5.1: Communities and ecosystems
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A group of living thing that can interbreed to produce fertile offspring.
The place or environment where a particular organism lives.
Members of a single species in a defined area at a particular time.
All populations living in a defined area at a particular time, often interacting with each other.
All organisms and their environment in a define area.
The study of the interactions of organisms with their envrionement and with each other.
Distinguish between autotroph and heterotroph
Autotrophs are organisms that are able to synthesise organic compounds from inorganic raw materials, e.g. photosynthetic plants and bacteria. Heterotrophs are organisms which is unable to make its own food and depends on organic compounds from other organisms, e.g. all animals.
Distinguish between consumers, detritivores and saprotrophs
Consumers are organisms that use other organisms as a source of food, e.g. primary consumers are herbivores and feed on plants. Detritivores are organisms that use dead organic matter (detritus) as a source of food. Saprotrophs are organisms that live on or in dead organic matter and uses it as a source of food by secreting digestive enzymes to break down the matter.
Define trophic level.
A feeding level or step in the energy flow of a food chain. Producers are the first trophic level, primary consumers the second level, secondary consumers the third level etc.
In a food chain, what is the meaning of the arrow?
In a food chain, the arrow means 'is eaten by'. It represents the energy and nutrients passing from one organism and entering another organism.
Describe why food webs are used in preference to a food chain.
A food chain shows a single series of feeding relationships. In nature, feeding relationships are more complicated with a network of interactions. A food web is more useful than a food chain in identifying the complexities of interrelationships and how a change in one population will affect several other populations.
Identify the tropic level of each organism in the following food chain.
Filamentous algae --> mayfly nymph --> dragonfly nymph --> fish --> waterbird.
- The trophic levels of the organisms are: filamentous algae = producer.
- mayfly numph = 1st order consumer,
- dragonfly nymph - 2nd order consumer
- fish = 3rd order consumer
- waterbird = 4th order consumer.
Explain why the terms herbivore and carnivore do not necessarily show the trophic level of a consumer
A herbivore eats producers (plants) and this term is interchangeable with primary consumer. A carnivore eats meat. However, the term carnivore does not specify if the animal eats herbivores (secondary consumer) or is a higher order consumer. In a complicated food web, many carnivores can occupy several trophic levels, e.g. they can eat herbivores or other carnivores.
In nature, most food chains are short. Suggest one reason why most food chains are relatively short.
Food chains in nature are usually short due to the inefficiency of energy transfer from one trophic level to the net. The biomass of producers needed to support a population of high order consumers limits the food chain length.
Outline why mistletoe occupies an unusual place in the food web.
Misletoe grows on a host tree and is a parasite on the eucalypt. Tissue from the mistletoe grows into the host and connects with the host's conducting tissue. The host provides water, mineral ions, organic compounds and holds the mistletoe high in the air. Mistletoe is thus a primary consumer. However, mistletoe is green and is also a producer.
Identify the initial source of energy for most communities.
The sun is the initial source of energy for most communities. Light energy is used in photosynthesis to produce organic material from inorganic raw materials.
Use an example to show that some communities do not begin with light as the source of energy.
Food webs around deep-sea hydrothermal vents, e.g. on the mid-Atlantic ridge, begin with extreme thermophiles that can utilise the inorganic nutrients being emitted from the vent.
State the law of conservation of energy.
The law of conservation of energy states that energy cannot be created or destroyed but only transformed from one state to another.
Outline how energy moves through a food chain.
Energy flows through a food chain from the original source of energy, e.g. Sun through each trophic level. The energy can be stored in organic molecules and at each trophic level energy is released in respiration to power body processes and energy is lost as heat.
Outline the efficiency of energy transformations.
Energy transformations are not 100% efficient. In every transformation some energy is lost to the system as heat.
Explain the difference in the movement of energy and matter in ecosystems.
There is a recycling of matter in ecosystems while there is no recycling of energy. Some matter, both organic matter and inorganic matter, flows through an ecosystem, e.g. migration of animals to another area, seed dispersal, ash from a fire carried by the wind or soil particles from weathered rocks moves to another area. Energy only flows through the ecosystem, e.g. energy enters as light and leaves as heat.
Outline the role of decomposers in an ecosystem.
Decomposers obtain their energy from dead organisms and recycle matter (nutrients) in an ecosystem. Decomposers include saprotrophs (bacteria and fungi which absorb soluble organic compounds by secreting digestive enzymes) and detritivores (earthworms which feed off and ingest detritus).
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