What is an ecosystem?
An ecosystem is an easily described system or area where organisms interact with their physical environment.
What is a producer?
organisms which make their own food (e.g. photosynthesising plants)
What is a consumer?
organisms which eat other living things (e.g. animals)
What is a decomposer?
organisms which secrete digestive enzymes to decay (breakdown) dead organic matter to obtain their food; they help to recycle nutrients
What is a population?
the total number of individuals of one species in a particular habitat at a particular time.
How would we measure the population density of a plant in a certain area?
- Measure out a 20 by 20 metre squared area.
- Use a random number generator to generate coordinates (this eliminates bias)
- Walk to coordinate and place down quadrat.
- Count the number of organisms in the area.
- Repeat at least 20 times
- Calculate average no. of organisms
Population density = average number of organisms/size of quadrat
What does a pyramid of number show?
Drawn to show the number of each organism counted in the ecosystem. They can be odd shapes due to the different masses of organisms.
What does a pyramid of biomass show?
Drawn to show the total mass of the organisms in each trophic level. These are a more accurate way of looking at the relative amounts of organisms
What does a pyramid of energy show?
Drawn to show the total energy available in each trophic level per square metre per year. There should be a decrease in energy between each trophic level.
Why is energy lost from one energy level to the next?
- Some parts of the organisms are not eaten.
- Some parts are not digested and absorbed - they are egested as faeces.
- Some materials are respired to release energy - the energy is used for:
○ Muscle contraction
○ Maintaining a constant body temperature
○ Synthesising biological molecules
○ Movement of molecules
○ Cell division
How does carbon enter our atmosphere?
- Fossil fuels burning
- Plants, animals and decomposers respiring.
What is decomposition?
Protein in dead plants and animals is broken down. Ammonia is released into the soil.
Bacteria involved: Decomposing bacteria
How does carbon travel from the air to plants
photosynthesis.
What is nitrogen fixation?
Nitrogen gas is converted to ammonia in bacteria, when the bacteria die their proteins decompose, releasing ammonia
back into the soil.
Bacteria involved: nitrogen-fixing bacteria found in soil.
What is nitrification?
Ammonia is converted to nitrites, and nitrites are converted into nitrates.
Bacteria involved: nitrifying bacteria
What is saprotrophic nutrition?
When a plant or animal dies its tissues are decomposed by bacteria and fungi.
What is denitrification?
Nitrates are converted to nitrogen gas (denitrification makes the soil less fertile).
Bacteria involved: denitrifying bacteria
Why do farmers add crops such as peas into their soil?
They add nitrates to the ground.
What gases cause the greenhouse effect?
Gases which cause this effect are water vapour, carbon dioxide,
methane, nitrous oxides and CFCs.
Where does CO2 come from?
- Burning fossil fuels
- Slash and burn forest clearance
Where does methane come from?
Generated by bacteria in anaerobic conditions, for example;
- Ruminants such as cattle produce
- Bacteria in waterlogged fields for rice cultivation give off methane
Where do nitrous oxides come from?
- Burning fossil fuels
Where do CFCs come from?
Until the 1990’s CFCs were used as a solvent for aerosols such as
deodorants. They were also used in fridges and freezers.
What are the effects of global warming?
- melting ice caps
- destruction of habitats
- drought and desertification
- extreme weather events
- spread of diseases
- change in crop
