Name
Date
Period
Freshwater Biomes and Limiting Factors
Observations:


Different organisms can be found in different parts of a lake.
The water depth is not the same in all areas of the lake.
Purpose:
The purpose of this investigation is to determine if the depth of water in a freshwater
biome, such as a lake, affects the population of phytoplankton in the lake.
Background Information:
1. What is meant by the term ‘limiting factor’ in an ecosystem?
2. List at least four (4) limiting factors in a lake ecosystem.
3. Phytoplankton are like floating plants that use the sun’s energy to make food and
serve as a food source for animal life in the lake. How do you think the depth of
the lake affects the amount of phytoplankton found in the lake at that depth?
Hypothesis:
 If the depth of the lake water increases, then the amount of phytoplankton found
_____________________________________________________________________________.
Materials/Procedures:
A group of scientists collected specimens of phytoplankton from the same lake. The
scientists’ findings on the phytoplankton are shown in Tables 1-3. The scientists
measured the concentration of oxygen at different depths of the lake and recorded
their findings (Table 1). The amount of light that penetrated the lake water at the
various depths was also measured and recorded on Table 2.
Data:
Table 1. Oxygen
Concentration at
Different Depths of the
Lake
Oxygen
Depth
Concentration
(m)
(mg/L)
0
8.5
Table 2. Light Penetration
at Different Depths of the
Lake
Table 3. Amount of
Phytoplankton at Different
Depths of the Lake
Depth
(m)
Phytoplankton
(# individuals/L)
0
Light
Penetration
(%)
100.0
0
800
Depth
(m)
1
2
8.5
8.5
1
2
32.0
23.0
1
2
3500
2800
3
4
5
6
7
8
9
10
11
12
8.5
9.0
17.0
16.0
14.0
12.0
10.0
5.0
2.0
0.0
3
4
5
6
7
8
9
10
11
12
18.0
12.0
10.0
9.0
7.0
5.0
2.0
1.0
0.5
0.0
3
4
5
6
7
8
9
10
11
12
4000
5700
183000
96000
30000
10000
2000
600
500
50
Analysis:
Construct a graph of the data above that includes the following three lines:
Line 1: Show oxygen concentration in relation to depth of the lake.
Line 2: Show the percent of light penetration in relation to depth of the lake.
Line 3: Show the amount of phytoplankton at various depths in the lake.
NOTE: Don’t forget to include a key to indicate what each line represents.
Conclusion:
On the back of the graph paper, please include a full explanation of the outcome of
the experiment (using your graph as evidence of your conclusion). Make sure to:
 restate and evaluate your hypothesis
 concisely explain what was achieved by performing this experiment
 reflect on what you or other scientists could do for a follow-up on this
experiment