4. How would warming of the leaf affect the O2 evolution curve?

Curve B shows two effects of leaf warming. Notice that photosynthesis never reaches a steady state--the curve is 'sygmoidal'. Initially, the rate of photosynthesis increases continually--it never attains a steady, linear rate. This is because, moderate increases in temperature cause the rate of enzymes to increase. As the leaf warms, the Calvin-Benson cycle enzymes catalyze reactions more rapidly, and the rate of photosynthesis continually increases.

If the temperature in the leaf chamber becomes too high, it may eventually inhibit photosynthesis, and the rate of O2 evolution will begin to level off. All enzymes and proteins have an optimum temperature range, and when this is exceeded the enzymes become less efficient. At very high temperatures, cell damage may occur -- the leaf becomes "cooked!"


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Copyright (C) 1998, Steven R. Spilatro, spilatrs@marietta.edu. All rights reserved