When one population changes
Remove one species and the effects spread further than anyone expects — Yellowstone's wolves are the classic case.
Part of your national curriculum
- Biology: interactions and interdependencies: Understand the interdependence of organisms in an ecosystem, including food webs and insect pollinated crops
- 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
Describe the effect of changes in population size
Key learning points
- • Predator and prey cycles
- • Cascades
This lesson at a glance
- 25 minutes
- 9 parts to scroll through
- 3 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 9
Watch first
When one population changes
An English teaching video on this topic from Cognito. Watch it, then scroll down for the lesson.
In a nutshell
Describe the effect of changes in population size
Explore the idea
Part 2 of 9
Learn
Predator and prey cycles
Prey numbers rise, predators follow, prey fall, predators fall. The two curves chase each other with a lag.
Explore the idea
Part 3 of 9
Learn
Cascades
A change at the top can reshape vegetation and even landforms. Interdependence means no species can be removed cleanly.
Quick check
Part 4 of 9
Quick check
Predator numbers usually peak…
Quick check
Part 5 of 9
Quick check
A knock-on change across levels is a…
Quick check
Part 6 of 9
Quick check
Removing a keystone species…
Challenge round
Part 7 of 9
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 8 of 9
Marked quiz
End of lesson quiz: When one population changes
3 questions, marked with the reasoning shown. No timer.
1. Predator numbers usually peak…
2. A knock-on change across levels is a…
3. Removing a keystone species…
Lesson round-up
Part 9 of 9
Lesson round-up
Ready when you are
Quiz score
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Points this lesson
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Best run
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Luna: 0 out of 3 on the practice checks. Only if you feel up to it — one more?
Ask LunaDo 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.
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.
Method and results
WritingWrite 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
WritingExplain 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
DiagramDraw the apparatus or the process in pencil, label it fully, and photograph it.
1 labelled diagram
Reading and notes
ReadingRead 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 9 · Watch & discover
How this is going
- Not looked at yet
Understand the interdependence of organisms in an ecosystem, including food webs and insect pollinated crops
- Not looked at yet
Understand how organisms affect, and are affected by, their environment, including the accumulation of toxic materials