IB BIOLOGY OPTION G UNIT 5 NOTES

Topics: Carbon dioxide, Species, Food chain Pages: 24 (5480 words) Published: August 27, 2014

G1, G2 & G3 // 5.1, 5.2, 5.3

5.1.1 Define species, habitat, population, community, ecosystem and ecology Species: A group of organisms that can interbreed and produce fertile, viable 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 synthesises its organic molecules from simple inorgance substances (e.g. CO2 and nitrates) - autotrophs are producers Heterotroph: An organism that obtains organic molecules from other organisms - heterotrophs are consumers

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 Decribe what is meant by a food chain, giving three examples, each with at least three linkages (four organisms) 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.)

Examples of Food Chains
5.1.5 Describe what is meant by a food web
A food web is a diagram that shows how food chains are linked together into more complex feeding relationships within a community There can be more than one producer in a food web, and consumers can occupy multiple positions (trophic levels)

5.1.6 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 The trophic levels in a community are:

5.1.7 Deduce the trophic levels of organisms in a food web and food chain The trophic level of an organism can be determined by counting the number of feeding relationships preceding it and adding one (producer always first) Trophic Level = Number of arrows (in sequence) before organism + 1 In food webs, a single organism may occupy multiple trophic levels

5.1.8 Construct a food web containing up to 10 organisms, using appropriate information Hint: When constructing a food web, always try to position an organism relative to its highest trophic level (to keep all arrows pointing in same direction)

5.1.9 State that 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)

5.1.10 Explain the energy flow in a food chain

* Energy enters most communities as light, where it is absorbed by autotrophs (e.g. plants) and converted into chemical energy via photosynthesis * Energy then gets passed to the primary consumer (herbivore) when they eat the plant, and then gets passed to successive consumers (carnivores) as they are eaten in turn * Only ~10% of energy is passed from one trophic level to the next, the rest is lost * Because ~90% of energy is lost between trophic levels, the number of...
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