Photosystems and Electron Flow

Photosynthesis

Photosynthesis

________ involves increases and decreases in the energy of an electron as it moves from PSII through PSI to NADPH.

H2O

________ is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680.

Energy

________ released by the fall drives the creation of a proton gradient across the thylakoid membrane.

Diffusion of H+

________ (protons) across the membrane drives ATP synthesis.

Photosystem I

________ boosts the electron to an even higher energy level.

light harvesting complexes

The ________ (pigment molecules bound to proteins) funnel the energy of photons to the reaction center.

photosystem

A(n) ________ consists of a.

Solar

________- powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor is the first step of the light reactions.

PSII

Light excites the electron in ________.

pigment molecules

A photon hits a pigment and its energy is passed among ________ until it excites P680.

Cyclic electron flow

________ generates surplus ATP, satisfying the higher demand in the Calvin cycle.

Electron

________ on a nonexcited pigment molecule in PSII starts with the lowest energy.

Cyclic electron flow

________ produces ATP, but not NADPH.

During the light reactions, there are two possible routes for electron flow

cyclic and linear

Linear electron flow

the primary pathway; involves both photosystems and produces ATP and NADPH using light energy

Cyclic electron flow

uses only photosystem I  and produces ATP, but not NADPH

A photosystem consists of

reaction-center complex (a type of protein complex)

surrounded by light-harvesting complexes

Light-harvesting complexes

pigment molecules bound to proteins; funnel the energy of photons to the reaction center

First step of the light reactions

Solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor

Z Scheme

Light excites the electron in PSII

Photosystem I boosts the electron to an even higher energy level

Each electron “falls” down an electron transport chain from the primary electron acceptor of PS I to the protein ferredoxin (Fd)

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