The Calvin Cycle Or the Dark Side of Photosynthesis II NOTE: ONLY WRITE DOWN THE SLIDES WITH THE BLACK BACKGROUND!!! THEY ARE A SUMMARY OF THE PREVIOUS SLIDES!

While the purpose of photosynthesis is for plants to make glucose from carbon dioxide, but there is a second reason why plants do photosynthesis- to make organic molecules from the PGAL skeleton.

A second function of the dark reaction is to make other compounds needed by the plant. #1, #2

There are environmental factors that can affect the rate of photosynthesis. 1. Light intensity- At first an increase in the light intensity will result in a corresponding increase in the rate of photosynthesis as the photosystems become activated. Then as the photosystems become saturated, an increase in light intensity will not increase the rate of photosynthesis.

2. Temperature- At first an increase in temperature results in an in-crease in the rate of photosynthesis because the molecules are moving faster, but at a higher temperature the reaction rate decreases because enzymes denature.

3. If a plant is given an increase in oxygen, the rate of photosynthesis decreases because of phenomenon of photorespiration.

Envrionmental factors that effect the rate of photosynthesis 1. Light intensity-An increase in light intensity will increase photo-synthesis until it reaches the saturation of photosystems #3, #4 2.Temperature-At first an increase in temperature will increase the rate of photosynthesis but after a certain temperature the enzymes denature and the plant cells are killed. (The plant is being cooked) 3. Increasing the concentration of oxygen, decreases the rate of photosynthesis because of increase in photorespiration.

The enzyme that puts the CO2 onto ribulose biphosphate is rubisco The enzyme that puts the CO2 onto ribulose biphosphate is rubisco. Somtimes rubisco can make a mistake and put oxygen on to ribulose biphosphate. This happens when the concentration of oxygen gas is greater than carbon dioxide. This happens when the plant is water stressed and the stomates are closed.

Gas exchange takes through pores on the bottom of the plant called stomates. Guard cells regulates these openings but as gas exchange occurs water leaves the stomates via transpiration. When a plant becomes water stressed, stomates close to conserve water. water, but this will stop gas exchange. This will increase the O2 and decrease CO2. Photorespiration begins. C3 photosynthesis is a plant that does the Calvin cycle and the light reaction. There are plants that modify C3 photosynthesis by adding an additional pathway-

The enzyme that puts the CO2 onto ribulose biphosphate is rubisco The enzyme that puts the CO2 onto ribulose biphosphate is rubisco. Rubisco can make a mistake of putting O2 on ribulose biphosphate. This happens when the concentration of oxygen gas is greater than carbon dioxide. This occurs when the plant is water stressed and the stomates (pores on bottom of leave) are closed. Guard cells open and close stomates. This stops transpriation (water loss through stomates) but also stops gas exchange. This increases the O2 and decreases CO2. Photorespiration begins. C3 Photosynthesis= Light reaction + Calvin Cycle There are plants that modify C3 photosynthesis by adding an additional pathway- #5, #6,#7

The leaf of a C3 plant. Chloroplasts are located in the palisade and spongy mesophyll. There are no chloroplasts in the bundle sheath cells.

#8 The leaf of a C3 plant. Chloroplasts are located in the palisade and spongy mesophyll. There are no chloroplasts in the bundle sheath cells.

C4 photosyntheis includes the light reaction, the Calvin cycle and the Hatch-Slack pathway. These C4 plants also have a different anatomy. This Hatch-Slack pathway is able to deliver dwindling supplies of CO2 when the stomates are closed. The enzyme that combines the CO2, combines it with a three carbon compound to form a four carbon compound. This enzyme does not make a mistake like rubisco. The leaf of a C4 plant. There are no palisade mesophyll cells. Instead there is a layer of mesophyll around the the bundle sheath cells. Chloroplasts are located in the these mesophyll and spongy mesophyll..

C4 photosyntheis includes the light reaction, the Calvin cycle and the Hatch-Slack pathway. These C4 plants also have a different anatomy. This Hatch-Slack pathway is able to deliver dwindling supplies of CO2 when the stomates are closed. The enzyme that combines the CO2 combines it with a three carbon compound to form a four carbon compound, does not make a mistake like rubisco. The leaf of a C4 plant. There are no palisade mesophyll cells. Instead there is a layer of mesophyll around the the bundle sheath cells. Chloroplasts are located in the these mesophyll and and spongy mesophyll.

Another variation of photosynthesis is CAM (crassulacean acid metabolism). These are succulent plants. Because of the intense heat and arid conditions, these plants only open up their stomates at night for gas exchange. The CO2 is converted to organic acid and stored until the day. During day stomates are closed and the cell releases the CO2 from the organic acid.

Another variation of photosynthesis is CAM (crassulacean acid metabolism). These are succulent plants. Because of the intense heat and arid conditions, these plants only open up their stomates at night for gas exchange. The CO2 is converted to organic acid and stored until the day. During day stomates are closed and the cell releases the CO2 from the organic acid.