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Factors Affecting Photosynthesis

Introduction

The rate at which photosynthesis occurs is not always the same. The availability of all the materials and energy needed for photosynthesis—light, water, CO2 and soil minerals—all affect the rate at which photosynthesis can occur. Laboratory studies often measure changes in the amount of sugars the plant is producing as a measure of photosynthetic rate. The more sugar made, the greater the rate of photosynthesis and the greater the rate of photosynthesis, the greater the growth of the plant.

The two data sets show the effects of light levels and temperature on the rate of photosynthesis in a typical C3 land plant. NOTE: light intensity is in lumens. A bright, clear day is around 10,000 lumens, a cloudy day about 1,000 lumens and indoor artificial lighting averages around 500-750 lumens (but is variable based on the light source, a small lamp much less and an array of fluorescent lights somewhat more than this range.)

Plot each graph on the back of this paper in the space provided. Label and scale axes correctly.

1. What does the general pattern of Graph A tell about the effect of light intensity on photosynthesis?

a. Aside from the general pattern, what specifically happens when light levels approach and exceed 9,000 lumens?

2. True or false: Plants grow on cloudy days. Explain your answer.

3. What does the general pattern of Graph B tell about the effect of temperature on photosynthesis?

a. Aside from the general pattern, what specifically happens when temperature exceeds 33̊ C?

4. Explain the direct temperature effect on the chemistry of photosynthesis, including both the rising section and the reason for the decline.

5. List at least two indirect factors that would reduce the rate of photosynthesis as temperature increased.

6. What light intensity and temperature combination allows for the maximum photosynthetic rate?

a. What time(s) of year might you likely find these conditions in Connecticut?

lumens (x-axis) |0 |250 |500 |750 |1000 |1250 |1500 |2000 |2750 |4250 |6000 |9000 |10000 |15000 | |rate of photosynthesis

(y-axis) |0 |10 |20 |30 |40 |50 |60 |70 |80 |90 |95 |98 |99 |100 | |temperature (x-axis) |5 |10 |12 |15 |18 |20 |22 |24 |26 |28 |32 |35 |38 |40 | |rate of photosynthesis

(y-axis) |5 |10 |12 |15 |22 |28 |35 |45 |60 |80 |100 |60 |20 |0 | |

Graph A: (title)

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Graph B: (title)

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