4.4.2Unit 4: Energy, Environment, Microbiology and Immunity
The Variety of Life — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 4 parts Lesson 22 of 28 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 4Human Pressure
Natural selection has increased the variety of life over time, but human activity now threatens many species.
Human Pressure
Population growth
- Population growth The human population has grown exponentially for about 150 years because of more food and better medicine and hygiene.
Resource demand
- Resource demand More people and more development increase demand for land, water, timber and fossil fuels.
Conflict
- Conflict This creates a conflict between meeting human needs and conserving biodiversity.
Main factors
- Main factors Habitat destruction, overexploitation, hunting, agriculture and climate change are the principal causes of loss.
Section 2 of 4Habitat and Exploitation
Land clearing and over-use remove species faster than they can recover.
Habitat loss
- Habitat loss Clearing land for farming, industry, housing and transport removes the habitats of plants and animals completely.
Fragmentation
- Fragmentation Habitats split into small patches, so populations become isolated and more likely to suffer inbreeding or local extinction.
Marine habitats
- Marine habitats Dynamite fishing damages coral reefs, and trawling drags nets along the sea bed and destroys it.
Overexploitation
- Overexploitation Resources such as timber and fish are used faster than they are replaced, which also harms animals that feed on the fish.
Hunting
- Hunting Wild species such as primates hunted for bush meat are removed faster than their populations can recover.
Section 3 of 4Agriculture and Climate
Modern farming and climate change both reduce diversity.
1
Post-war farming became more specialised, with monocultures that support far fewer species than natural habitats.
2
Hedgerows and ponds were removed to enlarge fields, which destroyed nesting and feeding sites for insects, mammals and birds.
3
Fertilisers leach into waterways and cause eutrophication, while insecticides kill non-target insects such as pollinating bees.
4
Climate change alters weather and can occur too fast for species to adapt, so some move towards the poles or higher ground.
5
Rising carbon dioxide acidifies oceans and affects shell-forming organisms, and higher temperatures cause coral bleaching.
Section 4 of 4Exam Checklist & Tips
4.4.2 – Key Points for the Exam
- Habitat fragmentation Division of a habitat into small isolated patches.
- Overexploitation Using a resource faster than it can be replaced.
- Monoculture Growing a single crop over a large area.
- Eutrophication Excess nutrients in water leading to algal growth and oxygen depletion.
- Ocean acidification Decrease in the pH of seawater as more carbon dioxide dissolves.
Common Mistakes
- Treating habitat loss and habitat fragmentation as the same; fragmentation leaves small isolated patches.
- Saying fertilisers directly kill fish, rather than causing eutrophication which leads to deaths of aquatic organisms.
- Forgetting that pesticides also harm non-target species such as pollinators.
- Describing the human population as growing linearly, when it has grown exponentially.
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