The Microscope in Cell Studies — Structured Questions (Cambridge International A-Level Biology): Exam Questions

Extract:

• Accept "object" or a named specimen (e.g. "cell", "tissue", "organism", "structure") for "specimen".
• Do not accept answers that describe the object/specimen itself being larger than its real size without reference to the image.

Define the term magnification.

Define the term resolution.

A student is reading a biology textbook. There is an image of a cell with the magnification stated as ×10 000.

Describe how the student would calculate the actual length of the cell.

Assume that the student has a ruler which measures in cm and mm.

The student wanted to make a biological drawing of the photomicrograph of the cell.

State three conventions for biological drawing that the student should follow.

A student wants to prepare a temporary mount of some cells isolated from the root tip of a garlic bulb. They placed a thin layer of tissue onto a slide before adding a drop of iodine and a coverslip.

Explain how the coverslip should be added to the slide.

Extract:

A student wants to prepare a temporary mount of some cells isolated from the root tip of a garlic bulb. They placed a thin layer of tissue onto a slide before adding a drop of iodine and a coverslip.

State how the procedure described in (a) would differ if animal tissue were being viewed rather than plant tissue.

Fig. 1 shows an image as seen down the microscope.

The actual diameter of the structure, labelled X, is 200 µm.

A student used a ruler and measured the length of X as 8 cm.

Fig. 1

Calculate the magnification of the image.

Fig. 2 shows a labelled organelle taken using an electron microscope.

Fig. 2

Explain the evidence from Fig. 2 that shows that this is an image from an electron microscope.

Table 1 compares some of the features of light and electron microscopes.

Table 1

Identify the missing words labelled A-E.

A student used a light microscope to view a specimen. They wanted to work out the actual size of the specimen and decided to use a stage micrometer together with an eyepiece graticule.

Explain why the stage micrometer is needed as well as the eyepiece graticule.

The specimen the student wanted to view required a stain.

State why stain is needed for some structures and specimens.

The specimen also needs to be thin to view with a light microscope.

Explain why.

Fig. 1 shows a cell as viewed down a scanning electron microscope.

x 400

Fig. 1

In the space below sketch a biological drawing of the field of view. Do not include labels.

Extract:

Fig. 1 shows a cell as viewed down a scanning electron microscope.

x 400

Fig. 1

In the space below sketch a biological drawing of the field of view. Do not include labels.

Identify visible organelles in your biological drawing by adding appropriate labels.

The cells in Fig. 1 appear blue when viewed down the microscope lens.

Suggest why.

Extract:

The labels added should include:

• Nucleus/nuclei; [1 mark]
• Cell membrane; [1 mark]
• Cytoplasm; [1 mark]
• Bacteria OR mitochondria/mitochondrion labelled; [1 mark]

State the function of one of the organelles labelled in part (b).

State the name of the organelle to which your answer refers.

Fig. 1 shows an electron micrograph of ciliated epithelial cells. The actual height of the cilia cell is 30 µm, and the image height is 28 mm.

Fig. 1

Calculate the magnification used to generate the image. Give your answer to three significant figures.

Although cilia can be viewed under a light microscope, they are best seen with an electron microscope.

Suggest why this is the case.

Extract:

Although cilia can be viewed under a light microscope, they are best seen with an electron microscope.

When viewed under a light microscope it is hard to distinguish individual cilia.

Explain why.

Light microscopes have limitations that make some structures difficult to study in detail. Electron microscopes also have limitations.

State one limitation of an electron microscope.

Fig. 1 is a drawing of part of a plant cell as seen with an electron microscope. The scale bar (measuring 45 mm in length) on this drawing represents a length of 10 μm.

Fig. 1

Calculate the magnification of the drawing in Fig. 1

Extract:

Fig. 1 is a drawing of part of a plant cell as seen with an electron microscope. The scale bar (measuring 45 mm in length) on this drawing represents a length of 10 μm.

Calculate the actual width of the cell in Fig. 1 from A to B. Give your answer in micrometres (µm).

Fig. 2 is a drawing of a mitochondrion at a magnification of ×20 000. The distance between points A and B in the diagram is 6.4 cm.

Fig. 2

Calculate the actual length of the mitochondrion in Fig. 2 in micrometres (µm).

The circumference of a mitochondrion, labelled C in Fig. 2, is 1.5 µm. A student is making an accurate scale model of a mitochondrion for a school science project and wants to magnify a mitochondrion 50,000 times.

Calculate (in cm) what the circumference of the student’s model will be.

A student is given a sample of plant tissue.

Describe how the student would prepare a sample of cells from this tissue to be viewed using a light microscope.

Extract:

A student is given a sample of plant tissue.

Describe how the student would prepare a sample of cells from this tissue 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.

Extract:

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

Fig. 1 shows some cell organelles inside the cells of the leaf, but it doesn't show structures such as ribosomes or cell membranes.

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 an electron microscope.

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

*SecretDisc, CC BY-SA 3.0, via *Wikimedia Commons

Fig. 2

For the image shown in Fig. 2

i) Name the type of microscope used to produce this image.

ii) Give one piece of evidence to support your answer to part i)

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 an 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

(i) Draw a biological drawing of the cells in Fig. 1.

