Photosynthesis G10 Team AISG

Goal of Photosynthesis: Produce Glucose and A happy bi-product: Oxygen!

Overview: Electrons are taken from chlorophyll molecules are boosted uphill by the energy from sunlight. (Lost electrons are replaced by electrons from water splitting.) The chloroplast uses these “excited” electrons, along with carbon dioxide and hydrogen ions, to produce sugar molecules. The reaction steps add up to the overall chemical equation for photosynthesis. See Below

Two Stages: The Light Reactions The Calvin Cycle Photosynthesis happens in two main stages, each includes many steps: The Light Reactions The Calvin Cycle Aka (light independent reactions)

Location, Location, Location This ‘road map’ shows the two main stages of photosynthesis: the light reaction (happens in the THYLAKOIDS) and the Calvin Cycle (occurs in the STROMA)

Light Reaction: require light energy to boost electron energy into an energy carrying molecule

Light Reaction: require light energy to boost electron energy into an energy carrying molecule

Light Reaction: how does energy get put into the energy carrier molecules?

Light Reaction: Light Reactions convert energy in sunlight (aka light energy) to chemical energy. These reactions depend on molecules built into the membranes of the thylakoids. First, the green pigment, CHLOROPHYLL, found in the membranes captures light energy. Then, chloroplasts use the captured energy to remove electrons from water. This splits water into oxygen and hydrogen ions.

Light Reaction, Continues The oxygen formed is a ‘waste product’ of photosynthesis (not used in the process) Oxygen escapes to the atmosphere through the STOMATA of leaves.

What happens to e- and H+ from water??? Chloroplasts use them to make an energy-rich molecule called NADPH. NADPH is an electron carrier that delivers the energy rich electrons to the Calvin Cycle so sugar can be made. Chloroplasts also use the captured light energy to generate ATP. The overall result of the light reactions is the conversion of light energy to chemical energy stored in two compounds: NADPH and ATP.

Check Point: Explain why a leaf appears green? Besides oxygen, what two molecules are produced by the light reactions? Where in the chloroplast do the light reactions take place?

Explain why a leaf appears green? Other colors from the visible spectrum are absorbed into the leaf, so the green is reflected. Besides oxygen, what two molecules are produced by the light reactions? ATP and NADPH Where in the chloroplast do the light reactions take place? THYLAKOIDS

Light Reaction to Calvin Cycle Recall: Light reactions convert light energy to the chemical energy of ATP and NADPH. Do you remember photosynthesis also produces SUGAR??? But this hasn’t been produced yet.  This is the job of the Calvin Cycle, which uses the ATP and NADPH produced in the light reaction.

Calvin Cycle: So, the Calvin cycle has chemical inputs and outputs. Inputs: CO2 from the air, ATP, and NADPH produced from light reactions The Calvin Cycle uses carbon from the CO2, energy from the ATP, and high-energy electrons and hydrogen ions from the NADPH. Output: energy rich sugar molecule. This sugar produced is a small sugar molecule named G3P. This will be used as a raw material to make glucose and other organic molecules the plant needs.

What’s that look like? Don’t be afraid…click to the next slide.

Hold on don’t fret…use the previous slide to… Make sure you understand how carbon dioxide is used…where does the carbon from the carbon dioxide finally end up? Make sure you realize where the energy carrying molecules of the light reactions are being used…what happens to those molecules after they drop off the energy, electron and hydrogen…where do they go? Make sure you know what the final product of the Calvin cycle actually is.

Calvin Cycle Debate: The Calvin Cycle is sometimes referred to as the “light-independent reactions” or the “Dark reactions” (sounds so mysterious). Defend the use of these terms to describe the Calvin cycle. Refute the use of these terms to describe the Calvin cycle. The Calvin Cycle is sometimes referred to as the “light-independent reactions” because, unlike the light reactions, it does not directly require light to begin. However, this does not mean that the Calvin Cycle can continue running in a plant kept in the dark. The Calvin Cycle requires two inputs supplied by the light reactions, ATP and NADPH.

Summary of Photosynthesis Overall process: 6 CO2 + 6 H2O  C6H12O6 + 6O2 The light reactions, which take place in the thylakoid membranes, convert light energy to the chemical energy of ATP and NADPH. The light reactions use the reactant water from the equation and release the product oxygen. The Calvin Cycle, which takes place in the stroma, uses ATP and NADPH to convert carbon dioxide to sugar

Relate to Ecosystem By converting light energy to chemical energy, photosynthesis is the first step in the flow of energy through an ecosystem. Some of that chemical energy then passes from producers to consumers. Think about eating meat… what did the animal that you are consuming consume? We can go back to photosynthesis. Photosynthesis is the ultimate source of all the food you eat and all the oxygen you breathe.

Concept Check: What are the inputs and outputs of the Calvin Cycle? Which stage of photosynthesis uses each reactant from the overall photosynthesis equation? Which stage generates each product from the overall photosynthesis equation? What molecule is the direct product of photosynthesis? How is that molecule then used by plant cells?