B3.2 Human interaction · KS3 Science

Biodiversity

Biodiversity is the variety of all the different species in an area, or on Earth.
High biodiversity makes an ecosystem more stable, because species depend less on any one other species for food and shelter.
Humans depend on biodiversity for food, medicines and materials.

As the human population grows, more land is used for building, farming, quarrying and dumping waste.
Deforestation (clearing forests for farming, cattle and timber) destroys habitats and adds carbon dioxide to the air, because burnt or rotting trees release it and fewer trees are left to absorb it.
Pollution: sewage, fertilisers and toxic chemicals pollute water; landfill and pesticides pollute land; smoke and acidic gases pollute the air.
Indicator species show how polluted a place is: lots of lichens mean clean air, mayfly larvae mean clean water, and sludgeworms mean polluted water.
Greenhouse gases such as carbon dioxide and methane trap heat, causing global warming. This leads to climate change: melting ice, rising sea levels, flooding, extreme weather, and species moving or dying out.

Breeding programmes for endangered species, protecting habitats in nature reserves, replanting hedgerows and field margins, and seed banks.
Reducing deforestation, cutting carbon dioxide emissions and recycling more instead of sending waste to landfill.

A pyramid of biomass shows the mass of living material at each trophic level. It is usually pyramid-shaped because only about 10% of the biomass passes to the next level; the rest is lost in respiration, movement and waste such as faeces.
Food security means everyone having enough safe, nutritious food. Threats include a growing population, changing diets, new pests and diseases, climate change, conflict and the cost of farming.
Solutions include better farming methods, fish farms, and biotechnology such as genetically modified (GM) crops that resist pests, give bigger yields or contain extra vitamins. Some people worry about the effects of GM crops on health and wildlife.

Biodiversity: The variety of all the different species in an area.
Deforestation: Cutting down large areas of forest.
Pollution: Harmful substances released into the environment.
Indicator species: A species whose presence or absence shows how polluted a place is.
Greenhouse gas: A gas that traps heat in the atmosphere, such as carbon dioxide or methane.
Global warming: The rise in the Earth's average temperature.
Climate change: Long-term changes in weather patterns, including those caused by global warming.
Conservation: Protecting species and habitats.
Biomass: The mass of living material.
Pyramid of biomass: A diagram showing the biomass at each trophic level.
Food security: Everyone having enough safe, nutritious food.
Genetically modified crop: A crop whose genes have been changed, for example to resist pests.