Practical 5: Using the transmission microscope – Measurement of cell size

What are the two types of cells you examined under the transmission microscope in Practical 5?

Rhoeo discolor (plant cells) and squamous epithelial cells (animal cells).

What magnifications were used in Practical 5 for focusing on plant and animal cells?

Medium (10X) and high power (40X) objectives.

How do you calculate the magnification of your drawing?

Magnification = (Length of drawing in mm) / (Actual length of the specimen in mm).

What are the key structures visible in Rhoeo discolor cells under a microscope?

Cell wall, central vacuole, and chloroplasts.

What stain was used to observe the nucleus in Rhoeo discolor cells?

Iodine.

How were squamous epithelial cells obtained for microscopic observation?

By scraping the inside of the cheek with a toothpick.

What stain was used for observing squamous epithelial cells?

Methylene blue.

What tool in the microscope is used to measure cell size?

Eyepiece graticule.

How do you determine the size of a specimen using an eyepiece graticule?

By calibrating the graticule with a micrometer slide and counting subdivisions.

Why is it important to shut down the diaphragm to a minimum when using the medium-power objective?

To provide sufficient contrast and improve visibility of the specimen.

What structures are present in plant cells but absent in animal cells?

Cell wall, chloroplasts, and large central vacuole.

If you enlarge your drawing, does it change the actual size of the specimen?

No, the actual size of the specimen remains the same.

What is the purpose of Practical 5?

To practice focusing the microscope, study and compare plant and animal cells, and learn how to measure cell size using an eyepiece graticule and micrometer slide.

What materials were used in Practical 5 for preparing plant and animal cell slides?

Rhoeo discolor leaf, iodine, methylene blue, toothpick, slides, cover slips, and a transmission microscope.

Why is iodine added to Rhoeo discolor cells?

To make the nucleus more visible.

Why are squamous epithelial cells stained with methylene blue?

Because they are transparent and require staining to see their structures clearly.

What is a micrometer slide used for ?

To calibrate the eyepiece graticule for accurate size measurement of cells.

Steps for measuring the five cells and recording their sizes?

Count the number of graticule subdivisions for each cell, convert to millimeters using the calibration, and record maximum, minimum, and mean lengths.

What should you do to ensure accurate measurements when switching between objectives?

Recalibrate the eyepiece graticule for each magnification used.

What precaution must be taken when using high power (40X) objective?

Only use the fine focus knob to prevent breaking the slide.

What role does the iris diaphragm play?

It controls the amount of light entering the lens for optimal contrast.

What is the difference between the eyepiece graticule and the micrometer slide?

The eyepiece graticule is a fixed scale in the microscope, while the micrometer slide has a known measurement used for calibration.

What happens if you don't calibrate your eyepiece graticule before measuring a specimen?

Your measurements will be inaccurate because the scale changes with different objectives.

The graticule can be found in the _______.

Eyepiece

In today's lab, you'll stain epithelial cells using:

Methylene blue

Which of the following are present in both animal and plant cells?

Cell membrane

The formula used to calculate the magnification of your drawing is:

Drawing length / Actual length

To observe the nucleus of plant cells clearly, you are going to use:

Iodine