Lab: Exploring the Rate of Photosynthesis

Problem: How will _____________ (independent variable) affect the rate of oxygen production during photosynthesis in an Aquatic Plant.

Materials: test tube, Elodea cuttings, sodium bicarbonate (baking soda), beaker with water, lamp

Part 1: Measurement of Photosynthesis

There are various set-ups that can be used to measure the rate of photosynthesis, each relies on counting the oxygen produced during the reaction. To improve results, add a pinch of baking soda to the water in the test tube. Cut elodea stems at an angle and use your fingers to crush the end of the stem. The water in the beaker is meant to absorb the heat from the light.

Design 1: Heat sinks (beaker with water) may not be necessary if using CFL bulbs. Count the bubbles to measure the rate of reaction

Lab: Exploring the Rate of Photosynthesis

Design 2: The test tube can be inverted and the air pocket can be measured.

Photosynthesis is the process by which plants take carbon dioxide from the atmosphere, add water, and use the energy of sunlight to produce sugar.

Photosynthesis occurs in the chloroplast, an organelle in plant cells that contains the molecule chlorophyll. Chlorophyll absorbs the energy of sunlight. That light energy is converted to chemical energy through the steps of photosynthesis.

The reactions of photosynthesis can be divided into two major types: light-dependent reactions and light-independent reactions. The light-dependent reactions convert energy from the sun into a form that the chloroplast can then use to make sugar from carbon dioxide, in the process producing oxygen as a waste product. The light-independent reactions use that energy to make glucose from carbon dioxide and water.

Design 3: A marker can be used to measure the amount of oxygen in the test tube rather than measuring bubbles.

If you do not see bubbles right away, re-cut and crush the stems, experiment with moving the light closer to the apparatus or remove the heat sink if using CFL bulbs. Your goal is to find a way to consistently measure the rate of photosynthesis using any of the designs above.

Part 2: Conditions for Photosynthesis

1. Brainstorm variables which may affect the rates of photosynthesis.

2. Form a hypothesis to test your variable.

3. Design an experiment to test your hypothesis. (check with instructor about available materials)

4. After discussing your plan with your instructor, perform your experiment.

5. Record all data and determine if your data supports or refutes your hypothesis.

Lab Report

Include the following sections in your lab report, which should be typed. You may also include photos of your experiment.

Problem: Write a problem which resembles this format...

How will _____________ (independent variable) affect the rate of oxygen production during photosynthesis in an Aquatic Plant.Introduction:

Hypothesis: Write a hypothesis to answer your initial question in a cause and effect format.

Method: Write the experimental set-up you used and how it was used to measure the rate of photosynthesis.

Results: Include a table or graph of the data you collected. Be sure to include units of measure, titles and headings.

Discussion: Accept or reject your hypothesis and support your conclusion by referencing your data collected. Answer your experimental question or hypothesis by using your data to support or refute your claim (conclusion). Discuss any experimental errors or problems you encountered.