1. The Reactions of Photosynthesis 8-3 continued

2. The Calvin Cycle Also known as light-independent reactions, or dark reactionsAlso known as light-independent reactions, or dark reactions Does not require lightDoes not require light Named after Melvin CalvinNamed after Melvin Calvin –Worked out the details of the cycle

3. Uses ATP and NADPH produced in the light-dependent reactionUses ATP and NADPH produced in the light-dependent reaction Creates high energy sugarsCreates high energy sugars

4. Step A Six CO 2 molecules enter the cycle from the atmosphereSix CO 2 molecules enter the cycle from the atmosphere The 6-CO 2 molecules join with 6 5- carbon moleculesThe 6-CO 2 molecules join with 6 5- carbon molecules They create 12 3-carbon moleculesThey create 12 3-carbon molecules

5. Step B The 12 3-carbon molecules are converted to a higher energy formThe 12 3-carbon molecules are converted to a higher energy form The energy that makes this possible comes from ATP and the high-energy electrons in NADPHThe energy that makes this possible comes from ATP and the high-energy electrons in NADPH

6. Step C Two of the 12 3-carbon molecules are removed from the cycleTwo of the 12 3-carbon molecules are removed from the cycle They are used to produce:They are used to produce: –Sugars –Lipids –Amino acid –other compounds needed for plant metabolism and growth

7. Step D The remaining 10 3-carbon molecules are converted back to 6 5-carbon moleculesThe remaining 10 3-carbon molecules are converted back to 6 5-carbon molecules They combine with 6 new CO 2 molecules to begin the next cycleThey combine with 6 new CO 2 molecules to begin the next cycle

8. The Calvin cycle uses 6 molecules of CO2 from the atmosphereThe Calvin cycle uses 6 molecules of CO2 from the atmosphere It produces energy-rich sugarsIt produces energy-rich sugars The sugars are used to meet the plant’s energy needs and build more complex macromoleculesThe sugars are used to meet the plant’s energy needs and build more complex macromolecules –Ex: cellulose needed for growth and development

9. Factors Affecting Photosynthesis Several factors affect the rate of photosynthesisSeveral factors affect the rate of photosynthesis One factor is waterOne factor is water –A shortage of water can slow down or even stop photosynthesis Plants that live in dry conditions have leaves with waxy coatings to prevent water lossPlants that live in dry conditions have leaves with waxy coatings to prevent water loss

10. Another factor is temperatureAnother factor is temperature Photosynthesis depends on enzymes that function best between 0 o C and 35 o CPhotosynthesis depends on enzymes that function best between 0 o C and 35 o C Temperatures above or below 0 o C and 35 o C can slow down or stop photosynthesisTemperatures above or below 0 o C and 35 o C can slow down or stop photosynthesis

11. Light intensity also affects the rate of photosynthesisLight intensity also affects the rate of photosynthesis As you increase intensity, the rate of photosynthesis will increase to a point and then level offAs you increase intensity, the rate of photosynthesis will increase to a point and then level off