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Cells
Anne Tierney, University TeacherRoom 938, Boyd Orr Building
[email protected] through the Centre for Biosciencewww.bioscience.heacademy.ac.uk/resources/projects/tierney.aspx
Intended learning outcomes
• Know what constitutes a cell
• Describe a typical cell– Prokaryote– Eukaryote
• Calibrate a light microscope
• Measure cells using a light microscope
What is a cell?
• Get into groups of two or three
– You have five minutes to think of everything you can that defines what a cell is
– Feed back to the class
Types of cell - prokaryote
• Prokaryote– Simple
– 1-2μm
– No nucleus
– No organelles
– Single chromosome
The most common shapes of prokaryotes
a. Cocci – round
b. Bacilli – rod-shaped
c. Spiral
Types of cell - eukaryote
• Eukaryote– Complex
– 5-100μm
– Membrane-bound nucleus
– Several types of organelle
– Several chromosomes
– Single-celled organisms
– Multi-cellular organisms
A eukaryotic cell - animal
A eukaryotic cell - plant
How do we measure cells?
• Cells are (usually) too small to see with the naked eye
• Visualised with a microscope
• How can we measure with a microscope?– Done indirectly– Comparing a known scale with a scale that can
be calibrated
Measuring cells
• eyepiece graticule
• stage micrometer
How do we do it?
• We compare the known scale (stage micrometer) to the scale that is to be calibrated
Calibrating the eyepiece graticule
• The eyepiece scale is UNKNOWN
• The stage scale is KNOWN– 100 stage divisions = 10mm
• Calibration must be done for every magnification
Calibrating the eyepiece graticule
• 100 eyepiece divisions = ____ *stage divisions• We know that 100 stage divisions = 10mm• 1 stage division = ____mm• ____ *stage divisions = ____mm• 100 eyepiece divisions = ____mm• 1 eyepiece division = ____ mm or ____μm
• Repeat this for each magnification