Trapping Light Energy to Build Carbohydrates Photosynthesis Trapping Light Energy to Build Carbohydrates

Which organisms are photosynthetic? Photoautotrophs Plants Algae Some bacteria

What is photosynthesis?

What is photosynthesis? Process by which plants use light energy to build carbohydrates (food). Chemical equation: light + chlorophyll 6CO2 + 6H2O C6H12O6 + 6O2 carbon dioxide + water yields carbohydrate + oxygen gas in the presence of light & chlorophyll

Why are plants mostly green? Chlorophyll Green pigment Located in chloroplasts Are they always green? No! Think about the leaves in the fall – what happens to them? Chlorophyll is the most dominant pigment so we see it most, but when it dies out the other pigments show through

Chloroplast Structure Chloroplast Membranes Two of them Inner and outer Both composed of a lipid bilayer Thylakoids Disks of membranes Contain chlorophyll Grana Stacks of thylakoids Stroma Fluid inside the chloroplast http://www.ualr.edu/botany/chloroplast.jpg

A closer look at where it all takes place… http://www.ftexploring.com

Photosynthesis Reactions Light Reactions Need light Take place in the thylakoids Dark Reactions/Calvin Cycle Do not need light Take place in the stroma

Light Reactions Trap Energy GOAL: To make NADPH & ATP for the Calvin Cycle BYPRODUCT: Oxygen gas

Stage 1: Energy is Captured from Sunlight Chlorophyll absorbs light Light energy excites chlorophyll electrons Excited electrons enter the electron transport chain (stage 2B)

Stage 2A: Photolysis Photolysis: An enzyme splits water molecules 2H2O  O2 + 4H+ + 4e- Oxygen is released by chloroplasts as a waste product! Oxygen gas supplies nearly all the oxygen in the atmosphere Electrons replace excited electrons in chlorophyll of the thylakoids

Stage 2B: Electron Transport Chain Excited electrons from chlorophyll and H+ from split water travel through the thylakoids and move to NADP+ Nicotinamide dinucleotide phosphate (you do not need to know this name) Coenzyme: act as carriers in many biological processes (“the shuttle bus”) NADPH is formed e- + H+ + NADP+  NADPH NADPH travels to the Calvin Cycle (Stage 3) ATP is formed and travels to the Calvin Cycle (stage 3) to provide energy

The Light Reactions of Photosynthesis NADPH H+ e The Products of the Light Reactions ATP

Stage 3: Calvin Cycle The Dark Reactions GOAL: To make simple sugars

Carbon Fixation Calvin Cycle consists of carbon fixation CO2 from the air is converted into a form that is usable by living things “fixed” into 6 carbon sugars Eventually become glucose and other sugars

Calvin Cycle Reaction Basics Reactants 5-carbon molecule CO2 H from NADPH from Light Reaction’s splitting of H2O Products Simple sugars Used to make other carbohydrates ATP from Light Reactions powers the Calvin Cycle

The Overall Net Result of Photosynthesis The overall result of photosynthesis is that for every 6 carbon dioxide molecules (plus 6 water) that a plant uses, 1 glucose molecule (plus 6 oxygen) is created.

ELECTRON CARRIERS

Discussion Questions Where do the light reactions take place? What are the products of the light reactions? Where do the chlorophyll replacement electrons come from? Where do the dark reactions take place? Where does the NADPH in the Calvin Cycle come from? Where does the ATP in the Calvin Cycle come from? What are the products of the Calvin Cycle? What are chemoautotrophs?