Biological magnification is a rising concern amongst researchers who examine the ways that chemicals and pollutants may have long-term effects on ecosystems.  In this article, we’ll dive deep into what it is and the impacts it’s already had on our environment. 

Biology researchers and students are likely familiar with the field of ecotoxicology, or the study of how chemicals and toxins affect ecosystems and their organisms.  In this field, the term biological magnification is frequently used to describe the amplified concentrations of these substances as you move up through the food chain.

Also fittingly called bioamplification or biomagnification, this process explains why harmful substances like have metals, or chemicals found in fertilizers or pesticides, present in even the largest, carnivorous predators.

In this article, we will discuss the process of biomagnification and how it works.  We will define the terminology, and then give real-life examples and case studies documenting how chemicals travel through soil, water, and smaller organisms to eventually make their way to the top of the food chain in large concentrations.  

What is Biological Magnification?

Put simply; the term biological magnification is used to describe the process by which substances used in farming or produced in industrial waste make their way into and up the food chain.

We see increased levels of these toxins and chemicals accumulating through the trophic levels of the food chain thanks to this phenomena.

Pesticides, fertilizers, and heavy metals from industrial waste are some of the most common culprits who contribute to the problem.

Typically, the materials are carried through water sources like rivers, lakes, and streams as a result of surface runoff where they are then ingested by aquatic animals like frogs or fish.  These small organisms are then preyed upon by predators higher up in the food chain, like birds, larger fish, or animals, which is how these same substances make their way into their body.

Many of these toxins and chemicals are fat soluble and get stored in their internal organs or fat tissue.  This results in an accumulation of the substance over time and in greater concentrations the higher up the food chain you go.  This phenomenon is called food chain energetics.

Although biomagnification doesn’t always have a direct effect on living organisms, long-term exposure to harmful chemicals may result in unpleasant and irreversible side effects that could threaten a species.

Biological Magnification vs. Bioaccumulation

It’s important to note that there is a significant difference between biomagnification and bioaccumulation.  Although some may use the words interchangeably, they actually describe different scenarios in an organism.

Biological magnification specifically refers to increasing concentration of materials in each higher link in the food chain.  However, bioaccumulation examines the increased presence of a particular substance inside a single organism.

While the two processes may be interconnected, for the purpose of this article it’s important to differentiate the terminology to understand the real-life examples and practice.

Examples of Biological Magnification

There are numerous, well-documented examples of biomagnification where researchers find high concentrations of chemicals in apex predators.  Many of these studies also demonstrate the potential negative consequences of this build up over time. Here are a few examples.

Bald Eagles

During World War II troops faced a plethora of health issues, including outbreaks of malaria, body lice, typhus and bubonic plague spreading through mosquito bites at encampments throughout the world.

DDT is a pesticide that was developed to kill these biting bugs to help control the spread of these diseases, and following the war had agricultural applications.  Farmers used the product on their crops to control pests, and it was both popular and widespread thanks to its low cost and easy application.

It was approved as being safe and effective by the EPA at the time because there did not appear to be any harmful side effects of ingesting the chemical in animals or humans.  However, this did not take into account the possibility of biomagnification. 

DDT doesn’t break down over short periods of time in the environment and is a substance that gets stored in the fatty tissues of animals who consume it.  This became particularly problematic for bald eagles.

A predator near the top of the food chain, bald eagles were consuming large quantities of fish who had been affected by the chemical.  Runoffs from farms hit the waterways, and DDT infiltrated aquatic plants and animal life, and the eagles ingested the chemical with each meal they ate.

Over time, the chemical disrupted their ability to lay eggs with strong shells, causing the bald eagle population to decrease to the point of near extinction.  In 1940, Congress stepped in to pass an act to protect the species, but DDT wasn’t banned until 1972.

It wasn’t just species of eagles affected.  Other predator birds like brown pelicans and peregrine falcons saw the same side effects.  The thinning off the eggshells made incubation and hatching near impossible and also threatened these bird populations.

Fish and Pregnancy

Another notable example of biomagnification is in predator fish.  Species like Shark, Swordfish, Orange Roughy, Tuna, King Mackerel, or Tilefish contain proportionally larger levels of toxic mercury than smaller fish and shellfish.

In fact, the levels are so high that the FDA advises that pregnant women avoid consuming these species for fear of exposing developing fetuses to levels that may cause nerve damage.

