Lesson Background and Concepts for Teachers
Algae are very small—some are too small to see without a microscope, such as in this high-magnification photograph. But since they grow so fast in many different biomes, we can use them to make a renewable energy source called biofuel.
Learning objectives. During the course of today’s lesson, these are the questions that we will explore. By the end of the lesson, you will know the answers. (For instructor reference, the questions and answers are provided below.)
What are the similarities and differences between biofuels and fossil fuels? (Answer: Both biofuels and fossil fuels come from plants or other living things. The difference between them is that biofuels can be made in hours or days, while fossil fuels take millions of years to be created.)
What are algae and what can biological engineers make out of algae? (Answer: Algae are very small plants that live in water. Biological engineers use them to make biofuels for three reasons: 1) they have three parts that can be made into biofuel, 2) they grow very fast, and 3) using them for fuel does not waste food since people do not usually eat this type of algae. Note that seaweed is a type of algae and people DO eat seaweed.)
Why is breaking the algal cell wall important for biological engineers? (Answer: Biological engineers need to break down the cell wall to get to the starch and oil inside the cells. The broken-down cell walls can also be made into biofuel.)
Please write down in your notebooks the definition of biofuels. (click to reveal definition) Biofuels are chemicals from plants that we can use for energy (chemical energy). The bus in this photograph is designed to use biofuel from soybeans (a plant) to run instead of fossil fuels (like petroleum oil, gasoline, diesel, natural gas) like many buses and cars.
(Click to reveal question) What is another source of chemical energy? (Answers: Fossil fuels, batteries, food, firewood.)
(click to reveal question) How are petroleum oil, coal and natural gas different than biofuels? (Answer: Biofuels are different from fossil fuels because they can be made in hours or days, not millions of years like fossil fuels.)
(click to reveal definition) Biological engineers are experts in biology but also use math, physics, chemistry, mechanical systems, and computer technology to solve problems. These photos show biological engineers at work growing algae for biofuels and examining different types of plants and compost for improving soil for farming.
(click to reveal question) Name a problem that biological engineers might be able to help you with. (Correct answers include: new watering techniques to help plants survive droughts, to develop a medicine for a new type of illness, a certain kind of food contains harmful bacteria and new processing or quality control methods are needed, to develop a biofuel to replace the use of fossil fuel, and picking strawberries requires crouching in uncomfortable positions for a long time.)
This photograph shows a blue-green algae bloom in Lake Erie. You may have seen algae growing like this in natural waterways or pools. (click to bring up two additional pictures) What do you think we’re looking at in the photo to the right? (It might take them a bit to guess that it is a human hair.) These microscopic photos, both at 400x magnification, show how small algal cells are compared to human hair.
Record this definition of algae in your notebooks. “Algae” is plural and “alga” is singular. (click to reveal the definition) Very small plants. (click) Live in water in many places around the world. (click) They grow fast. Have you ever seen a pond that looks like this (left photo), with algae covering the water surface? And here’s (right photo) what algae look like under high magnification.
Algae grow very fast. The types of algae that many engineers use for biofuel grow twice their size in a day! (Expect students to be able to follow the number sequence on the slide to calculate the weight of the growing algae for the days of the week.) Compared to human growth, it would be like: On Monday, you weigh 50 pounds. (click to show Tuesday) Tuesday you weigh 100 pounds. (click to show Wednesday) How much would you weigh on Wednesday? (Answer: 200 pounds.) On Thursday (Answer: 400 pounds.) (click to show Friday) By Friday, you would weigh 800 pounds! (click to show next question) From where does the alga growth come? (Answer: Plants grow through photosynthesis. This is a transitional leading question, although some students may already be familiar with photosynthesis.)
Look at the parts of the word “photosynthesis” to understand its meaning. (click to show) Photo means light and (click) synthesize means to make, usually a chemical. Plants use light to make chemicals—most importantly, carbohydrates/sugars. Plants use the sugar for energy.
