Photosynthesis Professor Andrea Garrison Biology 11 Illustrations ©2010 Pearson Education, Inc.

Photosynthesis 2

Converts solar energy to molecular bond energy Occurs in chloroplasts of eukaryotes Requires – Visible light for energy – Chlorophyll to trap the light – CO 2 for carbon to build sugars – H 2 O for electrons to make bonds – NADPH to carry electrons Photosynthesis3

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Occurs in two stages – Light reactions Occur on thylakoid membranes Require light Supply ATP and NADPH for Calvin Cycle Photosynthesis6

Occurs in two stages – Light reactions Occur on thylakoid membranes Require light Supply ATP and NADPH for Calvin Cycle – Calvin Cycle Need no light, but will occur in light Use products of light reactions Produce carbohydrates Photosynthesis7

Light Reactions Use visible spectrum of sunlight Photosynthesis8

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Engelmann’s Experiment O 2 loving bacteria cluster around algae producing most O 2 Photosynthesis10

Light used by chlorophyll Chlorophyll absorbs light in red/orange wavelengths and blue/violet wavelengths Chlorophyll does not absorb green light – Plants look green Photosynthesis11

Accessory Pigments Carotenoids – Absorb blue-green light – Some pass the energy to chlorophyll – Some absorb excessive light energy which might damage chlorophyll Photosynthesis12

Light Reactions Pigments harvest light energy through excited e - s Photon strikes e - – Excited e - jumps to higher energy shell – e - falls back down Releases energy Photosynthesis13

Light Reactions Sometimes an electron can get so excited it flies off the molecule and binds to an e - acceptor, then moves down an e - transport chain Photosynthesis14 Energy released

Light Reactions Two photosystems – Involve both excited e - s falling back to their original energy state and excited e - s leaving the molecule and moving down electron transport chains – Trap solar energy as excited e - s and use the energy to make ATP and NADPH for Calvin Cycle Photosynthesis15

Photosystems Cluster of pigment molecules gather light energy in excited electrons pass that energy between molecules and eventually to reaction center Photosynthesis16

NADPH-Producing Photosystem Photon hits photosystem pigment Energy eventually passed to reaction center e - s leave reaction center, trapped by primary e - acceptor Photosynthesis17

NADPH-Producing Photosystem Photon hits photosystem pigment Energy eventually passed to reaction center e - s leave reaction center, trapped by primary e - acceptor e - s passed down e - transport to NADP → NADPH Photosynthesis18

Water-Splitting Photosystem Photon hits photosystem pigment Energy eventually passed to reaction center e - s leave reaction center, trapped by primary e - acceptor Water split to release e - s to replace those lost from reaction center Photosynthesis19

Water-Splitting Photosystem Photon hits photosystem pigment Energy eventually passed to reaction center e - s leave reaction center, trapped by primary e - acceptor Water split to release e - s to replace those lost from reaction center e - s passed down e - transport to make ATP Photosynthesis20

Summary of Light Reactions Photosynthesis21

Calvin Cycle Uses ATP for energy and NADPH for e - s to make bonds of sugar Uses CO 2 for atoms of sugar Photosynthesis22

Calvin Cycle Photosynthesis23

Calvin Cycle Photosynthesis24

Calvin Cycle Photosynthesis25

Calvin Cycle Photosynthesis26

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