OCR · A-Level · Biology
Course version: H420 · Version from Sept 2025
(b) the preparation and examination of microscope slides for use in light…
Full specification wording
Cell structure: (b) the preparation and examination of microscope slides for use in light microscopy
This specification point covers both making a temporary slide and using a light microscope to examine it.
Checked against the OCR H420 specification (opens in a new tab) on .
- Point 2 of 10
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This specification point covers both making a temporary slide and using a light microscope to examine it. Preparation means selecting suitable material, placing it on a clean slide, adding a mounting medium such as water, lowering a coverslip carefully to avoid air bubbles, and where needed staining or squashing the specimen. Examination means setting the microscope up correctly: placing the slide on the stage and securing it with clips, selecting the lowest-power objective first, adjusting the coarse focus to find the image, then switching to a higher-power objective and using the fine focus. Learners should also know how to calculate total magnification by multiplying eyepiece magnification by objective magnification, and how to measure specimen size using an eyepiece graticule calibrated with a stage micrometer.
What earns the marks
- Preparation requires a clean slide, a specimen mounted in a suitable medium, and a coverslip lowered at an angle to reduce trapped air bubbles.
- The microscope is set up with the lowest-power objective first, the image located using coarse focus, then higher power with fine focus.
- Total magnification equals eyepiece magnification multiplied by objective magnification.
- An eyepiece graticule must be calibrated against a stage micrometer before it can be used to measure specimen size.
- Squashing or staining may be needed to make cells visible and to obtain a single layer for light transmission.
Common mistakes and how to put them right
Learners drop the coverslip flat, trapping large air bubbles.
Put it right: Lower it slowly at an angle.
Learners start on the highest-power objective.
Put it right: Begin on the lowest power and focus upwards.
Learners add eyepiece and objective magnifications instead of multiplying them.
Put it right: Multiply the two values.
Exam tips
- Read the stem carefully to identify whether the question asks about preparation or examination.
- Check the order of steps in any sequencing item before selecting an answer.
- Recalculate magnification using multiplication, not addition, and check units.
Try the lesson
The start of the Cell structure: (b) the preparation and examination of microscope slides for use in light microscopy lesson, made from checked teaching notes for this specification point.
Have a go first
A student places a thin section of onion epidermis on a slide and lowers a coverslip onto it. Why is the coverslip lowered slowly at an angle rather than dropped flat?
Listen
This specification point covers both making a temporary slide and using a light microscope to examine it. Preparation means selecting suitable material, placing it on a clean slide, adding a mounting medium such as water, lowering a coverslip carefully to avoid air bubbles, and where needed staining or squashing the specimen. Examination means setting the microscope up correctly: placing the slide on the stage and securing it with clips, selecting the lowest-power objective first, adjusting the coarse focus to find the image, then switching to a higher-power objective and using the fine focus. Learners should also know how to calculate total magnification by multiplying eyepiece magnification by objective magnification, and how to measure specimen size using an eyepiece graticule calibrated with a stage micrometer. A strong answer earns marks for these points. Preparation requires a clean slide, a specimen mounted in a suitable medium, and a coverslip lowered at an angle to reduce trapped air bubbles. The microscope is set up with the lowest-power objective first, the image located using coarse focus, then higher power with fine focus. Total magnification equals eyepiece magnification multiplied by objective magnification. An eyepiece graticule must be calibrated against a stage micrometer before it can be used to measure specimen size. A common slip: Learners drop the coverslip flat, trapping large air bubbles. Instead, lower it slowly at an angle. Exam tip: Read the stem carefully to identify whether the question asks about preparation or examination.
Key words
Say what each word means before you turn the card.
Slide preparation technique
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Correct use of the light microscope
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Magnification calculation
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Calibration and measurement
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See every definition
- Slide preparation technique
- Selecting suitable material, placing it on a clean slide, adding a mounting medium such as water, and lowering a coverslip carefully to avoid air bubbles.
- Correct use of the light microscope
- Placing the slide on the stage and securing it with clips, selecting the lowest-power objective first, adjusting the coarse focus to find the image, then switching to a higher-power objective and using the fine focus.
- Magnification calculation
- Total magnification is calculated by multiplying eyepiece magnification by objective magnification.
- Calibration and measurement
- Specimen size is measured using an eyepiece graticule calibrated with a stage micrometer.
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