Photosynthesis Part II: Leaf Structure and Light & Dark Reactions KL Biology L.Buechler

Leaf Structure Terms you’ve already had in Unit I Chloroplast Chlorophyll

Leaf Structure Mesophyll= inside layer of a leaf which contains chloroplasts Stomata= “Pores”  allow O 2 out and CO 2 in Stroma= Solution that surrounds the thylakoids Thylakoid= flat, membrane bound sac inside the chloroplast Granum=stacks of thylakoids Veins=transports water to all parts of the plant. Water leaves through the Stomata

Overview of Light & Dark Reactions

Light (Dependent) Reactions- Chloroplasts can convert solar energy into chemical energy Chlorophyll a is the specific pigment used to capture solar energy

Light (Dependent) Reactions Photons= packet of energy transmitted by the sun The shorter the wavelength of light, the greater the energy it carries Pigments absorb photons Can be in an “excited” high energy state or “ground” state with low energy released Pigment absorbs photon  electron in pigment molecule gains energy

Photosynthetic pigments are arranged as “photosystems”

Light (Dependent)Reactions Photosystem= cluster of a pigment cells that acts like a light gathering antennae Primary Electron Receptor= traps light energy by taking electrons from the photons

H 2 O is split by light energy  Oxygen, H+ and electrons

Stroma O2O2 H2OH2O 1212 H+H+ NADP + NADPH Photon Photosystem II Electron transport chain Provides energy for synthesis of by chemiosmosis + 2 Primary acceptor 1 Thylakoid mem- brane P Thylakoid space e–e– e–e– 5 Primary acceptor P700 6 Photon Photosystem I ATP H+H+ + H+ are stripped from H 2 O  Oxygen released  H+ moves through photosystems  Electrons stripped from Hydrogens  NADP+ (and ATP Synthase)

+ O2O2 H2OH2O 1212 H+H+ NADP + H+H+ NADPH + 2 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Photosystem II Photosystem I Electron transport chain ATP synthase Light Stroma (low H + concentration) Thylakoid space (high H + concentration) ADP + P ATP H+ stripped from H 2 O  O 2 released  H+ moves through photosystems  Electrons stripped from H+  NADP+ gets some H+  ATP Synthase gets the rest

Dark Reactions (Light Independent Reactions) Happen in light AND in dark ATP from light Reaction drives the Calvin Cycle (makes glucose and other monosaccharides) Monosaccharides are used to “build” polysaccharides (eg. Starch). Image from: Biology 11: College Preparation. Pg 74. Nelson, Toronto H2OH2O

The Calvin Cycle

Calvin Cycle Ingredients from Light Reaction: CO 2, ATP, & NADPH A 3-carbon sugar is produced glyceraldehyde-3- phosphate (G3P) Use G3P to make glucose Copyright © 2009 Pearson Education, Inc. CO 2 ATP NADPH Input C ALVIN CYCLE G3P Output:

Inputs/Outputs

Respiration vs. Photosynthesis