A-LEVEL BIOLOGY
ECOSYSTEMS
ECOLOGY
Introduction
,Ecology: study of relationships between organisms and their environment
Biome: large naturally occurring community of flora and fauna occupying a major habitat
Ecosystem: living organisms interacting with one another in a defined area, and also the
physical factors present in that region.
Vary in size :
Eg. tiny bacterial colony, entire biosphere of Earth
Dynamic: constantly changing as a result of living organisms and environmental conditions
Factors
Biotic: (living) eg. size of population and competition for a food source
Interactions btw organisms living/once lived
Involve intraspecific/interspecific competition
Abiotic: (non-living/physical) eg. amount of rainfall, yearly temperature range
● Plants develop strategies to cope with diff light intensities
Eg. low light = larger leaves
Photosynthetic pigments requiring less light
Reproductive systems operating only when optimum light availability
● Changes in temperature due to changing seasons trigger migration + hibernation. In
plants, triggers leaf fall, dormancy and flowering
● Lack of water = plants wilt as as cells not turgid + upright
● Aquatic ecosystems: fast flowing cold water has high concentrations of oxygen
Water too warm/ Flow rate too slow: drop in oxygen concentration
2
, Waterlogged soils: air spaces btw soil particles filled with water = reduces oxygen
availability
● Edaphic (soil) factors : diff soil types have diff particle sizes
- Clay : fine particles, easily waterlogged, clumps when wet
- Loam: retains water but not waterlogged
- Sandy: coarse,well-separated particles for free draining, no water retained, easily
eroded
BIOMASS TRANSFER
All organisms require source of energy to perform functions needed to survive
Sun: source of light energy converted into chemical energy by photosynthesis, which is
then transferred to other non-photosynthetic organisms as food.
Food chains + webs show transfer of biomass (mass of living/dead material) through
organisms
Each stage = trophic level
1st: producer (photosynthetic)
2nd: primary consumer eating a producer (herbivore)
Subsequent levels: consumers that obtain energy by feeding on other organisms
Rarely 4+ trophic levels: not sufficient biomass + stored energy left to support any further
organisms
Decomposers break down dead organisms, releasing nutrients back into the ecosystem
Pyramid of numbers: represents number of organisms at each trophic level
Producers always at bottom with subsequent levels added above
3
ECOSYSTEMS
ECOLOGY
Introduction
,Ecology: study of relationships between organisms and their environment
Biome: large naturally occurring community of flora and fauna occupying a major habitat
Ecosystem: living organisms interacting with one another in a defined area, and also the
physical factors present in that region.
Vary in size :
Eg. tiny bacterial colony, entire biosphere of Earth
Dynamic: constantly changing as a result of living organisms and environmental conditions
Factors
Biotic: (living) eg. size of population and competition for a food source
Interactions btw organisms living/once lived
Involve intraspecific/interspecific competition
Abiotic: (non-living/physical) eg. amount of rainfall, yearly temperature range
● Plants develop strategies to cope with diff light intensities
Eg. low light = larger leaves
Photosynthetic pigments requiring less light
Reproductive systems operating only when optimum light availability
● Changes in temperature due to changing seasons trigger migration + hibernation. In
plants, triggers leaf fall, dormancy and flowering
● Lack of water = plants wilt as as cells not turgid + upright
● Aquatic ecosystems: fast flowing cold water has high concentrations of oxygen
Water too warm/ Flow rate too slow: drop in oxygen concentration
2
, Waterlogged soils: air spaces btw soil particles filled with water = reduces oxygen
availability
● Edaphic (soil) factors : diff soil types have diff particle sizes
- Clay : fine particles, easily waterlogged, clumps when wet
- Loam: retains water but not waterlogged
- Sandy: coarse,well-separated particles for free draining, no water retained, easily
eroded
BIOMASS TRANSFER
All organisms require source of energy to perform functions needed to survive
Sun: source of light energy converted into chemical energy by photosynthesis, which is
then transferred to other non-photosynthetic organisms as food.
Food chains + webs show transfer of biomass (mass of living/dead material) through
organisms
Each stage = trophic level
1st: producer (photosynthetic)
2nd: primary consumer eating a producer (herbivore)
Subsequent levels: consumers that obtain energy by feeding on other organisms
Rarely 4+ trophic levels: not sufficient biomass + stored energy left to support any further
organisms
Decomposers break down dead organisms, releasing nutrients back into the ecosystem
Pyramid of numbers: represents number of organisms at each trophic level
Producers always at bottom with subsequent levels added above
3
