Human impact and conservationIB MYP Sciences: Revision notes
Section 1
How humans affect ecosystems
An ecosystem is a community of living things interacting with their environment. Human activity can reduce biodiversity (the variety of living things) in five main ways: deforestation, pollution, overfishing, introduced species and climate change.
Most damage happens because humans use resources faster than ecosystems can recover, or change the habitat so organisms can no longer survive there.
Section 2
Deforestation
Deforestation is the clearing of forests, often for farming, plantations, timber or building.
- Habitat loss: animals lose shelter, nesting sites and food, so populations fall or die out.
- Less photosynthesis: fewer trees remove less carbon dioxide from the air, and burning cleared wood releases more.
- Soil erosion: without roots to bind it, soil is washed away by rain, which also carries nutrients into rivers.
Always link deforestation to both habitat loss and the carbon cycle in a full answer.
Section 3
Pollution
Pollution is the release of harmful substances into the environment.
- Fertiliser run-off: rain washes nitrates from farmland into rivers and lakes. Algae grow quickly (an algal bloom), block light, then die. Bacteria decompose the dead algae and use up oxygen, so fish suffocate. This is called eutrophication.
- Plastic waste: animals swallow it or become trapped in it, and it breaks into microplastics.
- Air pollution: gases such as sulfur dioxide dissolve in rain to form acid rain, which harms trees and lakes.
- Pesticides can build up along a food chain and harm top predators.
Fertiliser does not poison fish directly. The fish die because decomposers use up the oxygen.
Section 4
Overfishing and introduced species
Overfishing means catching fish faster than they can breed. Stocks fall, food webs are disrupted, and some species may become endangered.
An introduced species is brought, on purpose or by accident, to a place where it does not naturally live. With no natural predators or diseases, it can multiply quickly, eat or outcompete native species and damage the food web. Examples are cane toads in Australia and rats on islands.
Section 5
Climate change
Burning fossil fuels and deforestation release carbon dioxide, which strengthens the greenhouse effect and warms the Earth. This climate change affects ecosystems because:
- habitats change faster than species can adapt or move
- ice melts and sea levels rise, flooding coastal habitats
- warmer seas cause coral bleaching, when corals expel the algae that feed them
- changing seasons upset food chains and migration patterns.
Section 6
Conservation and sustainability
Conservation is protecting and managing living things and their habitats. Sustainability means meeting today's needs without damaging the ability of future generations to meet theirs.
Strategies include:
- protected areas and national parks, including no-fishing zones
- fishing quotas and bigger net mesh sizes so young fish survive
- replanting trees and managed, sustainable forestry
- captive breeding and seed banks to protect endangered species
- laws against hunting and trading in endangered species, plus education
- reducing pollution, for example using less fertiliser and recycling.
Section 7
Evaluating science and technology (criterion D)
Technology can help conservation, for example satellites to track illegal logging or drones to count animals. In a criterion D answer you should weigh up the impact:
- State the benefits (environmental, economic, social).
- State the drawbacks, including costs and who loses out.
- Consider different stakeholders, such as local people, businesses and governments.
- Give a justified conclusion, explaining why one side outweighs the other.
A conclusion that only repeats one list is not enough. Say why the benefits or drawbacks matter more.
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Human impact and conservation
- In Borneo, a large area of tropical rainforest has been cleared so that palm oil plantations can be planted. Conservation scientists are recording what happens to the local ecosystem over the following ten years.Explain why the population of orang-utans in the area is likely to fall after the forest is cleared.2 marks
- Cane toads were brought to north-eastern Australia in 1935 to eat beetles that damaged sugar cane crops. The toads spread rapidly across the north of the country. They produce a poison, and native predators such as quolls that eat them often die.Explain how the cane toads could cause the numbers of native species such as quolls to fall.2 marks
- A class in a school near Lake Victoria wants to find out how fertiliser run-off from farms affects a pond. They add different amounts of nitrate fertiliser to five identical tanks, each containing 2 dm³ of pond water. The tanks are kept in the same sunny window, and the students measure the percentage of the water surface covered by algae after 14 days.State the independent variable, the dependent variable and one control variable in this investigation.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).