Ecosystems and human impact for high-school biology: study cards over three tiers, the tricky ones, a practice quiz at three levels — Foundation, On-Level, and Challenge — and a lab where you label the carbon cycle from photosynthesis to the smokestack, graph island deer to find carrying capacity, sort a prairie into biotic and abiotic, and argue from the numbers what makes the Gulf of Mexico dead zone. Work here, or print it and use a pencil — both count.
A population starts small and climbs fast. Plenty of food, plenty of room.
K is the plateau a population settles at, not a peak it climbs past safely. An overshoot above K always ends in a crash, because the extra individuals eat into the very supply that sets K.
What people get wrong
⚠️People often think…
Energy is recycled through an ecosystem the way matter is.
Energy flows in as light and out as heat, one direction only. Matter is what cycles — the same carbon and nitrogen atoms go round for billions of years. That is why ecosystems need a constant energy input and do not need a constant matter input.
Energy flows once. Matter goes round.
⚠️People often think…
In a dead zone, the fertilizer itself uses up the oxygen.
Trace the chain. Fertilizer feeds an algae bloom, the algae die, and BACTERIA decomposing all that dead algae are what strip the oxygen out. The fertilizer never touched the oxygen.
Bacteria decomposing the die-off take the oxygen.
⚠️People often think…
Breathing and burning coal both release CO₂, so they are the same problem.
The carbon you exhale was in a plant last season — it is already in the loop. Fossil carbon has been locked OUT of the loop for millions of years, so burning it adds carbon the current cycle was never balanced for.
Fossil carbon was out of the loop.
⚠️People often think…
A dead log is abiotic, because it is not alive.
Biotic means it came from something living — dead or alive. A log, a shell, a leaf on the ground are all biotic. Sunlight, water and rock never were alive, and those are the abiotic ones.
Biotic means it came from life.
Flows, cycles, limits, impacts
1Watch one
Fertilizer runs off a field and a dead zone appears offshore. Trace it.
The fertilizer is plant food, so the algae bloom.
The bloom is short-lived — the algae die in huge numbers.
Bacteria decompose all that dead algae, and decomposing uses oxygen.
The oxygen drops below what fish can survive. The fix has to hit the runoff, not the fish. ✓
2Do one with me
Fill in what moves and what stays.
The thing that cycles through an ecosystem is
The oxygen in a dead zone is used by
A dead log counts as
💬One sentence, then you move on
Why does an overshoot above K end in a crash?
3Try one
A predator is removed. What happens to the prey population first?
I want a hint first
Nothing is eating them any more, and their food has not run out yet.
💬Last one — then you're done here
Why is fossil carbon a different problem from the carbon you exhale?
Where this goes
Where this lives
Farm runoff into the Illinois River, deer numbers in a county with no wolves, why a fishing limit is set at a number instead of banning fishing.
What this feeds
Next unit is matter and reactions — the chemistry under all of this.
Name one limit where you live that sets a carrying capacity.
One card at a time — tap “Show me” to check yourself, then Next. Start at Foundation; when those feel easy, climb.
Helpful Hints
🪜 Ecosystems — the ladder
An ecosystem is biotic plus abiotic → energy enters as sunlight, moves up the food web losing 90% per level, and leaves as heat → matter cycles: carbon goes air → plant → animal → decomposer → air, with a slow detour into fossil fuel → populations grow exponentially until a limiting factor sets K, the carrying capacity → biodiversity and keystone species keep the web standing → human impacts — habitat loss, pollution, invasive species, fossil carbon — tear it, and fixes work when they hit the mechanism.
Energy flows, matter cycles, populations hit K, humans push, fixes pull.
🤝 The whole idea
Everything in an ecosystem is connected by what eats what and what breathes what. Pull one thread — a predator, a nutrient, a buried carbon deposit — and the pull shows up somewhere you didn’t expect.
Pull one thread, watch the far end move.
⚠️ Tricky ones
Energy is NOT recycled. It flows in as light and out as heat. Only matter cycles.
K is the PLATEAU, not the peak. An overshoot above K ends in a crash.
In a dead zone the oxygen is used by BACTERIA decomposing dead algae — not by the fertilizer, not by the living algae.
Respiration and fossil-fuel burning both release CO₂ — but only fossil carbon was OUT of the loop for millions of years.
Removing a predator does not help the prey for long. Trophic cascades run downhill.
A dead log is BIOTIC — it was alive. Sunlight never was.
Read across a row: the fix is aimed at the mechanism, not the symptom.
🎯 How the test will ask
An S-shaped population graph — “identify K and explain the shape.”
An energy pyramid with numbers — “how much reaches the top level, and why so little?”
A carbon-cycle diagram with blank arrows — “name the process at each arrow.”
Dead-zone data (nitrogen load, area, oxygen) — “explain the cause-and-effect chain.”
“Predict what happens to the ecosystem if this species is removed.” (trophic cascade).
“Propose a solution and explain how it reduces the impact.”
✅ Can you…
Sort a list into biotic and abiotic, including a dead log?
Apply the 10% rule across three levels?
Read a logistic curve and find K — even after an overshoot?
Label every arrow of the carbon cycle, including the fossil detour?
Explain the dead zone as a chain — with the numbers?
Match a fix to the mechanism it interrupts?
Pick your level
Look back at anything you missed — the hint that appeared is exactly what to reread tonight.
How sure did you feel?
Lab
Work like a scientist: label the diagrams, turn the table into a graph, then write a claim with evidence and reasoning. Every lab checks itself on the spot, and hints are free.
Your practice never leaves this device. There is no account and no sign-in. Your work is saved in this browser only, and you can erase it whenever you want.
Your practice record — saved on this device
This is your record of the module on screen — it stays here and goes nowhere. Independent means you got it right on the first tap; supported means you got it after the explain-and-retry, or marked ‘I had it’ on a revealed answer. Both count, and neither is a grade. If your teacher asks, copy the row or show them this screen.
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The answer key is for a teacher: it prints only from here, for the unit on screen. Print the study packet prints the study pages and a blank quiz — never the answers.