Microscopy

Microscopy can be used to examine the structure of stem cells.

The image shows a stem cell from a fish embryo viewed under a light microscope.

Identify two pieces of evidence that suggest that the image was produced by a light microscope rather than a scanning electron microscope.

Calculate the horizontal diameter of the cell shown in the image.

Give your answer in m.

Diameter =........ m

Explain why staining is useful in microscopy.

Use structures visible in the image to support your answer.

State two features of stem cells, not visible under the microscope, that distinguish them from specialised cells.

Stem cells have a number of uses in medicine.

Explain why stem cells are useful tools in medical research.

* The development of body form begins in embryonic stem cells.

Using examples, explain the importance of mitosis and apoptosis as mechanisms controlling the development of body form.

Extra answer space if required.

Microscopes vary in terms of magnification and resolution.

Which option describes the terms magnification and resolution?

A Magnification is the size of an image under a microscope and resolution is the sharpness of that image.

B Magnification is the size of the image compared to the actual size and resolution is the ability to distinguish two objects from one another.

C Resolution is the ability to make small objects appear larger and magnification is the ability to distinguish two objects from one another.

D Resolution is the size of an image under a microscope and magnification is the sharpness of that image.

Blood cells can be examined using microscopy.

This is some equipment that could be used when preparing a blood smear.

Describe how to use the equipment to prepare a blood smear that could then be stained and viewed under a microscope.

This is a light micrograph of a human blood smear.

The cell labelled A is sometimes known as a red blood cell.

Name cell A.

In the space below, draw a labelled diagram of cell C.

The image was taken using a 40 objective lens. The eyepiece graticule scale for the 40 objective lens was calibrated using the stage micrometer shown below.

Each of the three large divisions on the stage micrometer scale measured exactly 0.01 mm.

Calculate the diameter of cell B.

Give your answer in m to 2 significant figures.

Diameter =........ m

Xylem vessels maintain the transpiration stream by transporting water up plant stems.

The sentences describe the role of meristems in producing xylem vessels.

Complete the sentences using the most appropriate words or phrases.

Meristem cells are located between xylem and........ tissues in

plants. Cells of either of these vascular tissues can be produced when meristem cells divide and

A pair of students dissect the vascular tissue of the primrose plant, Primula vulgaris.

State and explain one safety precaution that the students should take when dissecting the vascular tissue.

This is a light micrograph of a transverse section through the stem of P. vulgaris.

The diameter of one of the vascular bundles is shown by the line labelled V.

Calculate the actual diameter of the vascular bundle labelled V.

Give your answer in mm and to 2 significant figures.

A scientist plans to investigate the effect of temperature on the rate of transpiration in P. vulgaris.

The scientist uses a potometer in their investigation, as shown in the diagram below.

The scientist plans to calculate the rate of transpiration by measuring the distance moved by the air bubble.

The scientist carries out a preliminary trial by measuring the distance moved by the air bubble in 30 minutes at 20 C.

The bubble moves 18 mm in 30 minutes. The diameter of the capillary tubing in the potometer is 1 mm.

Calculate the rate of transpiration, in mm³ h^–1, during this preliminary trial.

Use the formula: Volume of cylinder = r²l

Rate of transpiration =........ mm³ h^–1

* Describe how the scientist could use the potometer to collect the data needed to assess the effect of temperature on the rate of transpiration in P. vulgaris.

Details of how to set up and use a potometer are not needed.

In your answer you should name an appropriate statistical test that could be used to analyse the data.

Extra answer space if required.

Many plants, such as Erica cinerea (bell heather), have evolved adaptations to limit water loss by transpiration.

This is a drawing of a leaf of E. cinerea.

State and explain how the leaf of E. cinerea is adapted to limit water loss by transpiration.

A student was observing and measuring cells using a light microscope.

Which option describes a method that would enable the student to accurately measure the length of a cell?

A View the cells using a calibrated eyepiece graticule and note the magnification of the eyepiece lens.

B View the cells using a calibrated eyepiece graticule and note the magnification of the objective lens.

C View the cells using a stage micrometer and note the magnification of the eyepiece lens.

D View the cells using a stage micrometer and note the magnification of the objective lens.

