Biology revision (F215)

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What is the definition of Ecosystem?	A group of living organisms inhabiting the same environment and interacting with each other and the abiotic (non living) components of the environment.
What are Biotic factors?	They refer to the condition in the ecosystem created by living components e.g. supply of food, predators, disease.
What are Abiotic factors?	They are the non living components in an ecosystem e.g. temperature, pH, soil, water supply, light, inorganic nutrients which affect the organisms inhabiting the ecosystem.
What is a Habitat?	Refers to the physical environment in which an organism lives.
What is a Species?	A group of organisms capable of interbreeding and producing fertile offspring.
What is a Population?	A group of organisms of the same species occupying the same habitat at the same time.
What is a Community?	It refers to all the different populations inhabiting the same location at the same time and interacting with each other and their environment.
What is a Niche?	The role of a species in an ecosystem, it includes its habitat and its position in the food chain only one species can occupy a particular niche at any one time.
What happens if there is more than one species in a niche?	If another species moves in there will be inter-specific competition and eventually one species will out-compete the other.
What are Autotrophs?	Organisms that can synthesise their own organic food molecules from in organic materials and a source of energy.
Name two types of autotrophs?	Green plants- use light energy to convert carbon dioxide and water into sugars by Photosynthesis. Autotrophic bacteria- use energy from chemical reactions to synthesise organic food in Chemosynthesis.
What are Heterotrophs?	Organisms that must take in organic molecules as a source of energy and material.
What types of animals are Heterotrophs?	All animals are Heterotrophs as they are consumers and ultimately they all depend upon autotrophs for food.
Name a type of primary consumer?	A herbivore is a primary consumer as they eat the autotrophs (produces).
Name a type of secondary consumers?	A carnivore is a secondary consumers as they feed on the primary consumers (herbivores).
Name a type of tertiary consumer?	A carnivore is a tertiary consumer as it eats other consumers, they are sometimes called top carnivores.
What are Detritivores?	They are a primary consumer that feed on fragments of dead material called detritus, which shred it into smaller partials. They include animals like earthworms, woodlice, freshwater shrimp and hog-lice.
What cant food webs give information on?	Food webs cant give information about the number or quantities of organisms involved or their mass or the energy involved.
What is a pyramid of number?	Its essentially a bar chart that is plotted horizontally, the area of each bar is proportional to the number of individuals at that trophic level.
How do you construct a pyramid of number?	First randomly sample the organisms, this may involve quadrat analysis, use of nets or humane trapping. The sample is divided up into each trophic level and the number of individuals counted. Units are normally per square metre.
What are the problems with pyramids of number?	Their major draw back is that they do not take into account the relative biomass of organism at each trophic level, e.g. both an oak tree and grass count as just one organism but an oak tree is able to support more primary comsumers.
What are pyramids of biomass?	It shows the mass of living organisms at a particular trophic level, per unit area or volume at a particular time (kg m ).
How do you construct a pyramid of biomass?	Take random samples, usually harvesting all of the organisms in the quadrat. Then divide the organisms up into there respective trophic levels and weigh them. This is known as wet mass.
How do you construct a pyramid of biomass?	Then find the average mass for each trophic level and multiply the average by the estimated number of organisms to give the biomass at each trophic level.
What do some scientists prefer to use with pyramids of biomass?	Some prefer to use dry mass, since the water content of organisms can vary a great deal. Obtaining dry mass data involves heating the sample in an oven at 110 C to remove all the water. This isn't practical or desirable as it kills the organisms being sampled.
What are the problems with a pyramid of biomass?	It is a snap shot in time, they give no indication of the rate at which organisms grow. Productivity is the rate at which organic materials are produced unit area or volume per unit time, this isn't took into account.
What are the problems with a pyramid of biomass?	The biomass can also vary with seasons e.g. the biomass of a beech tree will be far greater in the summer than in the winter as in the winter the tree will have shed its leaves and flowers and fruits will develop in the summer.
What is a pyramid of energy?	Its the most accurate way to represent the feeding relationships in a community as it shows the amount of energy transferred from one trophic level to the next, per unit area or volume per unit time.
What doesn't affect a pyramid of energy?	Pyramid of energy shape is not affected by the size of the organism or their numbers, it simply reflects the amount of energy that is passed on.
What do pyramids of energy make easy to compare?	Easy to compare the efficiency of energy transfer from one trophic level to the next in different communities. Reflects the productivity at each trophic level.
What do energy pyramids give a better representation of?	The transfer of food energy between trophic levels than pyramids of number and biomass.
How easy is it to obtain the data?	It is difficult to obtain. Requires incineration of the sample in a calorimeter to estimate the energy content.
Where does energy in an ecosystem originate?	From sunlight, it can be transferred from one form to another but it can never be created or destroyed.
How does solar energy enter the food chain?	It enters at the producer level during photosynthesis, energy is then passed onto consumers but eventually all of it will leave the system as heat produced during respiration.
What do all organisms depend upon?	Depend directly or indirectly upon primary production.

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