Intro to Photosynthesis & the Light ReactionsAP BiologyChapter 10.1-10.2

Learning Target 1 (10.1)I can describe how photosynthesis converts light energy into the chemical energy of food.

Quick Review: Obtaining Energy Life on Earth is solar

powered Directly: autotrophs Indirectly:

heterotrophs

Chloroplasts

Photosynthetic prokaryotes lack chloroplasts photosynthetic membranes = enfolded regions

of the plasma membrane

Key structures:o Stromao Thylakoido Grana

Photosynthesis Equation:

Part I: Light Dependent Reactions (thylakoid membrane)

Part II: Light Independent Reactions (stroma)

oxidation

reduction

Plant Structure Roots Stems Leaves

Epidermis Waxy covering to prevent excess water loss

Mesophyll Contains photosynthetic cells

Stoma Openings for gas exchange Guard cells control

Learning Target 2 (10.2)I can explain how the light reactions work to convert solar energy to the chemical energy of ATP and NADPH.

Light Form of electromagnetic radiation Energy is inversely related to its

wavelength Shorter wavelengths pack more energy

Visible light is 380-750 nm

Plants are green because… Chlorophyll absorbs two wavelengths of

light: Blue (420 nm) Red (660 nm)

Green light is reflected

Light ReactionsPart of photosynthesis that prepares to make glucose

Photosystems Photosynthetic units within chloroplast

grana

Electron Carrier NADP+

Same function as carriers in CR Remember “P” for photosynthesis

Light Dependent Reactions – Non-cyclic (Linear) Electron Flow Produces ATP and NADPH using

Photosystems I & II

1. Sunlight strikes the Photosystem II complex and excites electrons, eventually passing it to the primary electron acceptor

2. Excited electron splits H2O into H+ ions and O2 gas

3. Electrons flow through a series of membrane proteins, pumping H+ ions into the thylakoid space

4. Collection of H+ ions pass back to stroma through ATP synthase in thylakoid membrane

5. ADP is converted into ATP

6. Sluggish electrons receive another photon of light in PSI

7. Excited electrons are passed to NADP reducing it into NADPH

Light Reaction Summary Reactants:

H2O Light NADP+

ADP + Pi Products:

O2 NADPH ATP

Light Dependent Reactions – Cyclic Electron Flow Produces ATP only using photosystem I Evolutionary “leftover” of

photosynthetic bacteria?

Light Dependent Reaction Animation http://

highered.mcgraw-hill.com/olc/dl/120072/bio13.swf