BIOLOGY · Stage 8 · Chapter 7: The Health of the Environment
Biology 7.8 Chapter 7 Review: The Health of the Environment — Alhussan International Academy - Biology (Stages 7-9) Revision Notes & Topical Questions
5 min read 6 parts Lesson 8 of 8
Lesson summary
7.8 Chapter 7 Review: The Health of the Environment — Alhussan International Academy — Biology (Stages 7–9) notes: Revise ecosystems, habitats, interdependence, pesticides, invasive species and sampling methods from Chapter 7.Ecosystem — a community and its non-living surrounding…
- Biodiversity
- Habitat, population and community
- Distribution
- Food chains
- Energy loss
- Population changes
Section 1 of 6Ecosystems, habitats and biodiversity
- Ecosystem
- a community and its non-living surroundings.
- Biome
- a large ecosystem with a characteristic climate, such as rainforest, desert or tundra.
- Biodiversity
- the variety of species, highest in the warm, wet tropics.
- Habitat, population and community
- a habitat is where an organism lives, a population is one species in the habitat and a community is all the populations together.
- Distribution
- abiotic factors such as light, temperature and water, and biotic factors such as competition and predation, decide what lives where.
Section 2 of 6Food webs and interdependence
- Food chains
- they start with producers and pass energy to consumers, with arrows pointing from food to eater.
- Energy loss
- energy is lost as heat at each step, so only about 10% passes on.
- Population changes
- a change to one population affects others in the web.
- Pollination
- plants and pollinators depend on each other, since pollen is carried between flowers and pollinated flowers form seeds and fruits.
Section 3 of 6Pesticides
- Benefit
- pesticides raise crop yield.
- Persistent pesticides
- they build up in organisms and become more concentrated up the food chain, harming top predators.
- (bioaccumulation)
- DDT is very effective, but it persists, so DDT sprayed on crops resulted in herons dying many months later.
- they build up in organisms and become more concentrated up the food chain, harming top predators.
| Term | Meaning |
|---|---|
| Bioaccumulation | Build-up of a toxin in one organism |
| Biomagnification | Increase in concentration along the food chain |
| Competition | Use of the same limited resource |
Section 4 of 6Invasive species and management
- Invasive species
- they compete with or prey on native species, often have no predators of their own, and lower biodiversity.
- Management
- prevention, trapping, chemical control, biological control, protected areas, captive breeding and seed banks.
Section 5 of 6Fieldwork and data
- Quadrats placed randomly estimate numbers in an area: population = mean per quadrat × (total area ÷ quadrat area).
- Random positions from a random number generator avoid bias, so results represent the whole area.
- Transects show how organisms change along an environmental gradient.
- Reliability improves with a large sample, repeats and fair tests.
- Population graphs
- the population rises fastest where the line is steepest, and falls for reasons such as disease, shortage of food or more predators.
- Changes in one population affect other animals, such as foxes that eat rabbits and plants that rabbits graze.
Section 6 of 6Linking the ideas
- Water hyacinth on a lake
- it reduces light for aquatic plants, so oxygen falls, fish die and birds that eat the fish decline.
- A persistent pesticide
- it may kill insects that pollinate crops and harm predators downstream.
- A complete explanation gives a cause, an effect on populations and an effect on the food web.
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