The table below shows measurements from a microscope calibration activity. A student used a stage micrometer, with divisions of 0.01 mm, to calibrate an eye...
Question 1 Report
The table below shows measurements from a microscope calibration activity. A student used a stage micrometer, with divisions of 0.01 mm, to calibrate an eyepiece graticule at two objective lenses. Fig. 1 shows a microscopic image of a strand of pondweed. The student wants to measure cells accurately before comparing how cell size changes along the strand. The black scale bar on the image represents an actual distance of 100 µm.
| Objective lens | Eyepiece divisions equal to 0.10 mm |
|---|---|
| ×10 | 20 |
| ×40 | 80 |
(a) What is the value of one eyepiece division at objective lens ×10, in mm? [1]
(b) Complete the calculation to give the value of one division at ×40 in µm. [2]
(c) Give one reason why calibration should be repeated when the objective lens is changed. [1]
Table 1 shows the width of cells observed in three prepared slides at a school laboratory. Each student used the same eyepiece graticule and calibration slide. Fig. 1 shows the outline of a bacterium from the yoghurt sample. Bacteria are single-celled organisms. They have a cell membrane, cytoplasm and genetic material, but their genetic material is not enclosed in a nucleus. The student also observed plant cells from spinach and animal cells from a fish gill.
| Slide | Mean cell width / µm |
|---|---|
| Yoghurt bacterium | 2 |
| Fish gill cell | 18 |
| Spinach leaf cell | 55 |
(a) What is the region labelled A? [1]
(b) Give one structure found in a spinach leaf cell but not in the bacterium. [1]
(c) Complete this sentence: the fish gill cell is ______ times wider than the bacterium. [1]
(d) Describe one difference between the genetic material in the bacterium and in a fish gill cell. [1]
Answer Details
Calibration investigation, (a) \[0.10\text{ mm}\div20=0.005\text{ mm}\] One eyepiece division at ×10 is 0.005 mm. [1]
Calibration investigation, (b) \[0.10\text{ mm}\div80=0.00125\text{ mm}\] Since \(1\text{ mm}=1000\text{ µm}\): \[0.00125\text{ mm}=1.25\text{ µm}\] One division at ×40 is 1.25 µm. [2]
Calibration investigation, (c) Calibration must be repeated because each objective lens gives a different magnification and therefore each eyepiece division represents a different actual size. [1]
Bacterium investigation, (a) Region A is genetic material, or DNA. [1]
Bacterium investigation, (b) A spinach cell, unlike the bacterium, may contain a nucleus, chloroplast, or large permanent vacuole. [1]
Bacterium investigation, (c) \[18\text{ µm}\div2\text{ µm}=9\] The fish gill cell is 9 times wider. [1]
Bacterium investigation, (d) Bacterial DNA is free in the cytoplasm, whereas DNA in a fish gill cell is enclosed inside a nucleus. [1]
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