29 WJEC Biology AS Level - Marianne Izen - 2nd Edition Flashcards
Describe the results for the practical test to determine glucose concentration?
Describe the graph for the practical test to determine glucose concentration?
What is a variable?
A variable is an experimental factor that may take different values.
Why are controlled variables so called?
Controlled variables are called ‘controlled’ factors because you control them.
Do not confuse this word with the term ‘control experiment
Where is the independent variable plotted on a graph?
Where is the dependent variable plotted on a graph?
The independent variable is plotted on the horizontal axis.
The dependent variable is plotted on the vertical axis.
Write an equation to show how the blue copper sulphate solution produces a red precipitate in the Benedict’s test.
Cu2+(blue) + e- —-> Cu+ (red)
Why are reducing sugars described as ‘reducing”?
Their aldehyde or ketone group can provide electrons which combine with, and therefore reduce, other groups.
Name a reducing sugar that is:
(1) Transported in the blood of mammals.
(2) Extracted from barley seeds for making beer.
(3) Present in RNA.
(4) Found in high concentration in many fruits.
(i) glucose
(ii) maltose
(iii) ribose
(iv) fructose
Is the sugar transported in the phloem of flowering plants reducing or non-reducing?
Non-reducing
If a Benedict’s test on a sugar does not produce the red precipitate, indicating it is non-reducing, what steps could you take to demonstrate that it is a sugar?
Incubate either with acid then neutralise with NaHCO3 or incubate with sucrase.
The red colour produced in a subsequent Benedict’s test shows that the original substance was a non-reducing sugar.
Describe the analysis for the practical test to determine glucose concentration?
Your analysis should explain the background to the experiment, in this case, an explanation of the Benedict’s test.
In this experiment, include the idea that as long as there is excess Benedict’s reagent, there is always more Cu2+ than can be reduced by the glucose present.
This means that the concentration of copper (I) oxide is proportional to the concentration of glucose.
Most experiments you perform will generate data that can be plotted as a graph.
The trend should be noted, including any peak, which suggests an optimum value of the independent variable, and any plateau.
Note if the gradient is positive or negative and if it changes.
Note if the line goes through the origin.
Describe the trend in terms of the dependent variable, rather than discussing ‘the line’ or ‘the graph’.
Where you make a calculation using the graph, explain what you are doing.
In this example, if a solution of unknown concentration has an absorbance of 0.5 AU, it is possible to read its concentration.
In this case, the red dotted lines drawn on to the graph show that the concentration is 0.40 mol dm3.
