20.2 Habitat destruction
- Syllabus
- 0610–2026–2027
- Topic
- 20.2
- Level
- —
Learning objectives
20.2.1Biodiversity as the number• Describe biodiversity as the number of different species that live in an area20.2.2Reasons for habitat destruction• Describe the reasons for habitat destruction, including: (a) increased area for housing, crop plant production and livestock production (b) extraction of natural resources (c) freshwater and marine pollution20.2.3Through altering food webs and food• State that through altering food webs and food chains, humans can have a negative impact on habitats20.2.4Undesirable effects of deforestation• Explain the undesirable effects of deforestation as an example of habitat destruction, to include: reducing biodiversity, extinction, loss of soil, flooding and increase of carbon dioxide in the atmosphere
Define biodiversity by species count
Biodiversity is the number of different species that live in an area.
Count different species, not the total number of individual organisms. An area with more species has greater biodiversity by this definition.
Biodiversity includes all species in the area, not only plants or only animals, and it is not the population size of one species.
Explain why humans destroy habitats
Habitats are destroyed when land or water is changed so that its organisms can no longer live there as before.
| Human reason | How habitat is destroyed |
|---|---|
| housing | land is cleared or built over |
| crop production | natural habitat is replaced by farmland |
| livestock production | land is cleared for grazing or animal facilities |
| extraction of natural resources | logging, mining or removal of materials damages the habitat |
| freshwater and marine pollution | pollutants change water conditions and harm organisms |
State both the human use and the habitat change. The required reasons cover land expansion, resource extraction and water pollution.
Trace habitat damage through a food web
Humans can damage habitats by altering food chains and food webs.
If human activity reduces or removes one species, organisms that feed on it have less food, while organisms it consumed may increase. These changes spread through connected feeding relationships.
The resulting population changes can disrupt energy transfer, reduce biodiversity and make the habitat less able to support its original community.
Do not stop at 'the food chain changes'. Name the affected organism and trace at least one consequence to another trophic level.
Explain five effects of deforestation
Deforestation removes trees and the habitat, roots and photosynthetic tissue they provide.
| Required effect | Causal explanation |
|---|---|
| reduced biodiversity | habitat and food sources are lost, so fewer species can survive |
| extinction | populations may fall to zero when organisms cannot move or adapt |
| loss of soil | without roots binding soil and canopy protection, erosion by water or wind increases |
| flooding | less interception and water uptake increases surface run-off |
| more atmospheric carbon dioxide | less photosynthesis removes less carbon dioxide; burning or decomposition of felled trees can release more |
These effects reinforce one another: soil and flood damage further reduce habitat quality, while biodiversity loss disrupts food webs.
Deforestation increases, rather than decreases, atmospheric carbon dioxide and flood risk. Explain each direction through a changed process.