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Cells and Living Things - Using a Microscope

Grade 6Cambridge (IGCSE)

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Light Microscope is the primary tool used in biology to observe cells. It uses visible light and lenses to magnify specimens.

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Total Magnification is the result of the combined power of the eyepiece lens and the objective lens. It is calculated as: Total Magnification=Eyepiece Power×Objective PowerTotal\ Magnification = Eyepiece\ Power \times Objective\ Power.

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The Magnification Triangle (I=A×MI = A \times M) is used to calculate the relationship between the Image size (II), Actual size (AA), and Magnification (MM).

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Units of measurement: Biological specimens are often measured in micrometers (μm\mu m). 1 mm=1000 μm1\ mm = 1000\ \mu m. To convert from mmmm to μm\mu m, multiply by 10310^3.

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Resolution is the ability to distinguish between two separate points. Higher resolution allows for more detail to be seen under the microscope.

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Staining is a technique used to make cell structures more visible. Common stains include iodine for plant cells and methylene blue for animal cells.

📐Formulae

Total Magnification=Eyepiece Magnification×Objective MagnificationTotal\ Magnification = Eyepiece\ Magnification \times Objective\ Magnification

Magnification (M)=Image Size (I)Actual Size (A)Magnification\ (M) = \frac{Image\ Size\ (I)}{Actual\ Size\ (A)}

Actual Size (A)=Image Size (I)Magnification (M)Actual\ Size\ (A) = \frac{Image\ Size\ (I)}{Magnification\ (M)}

1 mm=1000 μm1\ mm = 1000\ \mu m

💡Examples

Problem 1:

A student uses an eyepiece with 10×10\times magnification and an objective lens with 40×40\times magnification. What is the total magnification?

Solution:

10×40=400×10 \times 40 = 400\times

Explanation:

To find the total magnification, multiply the power of the eyepiece lens by the power of the objective lens currently in use.

Problem 2:

A cell in a textbook diagram has an image size (II) of 30 mm30\ mm. The magnification (MM) is stated as 500×500\times. Calculate the actual size (AA) of the cell in mmmm.

Solution:

A=30 mm500=0.06 mmA = \frac{30\ mm}{500} = 0.06\ mm

Explanation:

Using the formula A=IMA = \frac{I}{M}, divide the measured image size by the magnification factor.

Problem 3:

Convert the actual size of the cell from the previous example (0.06 mm0.06\ mm) into micrometers (μm\mu m).

Solution:

0.06 mm×1000=60 μm0.06\ mm \times 1000 = 60\ \mu m

Explanation:

Since 1 mm=1000 μm1\ mm = 1000\ \mu m, multiply the value in millimeters by 10001000 to get the size in micrometers.