NAME:_____________________________________
Lab Partner(s):__________________________________________________________________________
Why is the Water Green?
Introduction: Ever notice how bodies of water differ in color, odor, and clarity? Algae are among the most abundant life
forms present in all bodies of water, saltwater, and freshwater alike, and are a major contributor to water quality.
Background: Algae are a special group of organisms that can be found nearly everywhere—in saltwater, freshwater,
damp soil, ice, on rocks, lichens and even in the air. Considering that algae are photosynthetic organisms, they can
basically survive anywhere moisture, essential nutrients, and sunlight are present. Algae are responsible for the
production of a large portion of the Earth’s atmospheric oxygen, and marine and aquatic food chains rely greatly on
their presence. Algae are broadly defined by their pigment color, which are often described in terms such as blue-green,
green, brown, red, brown-yellow, etc. Algae come in many sizes from single-celled organisms to very large seaweed
varieties.
Nitrates and phosphates are necessary for plant and algae growth. Since soil often becomes stripped of these
nutrients due to constant farming, fertilizers are often added to replace these lost nutrients. However, these fertilizers
seep into the ground when it rains, and eventually reach the groundwater. Groundwater flows to larger bodies of water
where algae thrive. Unnaturally high levels of nutrients may cause rapid, excessive algae growth referred to as an algae
bloom. Most question, why is this such a bad thing? If algae produce oxygen and are at the bottom of the food chain,
then having more around should be a good thing, right? This is not the case for several reasons. First, if a thick blanket of
algae is present on the surface, it blocks the sunlight needed by other photosynthetic life inhabiting the water below the
surface. As plants and microorganisms die off from lack of sunlight bacteria levels increase. Algae require oxygen and
other nutrients to live, so as the populations increase, dissolved oxygen levels decrease. Dissolved oxygen is used by
other life forms such as fish, turtles, amphibians, etc. If the levels of dissolved oxygen fall below 3ppm (parts per
million), larger organisms begin to die of, creating stress on the entire ecosystem in the area. It may even indirectly have
an effect on humans—for example, if the area is frequented by fishermen. When certain fish are not readily available,
market prices go up, or the fish may not be available for consumption at all.
Pre-Lab Questions:
1. How do algae contribute to the well-being of the environment?
2. Define, in your own words, an algae bloom.
3. List a few reasons algae blooms are detrimental to an ecosystem.
Question: Certain types of environments cause algae to bloom. What type of environment causes the largest algae
bloom (one high in nitrates, one high in phosphates or one high in both nitrate and phosphates?
Write your Hypothesis below: (this should be in an if/than statement)
Materials:
- Algae Culture (40mL)
- Algae Media (80mL)
- Nitrate Solution (3mL)
- Phosphate Solution (3mL)
- 4 Culture Containers with a snap top
- Graduated Cylinder
- Permanent Marker
- Pipet
Procedure: Activity I
1. Label the lids of the four culture containers “Control,” “Nitrates,” “Phosphates,” and “Nitrates and Phosphates”
using a permanent marker. Also include your groups initials.
2. Obtain 40mL of algae culture in a beaker
3. Measure out 10mL of algae culture using a graduated cylinder and pour into the “Control” container.
4. Repeat step 3 for the remaining three cultures containers.
5. Add 20mL of algae media to each culture container using the same graduated cylinder. Each container should
now contain 30mL of diluted algae culture.
6. Using a pipet add 2mL (about 40 drops) of nitrate solution to the container labeled “Nitrate” and 1mL (about 20
drops) to the “Nitrate and Phosphate” container. Close the lids.
7. Rinse the pipet inside and out with water.
8. Using a pipet, add 2mL (about 40 drops) of the phosphate solution to the container labeled “Phosphate.” Close
the Lid.
9. Add 1mL (about 20 drops) of the phosphate solution to the “Nitrate and Phosphate” container. Close the lid.
10. On the data table write your observations in the “Start” column of each of the four containers.
11. Place the four culture containers at the assigned area.
Data Collection:
In the data table, write your observation of the observed algae growth level for each of the four containers according to
the following descriptions. Note: Place the cultures on a white sheet of paper to facilitate observation.
Tint: Slight green algae growth
Light: Noticeable amount of green algae growth
Medium: Very noticeable green color but not quite deep green in color
Dark: Deep green in color, possibly a layer or ring forming on the surface of the solution or container
Day
Start
4
5
6
7
8
11
Control
Nitrate Runoff
Phosphate Runoff
Nitrate and Phosphate Runoff
Data Analysis: Record an analysis of your data (from your data table) below.
Conclusion Questions:
1. What purpose did the control culture serve in this lab?
2. Which culture appeared to have the largest amount of algae growth?
3. What factors are responsible for rapid algae growth?
4. What conclusion can you draw about the culture with the most amount of growth?
5. The algae in this activity color the water samples green. What component of their cellular makeup creates this
coloration? Hint: Algal cells are like photosynthetic plants.
Procedure: Activity II
1. Obtain four slides and label them “C” for Control, “N” for nitrate, “P” for phosphate, and “NP” for the sample
containing both nitrate and phosphate solution with tape and a permanent marker. Note: Label the slides on
the far right or the far left leaving the middle of the slide open.
2. Check the lids of the culture to ensure they are on tightly. Shake the control sample gently to disperse the algal
cells.
3. Using a pipet place a drop of the solution on the slide labeled “C” and slowly lower a cover slip on to the sample
so that the bubbles are minimized.
4. Using three more clean pipets, repeat steps 2 and 3 for the nitrate, phosphate, and nitrate and phosphate
solution.
5. Set up the first slide (control) on the microscope stage and focus it under low power and then under medium
power.
6. Sketch the magnified view of the algae in the data section below.
7. Count an approximate number of algal cells in two different fields of view (by moving the slide and refocusing)
and record each count in the data table below. Note: Algal cells tend to clump together—try to count individual
cells.
8. Repeat steps 5-7 using the other three algae samples.
9. Determine the average counts for each sample and record the value in the data table below.
10. Clean up all materials according to Mrs. Treharne’s instructions.
Data Collection:
Sketch of each culture under medium magnification:
Control
Phosphate
Nitrate
Nitrate and Phosphate
Data Table:
Count Number
1
2
Average
Control
Nitrate
Phosphate
Nitrate and Phosphate
Data Analysis: Record an analysis of your data (from your sketches and data table) below.
Conclusion Questions:
1. Which culture had the highest microscopic algal count?
2. Assuming one drop is on twentieth of a milliliter and the algae cultures contain 30mL, approximately how many
algae cells are present in each culture? Show your work.
a. Control:
b. Nitrate:
c. Phosphate
d. Nitrate and Phosphate:
3. Did your results from activity I agree with your results from activity II? Explain your answer.
4. What did you learn from this lab?