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7.2 Organisation of an ecosystem ..................................................... 3
7.2.1 Levels of organization ..................................................................................................... 3
7.2.2 How materials are cycled ................................................................................................ 4
7.2.3 Decomposition (biology only) ......................................................................................... 4
7.3 Biodiversity and the effect of human interaction on ecosystems . 6
7.3.1 Biodiversity ..................................................................................................................... 6
7.3.2 Waste management........................................................................................................ 6
7.3.3 Land use .......................................................................................................................... 7
7.3.4 Deforestation .................................................................................................................. 7
7.3.5 Global warming ............................................................................................................... 8
7.3.6 Maintaining biodiversity ................................................................................................. 8
7.4 Food Trophic levels in an ecosystem (biology only) ..................... 9
7.4.1 Trophic levels .................................................................................................................. 9
7.4.2 Pyramids of biomass ....................................................................................................... 9
7.4.3 Transfer of biomass ...................................................................................................... 10
, AQA GCSE Biology notes Topic 7 – Ecology
7.1 Adaptations, interdependence and competition
7.1.1 Communities
Ecosystem - interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their
environment
Competition
Plants Animals
• Light • Food
• Space • Mates
• Water • Territory
• Mineral ions
Interdependence - within a community each species depends on other species for food, shelter,
pollination, seed dispersal etc. If one species is removed it can affect the whole community
Stable community
• All species & environmental factors are in balance → population sizes remain fairly constant
• No of predators & prey rise & fall in cycles
7.1.2 Abiotic factors 7.1.3 Biotic factors
• Light intensity • Availability of food
• Temperature • New predators arriving
• Moisture levels • New pathogens
• Soil pH & mineral content • One species outcompeting another so the
• Wind intensity & direction numbers are no longer sufficient to breed
• CO2 levels for plants
• O2 levels for aquatic animals
7.1.4 Adaptations
Structural Behavioural Functional
Definition Shape or colour of a part of an Way an organism behaves Reproduction / metabolism
organism
Description • Sharp teeth of a carnivore • Play dead → avoid • Late implantation of
• → tear meat apart predators embryos
• Camouflage • Basking in sun → • Conservation of water
• → avoid being spotted by absorb heat by producing little
prey • Courting → attract sweat
• Thick layer of fat mate
→ insulation
2
, AQA GCSE Biology notes Topic 7 – Ecology
Extremophiles - organisms live in extreme environments eg high temp, pressure, salt concentration
• Eg Bacteria living in deep sea vents
Suggest how needing less O2 helps animal to conserve water (2)
• Less breathing rate
• Less water lost through breath
• Less water from respiration
7.2 Organisation of an ecosystem
7.2.1 Levels of organization
Photosynthetic organisms - producers of biomass for life on Earth
Food chains - feeding relationships within a community
• Producers → primary consumers → secondary consumers → tertiary consumers
• Producer – synthesises molecules eg green plant or alga which makes glucose by photosynthesis
• Consumers – kill & eat other animals are predators
• Prey – eaten by consumers
Stable community – no of predators & prey rise and fall in cycles
Practicals
Quadrats - slow / non-motile organisms
Uniformly distributed - organisms equally spread
Randomly placed quadrats (population size that are uniformly distributed)
Describe how you could estimate the number of bluebells in a small woodland (5)
1. Use tape measures to create a grid
2. Use random no. generator to generate coordinates
3. Count number of individuals in quadrat
4. Repeat at least 30 times and calculate mean
!". "% &'(&)&(*+, "% + -./0&/-
5. 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 = 1"2+, +3/+
Belt transect (population changes over distance)
1. Place tape measure down shore in a straight line at a right angle
2. Place quadrat next to tape measure every 5m
3. Count frequency of species in quadrat
4. Repeat by placing another 30 transects at each interval
, AQA GCSE Biology notes Topic 7 – Ecology
7.2.2 How materials are cycled
Carbon cycle
• Returns carbon from organisms via
respiration to the atm as CO2 is used by
plants in photosynthesis
• Burning produces CO2
• Decomposition of dead organisms
o Microbial respiration → CO2
o Anaerobic respiration → mineral
ions in soil / convert to fossil fuels
How microorganisms help to recycle materials?
• Microorganisms decay
• Return carbon to atm as CO2 by microbial respiration and mineral ions to soil by anaerobic respiration
Water cycle
• Evaporation, Condensation, Precipitation
• Interception - precipitation caught by the vegetation
• Transpiration - water from vegetation transferred back to atmosphere
• Overland flow (surface runoff) - water flowing over ground surface
• Throughflow - sideways movement of water through soil towards river
• Groundwater flow - sideways movement of water through permeable rock towards river
• Infiltration - downward movement of water into soil
• Percolation - downward movement of water through permeable rock
7.2.3 Decomposition (biology only)
Factor How factor affects rate of decay
• Low temp - ↓ chemical reactions involving enzymes, ↓rate of decay
Temp • Warm temp - ↑ reactions involving enzymes, ↑rate of decay
• Too high – enzymes denature, ↓rate of decay
4
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