Primary Productivity and Energy Flow- Modified from Carolina Biological Lab

Primary Productivity and Energy Flow- Modified from Carolina Biological lab

Purpose: You will use data collected from plant samples to calculate respiration, net primary productivity, and gross primary productivity of the grass plants. You will also design an experiment to test the the following questions “ How does this variable affect primary productivity?”

Background:

Pre lab questions:

1.  In your own words, define gross primary productivity. How does gross primary productivity differ from net primary productivity?

2.  Which would you expect to have a higher value of gross primary productivity: a plant measured from 8 am to 8 pm or a plant measured from 8pm to 8am?

Materials for entire lab:

Grass seeds

Planter

Soil (various options available)

Water

Drying oven

Balance

Pipet

Aluminum foil

Procedures:

Note- this lab will be broken up over several weeks to allow the plants time to grow.

Control group- Planting of the seeds

1.  Each group will be given 3 planter, soil and seeds.

2.  Each planter must be filled halfway with soil and 20 seed must be planted.

3.  Label your planters with your groups names.

4.  Moisten soil and place the planter under the grow lights.

Control Group data collection

Week 1

1.  To determine the initial biomass of the grass, use one planter and complete the following steps:

a.  Remove the grass and vermiculite soil from the cell. Dust as much of the soil from the roots as possible. Place the roots in the beaker of water and gently swish to remove the remainder of the soil from the roots.

b.  Use a paper towel to blot the excess water from the roots.

c.  With a balance, measure the mass of the grass. Record it as “wet mass” in your data table.

d.  Place the grass on a piece of aluminum foil and fold the foil loosely around the grass.

e.  Label the foil packet and place in the drying oven.

f.  At the end of class we will mass the dry sample and record it in the data table as Dry mass.

2.  Label one of your groups remaining planters “dark” and place it in the tray labeled dark, The other planter will be labeled “light”, place this in the tray labeled Light.

3.  Make sure to water your plants before you leave class.

Week 2.

1.  Complete the following steps for the grass that was under the light and in the dark. Make sure to keep track of which is which.

a.  Remove the grass and vermiculite soil from the cell. Dust as much of the soil from the roots as possible. Place the roots in the beaker of water and gently swish to remove the remainder of the soil from the roots.

b.  Use a paper towel to blot the excess water from the roots.

c.  With a balance, measure the mass of the grass. Record it as “wet mass” in your data table.

d.  Place the grass on a piece of aluminum foil and fold the foil loosely around the grass.

e.  Label the foil packet and place in the drying oven.

f.  At the end of class we will mass the dry sample and record it in the data table as Dry mass.

Experiment group- Your lab group will be responsible for the design of this group. A reminder you can only change one variable, all other variable should be kept constant.

1.  Design experiment group- In your lab notebook you will need to state the question your group is testing, and the experiment design that will allow you to test the question.

2.  Plant the seeds according to your groups set up (you will need 3 planters still: base line, light and dark)

3.  After one week of growing we will start the data collection process following the same steps used for our control group for week 1 and week 2.

Possible materials to use:

Pebbles

Potting soil

Sand

Fertilizer

Natural light

LED light

Plant bags

IF you have other supplies you would like to bring in please get approval to use by your teacher.

Hypothesis: Your hypothesis should be related to the question your group is testing.

Data:

Control Group / Wet Mass / Appearance / Dry Mass / Appearance
Initial
Light
Dark
Experiment Group / Wet Mass / Appearance / Dry Mass / Appearance
Initial
Light
Dark

Calculate the Gross and Net Primary productivity for your control group and your experimental group.

Net primary productivity= mass of grass grown under light- initial mass

●  Find both wet mass and dry mass net primary productivity

Respiration= initial mass- mass of grass kept in the dark

●  Find both wet mass and dry mass net primary productivity

Gross primary productivity= net primary productivity + respiration

●  Find both wet mass and dry mass net primary productivity

Graph- Create a graph to compare the productivity of your samples.

Questions to Guide your analysis

1.  Describe the differences in appearance between the grass grown in the light and that grown in the dark. What was the purpose of growing the grass in the dark for a week?

2.  Describe the differences in appearance between the control group plants and the experimental group plants.

3.  Which calculation provide a more reliable rate of gross productivity for a plant community- those using the wet mass or those using the dry mass? Be able to justify your answer.

4.  What does the gross primary productivity value represent? How does the experiment relate to energy flow?

5.  Our current unit is on Biogeochemical cycles, Explain how productivity can be related to one of our biogeochemical cycles.

6.  Use your data to help you to explain the relationship between your independent variable and your dependent variable in this lab.

Don’t forget to Write Your Conclusion