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In
conclusion...
Monacia
Williams, Contributor
Hello
there! Did you have a good week? I
hope that by now things have settled
down, you have found your groove and
you are beginning to work seriously.
Soon, some of you will be paying those
dreaded exam fees. Like everything
else, your school-based assessments
(SBAs) will not disappear and will
soon become thorns in your flesh if
you continue to procrastinate and
ignore working on them. Do the work
now and get them out of the way so
that you can focus on the theory!
Last
week the lesson ended with the experiment
write-up at the result stage. This
week we will complete the write-up
with the discussion and the conclusion.
What is required in the discussion?
Many students tend to get nervous
when this word is mentioned but it
is nothing to be feared, you discuss
things every day. The only difference
now is that you will write down your
thoughts.
Your
report must be written in the past
tense, in Standard English and with
good grammar. Based on the given mark
scheme, you will need to include at
least two valid observation points,
for example: What is the pH at which
the rate of reaction was fastest?
How is the rate affected by the other
pHs?
In
your discussion you need to give points
to explain the rationale behind the
experiment, for example, what was
the reason for using Irish potato
extract? Why was hydrogen peroxide
used? What is the correlation between
the rise of the paper and the reaction?
Answers to these will provide the
four marks that are given for observation
and discussion. Let us see how we
can do this.
Discussion
Enzymes
are special proteins that act as biological
catalysts. This means that they have
the ability to alter the rates of
reactions. The fact that enzymes are
proteins means that they will be affected
by the same conditions which affect
proteins, hence they are affected
by changes in pH. Some enzymes work
best in alkaline conditions while
some work best in acidic conditions.
All enzymes have an optimum pH at
which they work best. At this pH,
the rate of reaction will be fastest.
Hydrogen
peroxide is one of the by-products
of metabolic reactions within living
organisms. This substance is toxic
so it cannot be allowed to accumulate
in the organism. The breakdown by
hydrogen peroxide is catalysed by
catalase, a common enzyme in living
systems. Catalase breaks down hydrogen
peroxide into water and oxygen.
H2O2-
H2O + O2
In
this experiment, catalase is provided
by the potato extract and the filter
paper soaked in the extract now provides
the enzyme. The rate of the reaction
is going to be determined by the rate
at which oxygen is produced. The circles
of paper will be the sites of the
reaction; this is where the hydrogen
peroxide is broken down. As the hydrogen
peroxide is broken down, the oxygen
is released. The bubbles of oxygen
form around the paper, causing it
to float to the surface. The faster
the rise, the faster the rate of reaction.
At pH 7 the paper took 13 seconds
to rise, this represents the fastest
time and hence the pH at which the
reaction was fastest. pH 7 is the
optimum pH for catalase. The rate
of the reaction was slower at the
two extremes, at pH 3 it took 37 seconds
and at pH 8 it took 2 seconds; the
rate decreased.
Conclusion
The
action of the enzyme catalase is affected
by changes in pH. Catalase works best
at pH 7, which is neutral. At low
pH, the rate is slower, at the higher
of 8, the rate again decreased.
The
discussion of your findings is important.
This is what you will be expected
to do when you are answering that
all-important first question on Paper
2. It also helps to build up those
all-important analytical skills.
Next
week we will look at an experiment
that is marked to test the skill of
analysis and interpretation. Until
then, have a beautiful week.
Monacia
Williams teaches at Glenmuir High
School. Send questions and comments
to kerry-ann.hepburn@gleanerjm.com
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