Ch. 7 Photosynthesis 7.6 – 7.9

Light reaction: converting solar energy to chemical energy Sunlight is what type of energy? Electromagnetic energy (radiation) What is a wavelength? Light travels in waves measured by the distance between two adjacent crests

Visible light only forms a small percent of the electromagnetic spectrum. Can plants use more than just visible light for photosynthesis? No, only certain wavelengths, or colors of visible light?

Do we see the wavelengths absorbed by the plant? No. We don’t see those colors. What happens to those other colors? Different pigments in chloroplasts absorb this light; (chlorophyll a, absorbs blue- violet and red, & chlorophyll b, absorbs mainly blue and orange light, & reflects (looks) yellow/green,

What is a carotenoid? Another type of yellow/green pigment (absorbs blue-green light) in chloroplasts that helps protect plant from excessive light energy. (absorb & dissipates energy)

What is the energy within a light wavelength called? Photons, They’re little packets, fixed units of energy in light. Since the shorter the wavelength = more energy (photons), which has more energy violet or red light? Violet has nearly twice as much energy!

What does that photon do? When a pigment absorbs a photon, that chlorophyll’s electron gains energy (gets excited & jumps up), and releases (falls back to ground) that energy as heat or light (aka: fluorescence)

What is the first step in the light reaction? Solar-powered electron transfer from chlorophyll to primary electron acceptor.

What makes up a reaction center? Collection of pigment molecules (chlorophyll a )and primary electron acceptor. What does the reaction center do? Triggers light reaction when chlorophyll donates an excited electron to primary e- acceptor, which passes an e- to electron transport chain. What is the overall combination of all this called? A photosystem

How many types of photosystems are there? 2. Photosystem I & II. How are they different? Photosystem I, its chlorophyll a absorbs red light best P700, and Photosystem II’s chlorophyll a absorbs an orange/red wavelength of light best P680.

Electron transport chain to make ATP, NADPH & 0 2 Where do electrons go to when leaving PS 1? Chlorophyll loses 2e- to Primary e- acceptor which go down electron transport chain (ETC) to end up on NADP -> NADPH Are those electrons ever replaced? Yes, PS 2 loses its electrons to PS 1 passed down via the ETC. What about those electrons…are they replaced? Yes when H2O is split releasing O2 & supplying electrons to PS 2.

What is happening in the ETC What drives the transport of hydrogen ions (H+) across the thylakoid membrane? Arrangements of electrons being passes from one photosystem (protein ie: blue & purple) to another.

ATP synthesis in light reactions What activates the pumping of H+ ions out of the stroma? The loss of energy each time an electron goes from one photosystem to the other. Where do the H+ ions go? They want to diffuse back in. Do they ever get back in? Yes, by facilitated diffusion via ATP synthase, releasing energy to make ATP from ADP & P. What is this process called? Photophosphorylation (ATP production from initial input of light energy)