Which of the following describes, from lowest to highest, the resolution of images than can be achieved by different types of microscope?

A Light microscope scanning electron microscope transmission electron microscope

B Light microscope transmission electron microscope laser scanning confocal microscope

C Light microscope transmission electron microscope scanning electron microscope

D Scanning electron microscope transmission electron microscope light microscope

Fig. 2.1 shows a light micrograph of a blood smear.

The cells labelled X and Y in Fig. 2.1 are two different types of white blood cell.

Identify the types of white blood cell labelled X and Y.

The blood cell labelled Z in Fig. 2.1 contains a high concentration of haemoglobin.

Outline two other ways in which the blood cell labelled Z is adapted for its function.

The diameter of another blood cell is represented by the line W in Fig. 2.1.

The magnification used to produce Fig. 2.1 was × 800.

Calculate the actual diameter, W, of the blood cell.

Give your answer in m.

Diameter =........ m

Some white blood cells have a high concentration of lysosomes.

State the role of lysosomes in white blood cells.

A scientist calculated two values for the lysosomes in a white blood cell:

• mean volume of a lysosome = 6.5 × 10^–14 cm³

• mean number of H⁺ ions per lysosome = 1.3 × 10^–21 mol

Use these values to calculate the mean H + ion concentration per lysosome in this white blood cell.

Give your answer in mol dm^–3.

Mean H⁺ ion concentration =........ mol dm^–3

The formula used to calculate pH is

pH = -log [H + ] where [H⁺] is H⁺ ion concentration in mol dm^–3.

Use your answer from part (ii) to calculate the mean pH of the lysosomes in this white blood cell.

Give your answer to 2 significant figures.

The scientist stained the lysosomes in a sample of living white blood cells.

The table shows the properties of five stains, A to E.

Select the most appropriate stain for the scientist to use, based on your answer from part (iii).

Differential staining can be used to distinguish between bacteria with thick cell walls and bacteria with thin cell walls.

Four substances are used when differentially staining bacteria:

• Crystal violet, which stains bacteria purple.

• Safranin, which stains bacteria pink but is not visible in the presence of crystal violet.

• Alcohol, which removes fixed stains from bacteria with thin cell walls.

• Iodide solution, which fixes crystal violet to bacterial cells.

Suggest a practical procedure for staining a slide that would allow thin-walled bacteria to be differentiated from thick-walled bacteria.

Fig. 2.2 shows stained tissue that includes two different blood vessels, labelled L and M, and a substance labelled N.

State whether L is an artery or a vein and give two pieces of evidence from Fig. 2.2 that allow you to reach your decision.

State the substance labelled N.

Which of the following statements, A to D, about differential staining is not true?

A Differential staining can distinguish between different organelles.

B Differential staining can distinguish between types of cell.

C Differential staining can distinguish between types of organism.

D Differential staining is a common feature of electron microscopy.

Your answer

Which of the following statements, A to D, about microscopes is correct?

A A light microscope with an eyepiece lens magnification of × 10 and an objective lens magnification of × 50 will have an overall magnification of × 60.

B Scanning electron microscopes and laser scanning confocal microscopes can both produce three dimensional images.

C The maximum resolution of a scanning electron microscope is lower than that of a light microscope.

D Transmission electron microscopes and laser scanning confocal microscopes can both produce three dimensional images.

Your answer

FURA-2 is a fluorescent dye that can be used to measure the concentration of Ca²⁺ ions inside 18 cells.

The structure of FURA-2 is shown below.

Use the information in the figure to explain why FURA-2 is unable to cross cell membranes.

Scientists have used FURA-2 to study the role of Ca²⁺ ions in the synapses of living nerve (b) tissue.

FURA-2 was injected into a single sensory neurone that was connected by a synapse to a relay neurone.

FURA-2 fluorescence inside the neurone was observed using a confocal microscope.

Explain one advantage of using a confocal microscope in this study.

The sensory neurone was stimulated electrically and the FURA-2 fluorescence in the synaptic bulb was measured. At the same time, an electrode recorded the membrane potential in a postsynaptic neurone.

The results of this study are shown in the table.

The intensity of FURA-2 fluorescence is proportional to the concentration of Ca²⁺ ions.

