FACTORS AFFECTING THE RATE OF PHOTOSYNTHESIS

Transcription

1 AP BIOLOGY CELLULAR ENERGETICS ACTIVITY #5 NAME DATE HOUR FACTORS AFFECTING THE RATE OF PHOTOSYNTHESIS OBJECTIVES: The purpose of this activity is to: Demonstrate how photosynthetic rates in different plants can change in response to factors such as light intensity, light quality, CO 2 concentration, and temperature. Compare photosynthesis in C 3 and C 4 plants. EXPERIMENTAL DESIGN The basic experimental design begins with a lamp as a source of visible light. The intensity of visible light produced by this lamp can be increased or decreased, and the wavelengths of visible light released by the lamp can be altered using different filters that will allow only certain wavelengths of visible light to strike the leaf you are studying. To prevent the leaf sample from drying out or burning due to heat from the lamp, a reservoir of water is placed between the lamp and the leaf. The leaf is contained in a sealed chamber. In addition to manipulating the quantity and quality of light striking the leaf in the chamber, the scientists can also manipulate various environmental conditions of the leaf chamber, such as gas flow, temperature, and CO 2 concentration. When collecting data, the concentration of CO 2 in the leaf chamber will be measured using an infrared gas analyzer (IRGA). Because water vapors that can affect the accuracy of the IRGA will be produced in the chamber when light strikes the leaf, air leaving the chamber is passed through a drying column prior to entering the IRGA. The IRGA measures the amount of infrared radiation absorbed by CO 2 in the air coming from the leaf chamber. Analyzing data on the amount of CO 2 consumed by the leaf will enable the scientists to study several different parameters of photosynthesis. The rate of photosynthesis is calculated using four equations. Each equation is described below. Equation 1: Calculates CO 2 consumption by subtracting C-out from C-in and reports this value as the change in CO 2 concentration ( CO 2 ). Equation 2: Converts CO 2 concentration from parts per million to µmol/liter, based on the temperature of the leaf flask. Equation 3: Calculates the rate of CO 2 that is available for exchange between the leaf and the flask by multiplying CO 2 concentration against gas flow. Equation 4: Net photosynthetic rate (P) is calculated by dividing the CO 2 available for exchange by the total surface area of the leaf being studied. This value is reported as the number of micromoles of CO 2 released per square meter of leaf surface area per second (µmol/m 2 /s). Cellular Energetics Activity #5 page 1

2 EXPERIMENT #1: EFFECT OF LIGHT INTENSITY ON THE RATE OF PHOTOSYNTHESIS What effect does light intensity have on the rate of photosynthesis in tomato (C-3 plant) and corn (C-4 plant)? HYPOTHESIS: Write a hypothesis to predict the effect of increasing light intensity on the rate of photosynthesis. TOMATO (C-3 PLANT) Gas Flow 500 ppm Leaf Area cm 2 CORN (C-4 PLANT) Gas Flow 5000 ppm Leaf Area cm Cellular Energetics Activity #5 page 2

3 Graph the data for photosynthetic rate. Independent Variable: Dependent Variable: Graph Title: Cellular Energetics Activity #5 page 3

4 EXPERIMENT # 1 QUESTIONS 1. What is the relationship between an increase in light intensity and photosynthetic rate in tomato leaves? 2. Does this relationship support the hypothesis that you formulated? 3. Photosynthetic saturation is the maximum rate of photosynthesis. What was the value for photosynthetic saturation in tomato leaves? 4. What value of light intensity produced photosynthetic saturation in tomato leaves? 5. Based on what you know about photosynthesis, provide possible reasons for what causes photosynthetic saturation. 6. Are there any differences between photosynthetic rate in corn compared with tomatoes? 7. If there are differences, what are they? 8. How do C 3 and C 4 plants differ in their capacity for photosynthesis? Cellular Energetics Activity #5 page 4

5 9. Are there differences in photosynthetic saturation in corn compared with tomatoes? 10. What are they? 11. Provide possible explanations for any differences that you observed. EXPERIMENT #2: EFFECT OF LIGHT QUALITY ON THE RATE OF PHOTOSYNTHESIS What effect will different colors of light (white, red, green, and blue) have on the rate of photosynthesis in corn leaves? HYPOTHESIS: Write a hypothesis to predict of the effect of different colors of light on the rate of photosynthesis in corn leaves. CORN LEAF UNDER WHITE LIGHT Gas Flow 5000 ppm Leaf Area 77.0 cm Cellular Energetics Activity #5 page 5

6 CORN LEAF UNDER RED LIGHT Gas Flow 5000 ppm Filter Red Leaf Area 77.0 cm CORN LEAF UNDER GREEN LIGHT Gas Flow 5000 ppm Filter Green Leaf Area 77.0 cm CORN LEAF UNDER BLUE LIGHT Gas Flow 5000 ppm Filter Blue Leaf Area 77.0 cm Cellular Energetics Activity #5 page 6

7 Graph the data for the effect of light color on the rate of photosynthetic. Independent Variable: Dependent Variable: Graph Title: Cellular Energetics Activity #5 page 7

8 EXPERIMENT #2 QUESTIONS 1. Which colors of visible light are most effective for photosynthesis in plants? 2. Which colors of visible light are least effective for photosynthesis? 3. Why are some colors more effective than other colors? 4. What effect does light quality have on the rate of photosynthesis? 5. Relate the results of this experiment back to your hypothesis. Cellular Energetics Activity #5 page 8

9 EXPERIMENT #3 What effect will temperature have on the rate of photosynthesis in a tomato leaf? HYPOTHESIS: Write a hypothesis to predict the effect of different temperatures on the rate of photosynthesis in tomato leaves. TOMATO LEAF AT 15 O C Gas Flow 500 ppm Temperature 15 o C Leaf Area cm TOMATO LEAF AT 20 O C Gas Flow 500 ppm Temperature 20 o C Leaf Area cm Cellular Energetics Activity #5 page 9

10 TOMATO LEAF AT 25 O C Gas Flow 500 ppm Leaf Area cm TOMATO LEAF AT 30 O C Gas Flow 500 ppm Temperature 30 o C Leaf Area cm Cellular Energetics Activity #5 page 10

11 Graph the data for the effect of temperature on the rate of photosynthetic. Independent Variable: Dependent Variable: Graph Title: Cellular Energetics Activity #5 page 11

12 EXPERIMENT #3 QUESTIONS 1. What effects does temperature have on the rate of photosynthesis in tomato leaves? 2. How might these effects be different in a C 4 plant such as corn? Cellular Energetics Activity #5 page 12