December 5, 2008 Objectives: - Discuss how different factors affect the rate of photosynthesis - Describe alternative pathways plants use to make sugars Drill: List 2 factors that can affect the rate of photosynthesis

Online Simulation Examined the effect of varying colors of light, light intensity, and amount of carbon dioxide on the rate of photosynthesis Measured the number of bubbles (oxygen) after 30 seconds

Factors Affecting Rate of Photosynthesis & Alternative Pathways

Factors that affect photosynthesis The rate at which plants carry out photosynthesis is affected by the plant’s environment. Three very important factors that can affect the rate of photosynthesis: Light intensity Level of CO2 Temperature

Light Intensity As the light intensity increases, the rate of photosynthesis increases, and then levels off. Leveling off represents maximum rate of photosynthesis.

Level of CO2 The Effect of the Level of Carbon Dioxide on the Rate of Photosynthesis As the level of CO2 increases, the rate of photosynthesis increases, and then levels off. Leveling off represents maximum rate of photosynthesis.

The Effect Temperature on the Rate of Photosynthesis Initially, as temperature increases, the rate of photosynthesis increases. The rate peaks and then starts to decreases because: Enzymes that catalyze the reactions become ineffective. Stomata start to close, limiting water loss and entry of carbon dioxide. The Effect Temperature on the Rate of Photosynthesis

C3 Plants REVIEW: During the Calvin cycle, CO2 is used to build sugars C3 plants (soybeans, wheat, rice) only use the Calvin Cycle to fix CO2 Given this name because CO2 is initially made into a three carbon compound. These plants operate during the day

Alternative Pathways Some plants that are found in hot, dry environments have adaptations that minimize water loss while still allowing photosynthesis to take place: C4 plants CAM plants They do not immediately enter into the Calvin cycle like C3 plants

C4 Plants Stomata partially closed during the day Have a specialized pathway that captures low levels of CO2 & build 4 carbon compounds that enter the Calvin cycle Examples: sugarcane, corn, crabgrass These 4 carbon compounds are then transported to other cells and then enter the Calvin Cycle.

CAM Plants CAM plants open stomata at night and close them during the day Have a specialized pathway that takes in CO2 at night and makes a variety of organic acids Then during the day, enzymes break down these organic acids, releasing CO2 that enters into the Calvin cycle Examples: cacti and pineapples Jade and snake plants crassulacean acid metabolism

Chemosynthesis Some bacteria that live on the floor of the ocean are autotrophs, but do not make food by photosynthesis Use a process called chemosynthesis- the process by which energy is obtained from inorganic sources such as sulfur to make food