The scientists concluded that changes in the concentration of Ca²⁺ ions in the presynaptic neurone caused an action potential in the postsynaptic neurone.

Evaluate and explain the scientists’ conclusion.

The image below is a photomicrograph of a mitochondrion.

State the type of microscope used to produce this image.

Identify the structures labelled M and N in the photomicrograph.

Describe two ways in which the structure of mitochondrial membranes is related to the function of a mitochondrion.

The endosymbiosis theory suggests that mitochondria may have evolved from bacteria that were taken inside other cells.

These cells then evolved into eukaryotes.

Give two structural features of mitochondria that support this theory.

Explain why early eukaryotes were able to grow more quickly than cells that did not possess mitochondria.

A student investigated the effect of different sugars on the respiration rate in yeast using the following procedure.

• Prepare a stock solution of yeast containing 10 g of dried yeast in 250 cm³ of pH5 buffer.

• Prepare solutions of each sugar containing 5 g of sugar in 250 cm³ of distilled water.

• Keep the yeast and sugar solutions in a water bath at 35 ºC until required.

• Set up the apparatus with a 250 cm³ conical flask connected by a rubber tube to a 100 cm³ gas syringe.

• Add 25 cm³ of yeast solution and 25 cm³ of sugar solution to the flask, immediately connect the flask to the gas syringe and start the clock.

• Record the volume of gas produced after 30 s and then every 30 s for 7 min.

• Repeat the experiment 5 times for each different sugar.

• Prepare a fresh yeast solution for each set of sugars.

Describe two precautions the student should take between each experiment to ensure repeatable results.

The student’s procedure did not include a negative control.

Describe one negative control that the student could have used.

The student calculated mean values for each sugar and plotted the results on a graph.

The graph is shown below.

Describe how the student could use the graph to calculate the rate of respiration for each type of sugar.

* The student concluded the following from the graph:

• The rates of respiration with glucose, maltose and sucrose were very similar.

• The yeast could not hydrolyse disaccharides.

Evaluate the student’s conclusions.

Additional answer space if required.

The student wanted to study the effect of the different sugars on the rate of growth of a yeast population.

They used a colorimeter to measure the absorbance of a culture of yeast cells.

The absorbance of the yeast culture is proportional to the concentration of yeast cells.

As the yeast multiplied, it was necessary to dilute the sample to obtain a reading on the colorimeter.

Describe how the student could use 1 cm³ pipettes and 10 cm³ measuring cylinders to (i) dilute the sample so that it was 10 000 times less concentrated.

A light microscope can be used to observe yeast cells.

State the equipment that would be needed, in addition to a microscope, to measure the average diameter of yeast cells.

The student prepared a starter culture using 2.5 × 10⁻³ g yeast cells in 1 dm³ nutrient (iii) broth.

The average mass of a yeast cell is 2.0 × 10⁻¹¹ g.

Calculate the number of cells in the starter culture.

Give your answer in standard form.

The population of this yeast doubles every 90 minutes when growing under ideal conditions.

A different starter culture was prepared containing 1 × 10⁷ cells.

Use the axes below to sketch the growth curve you would expect for the yeast culture over the first 15 h.

Identify the cellular components shown at A and B.

The real size of the line between C and D on Fig. 1.1 is 1.4 × 10⁻⁶ m.

Calculate the magnification that was used to produce the image in Fig. 1.1.

Give your answer to 2 significant figures.

Fig. 1.2 shows a student’s drawing of another sago pondweed cell, which was observed under a light microscope. The student used a sharp pencil but did not label the drawing.

Describe two other ways in which the drawing could be improved.

The student stained a sago pondweed sample to improve the contrast between cellular components when viewed under a microscope.

The student used the following procedure to stain the sample:

• Use forceps to place the sample on a glass slide.

• Use a pipette to place two drops of the stain in the centre of the sample.

• Carefully lower a cover slip onto the sample, ensuring that the cover slip is parallel with the slide as it is lowered.

Describe two improvements the student should make to their staining procedure.

Sago pondweed has evolved many adaptations to its aquatic environment. Three such adaptations are described below.

Explain the advantage of each adaptation.

Adaptation 1: No waxy cuticle

Adaptation 2: Stem tissue that contains air spaces

Adaptation 3: A thin, flexible stem