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Photorespiration AP BIO. Review Stomates need to be OPEN for gas exchange to occur in the leaf However, open stomates can lead to dehydration due to transpiration.

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Presentation on theme: "Photorespiration AP BIO. Review Stomates need to be OPEN for gas exchange to occur in the leaf However, open stomates can lead to dehydration due to transpiration."— Presentation transcript:

1 Photorespiration AP BIO

2 Review Stomates need to be OPEN for gas exchange to occur in the leaf However, open stomates can lead to dehydration due to transpiration

3 Transpiration: the loss of water from a plant through stomates Low water= closed stomates=little photosynthesis Result: CO2 levels in plant DECREASE; O2 levels in plant INCREASE This results in PHOTORESPIRATION! (This is a bad thing for the plant)

4 Photorespiration Photorespiration results from increased O2 levels in the plant *RUBISCO (from Calvin Cycle) -prefers to bind to O2 instead of CO2 so the Calvin cycle will continue but without the necessary Carbon -this uses ATP but produces no sugar =decrease in photosynthetic output O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 CO2

5 C ₃ PLANTS Examples: -rice -wheat -soybeans *create a 3 carbon compound in 1 st step of Calvin Cycle *photorespiration is a problem for these plants in dry/hot areas

6 How do plants adapt to Hot/ Dry Conditions? Here are some different types of plants and the strategies they use to overcome the challenges of doing photosynthesis in hot/dry conditions

7 Photosynthesis Adaptations for Hot Climates C4 Plants Examples: -corn -sugarcane -grasses *have two types of photosynthetic cells: -bundle sheath (around vein in picture on the left) -mesophyll cells

8 C4 Plants - continued *Calvin Cycle happens in bundle sheath cells *Calvin Cycle has a pre-step in the mesophyll cells - PEP carboxylase binds to CO2 to form a 4-carbon compound *PEP does NOT bind to O2 -4-carbon compound goes to bundle sheath cells and releases CO2 for Rubisco RESULT: high CO2 concentration and no photorespiration Photosynthesis Adaptations for Hot Climates (continued)

9 CAM Plants Photosynthesis Adaptations for Hot Climates (continued) Examples: -cacti, jade, pineapple -Do gas exchange at night! Open stomates at night and take in CO2 to store as organic acids -During the day, stomates close to prevent water loss -Stored organic acids are broken down to release CO2 into Calvin cycle so plant can make sugars

10 Before reading the next slides answer the following question. What are some factors that limit the rate of photosynthesis? – List as many as you can in your notes.

11 Limiting Factors for Photosynthesis Light Intensity *high light intensity increases rate of photosynthesis until it reaches saturation

12 Limiting Factors for Photosynthesis Temperature *temperature increase causes an increase in rate of photosynthesis until it reaches its ideal temperature, then it decreases

13 Limiting Factors for Photosynthesis CO2 and H2O Concentration *high levels of both CO2 and H2O increase the rate of photosynthesis until it reaches saturation. Then the rate levels off. Concentration of CO2 and H2O Rate of Photosynthesis

14 Limiting Factors for Photosynthesis O2 Concentration * high levels of O2 cause a decrease in the rate of photosynthesis, while lower levels increase the rate until it levels off Concentration of O2 Rate of Photosynthesis


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