1.1 The Microscope in Cell Studies

Give two advantages and two limitations of using electron microscopes to investigate cell structure.

Fig. 1

Name the structures labelled X.

Use the scale bar to calculate the magnification of the drawing in Fig. 1.Show your working.

Explain why an electron microscope gives a more detailed image of cell ultrastructure than a light microscope. 

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in a cell when using a light microscope.

Fig. 1

Compare the images shown by the two micrographs.

State the role of the cell type visible in Fig. 1.

[1]

Explain the adaptations of these cells.

[3]

A student doctor wanted to take a number of different measurements from a sample of blood cells in a blood smear. 

They used a light microscope, along with an eyepiece graticule, as part of their method but they did not use a stage micrometer.

Identify the type of error this would lead to and explain the effect on their data. 

Fig. 1 shows a photomicrograph of a transverse section through part of a stem.

Doc. RNDr. Josef Reischig, CSc., CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

Fig. 1

Draw a large tissue plan diagram of this part of the stem. Note that tissue plant diagrams show the areas of different tissue within a specimen.

Fig. 2 below shows the stage micrometer scale that was used to calibrate an eyepiece graticule in a light microscope. The upper scale is the micrometer while the lower scale is the eyepiece graticule.

The length of one division on this stage micrometer is 0.01 mm.

Note that one division is the distance between two adjacent vertical lines on either scale. 

Fig. 2

Using this stage micrometer, calculate the actual length of one eyepiece graticule division. Give your answer in µm and show your working.

The photomicrograph below in Fig. 3 was taken using the same microscope with the same lenses as part (b).

The same eyepiece graticule was also used and is shown in Fig. 3.

Use the calibration of the eyepiece graticule unit from part (b) and the information in the photomicrograph to estimate the actual length in μm of the region of plant tissue shown between A and B. 

A typical animal cell is surrounded by a cell membrane whose mean thickness has been measured as 8 nm, using electron microscopy.

A light microscope-generated image of the whole cell itself measures 5 cm across at a magnification of 1250×.

Calculate how many times wider the whole cell is compared to the thickness of its membrane. 

A light microscope and an electron microscope were used to examine the contents of a plant cell.

For the light microscope, two separate magnification settings were used to produce the images shown in Fig .1. The electron microscope images is also shown in Fig.1 

In all three images, the field of view contained the same piece of biological material.

Fig.1 

Suggest reasons for the differences in the appearance of the three images in Fig. 1. 

Give two suggestions of the cell components that the two objects seen in Fig. 1 could be. 

Assume that the setup of the microscopes and sample preparation has been carried out to give the best possible view of the specimens under observation in each case. 

The resolving power of light microscopes is widely recognised to be different to that of electron microscopes.

Explain the nature of this difference and give a reason for it. 

A student is given a sample of plant tissue. Describe how the student would prepare a sample of cells from this tissue, ready to be viewed using a light microscope.

Describe how the student in part (a) would then view their sample of cells using a light microscope.

Identify two structures in a eukaryotic cell that cannot be identified using a light microscope.

Fig. 1 below shows a cross-section of a leaf taken using a light microscope with a magnification of x250.

Fig. 1

Fig. 1 shows some cell organelles inside the cells of the leaf, but it doesn’t show structures such as ribosomes or cell membranes. Use your knowledge of microscopes to explain why this is the case.

If the leaf sample in Fig. 1 were viewed under an electron microscope, ribosomes and cell membranes could be viewed clearly. Explain why.

Outline the general advantages and disadvantages of using a transmission electron microscope (TEM).

Fig. 2 below shows an image of algae taken using an electron microscope.

Image courtesy of SecretDisc. Licensed under Creative Commons Attribution-Share Alike 3.0 Unported License. Reused and distributed under conditions found at: https://creativecommons.org/licenses/by-sa/3.0/deed.en

Fig. 2

For the image shown in Fig. 2

[1]

A student decided to produce a biological drawing of a plant cell they were viewed using a light microscope.

Give four conventions that the student must be sure to follow for their diagram to be classed as a biological drawing.

In order to produce a scale line for their biological drawing in part a), the student needs to calculate the size of each eyepiece graticule subdivision. Fig. 1 shows the field of view of the light microscope used by the student at a magnification of x200. The student is told that each subdivision on the stage micrometer represents 10 µm.

Fig. 1

Calculate the distance represented by one subdivision of the eyepiece graticule scale at this magnification.

The student in parts a) and b) wants to be able to draw more detail of the plant cell infrastructure.

Explain why a transmission electron microscope would give a more detailed image of the plant cell infrastructure than a light microscope.

With reference to resolution, explain the limitations of using a light microscope.

Fig. 1 shows a photomicrograph of onion epidermal cells at a magnification of x250.

Fig. 1

Draw a biological drawing of the cells in Fig. 1.

[5]

Name three organelles that are not visible in Fig. 1.

[3]

One of the cells of the image in Fig. 1 was measured to be 24 mm.

Calculate the actual width of one of the cells in Fig. 1. Give your answer in micrometres (µm).

Describe how a student would make a temporary mount of some onion epidermal tissue.