Grade Level: 6th - 8th; Type: Earth Science, Physical Science
The project looks at the oil content in different types of algae by comparing the surface beading of water droplets on the algal surfaces.
What are the goals? The goal is to have the student formulate, test and, if necessary, revise a hypothesis about oil production in algae.
- How and why do algae store oil?
- What types of algae produce the most oil?
- Under what conditions to algae produce the most oil?
- Can algal oil content be measured in this simple and inexpensive way?
Algae are found in most kinds of aquatic environments. Large multicellular macroalgae typically grow in fresh water ponds and in the ocean. They tend to be measurable in inches, although macroalgae in the ocean (giant kelp) can grow to more than 100 feet in length. Microalgae are tiny unicellular organisms that grow as suspensions in water; they are measurable in micrometers. They are frequently seen in bogs, marshes, and swamps.
All algae require sunlight, water, nutrients, and carbon dioxide for growth. Through the process of photosynthesis, algae convert the carbon dioxide into glucose (a sugar). The glucose is then broken down into fatty acids, which under normal conditions, are used to produce membranes for new algal cells. If, however, the algae are stressed, the fatty acids will produce fat molecules or lipids (oil). Most algae do not produce much oil unless they experience some sort of growth stress, which is to say deprived of their basic requirements for growth. Unfortunately for algal oil producers, algae produce much less mass when grown under starvation conditions.
When algae are dried in a microwave oven, the cell walls of the algae membrane are broken down, and the oil trapped inside can reach the surface. When a water droplet is placed on the oil-rich surface, it forms a bead-like drop rather than spreading.
Water beads up on oil surfaces because the oil underneath does not have enough surface energy to draw the water out. Although water will bead up to a certain extent on a physically intact algae surface, it does so less strongly than on oil because oil has a lower surface energy.
- Algae; collection jars; notebook; filter paper; microwave oven; water dropper
- Materials can be found at the following places: Algae (ponds, marshes, swamps, swimming pools, fish aquariums); filter paper (scientific supply houses, Internet), water dropper (drug stores)
- Conduct a literature review and learn how and why algae store oil.
- Formulate a hypothesis that will allow you to predict what kinds of algae will contain the most oil.
- Collect samples of algae (both macroalgae and microalgae) from various sources such as the ocean, ponds, marshes, swamps, fish aquariums, and swimming pools. Store each algae specimens in jars filled with water.
- Record data about the physical characteristics and conditions under which you found each specimen. Also note whether the conditions under which you found the algae specimens reflected light or nutrient starvation.
- Select one the specimens, and divide it into two samples.
- Place each of the two samples on a piece of filter paper.
- Allow the two samples to dry in air.
- Heat one of the samples in a microwave oven under low power. This will cause the cell walls in the algae membrane to crack and allow the oil inside to come to the surface. Do not allow the algae to burn.
An alternative way to release the oil is to grind the algae using a mortar and pestle. If you choose to use this method, use a nonporous mortar and pestle.
- Apply a drop of water to both the air-dried and microwave-dried samples.
- Observe whether there is any difference in the way the water drop beads up or spreads out on the surface of the algae. Record your observations.
- Repeat the same steps for each type of algae in your collection.
- Evaluate your hypothesis in light of your findings. Revise it if necessary and propose and perform further tests if necessary.
Beading characteristics (air dried)
Beading characteristics (microwave dried)
Terms/Concepts: Algae; Macroalgae; Microalgae; Photosynthesis; Lipids; Surface tension and energy; Wetting
- Dr. Terry Woodford-Thomas, Danforth Plant Science Center, St. Louis, MO, firstname.lastname@example.org