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MICROSCOPES
Two main types of microscopes exist: The light and electron microscopes.
The light microscope increases the ability to see minute objects using lens systems which
magnify images of specimens using light.
Light microscopes widely used in schools contain two lenses, the _________________
and _____________________ lenses, and are referred to as compound microscopes.
•
Total magnification of the image is determined by multiplying the individual eyepiece
and objective lens magnification values.
•
All images are presented in two dimensions.
A typical light microscope
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Summer School – Year 11 Biology – Book 1
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The light microscope is composed of numerous parts. Complete the following table outlining
microscope parts and their functions:
Microscope Part(s)
Function
Stage
Provide variation in image magnification
Coarse focus
Fine focussing of the image, particularly under high
magnification
Iris diaphragm
Condenser
To adjust the view under a light microscope you can increase the magnification, use the fine
focus adjustor or adjust the light using the iris diaphragm or condenser.
Stains
Particular stains improve the visibility of structures within a cell. Unfortunately, the cell dies
with their application.
E.g.
Iodine: _____________________________________________________________
Methylene Blue: _____________________________________________________
Electron Microscopes
The electron microscope uses beams of electrons to reveal complex internal structures of
cells, or to magnify the surface textures of specimens.
•
Transmission electron microscope (TEM): is used to reveal the internal detail of
stained dead cells.
•
Scanning electron microscope (SEM): provides detailed images of surfaces of dead
cells or specimens.
Resolution is a measure of the image detail or clarity of an image produced by a particular
microscope, i.e. the minimum distance required to distinguish between two lines. The human
eye has a minimum resolution of 0.1 mm.
Interesting differences in the powers of resolution between light and electron microscopes
exist.
 The School For Excellence 2016
Summer School – Year 11 Biology – Book 1
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Complete the following table of comparison between light and electron microscopes:
Light Microscope
Electron Microscope
Light
Electrons
Resolution
200 nm
0.2 nm
Specimens
Living or dead, true colour,
staining if desired
Thickness
Thin – fixation not required
Used to Create Image
Magnification
•
Very thin – fixation required
Fluorescence microscopes detail chemicals in cells, such as DNA.
(Campbell NA & JB Reece, 2002)
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Summer School – Year 11 Biology – Book 1
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Determining the size of a cell:
•
Measure width/diameter of field of view (FOV).
•
Estimate no. of cells that fit across FOV.
•
Divide FOV by number of cells that would fit across FOV.
Field of View (FOV)
Cell
Diameter of FOV
At 100x magnification, field of View might be 1.5 mm. That would equal 1500 µm.
•
The number of this type of cell that would fit across the FOV would be about four.
•
Therefore the approximate width of one cell would be 1500 µm/4 and would be 375 µm.
SHAPES OF CELLS
Cells are all three-dimensional and can vary in shape and size (nearly all are microscopic).
Being microscopic ensures that a cell has a high surface area (cell membrane) to volume
ratio. This results in the cell being efficient at exchanging substances.
When viewing cells with a microscope, the view seen is two dimensional and only a section
of the cell.
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Summer School – Year 11 Biology – Book 1
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QUESTION 1
Draw how a plant cell in the shape of a cylinder will appear if sliced in the directions as
shown:
C
B
A
(a)
(b)
(c)
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When viewing a cell under the microscope, one section may contain a nucleus while another
section from the same cell may not. Biologists often take many sections in the one plane
from a cell to determine what is inside the cell.
EXAMPLE
A
B
C
(a)
(b)
(c)
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SURFACE AREA TO VOLUME RATIO
In determining the surface area : volume of an organism or cell, its surface area needs to
be compared to its volume.
Surface area (SA) refers to the area of the outer covering of the cell or organism.
Volume (V) refers to the amount of space taken up by the cell or organism.
The ratio is achieved by calculating the total SA and dividing it by its total Volume.
•
A smaller organism/cell will have a greater SA:V compared to a larger one.
•
In terms of a cell, SA:V refers to the number of units of cell membrane (SA) that are
available to each unit of volume (cytoplasm).
•
The SA:V determines how quickly substances, or heat energy, can be
absorbed or released from a cell or organism.
For example:
Size of object
Surface Area
Volume
SA:V ratio
Rate of Diffusion
1 cm sided cube
6 cm²
1 cm³
6.0 : 1
Quick
10 cm sided
cube
600 cm²
1000 cm³
0.6 : 1
Slow
Hence, as an object increases in size, its SA:V decreases.
The shape can also affect the SA:V ratio.
