Using quadrats and transects to sample organisms, the meaning of biodiversity, the causes and effects of pollution including the use of indicator species, the consequences of habitat destruction and deforestation, and conservation measures.

What this dot point is asking

CCEA Double Award wants the sampling techniques quadrats and transects, what biodiversity means, the causes and effects of pollution including indicator species, the consequences of habitat destruction and deforestation, and conservation measures. Sampling is a practical skill, and the human-impact material is often a longer evaluation question.

Sampling with quadrats and transects

To estimate abundance fairly, quadrats must be placed at random (for example using random coordinates) to avoid bias. You count the organisms in each quadrat, repeat many times, find the mean, and scale up to the whole area. A belt transect uses quadrats placed at intervals along a line, which is useful where conditions change, such as from the shore inland.

Biodiversity

Biodiversity is the variety of different species living in an area. A habitat with high biodiversity has many different species and tends to be more stable, because food webs have more alternative routes. Human activities often reduce biodiversity.

Pollution and indicator species

Burning fuels and releasing waste cause air and water pollution. Indicator species show the level of pollution because of their tolerance:

• Clean water supports sensitive species such as mayfly and stonefly larvae.
• Polluted water (low oxygen) supports tolerant species such as sludgeworms and rat-tailed maggots.
• Clean air supports lichens, which are sensitive to sulfur dioxide; their absence indicates polluted air.

Habitat destruction and conservation

Habitat destruction, including deforestation for farming and building, removes the places where species live, reducing biodiversity and threatening species with extinction. Deforestation also reduces photosynthesis (less carbon dioxide removed) and increases soil erosion.

Conservation measures protect biodiversity: setting up nature reserves and protected areas, replanting forests, controlling pollution, managing fishing with quotas, and protecting endangered species. The aim is to keep ecosystems healthy and maintain the variety of life.

Examples in context

Example 1. Comparing two streams. A student finds mayfly larvae in one stream but only sludgeworms in another. The first stream is clean and well oxygenated; the second is polluted. Using indicator species avoids the need to measure oxygen directly and gives a quick judgement of water quality.

Example 2. Replanting after logging. A forestry company replants two trees for every one felled and leaves wildlife corridors. This conserves biodiversity by maintaining habitats and food webs, showing a practical conservation measure that balances human needs with the environment.

Try this

Q1. Why must quadrats be placed at random? [1 mark]

• Cue. To avoid bias and get a fair, representative sample.

Q2. Name one indicator species of clean water. [1 mark]

• Cue. Mayfly larvae (or stonefly larvae).