5 - Energy and Ecosystems
- Created by: Rosie
- Created on: 07-01-13 19:36
5.1 - Food Chains and Webs (key definitions)
Producers: Photosynthetic organisms that maufacture organic substances from light energy, water and carbon dioxide.
Primary Consumers: Obtein their energy from feeding on producers (other organisms)
Secondary Consumers: Obtein their energy from consuming primary consumers
Tertiary Consumers: Obtein their energy from consuming secondary consumers
Secondary and tertiary consumers tend to be predators or parasites.
Food Chains: Producer - Primary consumer - secondary consumer - tertiary consumer
Each term is refered to as a trophic level
Food Webs: systems of interlocking and interdependent food chains.
(Many animals dont rely on just one food sources, and the diets of different animals may overlap if they compete for the same food)
5.2 - Energy Transfer Between Trophic Levels
Energy Loss:
Producers:
- sunlight reflected back into space
- not all wavelengths can be absorbed in photosynthesis
- light may not fall on chlorophyll molecule
- limiting factors
Consumers:
- some of organism is not eaten
- some parts cannot be digested, lost as waste
- energy lost in excretion
- heat from respiration
- heat to environment
Calculating Efficiency of energy transfers
ENERGY TRANSFER =
ENERGY AVAILABLE AFTER TRANSFER
-------------------------------------------------------------------------B X 100
ENERGY AVAILABLE BEFORE TRANSFER
5.3 - Ecological Pyramids
Pyramids of numbers:
- measured in numbers
- no account taken of size
- number can be too large to represent
Pyramids of biomass:
- Biomass is the total mass of the plants or animals in a particular place
- measured in grams per square meter
- seasonal differences are not apparent (significant in marine ecosystems)
Pyramids of energy:
- Most accurate
- difficult to collect data
- results are more reliable than pyramids of biomass
5.4 - Agricultural Ecosystems
Ecosystems:
- used to produce foor for mankind
- minimise energy loss between trophic levels
- as much energy from food web to humans as possible
Productivity:
- Rate at which something is produced
- Net productivity= gross productivity - respiratory losses
Affected by:
- Efficiency of photosynthesising crop (can be improved by removing limiting factors)
- Area of ground covered by crop
Comparison of natural and agricultural ecosystems
Natural
- Solar energy only, no aditional input
- lower productivity
- more species diversity
- more genetic diversity in species'
- nutrients naturally recycled in ecosystem
- populations controlled by natural means
- natural climax community
Agricultural
- solar energy plus fossil fuels ect
- higher productivity
- less species diversity
- less genetic diversity in species
- artificial fertilisers used as nutrient source
- population controlled by natural and use of pesticides and cultivation
- prevented from reaching natural climax?
5.5 - Pest control
Pesticides: poisonous chemicals that kill pests
Pesticides should be:
- specific to direct organism
- biodegradable - breaks down into harmless chemicals
- cost effective
- not accumulate - does not build up in organisms or down food chain
Biological agents:
- very specific
- once introduced, the organism reproduces itself
- pests do not become resistant
Chemical pesticides:
- Effects on non- target species
- must be reapplied
- pests develop genetic resistance
Agricultural pests
Integrated pest control:
- choosing well suited crops/ animals that are pest resistant
- provide suitable habitats for natural predators
- monitor for signs of pests
- removing pests mechanically
- biological agents
- pesticides as last resource
How pests affect productivity:
- Reduce productivity
- Compete for resources
- lacking resources may become limiting factor for photosynthesis or growth
- damaging to crops
- disease causing to animals
- consuming crops, competition to humans
- monocultures enable rapid spread of pests or fungi
5.6 - Intensive rearing of domestic livestock
Effect of intensive rearing on energy conversion:
- movement restricted - less energy lost in muscle contraction
- warm environment - no heat loss to surroundings
- controlled feeding - optimum diet, minimum waste
- Predators excluded - no loss to other organisms in food web
- selective breeding - animals that are most efficient at converting food to body mass are bred with eachother to encourage this trait.
Features of intensive rearing
- efficient energy conversion
- low cost
- quality of food
- use of space
- safety
- disease
- use of drugs
- animal welfare
- pollution
- reduced genetic diversity
- use of fossil fuels
Environmental issues
- animal welfare
- destruction of habitats
- reducing genetic variation
- over grazing land
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