2.1.1 Cell Structure Flashcards
Outline how a student could prepare a
temporary mount of tissue for a light
microscope.
- Obtain thin section of tissue e.g. using ultratome or
by maceration. - Place plant tissue in a drop of water.
- Stain tissue on a slide to make structures visible.
- Add coverslip using mounted needle at 45° to
avoid trapping air bubbles.
Describe how light microscopes work.
- Lenses focus rays of light and magnify the
view of a thin slice of specimen. - Different structures absorb different amounts
and wavelengths of light. - Reflected light is transmitted to the observer
via the objective lens and eyepiece.
Describe how a transmission electron
microscope (TEM) works.
- Pass a high energy beam of electrons through
a thin slice of specimen. - More dense structures appear darker since
they absorb more electrons. - Focus image onto fluorescent screen or
photographic plate using magnetic lenses.
Describe how a scanning electron
microscope (SEM) works.
- Focus a beam of electrons onto a specimen’s
surface using electromagnetic lenses. - Reflected electrons hit a collecting device and
are amplified to produce an image on a
photographic plate.
Describe how a laser scanning confocal
microscope works.
- Focus a laser beam onto a small area on a
sample’s surface using objective lenses. - Fluorophores in the sample emit photons.
- Photomultiplier tube amplifies the signal onto a
detector. An image is produced pixel by pixel in
the correct order.
How should the field of view in
microscopy be recorded?
Draw a diagram with a sharp pencil. Do not use sketchy lines or shading. Include a scale bar. Annotate visible structures.
State an equation to calculate the actual
size of a structure from microscopy.
actual size = image size / magnification
Define magnification and resolution.
Magnification: factor by which the image is larger than the actual specimen. Resolution: smallest separation distance at which 2 separate structures can be distinguished from one another.
Why do samples need to be stained for
light microscopes?
Coloured dye binds to the structures.
Facilitates absorption of wavelengths of light to
produce image. Differential staining: contrast
between heavily & lightly stained areas
distinguishes structures.
State the magnification and resolution of
a compound light microscope.
magnification: x 2000
resolution: 200 nm
State the magnification and resolution of
a TEM.
magnification: x 500 000
resolution: 0.5 nm
State the magnification and resolution of
an SEM.
magnification: x 500 000
resolution: 3 - 10 nm
Explain how to use an eyepiece graticule
and stage micrometer to measure the
size of a structure.
- Place micrometer on stage to calibrate eyepiece graticule.
- Line up scales on graticule and micrometer. Count how
many graticule divisions are in 100μm on the micrometer. - Length of 1 eyepiece division = 100μm / number of
divisions. - Use calibrated values to calculate actual length of
structures.
Describe the structure of the nucleus.
● Surrounded by a nuclear envelope, a
semipermeable double membrane.
● Nuclear pores allow substances to enter/exit.
● Dense nucleolus made of RNA & proteins
assembles ribosomes.
Describe the function of the nucleus.
● Contains DNA coiled around chromatin into
chromosomes.
● Controls cellular processes: gene
expression determines specialisation & site
of mRNA transcription, mitosis,
semiconservative replication.
