absorb well? Why do plants have various pigments in the chloroplast?

They don't absorb blue green/yellow light bc they reflect it. Each pigment absorbs diff colors of light

What does light do in a photosystem?

a light excited pair of chlorophyll molecules in the reaxn center of a photosystem passing an excited electron to a primary electron receptor

Electrons flow from____to _____which is reduced to ______

from water to NADP+ which is reduced to NADPH

just like aerobic respiration electrons lose small amounts of energy as they bounce from one carrier to the next, the energy released is used to make what?

create ATP to make glucose

carbon fixation

the incorporation of carbon from CO2 into organic compounds lil the calvin cycle


consists of a number of light harvesting complexes surrounding a reaction center complex like light harvesting complex and reaction center complex

photosystem II

light energy enters and excites an electron of chlorophyll to a higher state, water is split into H+ (used in reaxn) and O2 (diffuses)

photosystem I

light enters exciting electrons which gives off energy to reduce NADP+H (which is the terminal electron acceptor) to NADPH

The Calvin Cycle takes place where in the chloroplast? How many carbon dioxide molecules are neeeded?

stroma, needs 3 CO2 molecules from the air through carbon fixation through the enzyme Rubisco

Inputs of Calvin Cycle

18 ATP, 12 NADPH, and 6 CO2

Outputs of Calvin Cycle


Inputs of Light Reaxns

water, ADP+P, NADP+H,light

Outputs of Light Reaxns


Things that incr CO2 in the atmosphere

burning fossil fuels, burning wood, cellular respiration, decomposition

Things that remove CO2 from the atmosphere


What happens to the oceans as they absorb more and more CO2

ocean life is affected, pH increases and animals die

global consequence for extra CO2 output

global warming

How are trees carbon sinks? Permanent or no?

They absorb more carbon than they release, only temporary they decay and decomposers put carbon back in the atmosphere

How does the plant get more electrons as they get used up by this process?

from water splitting

What do electrons have to do with making ATP and NADPH

it gives off energy to allow active transport which creates the H concentration gradient to make ADP+P & NADP+H

what organisms produce the biosphere's food supply?


carbon reservoir

living and nonliving biomass, carbonic acid in the oceans

If only chlorophyll a were involved in the light reactions, would blue light (wavelength about 490 nm) be effective in driving photosynthesis?

The graph indicates that chlorophyll a absorbs very little blue light, so we can predict that blue light would not be effective.

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