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OCR A Level Biology:复习笔记1.1.2 Identification of Variables

Category: A-level课程, 国际课程, 教材笔记, 福利干货 Date: 2022年11月16日 上午10:22

Identification of Variables

Types of variables

  • In an experiment, a variable is any factor that could change or be changed
  • There are different types of variables within an experiment
    • The?independent variable: the only variable that should be changed throughout an experiment
    • The?controlled/confounding variables: any other variables that may affect the results of the experiment that need to be controlled or monitored
    • The?dependent variable: the variable that is measured to determine the outcome of an experiment (the results)

     

  • It is essential that any variable that may affect the outcome of an experiment is controlled in order for the results to be?valid
  • Preliminary research and preliminary studies can be used to identify variables within an experiment and to determine ways of controlling these variables effectively
  • The science surrounding the issue/problem being investigated is likely to contain information about different factors or variables that may exist

Example of the science surrounding enzyme rate experiments

  • Enzyme rate experiments?are experiments that are carried out to determine the?effect?of?changing?a particular?factor?on the?rate of a reaction?that is catalysed by an enzyme
  • Factors that can be?changed?include:
    • Temperature
    • pH
    • Enzyme concentration
    • Substrate concentration

     

  • The?key?thing with enzyme rate experiments is to ensure that?only one?of these variables is?changed?during a particular experiment
    • This is known as the?independent?variable

     

  • All other variables must be?controlled?(they must stay the?same)
    • These are known as the?control?variables

     

  • For example, if investigating the effect of?temperature?on the rate of reaction, the?pH,?enzyme?concentration?and?substrate?concentration?must be exactly the same (kept constant) each time you run the experiment (at each different temperature you are investigating)
  • If these control variables are not kept constant, they could?affect the results?of the experiment
    • This would make the results?unreliable

 

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