(ii) Name three organelles that are not visible in Fig. 1.

Extract:

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

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.

A student used a light microscope to view a specimen. They wanted to work out the actual size of the specimen, and decided to use a stage micrometer, together with the ruler visible inside the eyepiece of the microscope (known as the eyepiece graticule).

Outline why a stage micrometer is needed as well as the eyepiece graticule.

Extract:

A student used a light microscope to view a specimen. They wanted to work out the actual size of the specimen, and decided to use a stage micrometer, together with the ruler visible inside the eyepiece of the microscope (known as the eyepiece graticule).

A stage micrometer is a slide with a small ruler that has divisions of known length which can be put on the microscope stage and viewed at the same time as the eyepiece graticule.

Describe the steps required to calibrate the eyepiece graticule of a light microscope using a stage micrometer.

Extract:

A student used a light microscope to view a specimen. They wanted to work out the actual size of the specimen, and decided to use a stage micrometer, together with the ruler visible inside the eyepiece of the microscope (known as the eyepiece graticule).

A stage micrometer is needed in addition to the eyepiece graticule because the size of the units of the eyepiece graticule change depending on the magnification being used; the stage micrometer can be used to calibrate the graticule / the graticule needs to be calibrated.

The graticule is the little ruler that you can see inside the eyepiece when you look down a microscope; it always stays the same size no matter what magnification you are using. This means that the length measured by the graticule changes at different magnifications and it therefore needs to be calibrated using a stage micrometer before it can be used to measure the size of a specimen.

A stage micrometer is a slide with a small ruler that has divisions of known length which can be put on the microscope stage and viewed at the same time as the eyepiece graticule.

The steps required to calibrate the eyepiece graticule of a light microscope using a stage micrometer are:

• Line up the scale of the graticule with the scale on the stage micrometer;
• Count the number of subdivisions of the stage micrometer that fit into each division of the eyepiece graticule;
• Multiply that number by the distance between each subdivision of the stage micrometer to give the distance between each division of the eyepiece graticule;

For example, the smallest subdivision etched onto the surface of most stage micrometers is 0.01 mm (10 µm). If 5 subdivisions of the stage micrometer fit into each division of the eyepiece graticule, then each division of the graticule is 5 x 10 = 50 μm.

Explain why the steps outlined in part (b) would need to be repeated when the student changes to a more powerful objective lens.

Fig. 1 shows the appearance of the scale of a stage micrometer. The length of the whole scale is 1 mm. Point A shows the point at which the edge of a human cheek cell appears in the microscope display. A typical cheek cell has diameter of approximately 50 μm.

Fig. 1

Indicate on Fig. 1, with an arrow labelled B, the position of the opposite edge of the cheek cell.

Biologists use two main types of microscope to examine cellular structure: optical microscopes and electron microscopes. Give two advantages and two limitations of using electron microscopes to investigate cell structure.

Fig. 1 shows an electron micrograph of part of an intestinal epithelial cell.

Fig. 1

Name the structures labelled X.

Extract:

Fig. 1 shows an electron micrograph of part of an intestinal epithelial cell.

Fig. 1

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

Extract:

Fig. 1 shows an electron micrograph of part of an intestinal epithelial cell.

Fig. 1

The two mitochondria identified in Fig. 1 appear to be different in shape.

Suggest two reasons for this difference.

Describe the process of making a temporary mount of a piece of plant tissue that would allow observation of starch grains within a cell with a light microscope.

Fig. 1 shows two micrographs.

Fig. 1

Compare the images shown by the two micrographs.

Extract:

Fig. 1 shows two micrographs.

The micrographs can be compared as follows...

Similarities

• Both micrographs show red blood cells;
• Both show the biconcave disc shape of the cells;

(i) State the role of the cell type visible in Fig. 1.

(ii) Explain the adaptations of these cells.

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 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. 2 below shows a stage micrometer scale and 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 0.1 mm.

Fig. 2

Calculate the actual length of one eyepiece graticule division using this stage micrometre. Give your answer in µm and show your working.

Extract:

Fig. 2 below shows a stage micrometer scale and 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 0.1 mm.

Calculate the actual length of one eyepiece graticule division using this stage micrometre. Give your answer in µm and show your working.

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

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

Fig. 3

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

Extract:

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

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

Fig. 3

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

The actual length in µm of the plant tissue from C to D is: 67.5 (μm)

Draw a biological drawing of at least four cells from Fig. 3, including the cell labelled C-D. Your drawing should be drawn to scale at x1000 magnification.

A typical animal cell is surrounded by a cell membrane with a mean thickness of 8 nm, measured using electron microscopy.

A light microscope-generated image of the whole cell itself measures 5 cm across at a magnification of x1250.

Calculate the number of times wider the whole cell is than the thickness of its membrane.

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

The light microscope was used at two different magnification settings to produce the images shown in Fig .1. The electron microscope image 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.

Extract:

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

The light microscope was used at two different magnification settings to produce the images shown in Fig .1. The electron microscope image is also shown in Fig.1

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

Fig.1

Give two possible names of cell components that could be shown in Fig. 1.

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.