Monsters Inside Me: Parasitic Protists (Part 1/2)
Objective
Big Idea
What Students Will Learn in this Lesson
Students will explore the variation seen in the Protist kingdom today and consider Giardia as a possible missing link. Students will also look at the problem Giardia cause to public health. Here is what students will learn today.
Hook/Checking for Preconceptions
Students will make wet mount slides of their hay infusions as they continue to collect data for the hay infusion lab that was started two school days ago. Students should make sketches of what they see at 6 different places on the slide. After eight minutes, have the students clean up their lab areas and return to their desks. Microscope slides should be disposed in the glassware bucket.
Preface the showing of the video clip by explaining that the protist that will serve as our model organism today is a parasite. Poll the students to determine how much they know about parasites. Have them complete a modified KWL graphic organizer with the headings What, Why, and How. Ask the following questions:
- What do you know about parasites?
- Why does a parasite need to be inside a host?
- How does a parasite get inside its host?
Have students place the graphic organizer in their lab notebooks.
Video Clip
Students will watch a clip for the series Monsters Inside Me (Season 2, Episode 7): Breeders. Start the video at 29:48-43:00. The video describes a young lady that has a Giardia infection.
Before starting the video, hand students the graphic organizer for the video. Students should fill out the organizer while watching the video. Students should begin to understand the process that doctors use to diagnosis an illness or infection. They should also notice the steps the body takes to maintain homeostasis and eliminate the parasite.
Here is an answer key for the graphic organizer.
Teacher Mini-Lecture: How Giardia Adapts
During this short mini-lecture, Giardia-A Missing Link?, discuss with the Giardia life cycle and use it as evidence for natural selection. Use the graphic of the life cycle from the CDC website. Students can add their own notes to the life cycle handout. (Note: I print these life cycles four per page and have student place them in their lab notebooks for reference. I also copy the description.)
Next, have students read through the student readings from Giardia: A Missing Link between Prokaryotes and Eukaryotes from the American Scientist. (Note: I save a pdf of the reading and provide my students a copy.) Read through the reading as a class. Advance the powerpoint with each section and provide talking points for the students.
Ask students the following questions:
- How is a prokaryote cell like a studio apartment?
(Possible answer: A studio apartment has everything is located in one room. There are not separate rooms. A prokaryote has all structures located simply within the cell membrane. There are not organelles.)
- How is an eukaryotes cell like a mansion?
(Possible answer: A mansion has many rooms. All rooms have a specific purpose. An eukaryote have specific organelles that carry out specific jobs.)
- What would be organelles would represent the different rooms?
(Possible answer: mitochrondria, nucleus, chloroplast, Golgi apparatus, Endoplasmic reticulum)
- How do the prokaryotic skeleton and the eukaryotic skeletons differ?
(Possible answer: Prokaryotic skeletons are external and made of cross-linked sugar and protein molecules surrounding a cell membrane. Eukaryotic skeletons are internal and made of a cytoskeleton.)
- What evidence do scientists have that the Earth was different than it is today?
(Possible answers: Fossil record, organic molecules found in old rock layers, study of the moon and solar system, modeling of chemical reactions done in the laboratory.)
- Are there any ecosystems on Earth now that might model an early Earth?
(Possible answers: Deep sea ocean vents, high salt pools, hot springs.)
- Summarize Lynn Margulis' theory of endosymbiosis in five words.
(Possible answers: You are what you eat.)
- Summarize Thomas Cavalier-Smith's theory of invagination in five words.
(Possible answers: Cytoskeleton, Food in, Waste out)
- The formation of what structure support Cavalier-Smith's invagination theory?
(Possible answers: The cytoskeleton)
- The formation of what cell process support Cavalier-Smith's invagination theory?
(Possible answers: Exocytosis, Endocytosis)
- Why might Giardia be a missing link?
(Possible answers: An analysis of the types and structures of the organelles in Giardia show that it might be a missing link. Giardia does not have mitochondria and must live in an environment with no oxygen. Comparison of the Giardia RNA with prokaryotic RNA.)
- What problems do Giardia pose to public health?
(Possible answers: Is a parasite that can live in the intestine and cause intestinal problems.)
- What is the possible evolutionary significance of the two equal-size nuclei of Giardia and their contents?
(Possible answers: If mutation happens in one of the nuclei, Giardia always has a back-up.)
( Note: My school is located next to a reservoir. In the past, the waters of that reservoir have tested positive for Giardia. Many of my students swim, boat, and fish in this reservoir so I feel that it is timely and necessary to discuss the life cycle of this organism.)
During our discussion, I have students list ways that Giardia has adapted by natural selection to live in a number of environments as well as the evidence that the scientists give that support Giardia being a "missing link".
Putting It All Together: What Type of Protists
Next refer students back to the flip book that they created in a previous lesson in this unit. Ask students to determine if Giardia is a fungus-like, plant-like, or animal-like protists.
(Note: taxonomists classify Giardia as an animal-like protist.)
Guide students in listing reasons why Giardia would be classified in the animal-like protists.
Possible answers include:
- It is motile for part of its life cycle.
- It is a heterotroph living off of the contents of its host's small intestine.
- It lacks a cell wall in its single cell.
Next, have students consider if subsections of animal-like protists needs to be added. Ask them if there needs to be a free-living category and a parasitic category. Then ask them how the parasitic category might have evolved?
Give students a chance to write their ideas down in their notebooks. Explain to them that answers to these questions will be addressed in a later lesson. (Note: Teachers that would like to explore in depth how scientists use model organisms to understand natural selection should check out this lesson.)
Have students turn in their lab notebooks for evaluation at the end of the period.