How does this toxicity occur?  Mercury is introduced into the ecosystem in one of two ways.  As a naturally occurring element, it can leach from rocks and volcanoes into our water supply over time, but those natural changes are not likely to significantly impact the environment.

However, when you take the natural occurrences and combine them with human contributions through coal-burning power plants which impact the air, rain, soil, and water around these facilities, the mercury levels rise drastically.

As we now know, once an element enters the water supply, it’s inevitable that it gets ingested by aquatic life at every level of the food chain.  When plankton and small crustaceans that make up the majority of the diet of the larger, predatory fish have moderate levels, then the species who eat them will have a compounded effect.

For example, according to the FDA, the average amount of mercury found in a serving of scallops is 0.003 parts per million.  Lobsters, one of the main predators of the scallop have a concentration of 0.107 parts per million.  

Monkfish love dining on lobster, and have an average of 0.161 parts per million of mercury in their system, and shark and swordfish at 0.979 and 0.995 parts per million respectively regularly dine on monkfish.

In this example, it’s easy to see how quickly the effects compound and how concentrated they become with only four steps up the food chain ladder.

What Causes Biological Magnification?

Although biomagnification is a natural phenomenon that happens in all organisms, the instances where it is worrisome are largely due to anthropogenic factors.  Materials that humans introduce into the environment can cause unexpected and hazardous side effects and typically fall into one of the following subcategories.

Organic Contaminants

We live in an age where the word organic is closely correlated with natural and healthy, but too much of anything could be bad.  Organic elements like phosphorus, nitrogen, and carbon are necessary for survival, but if they appear in excessive quantities in ecosystems, they may cause eutrophication.

Eutrophication is a phenomenon when an organism that thrives in these conditions, like algae, for example, experience exponential growth and suddenly have an overwhelming population.  This can then disrupt the ecosystem and kill off other organisms because there aren’t enough resources, like oxygen, to go around.

Waste

Waste produced from manufacturing plants, factories, and other industrial enterprises can release waste and toxins into the air and water that contribute to the problem. 

Agricultural and Industrial

Chemicals introduced into the environment from inorganic pesticides, fungicides, fertilizers and herbicides that mix with our natural water sources due to runoff when it rains release toxic elements as well.

Plastic Pollution

Not only does plastic physically impact our environment, often ending up in our oceans and disrupting marine ecosystems, but it can also leach toxic chemicals into water too.

For example, Bisphenol A, or BPA, has made headlines recently as a substance that can produce a range of health conditions in humans that is used in making plastic water bottles.  It is one of the leading chemical pollutants in the environment.

Heavy Meals

As we discussed in our earlier case study, heavy metals that enter our water sources can wreak havoc on the ecosystem.  Mining activities are sometimes at fault for releasing deposits that can pollute aquatic plants and contaminate water sources with elements like zinc or cobalt.  

Potential Negative Effects of Biological Magnification

DDT and mercury aren’t the only hazardous substances that have the potential to biomagnify.  Substances like polychlorinated biphenyls (PCB’s) that can impair reproductive systems, heavy metals, polynuclear aromatic hydrocarbons which are a known carcinogenic, cyanide, and selenium have been extensively studied and proven to have similar outcomes.

There are dozens of potential adverse effects to our environment, including but not limited to:

• Reproductive implications for marine and other animal life
• Killing coral reef ecosystems
• Disrupting the natural food chain as species die off

There is also a significant risk of health impacts on humans who consume many of the organisms affected by this process.  They include an increased risk of the following:

• Cancer
• Kidney failure
• Liver disease
• Birth defects
• Brain damage
• Respiratory disorders
• Heart disease

Final Thoughts

Bioamplification isn’t a new phenomenon, but the humans have introduced pollutants to the environment that makes it a threat to the ecosystem and our food sources.  Understanding how and why it occurs is the first step to combating the problem and preventing the destruction over time.

Conversations and advocacy for sustainability need to continue to ensure the long-term health of our environment.

Cells and Transport Teaching Resources · High school biology; AP extensions where noted.

A cell is a working system: its structures cooperate to maintain conditions for life. Use this reference before asking students to label diagrams, build models, or explain transport. Materials: paper, a cell diagram selected by the teacher, and colored pencils if useful. No laboratory equipment is required.

Learning objectives

• Connect a cell structure to a function rather than memorize a label alone.
• Compare a typical plant cell, animal cell, and bacterial cell.
• Explain how several structures cooperate to produce and export a protein.

