Case Study

Biblical Reference

So neither the one who plants nor the one who waters is anything, but only God, who makes things grow.

1 Corinthians 3:7

Biodiesel from Microalgae

• During the past few decades, scientists have explored using protists to produce biodiesel fuel.

• Protists are a group of microscopic organisms that usually live in water or moist environments.

• Biodiesel Video

Designing a Controlled Experiment

• Scientists use scientific inquiry to investigate the use of protists to make biodiesel.

• They design controlled experiments to test their hypotheses.

• A controlled experiment is a scientific investigation that tests how one variable affects another.

Variables• A variable is any factor in an experiment

that can have more than one value.

• There are two types of variables:– The dependent variable is the factor

measured or observed during an experiment.– The independent variable is the factor that

you want to test. It is changed by the investigator to observe how it affects a dependent variable.

• Constants are the factors in an experiment that remain the same.

Designing a Controlled Experiment

• A controlled experiment has two groups:

– The experimental group is used to study how a change in the independent variable changes the dependent variable.

– The control group contains the same factors as the experimental group, but the independent variable is not changed.

Biodiesel• Rudolph Diesel invented the diesel engine

using peanut oil to demonstrate how it worked.

• Oil-rich food crops, such as soybeans, can be used as a source of biodiesel.

Aquatic Specimen Program• In the late 1970s, the U.S. Department

of Energy began funding its Aquatic Species Program (ASP) to investigate ways to remove air pollutants.

• The program’s focus shifted to using microalgae to produce oils that could be processed into biodiesel.

Which Microalgae?• Microalgae are microscopic organisms

that live in marine or freshwater environments, use photosynthesis, and make sugar.

• Scientists collected and identified 3,000 promising microalgae species, focusing on microalgae they predicted were more resistant to changes in temperature and salt content in water.

Oil Production in Microalgae• Some studies suggested that starving

microalgae of nutrients, such as nitrogen, could increase the amount of oil they produced.– Starving microalgae caused them to be

smaller, resulting in no overall increase in oil production.

Describe a Controlled Experiment for Nitrogen and Microalgae oil production.

Microalgae Growing Methods• Three methods of growing microalgae are

examples of different hypotheses being tested in controlled experiments.

– Open Ponds– Plastic Bags– Bioreactors

List the pros and cons for each method.

Effects of Light• Scientists discovered that varying light

exposure affects the oil yield for microalgae.

– Data from experiments showed how microalgae in well-lit environments grow compared to those grown in dimmer environments.

– Scientists take light to microalgae instead of moving microalgae to light.

• Light rods and paddlewheels are used to bring light to microalgae.

Many Hypotheses• The ASP scientists developed numerous

hypotheses, because there were so many variables.

– Type of Microalgae– Growth Method– Amount of Nutrients– Changes in Temperature– Salt Content– Levels of Light– Etc.

Benefits of Growing Microalgae• In addition to growing microalgae for

biodiesel production, there are other benefits of growing microalgae.

– Microalgae remove pollutants from and add oxygen to the atmosphere.

– Other products include:• Human and Livestock Food• Pharmaceuticals• Cosmetics

The Future of Microalgae• The costs of growing microalgae and

extracting their oils are too high to compete with petroleum-based diesel.

– The combined efforts of government-funded programs and commercial biofuel companies might one day make microalgae-based biodiesel an affordable reality in the U.S.

A. constants

B. control group

C. controlled experiment

D. experimental group

Pop Quiz

Which term describes a scientific investigation that tests how one variable affects another?

A. constant

B. dependent variable

C. independent variable

D. variable

Which is a factor in an experiment that remains the same?

Pop Quiz

A. constant B. control group C. controlled experiment D. variable

Pop Quiz

Which contains the same factors as the experimental group, but does not have the independent variable changed?