5.1 Communities And Ecosystems Flashcards
Define species
A group of organisms that can interbreed and produce fertile, viable offspring
Define habitat
The environment in which a species normally lives or the location of a living organism
Define population
A group of organisms of the same species who live in the same area at the same time
Define community
A group of populations living and interacting with each other in an area
Define ecosystem
A community and its abiotic environment
Define ecology
The study of relationships between living organisms and between organisms and their environment
Define autotroph
- An organism that synthesises its organic molecules from simple inorganic substances (e.g. CO2and nitrates)
- Autotrophs areproducers
Define hetrotroph
- An organism that obtains organic molecules from other organisms
- Heterotrophs areconsumers
Define consumer
An organism that ingests other organic matter that is living or recently killed
Define detritivore
An organism that ingests non-living organic matter
Define saprotroph
An organism that dereives nourishment from decaying organic matter. Saprotrophs secrete digestive enzymes and absorbing the products of digestion.
Describe what is meant by a food chain
- A food chain shows the linear feeding relationships between species in a community
- The arrows represent the transfer of energy and matter as one organism is eaten by another (arrows point in the direction of energy flow)
- The first organism in the sequence is the producer, followed by consumers (1°, 2°, 3°, etc.)
- The position (level) of a species in a food chain (or food web) is called its trophic level
Give three examples of food chains
- Plankton → Krill → Mullet → Shark
- Oak tree → Caterpillar → Sparrow → Domestic Cat
- Rosebush → Aphid → Spider → Magpie
Describe what is meant by a food web
- A diagram that shows how food chains are linked together into more complex feeding relationships within a community or ecosystem
- Shows flow of energy within an ecosystem
- There can be more than one producer in a food web, and consumers can occupy multiple trophic levels
- Organisms rarely feed on only one other organism, usually fed on by more than one organism
- If one species becomes extinct, the ecosystem will adapt
Define trophic level
- An organism’s trophic level refers to the position it occupies in a food chain
- Producers always occupy the first trophic level, while saprotrophs would generally occupy the ultimate trophic level of a given food chain or food web
State the initial energy source for almost all communities
Light (the sun)
Explain how light is the initial energy source for almost all communities
- All green plants, and some bacteria, are photo-autotrophic - they use light as a source of energy for synthesising organic molecules
- This makes light the initial source of energy for almost all communities
- Some bacteria are chemo-autotrophic and use energy derived from chemical processes (e.g. nitrogen-fixating bacteria)
State how energy in a food chain is measured
Units of energy per unit area per unit time
Describe how energy transformations are never 100% efficient
- During transfer of energy between trophic levels, process is never 100% efficient
- Only ~10% of energy will be passed on to next level
- This energy may be lost as heat, be used up during cellular respiration, be excreted in faeces or remain unconsumed as the uneaten part of food
Describe energy flow in a food chain
- Light converted into chemical energy by autotrophs
- Energy passed to herbivores when they eat plants
- Energy passed to carnivores when they eat herbivores
Explain how energy is lost in a food chain
• Only ~10% of energy is passed from one trophic level to the next, the rest is lost
○ Not ingested
○ Not digested or assimilated
○ Excreted
○ Lost as heat from respiration
• Because ~90% of energy is lost between trophic levels, the number of trophic levels are limited as energy flow is reduced at higher levels.
• Ultimately, all energy lost as heat
Explain the reason 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
- Narrowing shape shows gradual loss of energy as trophic level increases
- Never appear inverted as some of the energy stored in one source is always lost when transferred to the next source
- Each level should be approximately one tenth the size of the level preceding it, as energy transformations are ~10% efficient
Explain how energy flows and leaves ecosystems
Energy cannot be recycled, and an ecosystem must be powered by a continuous influx of new energy from an external source (e.g. the sun)
At every trophic level, energy is lost as heat. The narrowing of the energy pyramid shows that all energy is eventually radiated as heat into space.
Explain how nutrients cycle within an ecosystem
New matter is not produced, nor is it lost the way energy is.
• Producers (autotrophs) take inorganic molecules and convert them into organic compounds, allowing them to be recycled and reused.
• Consumers take in this organic matter and use it for their own growth.
Carbon, nitrogen and oxygen are cycled this way.
Describe how saprotrophic bacteria and fungi (decomposers) recycle nutrients
Unlike energy, nutrients are not lost, but recycled and reused.
• In order for organisms to grow and reproduce, they need a supply of the elements of which they are made
• The saprotrophic activity of decomposers (certain bacteria and fungi), free inorganic materials from the dead bodies and waste products of organisms, ensuring a continual supply of raw materials for the producers (which can then be ingested by consumers)
• Thus saprotrophic bacteria and fungi play a vital role in recycling nutrients within an ecosystem
