MayaQuest/eProbe Activity 3: Bag an Ecosystem

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Activity: Introduction | 1 | 2 | 3 | 4 | 5 | Credits

Activity Three: BAG AN ECOSYSTEM

Discovery Question

How does pH of an aquatic ecosystem change with variation in light?

Introduction

This activity enables you to investigate the process of photosynthesis in an aquatic ecosystem.

Background

The lush green color of a tropical rain forest is created by the chlorophyll in the leaves of the trees and plants. The combination of strong sunlight, warmth, and a damp atmosphere helps to provide ideal conditions for photosynthesis. Plants are unique among living things because they make their own food. Through the process of photosynthesis which uses light, water, and carbon dioxide, plant and tree leaves make sugars that are important for growth. By placing a small aquatic plant and snail in a plastic bag filled with water, you can measure the change in rate of photosynthesis based on pH. The live snail produces carbon dioxide which is dissolved in the water in the form of carbonic acid. The plant needs the carbon dioxide for the process of photosynthesis . The plants will only undergo photosynthesis if ample light is available. If the level of carbon dioxide found in the water increases during the night or at lower light levels in the rain forest, the pH of the water will decrease.

Materials

pH probe
small plastic bag
snail or slug
small aquatic plant with roots
water

Safety

No specific safety issues.

Calibration

Use the built-in default calibration included with the eProbe software, or follow the instructions in your eProbe Users Guide and the probe manufacturer's documentation to manually calibrate the probe(s) for this activity.

Procedure

Place a snail and a small aquatic plant with attached roots into a small plastic bag filled with stream or pond water. Use eProbe Notes to draw a detailed sketch of your aquatic ecosystem. Place your bag in strong sunlight. Measure the pH of your aquatic ecosystem over a twenty-four hour period. Explain the causes for the different readings.

Analysis

Make a line chart of pH during the day.

Further Investigations

How would the pH change if the bag had more plants or snails?
Observe how the pH readings change at different levels (canopy, understory, floor, etc.) in the forest?
How does the pH change relate to light levels? Use a light probe to measure the light level at the same time pH is being recorded.

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