Fig. 1 shows a section of a microscope graticule used to measure cultured human cells. The distance between adjacent numbered lines is 0.1 mm. One cell exte...
Question 1 Report
Fig. 1 shows a section of a microscope graticule used to measure cultured human cells. The distance between adjacent numbered lines is 0.1 mm. One cell extends from line 2.3 to line 3.1 on the scale. The student needs to estimate the size of the cells before using them in an investigation of how rapidly cells divide in different nutrient solutions.
(a) Calculate the length of the cell in mm. Show your working. [2]
(b) Calculate the length of the cell in micrometres, µm. [2]
(c) Describe how the student could improve the reliability of the cell-size estimate using the microscope. [3]
(d) Explain why the nucleus is an important structure to observe when counting cells undergoing mitosis. [3]
Answer Details
(a) The cell extends from 2.3 to 3.1, a distance of:
\[3.1-2.3=0.8\text{ divisions}\]
Each division is 0.1 mm, so:
\[0.8\times0.1=0.08\text{ mm}\]
The cell length is 0.08 mm. [2]
(b) Since \(1\text{ mm}=1000\text{ µm}\):
\[0.08\times1000=80\text{ µm}\]
The cell length is 80 µm. [2]
(c) To improve reliability, measure many cells, use cells from several fields of view or slides, and calculate a mean. Repeating measurements and using the same magnification with a calibrated graticule are also valid improvements. Any three gain credit. [3]
(d) The nucleus contains chromosomes and DNA. During mitosis, chromosomes become visible and change position. Observing the nucleus therefore allows cells undergoing mitosis to be distinguished from non-dividing cells. [3]
Download The App On Google Playstore
Everything you need to excel in your exams