Structures to know

• Plasma membrane: the cell boundary that regulates exchange and carries proteins involved in transport and signaling. Plant cells have a plasma membrane inside the cell wall.
• Cytosol and cytoplasm: cytosol is the fluid portion; in a eukaryotic cell, cytoplasm includes cytosol and structures outside the nucleus.
• Nucleus: contains most of a eukaryotic cell’s DNA. The nucleolus helps assemble ribosomal subunits.
• Ribosomes: assemble proteins using instructions carried by messenger RNA. They are not membrane-bound; bacteria have them too.
• Rough endoplasmic reticulum: ribosomes associated with this membrane system make many proteins destined for secretion or membranes. The ER helps process those proteins.
• Smooth endoplasmic reticulum: participates in lipid production; its other functions depend on cell type.
• Golgi apparatus: modifies and sorts proteins and lipids for delivery.
• Mitochondria: support aerobic cellular respiration and ATP production. Plant cells have mitochondria as well as animal cells.
• Chloroplasts: carry out photosynthesis in photosynthetic plant cells. A root cell need not contain chloroplasts.
• Vacuoles and lysosomes: plant central vacuoles support storage, breakdown, and water balance. Animal lysosomes carry out digestion and recycling. Vacuoles do more than store water.
• Cell wall: a supporting layer outside the membrane. Plant walls contain cellulose; bacterial walls differ in composition.
• Cytoskeleton: protein filaments contribute to cell shape, internal organization, movement, and division.

Compare cells with evidence

Typical plant and animal cells have a nucleus and membrane-bound organelles; bacteria lack a membrane-bound nucleus. All three have DNA, ribosomes, cytoplasm, and a plasma membrane. Size and outline alone cannot reliably identify a cell. Both plants and animals grow through cell division and cell enlargement.

Use this in a lesson

1. Ask students to label only structures supported by the selected diagram; a simplified picture may omit real structures.
2. For each label, require one function and one connection to another structure.
3. Trace a secreted protein from an ER-associated ribosome through the ER and Golgi to a vesicle that fuses with the plasma membrane.
4. Finish with an unfamiliar example: why would a cell that secretes many proteins need extensive rough ER?

Check understanding

Question: Is a cell without chloroplasts necessarily an animal cell? Explanation: No. Many plant cells, including many root cells, lack chloroplasts. Look for other evidence such as a cellulose wall. Question: Do plants respire only at night? Explanation: No. Plant cells carry out respiration during the day and night; photosynthesis depends on suitable light.

Teaching note: Distinguish observations from inferences. A classroom light microscope does not normally resolve ribosomes or the detailed membrane bilayer. For AP biology, ask students to connect internal membranes to compartmentalization.

Continue the unit

• Practice with the cell structure study guide
• Build and evaluate a cell analogy
• Create a labeled cell model

Sources and further reading

• NHGRI: organelles
• NHGRI: ribosomes
• NHGRI: mitochondria

The Punnett square worksheet is a great teaching tool for genetics. This worksheet helps students get an idea of the different possible combinations for genetic traits and helps them calculate how likely each combination is. Here are some ideas for using the Punnett square in your classroom.

The Punnett square is a diagram used to make sense out of genetics and inheritance. The purpose of this diagram is to show the different possible combinations of alleles. This is a useful tool you can use to teach biology and probabilities regardless of the level of your students. Here are a few ideas to use the Punnett square in your classroom.

Understanding Dominant And Recessive Alleles

You should talk about genetics and alleles before introducing the Punnett square worksheet in your classroom. Students should ideally also have a good understanding of how to calculate probabilities.

Students should be familiar with genes and understand that genes are a unit of hereditary information while an allele is a possible sequence or variant of a gene.

You should also talk about observable genetic traits, also known as phenotypes. Students should understand that there are dominant and recessive alleles that won’t become phenotypes unless they are combined with another recessive allele. You can introduce the notion of codominant alleles with high school students.

Make sure the Punnett square activities are connected to lessons about genetics, inheritance, and alleles. You can use these activities to introduce these concepts or to help students get a more thorough understanding of genetics and probabilities.

The Punnett Square

The Punnett square is a simple diagram that shows the different possible combinations. Here is an example for the offspring of two organisms with the same Aa allele combination:

	A	a
A	AA	Aa
a	Aa	aa

 

Using this worksheet helps students see all the different possibilities and gives them an idea of which phenotype is more likely to occur.

