Photosynthesis

Part II

Step 2 - Light-Independent Reactions........

Glucose

.........Also known as The Calvin cycle

From Step 1 – Light-dependentReactions

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 CO2

6 x 3-C molecules (18 C)

1X 3-Cmolecule

5 x 3-C molecules3 x 5-C molecules

product/leaves the cycle2 of these make 1 glucose

Sugar ProductionWith 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

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.

Factors that Affect Photosynthesis• The process can speed up or slow down

depending on several factors• Temperature: enzymes work best between 15-

35 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