- In this lab you will prepare a culture of duckweed, observe the growth, and graph the data. Duckweed is a small common aquatic floating plant(see Figure 1) with leaf like lobes, and roots extending down into the water. Each lobe is actually considered a separate plant. You can collect duckweed from a local pond, or purchase it from a biological supply.
- The growth of the plants occurs by mitosis and can be quantified by counting the number of new buds found on the plant after a period of time. A population of plants establishing itself in a new area will exhibit the S-shaped curve that we see so many times in science. See Figure 2.
This growth curve consists of three phases:
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1. Lag phase - A period of slow growth.
2. Exponential growth phase - A period of very rapid growth.
3. Equilibrium phase - The population maintains itself at a fixed level.
MATERIALS:400-mL beaker
Light source
10 duckweed structures
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Each unit includes several lobes attached and roots growing beneath. Try to have structures with 3 lobes per structure, or a total of 30 lobes per container.
Pond water.
Inoculating loop or similar device to pick up and transfer duckweed.
Graph paperPROCEDURE:
1. Obtain a 400-mL beaker and add 300 mL of pond water to the beaker.
2. Using the inoculating loop, select 10 "plants" from the stock of duckweed. Remember that each "plant" is made of several real plants that look like lobes. Record in your data table the number of lobes in your original sample of duckweed as day 0.
3. Label your beaker, if necessary, and place under the light source.
4. For the next 14 days, make daily observations and count the lobes. Record the number of lobes, for the appropriate day, in your data table.
DATATABLE: Number of lobes counted. Day Number of lobes 
Day Number of lobes
0
8
1
9
2
10
3
11
4
12
5
13
6
14
7
DATA ANALYSIS:5. Graph your data, from the data table, with the independent variable on the x axis (days) and the dependent variable on the y axis (number of lobes).
6. Explain your results from the graph.
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- The growth of the plants occurs by mitosis and can be quantified by counting the number of new buds found on the plant after a period of time. A population of plants establishing itself in a new area will exhibit the S-shaped curve that we see so many times in science. See Figure 2.
OBSERVING GROWTH RATE
IN A CULTURE OF DUCKWEED
INTRODUCTION: