6CO 2 + 6H 2 O + Sunlight C 6 H 12 O 6 +6O 2 Process Location Reactants (Starting) Products (Ending) Light Reactions Calvin Cycle
Introduction to Photosynthesis Mrs. Meyer
Target SWBAT describe the reactants and products of photosynthesis and the role of the chloroplast.
Overall Reaction of Photosynthesis 6CO 2 + 6H 2 O + Sunlight C 6 H 12 O 6 +6O 2 Glucose
Chloroplast The organelle where photosynthesis occurs. Contains chlorophyll Pigments that absorb light
Types of Chlorophyll (Colors Reflected) Chlorophyll a: Green Chlorophyll b: Blue Green Carotenoids: Orange Yellow Anthocyanins: Pink and Purple Xanthophyll: Deep Yellow
Photosynthesis Takes place in two steps: Light Reactions Calvin Cycle
Thylakoid Contains chlorophyll Where the light reactions take place
Stroma Fluid surrounding the thylakoids Where the Calvin Cycle takes place
Light Reactions Photosynthesis
Light Reactions Photosynthesis occurs in the thylakoid membrane of the chloroplast. Thylakoids are individual disks that are piled into stacks called granum.
Thylakoid Chlorophyll and carotenoids are clustered in the thylakoid membrane. This is where the light reactions occur.
Pigment organization The chlorophyll and carotenoids are arranged into two groups Photosystem I Photosystem II
Step One Electrons in photosystem II are excited by light. Their energy level increases
Step Two The excited electron passes through an electron transport chain Energy is lost along the way
Step Three The energy lost by the electron is used to move protons (H+) into the thylakoid.
Step Four Light is absorbed by photosystem I The low energy electron from photosystem II is hit by this light and excited again.
Step Five The re-excited electron goes through a second electron transport chain. This time the energy given off combines the H+ proton with NADP+ and makes NADPH
What is NADPH? It is important during the second stage of photosynthesis--the Calvin Cycle.
How do we restart the process? New electrons must be added to photosystem II These electrons come from the splitting of water (H 2 O).
2H2O + 4H + 4e + O2
Where do all the parts go? 4H+ go to the outside of the thylakoid (brought in by the electron transport chain). 4e- go to photosystem II O 2 leaves the plant as waste
Look at those H+ again The movement of H+ protons into and out of the thylakoid membrane drives chemiosmosis.
Chemiosmosis H+ protons flow through a protein called ATP synthese As they do this the energy produced helps add a phosphate group to ADP (making ATP) This ATP drives the next part of photosynthesis
Calvin Cycle Photosynthesis
Target SWBAT describe what the Calvin Cycle produces and how it works with the light reactions.
Steps of Photosynthesis There are two important pathways that work together inside of a chloroplast. Calvin Cycle (Dark Reactions) Light Reactions (electron transport chain)
Calvin Cycle: Carbon Fixation This is where the CO 2 molecules collected from the air are fixed (turned) into organic compounds.
What are Organic Compounds? Proteins Lipids Nucleic Acids Carbohydrates (most common)
Where does this occur? In the stroma of the chloroplast.
Calvin Cycle: Step 1 CO 2 enters the stroma through the chloroplast membrane and combines with a 5 carbon carbohydrate called, RuBP This creates two 3 carbon molecules called PGA.
Calvin Cycle: Step 2 PGA is converted into PGAL (3 carbons) in two steps. 2 ATP give 1 phosphate group to each PGA molecule. NADPH gives a proton to PGA
Calvin Cycle: Step 3 Most PGAL is converted back to RuBP with the addition of a phosphate group from ATP Some PGAL leaves the Calvin Cycle and is turned into organic compounds like amino acids (for protein), lipids and carbohydrates.
What is the point of the Calvin Cycle? To make organic compounds, like glucose, for the plant to use as food.
Why can t it happen without the light reactions? Because it needs the ATP and NADPH made by the light reactions to function.
Can a plant do the light reactions in the dark? No
Can a plant do the Calvin Cycle in the dark? Yes! This is why the Calvin Cycle used to be called the dark reactions. However, since the Calvin Cycle also happens during the day they changed the name.