Topic 5: Ecology and Evolution
5.1 Communities and ecosystems
5.1.1 Define species, habitats, populations, community, ecosystems and
ecology
• Species: a group of organisms that can interbreed and produce fertile
offspring.
• Habitat: the environment in which a species normally lives or the location of a
living organism.
• Population: a group of organisms of the same species who live in the same
area at the same time.
• Community: a group of populations living and interacting with each other in
an area.
• Ecosystem: a community and its abiotic environment.
•
Ecology: the study of relationships between living organisms and between
organisms and their environment.
5.1.2 Distinguish between autotroph and heterotroph
• Autotroph: an organism that synthesizes its organic molecules from simple
inorganic substances.
• Heterotroph: an organism that obtains organic molecules from other
organisms.
5.1.3 Distinguish between consumers, detritivores and saprotrophs
• Consumer: an organism that ingests other organic matter that is living or
recently killed.
• Detritivore: an organism that ingests non-living organic matter.
•
Saprotroph: an organism that lives on or in non- living organic matter,
secreting digestive enzymes into it and absorbing the products of digestion.
5.1.4 Describe what is meant by a food chain, giving three examples, each with
at least three linkages (four organisms)
•
Food chain shows transfer of nutrients and energy in an ecosystem
•
•
From one trophic level to the next/between trophic levels.
•
Followed by at least 2 levels of consumers.
Start with a producer.
5.1.5 Describe what is meant by a food web
•
•
•
Food web is the branched interaction of multiple food chains.
•
Same consumer could be at different trophic levels in a food web.
Uses multiple producers as a source.
Transferring nutrients/energy to consumers from different food chains.
5.1.6 Define trophic level
The trophic level of an organism is its position in the food chain. Producers, primary
consumers, secondary consumers and tertiary consumers are examples of trophic
levels.
5.1.7 Deduce the trophic level of organisms in a food chain and a food web
5.1.8 Construct a food web containing up to 10 organisms, using appropriate
information
5.1.9 State that light is the initial energy source for almost all communities
Light is the initial energy source for almost all communities.
5.1.10 Explain the energy flow in a food chain AND 5.1.13 Explain that energy
enters and leaves ecosystems, but nutrients must be recycled
Energy
•
Energy enters from sunlight.
•
Producers capture sunlight.
•
Energy flows through the trophic levels in food chain.
•
Energy transfer is (approximately) 10% from one level to the next.
•
Heat energy is lost through (cell) respiration.
•
Energy loss due to material not consumed / assimilated / egested /
excreted.
•
Energy passes to decomposers / detritivores / saprotrophs in dead
organic matter.
Nutrients
•
Nutrient cycles within ecosystem (they are recycled).
•
Nutrients are absorbed by producers.
•
Nutrients move through (food chain) by digestion of other organisms.
•
Nutrients recycled from decomposition of dead organisms.
•
Nutrients from weathering of rocks enter ecosystem.
•
Nutrients lost by leaching / sedimentation (eg shells sinking to sea
bed).
5.1.11 State that energy transformations are never 100% efficient
Energy transformations are never 100% efficient.
5.1.12 Explain reasons for the shape of pyramids of energy
•
A pyramid of energy is a graphical representation of the amount of energy of
each tropic level in a food chain
•
They are expressed in units of energy per area per time (e.g. kJ m2 year -1)
•
Pyramids of energy will never appear inverted as some of the energy stored
in one source is always lost when transferred to the next source
•
This is an application of the second law of thermodynamics
•
Each level of the pyramid of energy should be approximately one tenth the
size of the level preceding it, as energy transformations are ~10% efficient
5.1.14 State that saprotrophic bacteria and fungi (decomposers) recycle
nutrients
Saprotrophic bacteria and fungi (decomposers) recycle nutrients.
5.2 The greenhouse effect
5.2.1 Draw and label a diagram of the carbon cycle to show the processes
involved
5.2.2 Analyse the changes in concentration of atmospheric carbon dioxide
using historical records
5.2.3 Explain the relationship between rises in concentrations of atmospheric
carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse
effect
The greenhouse effect is a natural process whereby the earth's atmosphere behaves
like a greenhouse to create the moderate temperatures to which life on earth has
adapted (without the greenhouse effect, temperatures would drop significantly every
night):
•
The incoming radiation from the sun is short-wave ultraviolet and visible
radiation
•
Some of this radiation is reflected by the earth's surface back into space
as long-wave infrared radiation
• Greenhouse gases absorb this infrared radiation and re-reflect it back
to the earth as heat, resulting in increased temperatures (the
greenhouse effect)
The enhanced greenhouse effect refers to the suggested link between the increase
in greenhouse gas emissions by man and changes in global temperatures and
climate conditions
The main greenhouse gases are water vapour, carbon dioxide (CO2), methane (CH4)
and oxides of nitrogen (e.g. NO2)
Causes:
•
Fossil fuel burning
•
Deforestation
•
Cattle ranching / methane production
•
Use of CFCs
•
Production of nitrogen oxides
Effects:
•
Increasing CO concentration
2
•
Increasing temperature
•
Increase in photosynthesis
•
Changing climate
•
Extinction of species