Ch. 7 Photosynthesis 7.6 – 7.9. Light reaction: converting solar energy to chemical energy Sunlight is what type of energy? Electromagnetic energy (radiation)

Ch. 7 PhotosynthesisCh. 7 Photosynthesis

7.6 – 7.97.6 – 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 & 02

• 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)