Good Learning Co.
SavannahYear 8
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ScienceEcosystems and interdependence25 min★★ difficulty

Toxic build-up along a food chain

A pollutant too dilute to harm a single organism can still kill a top predator, because food chains concentrate what they cannot excrete.

Part of your national curriculum
  • Biology: interactions and interdependencies: Understand how organisms affect, and are affected by, their environment, including the accumulation of toxic materials

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 concentration climbs
  • • Evidence in the field
  • • Other ways organisms change environments

This lesson at a glance

  • 25 minutes
  • 16 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 16 · Discover6%
1

Watch & discover

Part 1 of 16

Watch first

Toxic build-up along a food chain

An English teaching video on this topic from Cognito. 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

2

Learning cycle

Part 2 of 16

Learning cycle 1 of 2

Part 1 · Why concentration climbs

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

3

Explore the idea

Part 3 of 16

Learn

Why concentration climbs

Some substances, such as certain pesticides and mercury compounds, are not broken down or excreted. Each consumer eats many organisms from the level below, so the toxin from all of them accumulates in one body. At each step the concentration in tissue rises.

4

Explore the idea

Part 4 of 16

Learn

Evidence in the field

Populations of birds of prey fell sharply in the mid-twentieth century where persistent pesticides were used; thinning eggshells meant fewer chicks hatched. When the pesticides were restricted, populations slowly recovered — evidence linking cause and effect over time.

5

Quick check

Part 5 of 16

Quick check

Why do top predators accumulate the most toxin?

6

Quick check

Part 6 of 16

Quick check

Which property makes a pollutant accumulate?

7

Reset break

Part 7 of 16

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
8

Learning cycle

Part 8 of 16

Learning cycle 2 of 2

Part 2 · Other ways organisms change environments

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

9

Explore the idea

Part 9 of 16

Learn

Other ways organisms change environments

Accumulation is one route. Organisms also change their environment by competing, spreading disease, altering soil and, in the case of humans, changing land use, water flow and atmosphere composition.

10

Quick check

Part 10 of 16

Quick check

What evidence linked pesticides to falling bird numbers?

11

Quick check

Part 11 of 16

Quick check

Which unit is used above for concentration?

12

Explore the idea

Part 12 of 16

Worked example

Worked example: reading concentration data

Water 0.001 ppm, plankton 0.05 ppm, small fish 1 ppm, heron 20 ppm. Conclusion: concentration rises at each trophic level, so the toxin is persistent and stored in tissue. The heron is most at risk despite never touching a lethal dose in any single meal.

13

Challenge round

Part 13 of 16

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

14

Challenge round

Part 14 of 16

Game · Fill the gaps

Finish the sentences

Choose the word that belongs in each gap.

Each consumer eats many ____ from the level below, so the toxin from all of them accumulates in one body.

____ is one route.

Organisms also change their ____ by competing, spreading disease, altering soil and, in the case of humans, changing land use, water flow and atmosphere composition.

15

Mastery quiz

Part 15 of 16

Marked quiz

End of lesson quiz: Toxic build-up along a food chain

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

  1. 1. Why do top predators accumulate the most toxin?

  2. 2. Which property makes a pollutant accumulate?

  3. 3. What evidence linked pesticides to falling bird numbers?

  4. 4. Which unit is used above for concentration?

16

Lesson round-up

Part 16 of 16

Lesson round-up

Ready when you are

Quiz score

Not sat

Games

Not played

Points this lesson

0

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

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

  • 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

Saved as you type.

Part 1 of 16 · Watch & discover

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

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