Revision Notes for Prelim Biology

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  • Topic: Cell, Bacteria, Organelle
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  • Published : July 17, 2011
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~ Ecosystems: “any area that contains living organisms interacting with each other and their environment. In a balanced ecosystem, there is a flow of energy through it and recycling of some materials” Inputs and Outputs of Ecosystems include:

-the energy flow through the ecosystem; energy from the sun flows one way through, with heat loss at each trophic level -the input and recycling of inorganic and organic material (matter) -the movement of animals in and out of the habitat

Processes of an Ecosystem include:
- feeding interactions of members of the same species
- Interactions between members of different species
- And recycling of matter
The Boundaries of an Ecosystem:
-are defined by the physical and chemical features of the environment. A particular ecosystem can be described by considering: -the organisms present
-the physical and chemical features of the abiotic environment -where the ecosystem is found

1. Transects ~ a cross-section through an area. It is used to record the type and number of species present. It is useful for recording the relationship between a species and the abiotic factors in the area. Transects can only be used on animals that move very slowly or not at all, this method being most suitable to finding the population of trees and other flora. 2. Random quadrats ~ hoopie thingies. These can only be used for organisms that move very slowly or not at all, good for estimating the population of smaller organisms that do not move very far at all from original position. 3. Capture-Recapture ~ one of the most common methods of estimating population numbers. This method involves tagging or marking a sample of the population and then releasing it. The proportion of marked animals in subsequent recaptured samples gives a reasonable estimate of the population.

number of animals tagged x number recaptured
number tagged in recapture


Total of Tagging 2
ESTIMATED POPULATION = Total of Tagging 1 x
Total Recaptured

Some discrepancies with Capture-Recapture are that some animals don’t come back and animals in general move around a lot. This means that Capture-Recapture is not 100% accurate as discrepancies from the movement of animals lessens the accuracy. It’s especially difficult for larger numbers of animals.

~ Abundance: The abundance of a species means how many individuals there are in a specific area ~ Distribution: The distribution is where a species is found ~General factors that determine abundance and distribution are: -Climate: temperature, wind, rain, humidity, light intensity (this is an abiotic factor) -Shelter: (abiotic factor)

-Other resources: living space, soil, nesting material
-The interaction of organisms with others: can be beneficial or detrimental ~ There is a combination of factors which affect distribution and abundance: -The distribution and abundance of plants affects the distribution and abundance animals -The relationship between organisms, such as competition, commensalism, predation and mutualism affect distribution and abundance -In turn, human activity in an ecosystem affects distribution and abundance of plants and animals ~ Factors which affect distribution and abundance in aquatic environments: -The rate of water flow: tidal regions, still water such as lakes and ponds, fast flowing streams all have different characteristics. Oxygen availability is greater in moving water than in still water -Availability of light: plants need light to photosynthesize. Water absorbs light. The distribution of plants and animals is largely restricted to depths where light can penetrate- photosynthesis in the see can only take place in the first few metres. The vertical distribution of plants in water is related to the ability of...
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