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BIOLOGY EDEXCEL IAL UNIT 3 - PAST PAPER QUESTIONS
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BIOLOGY EDEXCEL IAL UNIT 3 - PAST PAPER QUESTIONS
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BIOLOGY: EDEXCEL IAL UNIT 3 - PAST PAPERQUESTIONS
Explain why its important to use equal sized beetroot cylinders in experiment testing
membrane permeability? - Answers- ø Same amount/volume of pigment.
ø Same surface area/number of cells on surface.
dependant variable = degree of redness.
Describe how the degree of redness could be measured. - Answers- ø colorimeter
Then any two from:
• shake before measurement
• use of appropriate colour filter
• zeroing against blank
• clean cuvettes
• wiping cuvettes
• measure absorbance / transmission
• enough liquid to allow light go through
Variables that should be controlled in the beetroot practical and how this could be done.
- Answers- 1) volume of water (in the boiling tube) ;
2) suitable method e.g. measuring cylinder/pipette / eq.
3) reference to rinsing;
4) until clear/fixed time for all.
5) similar {variety/density/eq} of beetroot.
6) method to ensure same variety e.g. same beetroot.
7) pre-treatment e.g. storage.
8) detail of above.
9) (use same) part of beetroot/eq.
10) detail e.g. cut from middle, peeling.
Explain why pieces of beetroot tissue were rinsed in distilled water before being cut -
Answers- 1) To remove any pigment from the surface of the beetroot.
2) which would affect the results/ so the results are valid/ to avoid anomalies.
Before measuring the absorbance/ transmittance of each coloured solution, the
colorimeter was set to zero using alcohol only.
Suggest why this was done. - Answers- 1) idea of taking account of a possible variable/
alcohol absorbance.
2) to ensure the absorbance (measured) is due to betalain only/ make results valid/
avoid zero error/ avoid offset error/ for a valid comparison
, Investigation where enzyme cellulase breaks down cellulose to glucose.
Explain how the optimum temperature could be determined. - Answers- 1) rate of
production of glucose after set time.
2) suitable range of temperatures used to test.
3) further detail of method (e.g. test for glucose (benedicts), controlled variables).
4) idea that optimum temperature is the temperature at which the reaction is quickest/
eq.
Plant material was crushed an shaken with ethanol (for antiseptic properties analysis).
Suggest improvements that could be made to this method. - Answers- 1) weigh
fixed/known amount of plant.
2) measured/known volume of ethanol/known concentration of ethanol.
3) shake/leave for known/stated time.
4) standardised crushing method.
5) separation/filtration/eq.
6) use same part of plant/same strain/variety of the plant.
Describe how you would prepare an agar plate that tested for antiseptic properties of
plants. Making use of:
. sterile petri dish.
. sterile nutrient agar.
. pure culture of a suitable bacterium in a bottle.
. some plant extract. - Answers- 1) description of plate pouring (e.g mixing agar with
bacteria).
2) description of bacteria spreading/or putting bacteria into molten agar and
swirl/mix/eq.
3) description of how plant extract is added (e.g filter paper)/eq.
4) incubate at stated temperature/eq.
5) incubate for appropriate amount of time/upside down/eq.
6) credit description of aseptic precaution (e.g flaming neck of bacteria bottle/swabbing
bench at beginning/sterilising using (lit) Bunsen flame at back/eq.
7) reference to biohazard (e.g pipette in disinfectant/autoclave used
equipment/swabbing bench at end/appropriate taping of lid (i.e not all round) eq.
experiment using enzymes in alkaline conditions.
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