Ten Ideas For Using The Punnett Square Worksheet In Your Classroom

Middle School

Introduce The Punnett Square With Legos

You can use Legos to introduce the Punnett square to your students. This visual approach would be ideal for an activity that you will use to introduce concepts like genetics and alleles.

You need to have Legos with two different shapes to represent the dominant and recessive alleles. Use cups or other small containers to represent the animals or plants that inherit the genetic material.

Start with two cups that contain a different combination of two Lego shapes to represent the parents. Have the students fill out the worksheet with the four possible combinations of Lego shapes.

The students can then place the four different combinations inside of four cups or small containers that represent the offspring.

This approach helps students understand the logic behind the Punnett square and gives them a visual reference you can use once you start talking about alleles.

Plant Genetics

Plants are a great example at the middle school level because you can easily identify a phenotype that students will understand, such as the color of a flower. You can even grow flowers in the classroom to illustrate the lesson.

Students can fill out a Punnett square worksheet for plant genetics. The purpose of this activity is to introduce the idea of dominant and recessive alleles and have students get used to seeing a capital letter for the dominant trait and a lowercase letter for the recessive trait.

Create a simple worksheet with four squares and ask students to write the different possible combinations. You can work with different phenotypes:

• Create a worksheet for a blue flower BB and a blue flower Bb.
• Create a worksheet for a blue flower Bb and a white flower bb.
• Create a worksheet for a tall plant TT and a tall plant Tt.
• Create a worksheet for a tall plant Tt and a small plant tt.

You can then ask students to identify the number of possible combinations and to calculate the probability of a flower being blue or of a plant being tall. You can also have students draw what the plants will look like.

High School

You can introduce advanced ideas at the high school level and connect the Punnett square with more real-life examples. You should introduce concepts like homozygous genes, heterozygous genes, or mutations.

You can also focus on probabilities and have students use a worksheet to calculate the probability of a trait appearing in offspring.

Predicted Outcome And Actual Outcome

Introduce the idea that the predicted outcome of a Punnett square doesn’t always reflect what happens in real life. Students should be aware that these worksheets will show how likely an allele combination is.

Have students use a Punnett square worksheet to predict the outcome of a coin flip or another random event. Once the worksheet is filled out, have students flip a coin and compare the outcome with what the Punnett square predicted.

Guessing The Parents’ Allele Combination

Provide students with different allele combination for the offspring and tell them how frequent each combination is.

Have them use the Punnett square to find the allele combinations of the parents. This is an activity that only takes a few minutes to complete, but it is a great way to brush up on how the Punnett square works and to make sure that students have a solid understanding of inheritance.

Bear Fur Color

You can work with phenotypes that are observable in animals and introduce the idea that there are different possible allele combinations for the same phenotype.

The brown bear fur color is an excellent example since a bear can have BB or Bb alleles and have brown fur. On the other hand, only a bear with a bb allele combination will have black fur.

Have your students use the Punnett square to calculate the probability of offspring having brown or black fur. This problem encourages students to create more complex tables since the bear parents can either have the BB or Bb allele combination.

Eye Color

Predicting eye color is another interesting activity you can introduce at the high school level. Start by making a list of the different possible allele combinations for each eye color.

You can have students calculate the probability of their eye color based on the eye color of their parents, or have students determine the allele combinations of two parents based on the phenotypes of their children.

Eye color is more complex than other phenotypes and gives students an opportunity to create more advanced worksheets that reflect the different possible allele combinations of the parents based on their phenotypes.

You can make things more complicated and combine eye color with hair color.

Research

Have students research different genetic traits and create a presentation on how these traits are inherited. You can have students work in groups and assign a trait to each group.

Students will have to define the trait you assigned to them, explain how it is inherited, and create different Punnett squares that show how the trait can be inherited or skip a generation.

Here are a few examples:

• A specific hair color.
• A specific eye color.
• Tongue rolling.
• Freckles.
• Free or attached earlobes.

This project will help students understand how complex genetic inheritance is and will also help them connect what they learned in class with real-world examples.

AP Level

Cat Coat Genetics

Students can look at pictures of cats and predict what the offspring will look like with Punnett squares. This is similar to the bear fur activity, but cat coat genetics are more complex.

