Required practical activity - microscopy - The key features of cells and their functions - OCR 21st Century - GCSE Combined Science Revision - OCR 21st Century

Required practical activity - microscopy

Investigating cells with a light microscope

Once slides have been prepared, they can be examined under a microscope.

Aims of the experiment:

to use a light microscope to examine animal or plant cells
to make observations and draw scale diagrams of cells

Method

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Rotate the objective lenses so that the low-power, eg x10, is in line with the stage.
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Turn the coarse focus so that the stage is as close to the objective lens as possible. You should not look through the microscope to do this.
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Place the microscope slide - either one you have prepared, or a permanent slide - on the stage.
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Line it up so that the specimen - if you can see it - is in the centre of the stage, where the light passes through. Focus the slide by turning the coarse focus so the stage moves away from the objective lens.
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Draw a low-power image or record a digital image of what you see.
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Rotate the objectives so that the high-power objective, eg x 40, is in line with the stage. Bring the slide back into focus using the fine focus adjustment. If you do not succeed, go back to low-power and re-focus, then try again.

Risks

Care must be taken when looking down the microscope if the illumination is too bright.
Care must be taken when using microscope stains.
Care must be taken when handling coverslips and microscope slides.

Drawing the image

Record microscope images using labelled diagrams - or you could produce digital images.

When first examining cells or tissues with low power, draw a diagram at this stage, even if going on to examine the slide with high-power.

A low power diagram is used:

as a plan to show the arrangement of any distinct regions of different tissues, for example the tissues in a plant root
to show the outline of groups of cells that make up the tissue, if the tissue is uniform

A high-power drawing is then produced - a detailed image of a part of the slide. It is usually drawn to show a single cell, eg of a single cheek cell or onion cell.

Make sure that microscope drawings are fully labelled with names, and any extra information to help interpret the drawing, including the scale.

A lower and high power diagram showing the number of cells

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The key features of cells and their functions - OCR 21st CenturyRequired practical activity - microscopy