Photosynthesis Part II

Step 2 - Light-Independent Reactions Glucose

Also known as The Calvin cycle

From Step 1 – Light-dependent Reactions From Air by way of Stomata

The Calvin Cycle Called a cycle because the starting material is regenerated each time the process occurs Enzymes join carbon dioxide molecules with molecules that are already in the cell - these molecules will regenerate each time The energy from ATP and NADPH are used in this process

3 X 5-C molecules ( 15 C) + 3 CO 2 6 x 3-C molecules (18 C) 1X 3-C molecule 5 x 3-C molecules3 x 5-C molecules product/leaves the cycle 2 of these make 1 glucose

Sugar Production With each turn of the Calvin cycle a few energy-rich carbohydrates leave the cycle These molecules become the building blocks that the plant cell uses to make sugars, lipids, amino acids and other compounds The plant will use these compounds as the food and building materials it needs to grow

Summary of Light Independent Reactions Calvin cycle uses ATP, NADPH and hydrogen from light dependent reactions and carbon dioxide from the air to make sugars Calvin cycle uses ATP, NADPH and hydrogen from light dependent reactions and carbon dioxide from the air to make sugars Plant uses the sugar to meet its energy needs and to build molecules needed for growth Plant uses the sugar to meet its energy needs and to build molecules needed for growth When other living things eat these plants they too will get the energy they need. When other living things eat these plants they too will get the energy they need.

Factors that Affect Photosynthesis The process can speed up or slow down depending on several factors Temperature: enzymes work best between degrees Celsius Light: very bright light speeds up photosynthesis Water levels

Water Loss and Photosynthesis Water is lost through the stomata where carbon dioxide enters If its hot the plants will close the stomata to keep from loosing water but photosynthesis will slow down due to the lack of carbon dioxide Some plants that live in dry areas have special ways to save water and carry out photosynthesis

C4 Plants Have a special chemical pathway that gets carbon dioxide into the Calvin cycle It uses extra ATP but it allows the plant to carry out photosynthesis when its hot Examples: Corn, sugar cane

CAM Plants Save water by taking air into their leaves only at night At night carbon dioxide is used to make acids During the day these acids are turned back into carbon dioxide for photosynthesis Example: Pineapples trees, desert cacti