Students will have to work with genotypes that affect hair length as well as color. Here are a few facts to help you get started with planning this activity:

• A cat with short hair will have an LL or Ll genotype.
• A cat with long hair will have an ll genotype.
• A cat that is entirely white can have a WW or Ww genotype. A cat with white fur and some colored hair has a ww genotype.
• White cats can have a W allele and another allele for a dense pigment or piebald spotting.
• There is a gene for dense pigment. A black, brown, or orange cat will have a DD or Dd allele combination.
• A cat with gray, cream or light brown fur will have a dd allele combination.
• Piebald cats with the SS and Ss allele combination have some white hair, while piebald cats with no white hair have the ss genotype.

Genetic Disorders

You can combine the Punnett square with topics like genetic disorders. Studying how sickle cell anemia is inherited could be an interesting project for AP level students.

You can have students create a worksheet to determine the probability of a child inheriting sickle cell anemia based on the parent’s allele combinations.

Have Students Create A Species

Have students design a species from scratch to test their understanding of genetic rules. Ask them to make a list of dominant and recessive traits. Determine how many traits students will have to work with depending on how much time you want them to spend on this project.

Creating a species and determining how common some genetic traits are going to be is a great way to make sure students have a solid understanding of the Punnett square. You can have students create illustrations for the different genetic combinations.

You can go further and ask students to create genetic traits for an imaginary species, determine which traits are dominant and recessive, and ask them to create problems that other students will have to solve.

 

Cells and Transport Teaching Resources · High school biology; AP extensions where noted.

Use this guide beside a classroom compound light microscope. Names and controls vary by model, so check the manufacturer’s manual before the first lab. A microscope with two eyepieces is not necessarily a stereo microscope.

Learning objectives and preparation

Students will identify the controls they need, calculate total magnification, and explain why greater magnification does not always reveal more detail. Begin with the difference between a specimen and its image. Materials: a microscope, its manual, and a prepared slide or teacher-approved wet mount.

Identify the parts on your instrument

• Eyepiece (ocular): the lens students look through, commonly marked 10×.
• Objective lenses: lenses near the specimen, often 4×, 10×, and 40×. Read the markings; do not assume every instrument has these powers.
• Revolving nosepiece: holds objectives and rotates to select one. Turn the nosepiece rather than push on a lens.
• Stage and slide holder: support and position the slide over the light path. Stage movement controls shift the specimen without changing the objective.
• Coarse focus: makes large changes in the distance between specimen and objective. Use only at the lowest power under the teacher’s directions.
• Fine focus: makes small focus changes, especially at higher power. Focus controls do not change magnification.
• Illuminator: provides light. Brightness control adjusts illumination; never use direct sunlight with a mirror microscope.
• Condenser and iris diaphragm: where present, organize the illuminating light and control its cone. The diaphragm influences contrast and resolution as well as brightness.
• Rack stop or focus stop: on models that include it, limits travel toward the slide to reduce the risk of objective–slide contact. It is not a magnification control. Leave its adjustment to the teacher or technician, and still watch lens clearance.
• Arm and base: support the instrument. Carry using the manufacturer’s designated grip with the base supported.

Calculate magnification

Total magnification = eyepiece magnification × objective magnification. A 10× eyepiece with a 4× objective produces 40×; with a 40× objective it produces 400×. A focus knob changes clarity, not this calculation. Resolution is the ability to distinguish nearby details. Enlarging a blurry image does not restore details that the optics failed to resolve.

A safe first-use sequence

1. Place the microscope on a stable surface with cords clear of walking routes.
2. Select the lowest-power objective and secure a slide.
3. Watch from the side whenever bringing the objective and slide close together; stop before contact.
4. Find and center the specimen at low power before changing objectives.
5. Use fine focus at high power. Stop if a control resists or a lens approaches the slide.
6. Remove the slide, return to the storage position specified in the manual, switch off, and cover after the light source has cooled if required.

Clean optics only with approved lens paper and the manufacturer’s cleaning method. Do not adjust mechanical stops. Use immersion oil only with a lens explicitly designed for oil and teacher supervision.

Quick troubleshooting

Dark view: check the light, nosepiece position, specimen alignment, and diaphragm. Specimen disappears at high power: return to low power and recenter it. Blur at all powers: check slide orientation and lens cleanliness with the teacher; do not force the controls.

Exit question: A student switches from 10× to 40× objective without moving the eyepiece. What changes? Total magnification increases fourfold and the field of view usually becomes smaller. The student should recenter first and then use fine focus.

Continue the unit

• Apply these controls in the microscope lab
• Connect microscope observations to cell structures

Sources and further reading

• OpenStax Biology 2e: studying cells