20 6-8 Lesson Example

Instructional Guide

Learn how the environment impacts

Intended Grade Level

8th grade

Students should be familiar with the scientific process. Prior to this lesson, students should be exposed to how humans may affect the environment. Students should be familiar with microscopes prior to this lesson. Students should be familiar with zebrafish anatomy.

Optional: Minnesota State Standards or NGSS:

NGSS

MS-ETS1-1: Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment.

• Application: Students can design an experiment to test how different environmental factors (e.g., light, temperature, or water quality) affect zebrafish embryo development, considering the scientific principles and limitations of their experiment.

Learning objectives:

Students will be able to compare and contrast zebrafish and human anatomy.

Students will be able to construct an experiment to test their hypothesis.

Students will be able to describe limitations of their experiment.

Lesson Format:

This lesson will take about 50 minutes. This lesson will involve whole class mini lectures and then break out into small group work. The lesson will involve zebrafish embryos, plus having volunteers in the room will be helpful. Students will each need a copy of the science journal.

Students will brainstorm ways humans affect the environment (5 minutes)

Large group discussion plus experiment introduction (10 minutes)

Students will work in groups of 3 to make observations at different stations (20 minutes)

Large group debrief  (10 minutes)

Students will write their final thoughts in their notebooks (5 minutes).

Lesson Background:

Zebrafish (Danio rerio) embryos are a widely used model organism in developmental biology due to their transparent bodies and rapid development. They provide valuable insights into vertebrate development and genetics. Here’s a breakdown of key anatomical structures in zebrafish embryos:

1. Chorion: The chorion is the outermost protective membrane that surrounds the zebrafish embryo. It is a translucent, acellular layer that serves as a barrier, protecting the developing embryo from mechanical stress, pathogens, and harmful substances. The chorion typically remains intact until hatching, which occurs around 48–72 hours post-fertilization when the embryo breaks through using its hatching gland enzymes.

Abnormalities:

1. 1. If the chorion is too thick or malformed, it can prevent the embryo from properly hatching or hinder its development by restricting movement or oxygen flow. Delayed hatching can also be an indication of abnormalities.
2. Yolk: The yolk is the large, nutrient-rich structure that sustains the embryo during early development. It contains proteins, lipids, and other nutrients necessary for growth. In zebrafish, the yolk is prominent and located at the ventral side of the embryo, contributing to nourishment until the embryo develops a mouth and begins feeding independently. The yolk gradually diminishes as the embryo metabolizes it for energy.

Abnormalities:

1. 1. Irregular heartbeat (arrhythmia) or delayed development of the heart are indicators of cardiac defects.
   2. Pericardial edema (swelling around the heart) can be a sign of heart failure or exposure to toxic substances.
   3. Malformed heart structures (like defects in the atrium or ventricle) could signal underlying genetic mutations or environmental stressors.
2. Heart: The zebrafish heart is one of the earliest organs to develop. It begins beating around 24 hours post-fertilization. The heart is initially a simple tube that later undergoes morphogenesis to form a two-chambered structure (an atrium and a ventricle). Studying heart development in zebrafish embryos is particularly valuable due to the similarities with human cardiovascular development.

Abnormalities:

1. 1. Irregular heartbeat (arrhythmia) or delayed development of the heart are indicators of cardiac defects.
   2. Pericardial edema (swelling around the heart) can be a sign of heart failure or exposure to toxic substances.
   3. Malformed heart structures (like defects in the atrium or ventricle) could signal underlying genetic mutations or environmental stressors.
2. Eyes: Zebrafish embryos develop eyes early in their development, and by the time they are fully formed, the eyes should be symmetrical and round.

Abnormalities:

1. 1. Malformed eyes (such as asymmetry, underdeveloped eyes, or cyclopia, where there is only one eye) can indicate genetic defects or exposure to harmful substances.
   2. Delayed eye development can also signal broader developmental delays or abnormalities in brain formation.
2. Otolith: Otoliths are small, calcium carbonate crystals located in the inner ear of zebrafish embryos. They play a crucial role in the sense of balance and spatial orientation. The otoliths help the developing embryo detect gravity and motion, functioning as a part of the vestibular system, which is essential for the zebrafish’s ability to orient itself in water.

Abnormalities:

1. 1. Missing or improperly formed otoliths can lead to balance issues. Zebrafish with abnormal otoliths might have trouble orienting themselves properly or swim erratically.
   2. This abnormality could indicate problems in the vestibular system, which is connected to sensory and neural development.

These structures highlight the intricate processes of zebrafish embryogenesis, making the species an important model for studying developmental biology and disease.

Activities:

At the start of the lesson have students take 5 minutes to write down as many ways as they can think of that humans impact the environment. Challenge them to write for the entire 5 minutes.

Ask students to share some of their answers, and follow up by asking them how they would measure this impact.

Ex. “Humans cause global warming” “How would you measure this? What evidence would you need to gather?”

Next, introduce the experiment.

“A corporation was producing different plastics which left them with lots of toxic byproducts. They didn’t want to pay for proper disposal and therefore dumped the chemicals in a near by river. Here we have some embryos that were harvested from the river at Station 1. At Station 2 we have embryos that were harvested from the same river upstream of the manufacturing plant. Look at both sets of embryos and write down any differences you see between the two groups. Pay attention to size, shape, and heart rate.”

After 20 minutes, students should come back together for a large group discussion. Ask for volunteers to share what they’ve seen between the two groups.

Next, let students know that these embryos were not actually from a river, but instead were treated in a laboratory with the chemicals found in the river. Why would we do that instead of finding fish in the river? What are limitations of gathering animals from the wild? What is a limitation of using lab grown embryos?

Ask students how they think humans would be affected if they came in contact with this mystery toxin. (Many zebrafish embryos will have heart defects. Students are likely to infer that humans will also have heart defects). Discuss the use of animal models, and how they can help us learn about the environment or about different problems we might encounter.

During the last 5 minutes, ask students to look over their list from the beginning of class and have them write down how they would test this  problem. Then, what is one limitation of their experiment.

Common misconceptions and challenge points:

Students may struggle with identifying analogous body parts, you can help by starting with an example. “Zebrafish embryos have a yolk to get all their nutrients, what organ do we have that helps us break down food to get our nutrients?”

Students may struggle with limitations. You may need to give examples.

Key misconception to look out for is that the yolk is the stomach of the embryo, however at this point in the development the embryo does not have a true stomach. You can give an example of a chicken egg to help students understand.

Assessment:

Completed lab notebooks will help identify if students are able to label different body parts correctly and are able to compare and contrast human and zebrafish anatomy.

Student answers while they are making observations will help determine their ability to infer why animals have different organs.

Resources:

Science Journal pages