Question 1
Paper 2Medium16 marksA student makes a temporary mount of leaf epidermal cells and examines it using a light microscope. At the objective used, a length of 100 μm on a stage micrometer spans 40 eyepiece graticule divisions. One cell has a width of 24 eyepiece graticule divisions. A printed image of the same cell has a width of 6.0 mm. Assume that the printed image has not been resized.
Calculate the actual length represented by one eyepiece graticule division.
Calculate the actual width of the cell and the magnification of the printed image. State the length on the printed image of a scale bar representing 10 μm.
A fluorescent stain is used to make cell boundaries visible. To locate protein R, a fluorescently labelled antibody against R is used. Describe how immunofluorescence reveals the location of R and distinguish it from the use of the fluorescent stain.
In a further test, 100 cells were scored according to the location of the strongest detectable fluorescence signal.
| Preparation | Plasma membrane (%) | Cytoplasm (%) | No detectable signal (%) |
|---|---|---|---|
| Fluorescently labelled antibody against R | 70 | 25 | 5 |
| Fluorescently labelled non-specific antibody | 6 | 7 | 87 |
Assess the claim that protein R is located exclusively at the plasma membrane, using the data.
Another team wants to investigate the internal surfaces of cell membranes and the detailed structure of a protein complex while preserving it close to its native state. Outline how electron microscopy and its developments can be used to address these aims.