M2: Photosynthesis

Connect redox reactions to energy transformations that occur throughout photosynthesis

During photosynthesis, CO2 molecules are reduced to form higher-energy carbohydrate molecules. This requires both an input of energy from ATP and the transfer of electrons from an electron donor. In photosynthesis, energy from sunlight is used to produce ATP and electron donor molecules capable of reducing CO2.

Describe the role of Rubisco in the process of photosynthesis

In the first step of the Calvin cycle, CO2 is added to a 5-carbon sugar called ribulose 1,5-bisphosphate (RuBP). This step is catalyzed by the enzyme ribulose bisphosphate carboxylase oxygenase, or rubisco for short. An enzyme that adds CO2 to another molecule is called a carboxylase.

HELP: Predict how introducing changes in one stage of photosynthesis (e.g., altering the activity of an enzyme) will affect the production of NADPH, ATP, and sugar

It would cause the cause the Calvin Cycle to shut down

Explain how the Calvin Cycle transforms carbon dioxide into sugar and where the energy for this transformation comes from

Rubisco is responsible for the addition of the carbon atoms needed for the formation of carbohydrates, but by itself rubisco does not increase the amount of energy stored within the newly formed bonds. For this energy increase to take place, the carbon compounds formed by rubisco must be reduced. Nicotinamide adenine dinucleotide phosphate (NADPH) is the reducing agent used in the Calvin cycle. NADPH transfers the electrons that allow carbohydrates to be synthesized from CO2

Discuss what a plant cell can do with the products of photosynthesis once they are produced

The Calvin cycle is capable of producing more carbohydrates than the cell needs or, in a multicellular organism, more than the cell is able to export. If carbohydrates accumulated in the cell, they would cause water to enter the cell by osmosis, perhaps damaging the cell. Instead, excess carbohydrates are converted to starch because starch molecules are not soluble, they provide a means of carbohydrate storage that does not lead to osmosis. The formation of starch during the day provides photosynthetic cells with a source of carbohydrates that they can use during the night

Explain how light energy reaches photosystem reaction centers and what happens when it gets there

When visible light is absorbed by a chlorophyll molecule, one of its electrons is elevated to a higher energy state. Antenna chlorophylls deliver absorbed light energy to the reaction center, allowing electrons to be transferred to an electron acceptor molecule. After the reaction center has lost an electron, it is reduced by gaining an electron, so it is ready to absorb additional light energy.

Identify where the different stages of photosynthesis take place

light-dependent reactions take place in the thylakoid and the light-independent reactions (Calvin Cycle) take place in the stroma