Because there is a significant amount of high-level vocabulary in this article, it is best facilitated through a whole-class read-aloud with opportunities to pause for questions and clarification.
It begins by summarizing information students already know about plastic impacts, but continues to add information and lingering questions about toxic chemicals working their way up the food chain. To conclude the article, ask students to discuss one or two of the following questions with a partner, then invite several groups to share their responses with the class: In your opinion, what is the most serious health impact of plastics on animals addressed in this article? In your opinion, what is the most serious health impact of plastics on people brought up in this article?
Which of the solutions proposed in the article seem most effective? Guide students to confront both the evidence and the uncertainties about the impacts of ocean microplastics on humans. Label four large sections of your whiteboard with these titles: Plastics in the food chain are harming humans now.
Plastics in the food chain are not harming humans now, but may in the future. Plastics in the food chain do not harm humans, now or in the future. I still need more information to make a decision about this. Explain that each of these statements is a claim. Tell students that in science, a claim is like an opinion, but one that must be supported by facts and evidence. Organize students into their publishing teams and distribute several sticky notes to each student.
Ask students to consider all of the evidence they have learned so far and decide which of these four claims they most agree with. Prompt students to write two to three pieces of evidence on their sticky notes that support their claim.
Call students up by publishing team to place their sticky notes on the section of the board with the claim that most closely matches their current understanding. Students should be called up with their publishing teams, but should place their sticky notes individually.
Observe and discuss any patterns in the distribution of sticky notes. Beginning with the first claim, ask a student who chose this statement to defend their claim, citing evidence to support their position. Ask for other students who agree with this student to add further supporting evidence. Then, ask for a volunteer who disagrees with this first claim. Ask which claim they chose and on what evidence their claim is based. Continue in this fashion until all four claims have been addressed.
For the last claim, ask students what additional information they would need to make a decision, and what questions they have. Finally, ask if this discussion has caused any students to change their opinion about which claim is best supported by the evidence.
Give students an opportunity to move their sticky note and explain why they changed it. Remind students that scientists also disagree about this topic, and it is an active area of research where new information is being learned all the time. Tell students that there are two more concepts they should understand to grapple with this issue: bioaccumulation and biomagnification. These concepts will also help them complete the Food Web Infographic element of their final project. Ask students to review the Biomagnification and Bioaccumulation infographic with the goal of defining both words.
After reviewing the inforgraphic, invite students to help define bioaccumulation and biomagnification and add the words to your class unit word wall. Prompt publishing teams to add these entries to their magazine glossary list. Introduce and encourage alternate forms of these words, such as bioaccumulate and biomagnify. To reinforce the difference between these two similar-sounding concepts, display the simplified bioaccumulation and biomagnification infographic so that all students can see it clearly.
Ask: Based on this infographic, what is the difference between bioaccumulation and biomagnification? Bioaccumulation takes place in a single organism over the span of its life, resulting in a higher concentration in older individuals.
Biomagnification takes place as chemicals transfer from lower trophic levels to higher trophic levels within a food web, resulting in a higher concentration in apex predators. Elaborate by telling students that some of the toxic chemicals found in microplastics form chemical bonds with certain body parts, such as fatty tissues and organs.
Therefore, when the body excretes wastes, these chemicals often stay behind and continue accumulating instead of being flushed out with other wastes. Add that ingestion is not the only way microplastics can enter our bodies. In fact, some microplastic fibers from synthetic clothing, carpets, and furniture are small enough to float in the air, where we can breathe them in. Develop the concept of a marine ecosystem as a particular habitat within the ocean.
Refer to the Final Project Checklist and Rubric to remind students that their final project will contain a Food Web Infographic explaining the process of biomagnification. Explain that, just like plastic is not a single material but a whole family of materials, the ocean is not a single habitat, but consists of a variety of different ecosystems.
Define ecosystem and add it to your class unit word wall. Tell students to add this entry to their magazine glossary list, including the definition and an example sentence. Emphasize that an ecosystem consists of both living and nonliving things. The class has spent a lot of time discussing living things, or organisms, in the ocean. Ask: What are examples of nonliving parts of ocean ecosystems? Possible responses: water salt rocks sand light and sound energy macroplastics and microplastics other types of pollutants and litter.
Guide teams through the development of an ecosystem-specific food web to model biomagnification. Each ecosystem should have only one apex predator. Some organisms may fit in more than one trophic level.
For example, sea urchins and oysters can be considered both primary consumers and decomposers. Circulate around the room while students are working and correct any major misconceptions using the answer keys provided. Have each group select a color to represent photosynthesis, the flow of energy from the sun to primary producers.
Tell them to include this color in their Food Web Infographic legend, and then to draw arrows using that color from the sun to the producers. Use this image of producers in a coral reef as an example of correct arrow placement and direction. Bioaccumulation occurs at the base of a food web, usually within primary producers like phytoplankton.
These microscopic photosynthetic organisms absorb POPs directly from the seawater and accumulate them in their bodies over time. The toxins build up in their tissues because they are absorbed from the water at a rate faster than they can be metabolized.
Biomagnification occurs when slightly larger organisms called zooplankton feed upon the contaminated phytoplankton and in turn absorb POPs into their own tissues at a higher concentration. The more contaminated phytoplankton a zooplankton eats, the more pollutants it will have in its body.
In other words, the POPs can be passed from producer to consumer to consumer, to consumer, and so on… Biomagnification can continue all the way up the food web or chain. One large apex predator that is heavily impacted by the bioaccumulation and biomagnification of POPs is the orca.
PCBs are known to cause problems with reproduction, and studies are currently being conducted to see if and how POPs are impacting orcas in other ways.
Governments are slowly starting to realize the importance of countering the negative impacts of these pollutants. The production of DDT was banned in the United States in , and more chemicals are being banned each year. In , the Stockholm Convention on Persistent Organic Pollutants came into effect and internationally bans the production of PCBs and other harmful chemicals. These bans have proven to be mostly effective, and the environmental levels of many of these toxins have already started to noticeably decrease.
Therefore, if the lifetime of the substance is higher, the impact of it also gets higher. Usually, kidneys are responsible for removing the majority of unwanted substances from the body.
Blood carries them into the kidneys and then the production of urine happens through filtration and selective reabsorption. In order to remove toxins with urine, they should be water soluble. But, bioaccumulative substances are normally fat soluble and braking them down into smaller molecules is not possible. Therefore, they tend to remain in the body. Biomagnification is the increase of the concentration of a toxic substance over time when going along a lower level to a higher level in a food chain.
The pollutants must be long-lived in order to cause biomagnification. Also, it should be mobile, so that it easily enters into biological systems by means of food or water. If it is not mobile, it may stay inside one organism and will not pass into the next trophic level.
Moreover, if they are soluble in fat, they tend to remain in bodies of organisms for a longer period. Furthermore, in order for biomagnification to occur, the pollutant must be biologically active.
For example, DDT is a chlorinated hydrocarbon which can be biomagnified. It is toxic for insects and has a half-life of 15 years. Heavy metals like mercury, lead, cadmium, zinc are also toxic and can be biomagnified. Bioaccumulation is the increasing the concentration of a substance in one organism whereas biomagnification is increasing the level as you go up in a food chain.
So, this is the key difference between bioaccumulation and biomagnification.
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