photorespiration ap bio. review stomates need to be open for gas exchange to occur in the leaf...
TRANSCRIPT
Review• Stomates need
to be OPEN for gas exchange to occur in the leaf
• However, open stomates can lead to dehydration due to transpiration
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 INCREASEThis results in PHOTORESPIRATION! (This is a bad thing for the plant)
PhotorespirationPhotorespiration 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
O2
O2O2
O2
O2
O2CO2
C₃ PLANTSExamples:
-rice-wheat-soybeans
*create a 3 carbon compound in 1st step of Calvin
Cycle
*photorespiration is a problem for these
plants in dry/hot areas
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
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
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)
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
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.
Limiting Factors for Photosynthesis
Light Intensity
*high light intensity increases rate of photosynthesis until it reaches saturation
Limiting Factors for Photosynthesis
Temperature
*temperature increase causes an increase in rate of photosynthesis until it reaches its ideal temperature, then
it decreases
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 P
hoto
synt
hesi
s