P6 ALTERNATIVE TO PRACTICAL
Heating for same time, heating at same
temperature, same light intensity, same
mass used, same volume of reagent or
sample, same pH etc. choose according
to the experiment.
Repeat, calculate mean average. If
studying a property use same specimen
eg same carrot/ same species.
Use more than 50% of the provided space for diagrams…..
Water bath
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Precautions include use of gloves, safety goggles, water bath for heating
and tongs for holding test tubes. Biuret solution contains copper (II)
sulfate which is dangerous particularly if it gets in the eyes, so always wear goggles
Iodine is also an irritant to the eyes
Sodium hydroxide in biuret solution is corrosive, if any chemicals get onto your
skin wash your hands immediately
Ethanol is highly flammable; keep it away from any Bunsen burner
The Bunsen burner itself is a hazard due to the open flame
trachea
Purpose of soda lime, sodium hydroxide is to remove CO2.
Sodium hydrogen carbonate in water provides CO2 to aquatic plants.
Boiling, temp above 50 an unsuitable pH denature the enzyme.
Iodine solution can be used to identify chloroplast ..blue black color
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Starch is stored in the chloroplasts where photosynthesis occurs so testing a leaf
for starch is a reliable indicator of which parts of the leaf are photosynthesising 
Cobalt chloride paper turns pink in presence of water, used to determine amount
of water lost thus the number of stomata on leaf surface.
When describing food tests in exam answers, make sure you give the starting colour of the
solution and the colour it changes to for a positive result.
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starch the plant by placing it in a dark cupboard for 24-48 hours
o This ensures that any starch already present in the leaves will be used
up and will not affect the results of the experiment
Following de-starching, partially cover a leaf of the plant with aluminium foil and
place the plant in sunlight for a day
Remove the covered leaf and test for starch using iodine using the method below
Drop the leaf in boiling water
o This kills the tissue and breaks down the cell walls
Transfer the leaf into hot ethanol in a boiling tube for 5-10 minutes
o This removes the chlorophyll so colour changes from iodine can be seen
more clearly
Dip the leaf in boiling water
o This is done to soften the leaf tissue after being in ethanol
Spread the leaf out on a white tile and cover it with iodine solution
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Some of the factors that can influence heart rate include:
o Exercise
o Drugs
o Caffeine
o Alcohol
o Sex
o Weight
o Height
o Temperature
o Diet
o Dehydration
When designing experiments investigating a single factor, it is essential to try and
control the other variables
using the same group for the before and after measurements this is not as much of
an issue
If multiple groups were used care would need to be taken to find individuals with a
similar life history (same sex, age, weight and height etc.).
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Tube A should turn yellow as the seeds are respiring and producing carbon
dioxide
Tube B should remain orange as the dead seeds produce no carbon
dioxide.
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The thermometer in the flask with the germinating seeds (Flask B) should show
an increase in temperature
Flask A should remain at room temperature
This is because the seeds in flask B are respiring and producing heat energy in the
process
This shows that respiration is an exothermic reaction
The seeds in flask A are not respiring because they are dead, so the temperature
remains the same
if a plant cell is placed in a solution with a lower water potential than the plant cell
(such as a concentrated sucrose solution), water will leave the plant cell through it
partially permeable cell surface membrane by osmosis
As water leaves the vacuole of the plant cell, the volume of the plant cell decreases
The protoplast (living part of the cell inside the cell wall) gradually shrinks and no
longer exerts pressure on the cell wall
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As the protoplast continues to shrink, it begins to pull away from the cell wall
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This process is known as plasmolysis – the plant cell is plasmolysed
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If there is a potato cylinder that has not increased or decreased in mass, it means
there was no overall net movement of water into or out of the potato cells
This is because the solution that the cylinder was in was the same concentration as
the solution found in the cytoplasm of the potato cells, so there was no
concentration gradient
For each sucrose concentration, repeat the investigation with several potato
cylinders. Making a series of repeat experiments means that any anomalous
results can be identified and ignored when a mean is calculated.
Use same potato for experoments, same length, diameter etc
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