Sunday, May 4, 2014

How to Describe a Graph for maximum marks in the Edexcel Biology Unit 3 Paper

DESCRIBING A GRAPH CANNOT GET VERY DIFFICULT

There are 3 main techniques of learning how to describe a graph, which may help you gain maximum marks in your exam papers. Graphs seems to crop up in  every paper and come with atleast (5) marks.

Firstly, remember the 3 magic letters, G S M .

G - GENERAL TREND

How is the pattern of the graph generally?

Is there an overall increase? Is there an overall decrease in the data or, is there an increase and then a decrease in the data?
This 'General trend' should be the first part of your answer.
I shall explain the general trend using the graph below, it is a question for the Vitamin C experiment.
General Trend - There is an overall increase in the graph, however there is a slight decrease between 20 and 22 (degrees Celsius).

This kind of opening statement shall get you the the first mark.


S - SUB TREND    M-MANIPULATION 

Usually the sub-trend and manipulation follow each other,
The sub-trend requires you to explain the data and manipulate it using 'differences' taken of the y axis. 

I will show you an example of the same question that we did above.


When manipulating the data using differences from the y axis always use the word 'by'.
eg. As the temperature increases from 22(degrees Celsius) to 30(degrees celsius) the mean volume of juice needed to de-colourise DCPIP increased by 2.7 cm^3. (6.5 - 3.8=2.7, we took a difference of the y axis.
Manipulation- The largest increase is noted between 22 and 30 degrees Celsius .

    STANDARD DEVIATION(SD) AND ERROR BARS

- SD measures reliability.

-Small SD means better reliability.
-Large SD means poor reliability.
-Different sized SD'S indicate different level of reliability
-Proof of many replicates in results shows a better reliability.
-Overlap of SD means no significant difference in the results

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