CHAPTER 1:

CELL STRUCTURE
Learning Outcomes: 18 hours / 10% of course

1.1 1 Make temporary preparations of cellular material suitable for viewing with a light microscope.
1.1 2 Draw cells from microscope slides and photomicrographs.
1.1 3 Calculate magnifications of images and actual sizes of specimens from drawings, photomicrographs and electron micrographs (scanning and
transmission).
1.1 4 Use an eyepiece graticule and stage micrometre scale to make measurements and use the appropriate units, millimetre (mm), micrometre (μm)
and nanometre (nm).
1.1 5 Define resolution and magnification and explain the differences between these terms, with reference to light microscopy and electron
microscopy.
1.2 1 Recognise organelles and other cell structures found in eukaryotic cells and outline their structures and functions.
1.2 2 Describe and interpret photomicrographs, electron micrographs and drawings of typical plant and animal cells.
1.2 3 Compare the structure of typical plant and animal cells.
1.2.4 State that cells use ATP from respiration for energy-requiring processes.
1.2.5 Outline key structural features of a prokaryotic cell as found in a typical bacterium.
1.2.6 Compare the structure of a prokaryotic cell as found in a typical bacterium with the structures of typical eukaryotic cells in plants and animals.
1.2.7 State that all viruses are non-cellular structures with a nucleic acid core (either DNA or RNA) and a capsid made of protein, and that some
viruses have an outer envelope made of phospholipids.
Answers to activity 1
Feature Light microscope Electron microscope
Source of radiation Light Electrons
Wavelength of radiation used 400 – 700 nm (longer) About 0.005 nm (shorter)
Maximum resolution 200 nm (lower) 0.5 nm (higher)
Lenses Glass Electromagnets
Specimen Living, non-living or dead Non-living or dead
Stain Coloured dyes Heavy metals
Image Coloured Black and white
Answers to activity 2
Structures in an animal cell that can be seen with the electron microscope but not with the light
microscope include:
• In the nucleus → chromatin can be distinguished (i.e. seen in much greater detail).
• Nucleus → surrounded by a double membrane (envelope) with pores in it.
• Mitochondria → has a surrounding double membrane (envelope), the inner layer forming finger-like
folds pointing inwards.
• Endoplasmic reticulum → some with ribosomes (rough) and some without (smooth).
• Small structures seen under the light microscope can be distinguished by the electron microscope as
lysosomes and vesicles.
• Free ribosomes → seen throughout the cell.
• Centriole → seen to be two separate centrioles.
• Microvilli → seen as finger-like extensions of the cell surface membrane.
• Microtubules → visible in the cytoplasm.
Answers to activity 3
Structures in an animal cell that can be seen with the electron microscope but not with the light
microscope include:
• In the nucleus → chromatin can be distinguished (i.e. seen in much greater detail).
• Nuclear membrane → seen as a double structure (envelope).
• Rough endoplasmic reticulum is continuous with the nuclear membrane.
• Nuclear pores are visible.
• Extensive rough and smooth endoplasmic reticulum throughout the cell.
• Free ribosomes → visible in the cytoplasm.
• Microtubules → visible in the cytoplasm.
• Mitochondria → has a double membrane (envelope) with the inner layer having folds into the matrix.
• Chloroplasts → have a double outer membrane (envelope).
• Grana → seen in the chloroplast as stacks of sacs connected to other grana by longer sacs (thylakoids).
Micrographs
Micrographs: a picture taken with the aid of a microscope.
Photomicrographs: a photograph of a specimen as seen with a light microscope.
Electron micrograph: a photograph of a specimen as seen with an electron microscope.
Why do cells need to be stained?
Many of the cell Not all cells need to be
contents are stained. The
colourless and chloroplast that
transparent so they contain chlorophyll
need to be stained (green pigment) are
with coloured dyes to easily visible without
be seen. The staining in b).
chromatin in the
nuclei is heavily
stained in a).
a) Photomicrograph of b) Photomicrograph of
human cheek cells cells in a moss leaf
Measuring size and calculating
magnification
Magnification is the number of times larger an image of an object is than the real size of the
object.

Observed size of the image

Magnification =
Actual size
I
M =
A
Measuring cell size

To calibrate the eyepiece graticule,

a miniature transparent ruler
called a stage micrometer is
placed on the microscope stage
and is brought into focus.

The eyepiece graticule is It commonly has subdivisions of

placed in the microscope 0.1 and 0.01 mm. The images of
eyepiece so it can be seen the stage micrometer and the
at the same time as the The cell measures 20 eyepiece eyepiece graticule can then be
object being measured. units (60 – 40 = 20). superimposed (placed on top of
This eyepiece graticule We won’t know the actual size of one another).
has 100 divisions. the eyepiece units until the
eyepiece graticule is calibrated.
Calculating magnification
1) In the eyepiece graticule shown in the previous slide, 100 units measure 0.25 mm.
Calculate the value of each eyepiece unit.

2) Convert your answer in 1) to micrometres (μm)

3) If the diameter of a cell is measured as 20 eyepiece units, what is the actual diameter?
Calculating magnification answers
1) In the eyepiece graticule shown in the previous slide, 100 units measure 0.25 mm.
Calculate the value of each eyepiece unit.
0.25
The value of each eyepiece unit is = 0.0025 mm.
100

2) Convert your answer in 1) to micrometres (μm)

0.0025 mm x 1000 = 2.5 μm.

3) If the diameter of a cell is measured as 20 eyepiece units, what is the actual diameter?
20 x 2.5 μm = 50 μm.
Calculating magnification
Calculate the magnification of the drawing of the
plant cell labelled P.

The actual length of the cell is 80 μm.

Calculating magnification
1. Measure the length of cell P in mm.

2. Convert mm to μm so that all measurements

are in the same units.

3. Use the equation to calculate magnification.

Activity
1. Calculate the magnification of the drawing of the animal cell in Figure 1.4.

2. Calculate the actual length of the chloroplast labelled X in Figure 1.34.

Using a scale bar to calculate
magnification
1. Measure the scale bar in Figure 1.12.
32.5 mm

2. Convert mm to μm so that all measurements are in the

same units.
32.5 mm x 1000 = 32 500 μm

3. Use the equation to calculate magnification.

M = I/A
M = measured scale bar / measurement given on scale bar
M = 32 500 / 6
Figure 1.12
M = x 5417
Calculating the real size of an object from
its magnification
Figure 1.20 shows parts of three plant cells magnified x
5600. Calculate the actual length of the labelled
chloroplast in this electron micrograph.

1. Measure the chloroplast.

23 mm

2. Convert mm to μm so that all measurements are in the

same units.
23 mm x 1000 = 23 000 μm

3. Use the equation to calculate magnification.

M = I/A Figure 1.20
5600 = 23 000 / A
A = 4.1 μm
Activity: exam-style question no. 9 pg. 40
The electron micrograph shows part of a secretory cell from the pancreas. The cell
contains many secretory vesicles → these are Golgi vesicles. They appear as
small, roughly circular structures with black circular contents. The magnification is
x 8000.

Copy the table. Calculate the actual sizes of the structures listed in the table. Use
a ruler with mm divisions to help you. Show your measurements and calculations.
When you have your answers, complete the table with the required information.
Give your answers in micrometres.

Structures Observed diameter

Actual size
(measured with ruler)
Maximum diameter of a Golgi vesicle

Maximum diameter of nucleus Mitochondrion

Maximum length of the labelled
mitochondrion