The Microscope in Cell Studies (AQA A Level Biology)

The 3D image below (Figure 1) shows a section through a plant tissue at a magnification of ×400. The distance between points C and D in the image is 20mm.

Figure 1

Calculate the actual diameter (in µm) of the starch grain between points C and D.

For the image shown in Figure 1:

Describe and explain two reasons why starch is a good storage carbohydrate for plant cells.

State the test which would be used to show the presence of starch and the positive result of this test.

Scientists used a transmission electron microscope to study the structure of an unicellular, eukaryotic organism known as an amoeba.

Explain why.

Name three structures in a eukaryotic cell that cannot be identified using an optical microscope.

A transmission electron microscope (TEM) or a scanning electron microscope (SEM) can be used to observe prokaryotic cells.

Give one advantage of using a TEM, rather than an SEM.

Give two general limitations of using a transmission electron microscope (TEM) to investigate cell structure.

Figure 1 shows part of a plant cell as seen with an electron microscope.

Figure 1

Give three features shown in Figure 1 that show that this cell is eukaryotic.

The scale bar in Figure 1 (measuring 45mm in length) on this drawing represents a length of 10μm.

Using these two values, calculate the magnification of the drawing. Show your working.

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

Give two ways in which a typical animal cell differs from the cell shown in Figure 1.

The diagram in Figure 1 shows a cholera bacterium. It has been magnified 40,000 times.

Figure 1

Name structure E.

A transmission electron microscope (TEM) or a scanning electron microscope (SEM) can be used by scientists to observe cholera bacteria.

Give two advantages of using an SEM rather than a TEM.

Calculate the actual width of the cholera bacterium in Figure 1 between points G and F.

Give your answer in micrometres (µm) and show your working.

Calculate the actual length of the flagellum of the cholera bacterium in Figure 1.

Give your answer in micrometres (µm) and show your working.

The diagram in Figure 1 is of a mitochondrion at a magnification of ×20,000. The distance between points A and B in the diagram is 6.4cm.

Figure 1

Calculate the actual length of this mitochondrion in micrometres (µm). Show your working.

The circumference of a mitochondrion (labelled C in Figure 1)  is 1.5µm. 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.

In centimetres (cm), what will be in the circumference of the student’s model?

One scientific theory suggests that mitochondria are organelles that evolved from prokaryotic cells.

Give two pieces of evidence that support this theory.

What advantage(s) do mitochondria provide to the cells that contain them?

Biologists use two main types of microscope to examine cellular structure: optical microscopes and transmission electron microscopes (TEMs).  Give two advantages and two limitations of using a TEM to investigate cell structure.

Figure 1 shows a transmission electron micrograph of part of an intestinal epithelial cell.

Figure 1

Name the organelle labelled X and explain how these organelles facilitate the absorption of food molecules from the small intestine.

The scale bar in Figure 1 represents a length of 0.2 μm.

Calculate the magnification of the drawing. Show your working.

Explain why a transmission electron microscope gives a more detailed image of cell infrastructure than a light microscope.

Cholera bacteria can be viewed using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). Give one advantage of using a TEM and one advantage of using an SEM.

An example of a unicellular eukaryotic organism, the amoeba, is shown in Figure 1.

Figure 1

Name organelle A.

Researchers wishing to study the structure of an amoeba should use a transmission electron microscope. Explain why.

Name four structures in a eukaryotic cell that cannot be identified using an optical microscope.

Figure 1 shows an electron micrograph of a section through part of an alveolus from a lung and its adjacent tissue.

Figure 1

The diameter of a human red blood cell is 7 µm. Calculate the magnification of Figure 1. Show your working.

Explain what an artefact is in microscopy and why artefacts should be minimised.

Cells X and Y are biconcave discs. Explain two advantages of a biconcave disc over a spherical cell of the same volume in transporting oxygen.

Cell X is a eukaryotic cell. Give four features that may be found in a prokaryotic cell which are not found in cell X.

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

Figure 1 below shows an image drawn from an electron micrograph of a plant cell.

Figure 1

Give the name and function of the structures labelled W and Z.

Researchers wishing to examine the detailed structure of the lower epidermis layer of a leaf have a variety of microscopy techniques available to them. Suggest the best technique that they should use to obtain detailed images of the leaf surface. Justify your answer.

The theoretical resolving power of an electron microscope may often not be achieved in practice.  Explain why.  

Describe the steps required to calibrate the eyepiece graticule of an optical microscope.  

Explain why the steps outlined in Question 5a) would need to be repeated when the observer changes to a more powerful objective lens. 

Figure 1 shows the appearance of the scale of a stage micrometer. The length of the whole scale is 1.00 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.

Figure 1

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

Figure 2 shows an optical microscope’s field of view at a magnification of x200. 

The same stage micrometer is being used as in question 5 c). Calculate the distance represented by one subdivision of the eyepiece graticule scale at this magnification.