A sports science student collected cheek cells from volunteers using a sterile cotton swab. Fig. 1 shows a typical human cheek cell after methylene blue sta...
Question 1 Report
A sports science student collected cheek cells from volunteers using a sterile cotton swab. Fig. 1 shows a typical human cheek cell after methylene blue stain was added and the slide was viewed through a microscope. The student then considered how the cells would change if placed in very dilute salt solution.
(a) Describe four steps for making a cheek-cell slide safely and obtaining a clear image with a microscope. [4]
(b) Name three structures present in the cheek cell that are also present in a plant cell. [3]
(c) Explain why a cheek cell may burst when placed in very dilute salt solution. [3]
(d) Design an investigation to compare the effect of four salt concentrations on the diameter of cheek cells. [5]
Answer Details
(a) Use a sterile swab to gently collect cells from inside the cheek, smear the cells onto a clean slide, add methylene blue stain and a coverslip, then begin viewing with the low-power objective and focus before increasing magnification. [4] Low power makes it easier to locate and focus on the cells safely.
(b) The cheek cell and a plant cell both contain a cell membrane, cytoplasm, and a nucleus. [3]
(c) Very dilute salt solution has a higher water potential than the cheek-cell contents. Water enters through the partially permeable cell membrane by osmosis. Because an animal cell has no cell wall to resist the pressure, it can swell and burst. [3]
(d) Prepare four known salt concentrations using equal volumes. Place equal amounts of the same cheek-cell suspension in each concentration for the same time. Make slides and measure cell diameter using the same microscope magnification or calibrated eyepiece. Measure many cells in each condition and calculate a mean diameter. Keep temperature and cell source constant, and repeat the investigation to improve reliability. [5]
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