Explain how human activities such as habitat destruction, pollution, overexploitation, and climate change affect ecosystems and biodiversity, and evaluate solutions that support sustainability (MA STE HS-LS2-7, HS-LS4-6, stability and change).

What this topic is asking

The Massachusetts STE framework (HS-LS2-7 and HS-LS4-6) asks you to design or evaluate solutions that reduce human impacts on the environment and support biodiversity. On the High School Biology MCAS, this is often the most applied ecology topic: you are given a scenario of human activity, asked to explain its effect on the ecosystem, and asked to suggest or evaluate a solution. The crosscutting concept is stability and change: human activity disturbs ecosystems, and good solutions help restore stability.

How humans affect ecosystems

The MCAS expects you to name and explain the main human impacts:

• Habitat destruction. Clearing forests, draining wetlands, and developing land remove the habitats and food sources that species depend on, so populations decline or disappear. This is the biggest single cause of falling biodiversity.
• Pollution. Releasing harmful substances into air, water, and soil poisons organisms, disrupts food chains, and can cause problems such as algal blooms that remove oxygen from water.
• Overexploitation. Overfishing, overhunting, and overharvesting remove species faster than they can reproduce, which can collapse populations.
• Invasive species. Introducing species to new areas (deliberately or accidentally) can let them outcompete or prey on native species that have no defenses against them.
• Climate change. Burning fossil fuels raises atmospheric carbon dioxide, strengthening the greenhouse effect and warming the planet. Warming and shifting conditions change where species can live, disrupt food chains, and reduce biodiversity.

Each of these reduces biodiversity, and because biodiversity supports stability (see biodiversity and classification), the impacts threaten the resilience of whole ecosystems.

Why these impacts matter

The deeper point the MCAS tests is the link between human impact, biodiversity, and ecosystem stability. Ecosystems are systems of interacting parts (see ecosystem structure and organization) connected by energy flow and matter cycling. Removing a habitat or a key species, or changing the climate, disturbs these connections: food chains break, matter cycles are altered, and populations crash or explode. Lower biodiversity means fewer alternatives and less resilience, so a disturbed, low-biodiversity ecosystem recovers less easily. This is the stability and change idea applied to the real world.

Evaluating solutions

The framework asks you to design or evaluate solutions, so the MCAS often ends with "suggest a way to reduce the harm." Good answers connect the solution to the problem:

• Protecting habitats (reserves, national parks, wildlife corridors) preserves species and their interactions.
• Reducing pollution and emissions (using renewable energy, improving efficiency, treating waste) limits damage to organisms and the climate.
• Managing resources sustainably (fishing quotas, selective harvesting) lets populations recover and persist.
• Restoring ecosystems (replanting, removing invasive species) rebuilds biodiversity.

When evaluating a proposed solution, weigh how well it addresses the cause, alongside its costs and trade-offs. This kind of evidence-based reasoning is exactly what the science practices reward.

Try this

Q1. Name three human activities that reduce biodiversity. [2]

• Cue. Any three of: habitat destruction, pollution, overexploitation (overfishing or overhunting), introducing invasive species, climate change.

Q2. Explain how increasing atmospheric carbon dioxide can affect ecosystems. [2]

• Cue. It strengthens the greenhouse effect and warms the planet, which shifts where species can live, disrupts food chains, and can reduce biodiversity.