Do Now Why does photosystem I occur after photosystem II in the light-dependent reactions of photosynthesis? Did you thank a plant when you woke up this morning? Photosynthesis Light-independent Reactions (Calvin Cycle) ! Chloroplast Light-independent Reactions Also known as the Calvin cycle Uses energy from NADPH to build highenergy sugars Light-independent Reactions ATP cannot store energy for more than a few minutes Glucose better stores energy Cells need to make glucose in order to store energy over the long term Light-independent Reactions The light-independent reactions do NOT require the presence of sunlight They take place in the stroma that surrounds the thylakoids Steps to the Calvin Cycle Three carbon dioxide molecules enter the cycle from the atmosphere Three CO2 molecules combine with three 5carbon sugars This results in six 3-carbon molecules Steps to the Calvin Cycle The six 3-carbon molecules are converted into higher-energy forms by using ATP Six ATP are converted into six ADP Six NADPH are converted into six NADP+ Steps to the Calvin Cycle One of the six 3-carbon molecules is removed This is used to produce proteins, sugars, amino acids and other compounds needed for the plant Steps to the Calvin Cycle The cycle produces one 6-carbon sugar (glucose) The remaining five 3-carbon sugars are converted back into three 5-carbon molecules by ATP And the cycle begins again! Calvin Cycle Summary The Calvin cycle uses six molecules of ATP and NADPH to produce one 6-carbon sugar Factors Affecting Photosynthesis Water Shortage of water can slow or stop photosynthesis Plants that live in dry places have a wax on their leaves that reduces water loss Factors Affecting Photosynthesis Temperature Photosynthesis depends on enzymes that function best between 0 and 35 degrees C Temperatures above or below may damage the enzymes Factors Affecting Photosynthesis Light intensity Increasing light intensity increases the rate of photosynthesis Extended Constructed Response Describe the steps of the light-dependent reactions of photosynthesis from the point of view of an electron. Using the diagram on your worksheet, describe how the light-dependent and light-independent reactions of photosynthesis are interrelated.