GCSE EDEXCEL BIOLOGY CORE
PRACTICLES
CP01: LOOKING AT CELLS - correct answer ---
Describe how you would prepare a microscope slide for analysis - correct answer
- Peel off epidermal layer using forceps
- Place sample on drop of water on microscope slide
- Add drops of iodine solution to sample
- Lower cover slip onto sample using mounting needle
Why is a thin sample of tissue required? - correct answer Allows light to pass
through so internal structures can be observed
Why is water added to the slide before the sample is mounted? - correct answer
Allows the sample to be suspended between the slide and the cover slip, and ensures the cover slip
stays in place
Why is iodine solution added to stain the cells? - correct answer Iodine
solution adds contrast - reacts with starch in plant cells and turns blue-black; allows internal structures
(e.g. nucleus) to become more visible
Why is the cover slip lowered using a mounting needle? - correct answer
Ensures that no air bubbles are trapped
How would you measure the length of a cell viewed under the microscope? - correct answer
Measure using eyepiece graticule and calibrate with stage micrometer
How would you calculate the magnification of an image? - correct answer
Magnification = observed cell length / actual cell length