For example:
Shape of Container
Surface area
Volume
SA:V ratio
Rate of
Diffusion
Sheet of paper
(100 x 100 x 0.1 cm)
10,040 cm²
1,000 cm³
20.4 : 1
Rapid
Cube
(10 x 10 x 10 cm)
600 cm²
1,000 cm³
0.6 : 1
Slow
Sphere
(6.2 cm radius)
483 cm²
1,000 cm³
0.5 : 1
Slow
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Consider the following three shapes:
large SA:V
very large SA:V
low SA:V
•
The SA:V of an object/cell increases as its shape becomes flatter. A sphere has the
lowest SA:V of all shapes.
•
The SA:V of an object/cell increases as its size decreases. Hence, by being
microscopic in size, cells ensure that they gain nutrients and excrete wastes efficiently.
TYPES OF CELLS
All cells can be divided into two main groups: prokaryotic and eukaryotic cells. Any
persistent structure that has a particular function within either cell type is referred to as an
organelle (e.g. nucleus, ribosomes etc.). Organelles do not have to be membrane-bound,
e.g. ribosomes.
PROKARYOTIC CELLS
Prokaryotic organisms were the first to evolve on Earth. All prokaryotes are primitive in
structure, and smaller than eukaryotic cells. The following list includes features of prokaryotic
cells:
•
No membrane-bound nucleus. A circular DNA molecule floats freely in the cytoplasm,
and is not bound by a membrane. Most also possess smaller rings of DNA (plasmids).
•
No membrane bound organelles are present.
•
Free floating ribosomes are required for protein synthesis.
•
Can be photosynthetic (cyanobacteria) as they can contain free floating chlorophyll.
•
Divide by binary fission.
•
Examples are bacteria and cyanobacteria (blue-green algae).
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EUKARYOTIC CELLS
Eukaryotic cells are thought to have evolved from prokaryotic cells hundreds of millions of
years ago. They possess membrane-bound organelles, such as nuclei, in addition to their
non-membrane-bound organelles, such as ribosomes.
Eukaryotic cells:
•
Possess a distinct nucleus enclosed in a double membrane.
•
Contain membrane-bound organelles.
•
(e.g. mitochondria, golgi apparatus, etc.)
•
Possess ribosomes.
•
Found in animal, plant, fungi and protoctist kingdoms.
•
Divide by mitosis.
•
In multicellular organisms cells communicate by chemical means, and perform
cytoplasmic streaming.
scienceblogs.com
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THE FIVE KINGDOMS
Animalia:
Includes all vertebrate (e.g. mammals, reptiles etc.) and invertebrate animals
(e.g. insects, jellyfish etc.). All members are multicellular eukaryotic
heterotrophs (must consume organic nutrients to survive).
Plantae:
Includes flowering and non-flowering plants. All members are multicellular,
eukaryotic autotrophs (i.e. synthesise their own organic nutrients).
Fungi:
Includes all unicellular and multicellular fungi. All are eukaryotic heterotrophs
with cell walls of chitin.
Protista:
Unicellular eukaryotic organisms.
Monera:
Consists of all known prokaryotic cells.
All living organisms are classified into five Kingdoms. Each kingdom has particular cellular
characteristics:
KINGDOM
Monera
Protista
* unicellular
* prokaryotic
* unicellular
* eukaryotic
Fungi
Plants
Animals
Examples
Distinguishing
Features
* uni/multicellular
* heterotrophs
* chitin cell wall
*multicellular
* autotrophs
* multicellular
* heterotrophs
* motile
Tick the boxes below when the feature listed on the left
is part of a cell representative of the kingdom.
Cytoplasm
Nucleus
Cell Membrane
Cellulose Cell Wall
Chitin Cell Wall
Other Cell Wall
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Animalia:
•
Includes all vertebrate (e.g. mammals, reptiles) and invertebrate (e.g. insects, jellyfish)
animals.
•
All members are eukaryotic.
•
Heterotrophic and motile.
Plantae:
•
Includes flowering and non-flowering plants.
•
All are eukaryotic (e.g. Banksias, mosses).
•
Cellulose cell walls.
•
Autotrophs.
wild-wonders.com
Fungi:
•
Two main groups: Unicellular fungi (e.g. yeast) and multicellular fungi with thread-like
hyphae (e.g. mushrooms).
•
All are eukaryotic.
•
Chitin cell walls.
•
Heterotrophic
123rf.com
Protista:
•
Unicellular organisms.
•
Aquatic.
•
All are eukaryotic (e.g. Amoeba, Paramecium, Euglena).
Monera:
•
Simplest kingdom (has been divided by many
scientists into more kingdoms).
•
Prokaryotic cells (e.g. bacteria and cyanobacteria).
answersingenesis.org
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