Activity 06
PS-2820
Rate of Photosynthesis for an Aquatic Plant
Biology: Photosynthesis, respiration
Qty
1
1
1
1
1 sprig
1L
1
1
1
1L
DataStudio GLX setup file: photosynthesis.glx
Equipment and Materials
PASPORT Xplorer GLX
PASPORT Dissolved Oxygen Sensor
Photosynthesis Tank
Cloth, opaque, about 50 cm by 50 cm
Elodea (or equivalent aquatic plant)
Ice, crushed or cube (optional)
Lamp, 100 W (or equivalent)
Magnetic stirrer and stir bar
Rubber stopper, #3 (included with Photosynthesis Tank)
Water
Part Number
PS-2002
PS-2108
PS-2521
Purpose
The purpose of the activity is to explore the rate of photosynthesis for an aquatic plant (Elodea)
when it is exposed to different light conditions.
Background
The process of photosynthesis is the chemical pathway by which all plants and
some protists and monerans make food from carbon dioxide, water and sunlight.
The entire photosynthetic pathway is a complex series of enzyme
transformations that take place in chloroplasts. During the transformation,
hydrogen from water is added to molecules of carbon dioxide to make
carbohydrates. The generalized equation for this process is given below:
light/ chlorophyll
6CO2 + 6H2 O ⎯⎯
⎯⎯⎯⎯→ C6 H1 2O6 + 6O2
carbon dioxide + water --------------> carbohydrate + oxygen
Aquatic plants and photosynthetic microorganisms release the oxygen into the water where it
dissolves, forming dissolved oxygen. There is a limited amount of O2 that water can hold, so
when the concentration reaches a certain level (saturation), the O2 diffuses (or out-gases) into the
air.
The series of biochemical events that comprise photosynthesis have been classified into two
main sets: the light-dependent reactions and the light independent reactions. The set classified as
the light-dependent reactions at its most basic level is involved in capturing light energy into
energized molecules that are then used in the set of light-independent reactions to fuel the
synthesis of sugars from carbon dioxide and water. The light-dependent reactions are so named
because light energy is required. The light-independent reactions do not require light; however,
they can and do occur under lighted conditions.
Pre-lab Questions
Measure the dissolved oxygen concentration in water that contains an aquatic plant.
1.
What will happen to the concentration of dissolved oxygen in the water if the plant is
exposed to bright light?
Biology with Xplorer GLX
© 2005 PASCO
p. 35
Activity 06
1.
Rate of Photosynthesis for an Aquatic Plant
PS-2820
What will happen to the concentration of dissolved oxygen in the water if the plant is put
into a dark environment with no light?
Safety Precautions
•
Follow all directions for using the equipment.
•
Wear protective gear (e.g., safety goggles, gloves, apron).
Procedure
GLX Setup
1.
Plug the end of the
Dissolved Oxygen probe
cable into the connector on the top of the PASPORT Dissolved Oxygen Sensor.
1.
Open the GLX setup file labeled photosynthesis.glx (see the appendix at the end of this
activity). The file is set so the sensor will measure 2 times per second.
1.
Connect the Dissolved Oxygen Sensor into Port 1 on
the top of the Xplorer GLX.
•
The Graph Screen will automatically open with
Dissolved Oxygen (mg/L) versus Time (s).
Sensor Calibration (Optional)
•
See the appendix at the end of this activity.
Figure 1: Connect sensor to GLX
Equipment Setup
1.
Put a stir bar into the photosynthesis tank that contains water and the
sprig of Elodea plant. Put the large two-hole stopper into the top of
the tank.
1.
Place the photosynthesis tank on the magnetic stirrer.
1.
Put water into the outer chamber of the tank. [The water helps to
maintain the temperature of the inner tank.]
1.
Remove the storage bottle from the end of the Dissolved Oxygen
probe and carefully insert the end of the probe through the larger
opening in the two-hole stopper.
•
Make sure that the metal band on the Dissolved Oxygen probe is
below the surface of the water in the tank and that no air bubbles are
trapped on the end of the probe.
1.
Put a #3 rubber stopper into the other hole in the two-hole stopper.
1.
Place the lamp very near the photosynthesis tank so the light will shine on the Elodea
plant. DON’T’ turn the lamp on yet.
Biology with Xplorer GLX
© 2005 PASCO
Figure 2: Setup
p. 36
Activity 06
Rate of Photosynthesis for an Aquatic Plant
PS-2820
Record Data
1.
Turn on the magnetic stirrer to a moderate speed so the water circulates in the tank.
1.
Press the Start key
1.
After 60 seconds, turn on the lamp to its brightest setting.
1.
Continue to record data with the light on for 15 minutes, and then turn the lamp off and
carefully cover the setup with an opaque cloth so the plant is in darkness.
1.
Record data with the plant in darkness for 15 minutes and then stop recording data.
1.
Turn off the magnetic stirrer. Clean up the equipment as instructed.
on the GLX.
Analysis
1.
Draw a sketch of your Dissolved Oxygen versus Time graph as requested in the Lab
Report section.
1.
Use your recorded data to find the change in dissolved oxygen when the light is shining on
the plant, and the change in dissolved oxygen when the plant is in darkness.
•
In the Graph Screen, use the right-left cursor keys to move the cursor to the point where
the lamp is turned on. Press F3 to open the ‘Tools’ menu. Select ‘Delta Tool’ and press
‘Activate’. Move the cursor to the point where the lamp is turned off and the plant is in
darkness. The highlighted value on the vertical axis is the change in dissolved oxygen
concentration. The highlighted value on the horizontal axis is the change in time.
1.
Record your values in the Data Table in the Lab Report section.
•
How do your results compare with others in your class?
Record your results in the Lab Report.
------------------------
Biology with Xplorer GLX
© 2005 PASCO
p. 37
Activity 06
Rate of Photosynthesis for an Aquatic Plant
PS-2820
Appendix:
To open a specific GLX file, go to the home screen (press
). In the home screen, select ‘Data
Files’ and press ‘Activate’ (
). Use the cursor keys to navigate in the list to the file you want.
Press F1 ( ) to open the file.
Optional: To calibrate the PS-2108 Dissolved Oxygen Sensor, see the instructions provided by
the instructor.
Biology with Xplorer GLX
© 2005 PASCO
p. 38
Activity 06
Rate of Photosynthesis for an Aquatic Plant
PS-2820
Lab Report - Activity 06: Rate of Photosynthesis for an
Aquatic Plant
Name ________________________________ Date ___________
Pre-Lab Questions
Measure the dissolved oxygen concentration in water that contains an aquatic plant.
1.
What will happen to the concentration of dissolved oxygen in the water if the plant is
exposed to bright light?
1.
What will happen to the concentration of dissolved oxygen in the water if the plant is put
into a dark environment with no light?
Data
Make a sketch of one run of Dissolved Oxygen Concentration versus Time, including labels for
the y- and x-axes. Label the section of the graph that shows the light-dependent reaction of
photosynthesis.
Biology with Xplorer GLX
© 2005 PASCO
p. 39
Activity 06
Rate of Photosynthesis for an Aquatic Plant
PS-2820
Data
Write a description of the pattern of the graph:
•
Light:
•
Darkness:
Data Table
Light Condition
Dissolved O2 Concentration (mg/L)
Ambient light
Bright light
Darkness
Questions
1.
What happens to the level of dissolved oxygen when the plant is in bright light? Why does
this happen?
2.
What happens to the level of dissolved oxygen when the plant is in darkness? Why does
this happen?
Biology with Xplorer GLX
© 2005 PASCO
p. 40