ScienceHabitats under pressure30 min★★★ difficulty

Poisons up the food chain

A tiny dose of poison in the water can end up killing an otter. This lesson explains bioaccumulation — how toxins concentrate as they climb the food chain — through the true story of DDT and the peregrine falcon.

Lesson overview

What you'll learn in this lesson

Understand how organisms affect, and are affected by, their environment, including the accumulation of toxic materials

Key learning points

• Why the top gets the most
• Persistent is the key word
• DDT and the crashing falcons
• The modern versions

This lesson at a glance

30 minutes
19 parts to scroll through
4 quick checks
Marked quiz at the end
Gentle pace: short sittings with pauses

Words to know

organismsaffectaffectedenvironmentaccumulation

Scroll down — the lesson carries on below

Part 1 of 19 · Discover5%

Watch & discover

Part 1 of 19

Watch first

Poisons up the food chain

An English teaching video on this topic from Acestudents. Watch it, then scroll down for the lesson.

In a nutshell

Understand how organisms affect, and are affected by, their environment, including the accumulation of toxic materials

What you already know

Part 2 of 19

Before we start

What you already know

You know food chains and that only about a tenth of energy passes up each level.

Recap: Food webs in a British woodland

Key words

Part 3 of 19

Key words

Words you'll need today

bioaccumulation: The build-up of a substance in an organism faster than it can be got rid of.
biomagnification: The concentration of a toxin increasing at each level of a food chain.
persistent: Describes a chemical that does not break down in the environment.

Learning cycle

Part 4 of 19

Learning cycle 1 of 2

Part 1 — How poison climbs

A short piece of teaching, then a check to make sure it has landed.

Explore the idea

Part 5 of 19

Learn

Why the top gets the most

A persistent toxin sprayed on fields washes into streams. Algae absorb it; a thousand algae feed one water flea; a hundred fleas feed one fish; fifty fish feed one otter. Each animal keeps nearly every dose from everything it ever ate, so the otter ends up carrying the poison of a whole river.

Explore the idea

Part 6 of 19

Learn

Persistent is the key word

A toxin that broke down in days would do little harm. The dangerous ones — DDT, mercury, some PCBs — dissolve in fat, not water, so the body cannot flush them out. They sit in fatty tissue for life, and every meal adds more.

Quick check

Part 7 of 19

Quick check

Toxins concentrate up the food chain because...

Quick check

Part 8 of 19

Quick check

Persistent toxins are dangerous because they...

Reset break

Part 9 of 19

Pause

That's sitting 1 of 2 done

Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.

Stop here for now

Learning cycle

Part 10 of 19

Learning cycle 2 of 2

Part 2 — The peregrine story

A short piece of teaching, then a check to make sure it has landed.

Explore the idea

Part 11 of 19

Learn

DDT and the crashing falcons

In the 1950s and 60s, DDT was sprayed widely on crops. It built up in birds of prey and thinned their eggshells: peregrines and sparrowhawks were literally crushing their own eggs. Peregrine numbers collapsed across Britain. When DDT was banned in the 1980s, the shells thickened and the falcons returned.

Explore the idea

Part 12 of 19

Learn

The modern versions

The story is not over. Neonicotinoid pesticides move through pollen into bees; microplastics carry attached toxins into shellfish and up to us; rodent poison kills the owls that eat the rats. The lesson of DDT is to test what a chemical does at the top of the food chain, not just in the field.

Quick check

Part 13 of 19

Quick check

DDT harmed peregrines by...

Quick check

Part 14 of 19

Quick check

Peregrines recovered after...

Investigate evidence

Part 15 of 19

Evidence 1 of 1

primary

DDT levels in a food chain, 1960s measurements

Rachel Carson, Silent Spring, 1962

Water: 0.000003 parts per million. Plankton: 0.04 ppm. Small fish: 0.5 ppm. Fish-eating birds: 25 ppm. The poison became millions of times more concentrated by the top of the chain, and birds of prey laid eggs with shells too thin to survive.

Carson's book showed how a pesticide sprayed in tiny amounts accumulated up food chains — bioaccumulation — and nearly wiped out peregrines and other raptors. DDT was banned in the UK in 1984.

Think like a historian

The water contained an almost undetectable amount of DDT, yet top predators were poisoned. Use the figures to explain how that is possible.

Source: Published scientific reporting that led to worldwide pesticide bans.

View the archive record ↗

Common mix-ups

Part 16 of 19

Common mix-ups

Things people often get wrong

Thinking the poison is diluted as it climbs — it is concentrated.
Thinking a small dose in water is harmless — it multiplies up the chain.
Believing banned chemicals vanish quickly — persistent toxins linger for decades.

Challenge round

Part 17 of 19

Game · Sort it

Which of these are true?

Drag each card into the right column. Tap a card first if dragging is fiddly.

True

Not true

Mastery quiz

Part 18 of 19

Marked quiz

End of lesson quiz: Poisons up the food chain

3 questions, marked with the reasoning shown. No timer.

1. Biomagnification means...
2. Which animal ends up with the highest toxin load?
3. The DDT story teaches us to test chemicals...

Lesson round-up

Part 19 of 19

Lesson round-up

Ready when you are

Quiz score

Not sat

Games

Not played

Points this lesson

Best run

0 in a row

Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?

Ask Luna

Do the work

Your written work for this lesson

This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.

Case study

Why the school greenhouse failed

A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.

The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.

The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.

Written for Good Learning Co.

Reading questions

Name the variable the club changed the second time, and one variable they kept the same.
Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
Write a conclusion for the club's report, saying how far the evidence supports it.

Source for this lesson

Use this for the source work task below.

DDT levels in a food chain, 1960s measurements

primary

Rachel Carson, Silent Spring, 1962

Water: 0.000003 parts per million. Plankton: 0.04 ppm. Small fish: 0.5 ppm. Fish-eating birds: 25 ppm. The poison became millions of times more concentrated by the top of the chain, and birds of prey laid eggs with shells too thin to survive.

Carson's book showed how a pesticide sprayed in tiny amounts accumulated up food chains — bioaccumulation — and nearly wiped out peregrines and other raptors. DDT was banned in the UK in 1984.

Source: Published scientific reporting that led to worldwide pesticide bans.

View the original record ↗

Method and results
Writing
Write the aim, what you changed, what you measured and what you kept the same, then record your results in a table.
1 page + results table
Conclusion
Writing
Explain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.
6–8 sentences
Labelled diagram
Diagram
Draw the apparatus or the process in pencil, label it fully, and photograph it.
1 labelled diagram
Reading and notes
Reading
Read the lesson text again and write the key ideas in your own words.
Half a page of notes

Write your answer, notes or working here

Saved as you type.

Photos of paper work, diagrams or working outHow many minutes did the written work take?

Part 1 of 19 · Watch & discover

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