Principles of Biology Lab Fall, 2006

Lab Five: Photosynthesis - Assignment

Pre-Lab Quiz:

Questions will be drawn from the following:

1. After reading about paper chromatography (lab manual 6.3), determine the order that the pigments shown in lab manual Fig. 6.2 will travel up the paper.

2. Use your course textbook (Fig. 10.9, graph a) to determine which light wavelength(s) are maximally absorbed by Chlorophyll a, Chlorophyll b, and accessory pigments. (HINT: estimate where peaks are in terms of corresponding wavelength).

3. Given your previous answer, predict what you will see during the Manometer Experiment (substitution protocol below) for the 3 conditions being tested:

a. exposure to white light (380-750 nm)b. exposure to just 660-680 nm light

c. exposure to just 520-540 nm light

4. Given your answer to #2, answer Discussion Questions 1 through 3 on lab manual p. 139.

5. Name 4 variables that must be controlled during the Manometer Experiment.

6. Explain in your own words what a spectrophotometer is and does.

Procedures:

This lab will require multi-tasking by each team; carry out as recommended below.

Complete 6.3with the following modifications

use a narrow strip of chromatography paperinstead of a large cylinder

set or hang strips inside a large corked test tube; keep lid on as much as possible

watch separation for the entire 5-15 minutes it will take to avoid losing bands that run off the top of the strip

Complete your analysis as soon as the strip is dry, as the pigments will fade with time

Complete 6.4with the following modifications

Every team will analyze complete spinach extract and start at Step 3 on page 147 –

BUT DILUTE YOUR SPINACH EXTRACT WITH NaHCO3 NOT WITH ACETONE!!!!!, by placing about 2.5 ml of NaHCO3in each of two cuvettes. To the first cuvette add 10drops or less of extract andto the second cuvette, that you will use to “zero” the spectrophotometer, add a volume of acetone equal to the volume of extract that you placed in the first cuvette.

Your instructor will describe the operation of the spectrophotometer.

ADDITION TO MORGAN & CARTER’S LAB TOPIC 6: PHOTOSYNTHESIS

EXERCISE 6.5Light Wavelength and the Rate of Photosynthesis

In this exercise, each team will determine the color of light transmitted by a filter and how light of this color affects photosynthesis.

Introduction:

Photosynthesis uses light energy and light-absorbing pigments to make oxygen, glucose/starch, and ATP from carbon dioxide and water. In this exercise, the rate of photosynthesis will be assayed as a function of oxygen production under varying light wavelengths.

Look through your filter, observe the color of light that is transmitted, share with all other teams and record your observations in the table in #4 of the Lab Five: Photosynthesis - Worksheet

The plant system you will employ, Elodea, is aquatic; oxygen gas bubbles produced underwater displace liquid. Thus, you can employ a MANOMETER, illustrated below, to indirectly assay the amount of oxygen by measuring the amount of liquid that is displaced.

Procedure: A. Setup

  1. Obtain two test tubes; wrap one in aluminum foil
  2. Fill the two test tubes completely with sodium bicarbonate (provides the plant with CO2 and H2O)
  3. Take two similar pieces of Elodea, making fresh cuts at each end
  4. Over a sink, place Elodea into test tubes (this will displace liquid)
  5. Over a sink, SECURELY rubber stopper each test tube with a glass L tube (this will displace liquid)
  6. MAKE SURE that the short end of the L tube is below the level of the fluid in the test tube, that there are no air bubbles in the L tube and that the fluid level is visible somewhere along the long arm of the L tube (not too far!)
  7. Place the manometeryou constructed in steps 5. and 6. in a test tube rack in a filter box; point the L tube toward the wall of the lab
  8. Set up a beaker with water between the light and the filter box; point the light toward the wall
  9. Wait 5 full minutes to make sure there are no leaks in your manometer
  10. DO NOT turn on light until instructor tells you all teams are prepared.
  11. Lab lights will be turned off and bench lights turned on when every team is ready.

Procedure: B. Data Collection

  1. Mark the fluid position in the manometer tube at this time; this is the “zero time” mark.
  2. Mark the fluid position and measure the distance of each mark from the “zero time” time mark EVERY 5 MINUTES for 75 minutes
  3. Record your observations in the two “distance fluid moved” rows of the table in the Lab Five Worksheet, #6.

Procedure: C. Data Analysis

  1. Use the “distance fluid moved” data to calculate the volume of gas made and record these results in the two “volume gas made” rows of the table in the Lab Five Worksheet, #6.
  2. Complete #s 6 through 9 in the Lab Five Worksheet.

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