You are provided with a piece of celery, which is the leaf stalk of a plant, and with a slice of potato tuber. - Remove a thin slice of approximately $2\text{ mm}$ from one end of the celery and discard it. - Cut off a piece of the celery $4\text{ cm}$ long. - Stand this on its end on the white tile. - Cut a piece of the potato to the same length. - Stand this on its end on the tile. - Using a dropper, carefully cover the cut surface at the top of each specimen with iodine…

Biology 5090/32 — October/November 2011

Cambridge O-Level · Practical Test · worked solutions for every part, with the mark scheme

questions

marks

minutes

Topics Experimental Contexts · Observations and Measurements · Microscopy and Biological Drawing · Analysis, Conclusions and Evaluation · Use of Techniques, Apparatus and Materials · Planning Experiments and Investigations

Q120MMicroscopy and Biological DrawingExperimental ContextsObservations and MeasurementsAnalysis, Conclusions and EvaluationFree sample

You are provided with a piece of celery, which is the leaf stalk of a plant, and with a slice of potato tuber.

Remove a thin slice of approximately $2\text{ mm}$ from one end of the celery and discard it.
Cut off a piece of the celery $4\text{ cm}$ long.
Stand this on its end on the white tile.
Cut a piece of the potato to the same length.
Stand this on its end on the tile.
Using a dropper, carefully cover the cut surface at the top of each specimen with iodine solution, being careful not to allow any of the solution to run down the side.
Leave for 15 minutes.

Begin question 2 while you are waiting.

Wash both specimens under a tap to remove excess iodine solution.

(a)

Using the hand lens provided, carefully observe the end of the celery to which the iodine solution was applied.

(i)

Make a large, labelled drawing of this end to show the details of the structures that you can see and the effect of the iodine solution.

(ii)

Calculate the magnification of your drawing in (a)(i). Rule a line across your drawing to show where you measured. Show your working clearly.

magnification = ______

(b)

Cut the piece of celery vertically into three pieces, down through the stained tissue.

Cut the potato vertically into three pieces.

Observe the specimens with the hand lens.

(i)

Describe, with the help of a diagram, where the iodine solution stained the piece of celery.

(ii)

State two ways in which the stained pieces of celery and potato differ.

______
______

(c)

Describe and explain the differences in the structure of celery and potato as shown by the iodine solution.

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Q2Experimental Contexts · Use of Techniques, Apparatus and Materials · Observations and Measurements · Planning Experiments and Investigations20M

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