Plant roots absorb water and their leaves take in carbon dioxide from the air and light from the sun. Then plants use these ingredients to make sugar. Plants use the sugar they make for energy, similar to how we eat food (and sugar) for energy. The difference is that plants make their own sugar from sunlight, water and carbon dioxide.
To recap, what is the story of photosynthesis? (Answer: Plants use sunlight, water and carbon dioxide to make sugars for energy.)
In groups, think of reasons why biological engineers want to use algae for biofuels.
Reasons that we have talked about so far are: 1) they grow very fast and 2) they grow in many different places around the world. (click to reveal these two answers on the slide)
In addition, algae are good plants to make into biofuels because we don’t eat them. We don’t want to take away food for people in order to make fuel. (click to show that reason)
Algae make oil and sugars inside their cells. We remove those oils and sugars to make into fuels that are renewable. We can also make fuel out of algal cell walls. (click to show that reason)
Three parts of algae can be turned into energy. Look at this cartoon sketch of a plant cell. (click to advance animation) If we ignore the organelles of the cell, we see this simplified view of the plant cell. The parts of the algae we can use to make into fuel are (click) oil, (click) starch and (click) the cell wall. For this lesson, we are going to focus on the cell wall. To get to the oils and starch, we need to break apart the cell wall. And, we can use the broken-down cell wall for fuel, too. (Teacher note: The depicted plant cell is shown with adjacent cells; algae can be single-celled or multicellular.)
Add the following to your notes about algae: (click to show) “People don’t usually eat algae” and (click) “Composed of oil, starch and cell walls.”
As an analogy, think about the algal cell wall like a box made of LEGO® pieces. How would you open this LEGO container? (Expect students to say that they would take apart the box, piece by piece, using their fingers.) I agree that it is better to take apart the LEGO container piece by piece so that we can reuse the pieces for other projects and because it would take less effort than, say, smashing it with a hammer or heating it in an oven until the pieces melted. Raise your hand if you think it would be ridiculous to smash or melt the LEGO orb. I agree with you. It would be silly to use energy-intensive or wasteful methods to open the LEGO box.
Biological engineers face a similar challenge with cell walls. Right now, engineers only know how to open the cell wall with energy-intensive methods like using the hammer to smash or the oven to melt. But, if we knew more about the LEGO bricks—which represent the sugars present in the cell walls—we could open the cell walls using less energy and reuse the sugar for biofuels. So the research continues.
The definition of the algal cell wall is: (click to reveal answer) a structure made of sugar that surrounds and protects the cell, and (click) the sugars can be used to make more biofuel. Biological engineers study algae to find ways that we can more easily make biofuel by opening the cell walls to get to the oil and starch, and by recycling the sugars of the cell wall into biofuel.
(Review slides: click to reveal questions and answers.) Why are algae good for biofuels? What parts of algae can be made into biofuels? Why do we want to know about the sugars of the cell wall?
(Slides 17-20 are optional lesson extension slides for further enrichment.) How do people grow algae for biofuel?
We’ve talked a lot about how we can use algae for biofuels and how fast algae grow, but we have not talked much about ways to grow algae. Let’s learn about a few different ways.
Raceway ponds are a (click to reveal) way to grow very large quantities of algae. (click) Farmers use raceway ponds because they are inexpensive to build for the quantity of algae they can produce.
Photobioreactors. First, let’s break down the word. A reactor is a place where a reaction happens so a photobioreactor is a place where a light-life reaction takes place. Can you think of a process that living things do that uses light? (Answer: Photosynthesis.) Yes! Photosynthesis is happening in these tubes, which are designed to give the algae lots of light. (click to reveal) Photobioreactors can grow small to large amounts of algae but cost more than raceway ponds to build and maintain. (click) Biological engineers and farmers use photobioreactors. Why do you think photobioreactors are more expensive than raceway ponds? (Answer: They require more materials [glass or plastic for tubing, metal for stands] than the raceway ponds and the more complex equipment requires trained people to maintain it.)
Petri dishes are used to grow (click to reveal) small amounts of algae for testing and experimentation. (click) Biological engineers use petri dishes, which have a thin layer of gel at the bottom, to examine algae during experiments.