Topic 2: The microscope and its use
A microscope is an instrument that produces enlarged images of small objects, allowing them to be viewed at a scale convenient for examination and analysis.
The image may be formed by optical, acoustic, or electronic means, and it is received by direct imaging, electronic processing, or a combination of these methods. The microscope may be static, in which the object is viewed directly, or dynamic, in which the image is built up by successive scans of the object.
The magnifying power of a microscope is an expression of the number of times the object being examined appears to be enlarged. Magnifying power is a dimensionless ratio. The resolution of a microscope is a measure of the size of the smallest detail on the object that can be observed. Resolution is expressed in linear units, usually millimetres.
The most familiar type of microscope is the optical, or light, microscope, in which lenses are used to form the image. Optical microscopes can be simple, consisting of a single lens, or compound, consisting of several optical components in tandem. Simple optical magnifiers may have magnifying powers of from 1 to 10 magnitudes, with resolutions to about 0.01 millimetre (mm) possible. Compound optical microscopes have magnifying powers ranging from about 2.5 to 1,000 magnitudes and provide resolutions of 0.01 to 0.0002 mm.
There are two major types of microscopes: the light microscope and he electron microscope but the one that is usually used in school laboratories is the light microscope.
The light microscope uses light to pass through a tiny sliced specimen. It can magnify specimen to 400 times.
The electron microscope uses electrons and can have a magnifying power of over 4000 times.
The object to be studied is called the specimen and is placed on a piece of glass called the glass slide.
The glass slide is then mounted onto the stage of the microscope.
The mirror is adjusted so that it reflects light from a nearby window to the eye piece.
The magnification required is determined by any of the three power objectives mounted on to the turret.
A specimen can be seen by adjusting the coarse adjustment knob.
In high power a specimen can be seen clearly by adjusting the fine adjustment knob.
Some specimens are simply mounted on to the stage and studied for example pollen grains.
However, there are others where is need to put a drop of water and then cover the specimen using a cover slip for example the cells of an onion skin and tiny aquatic organisms that may move off the glass slide.
Control of the amount of light is done by the use of the diaphragm below the stage.
If the specimen has parts that are hard to see, it is stained with suitable dye.
PARTS OF A LIGHT MICROSCOPE
N.B: Microscopes are carried with two hands: one grasping the arm of the microscope and the other supporting at the base.
Always begin examining slides using the low power objectives.
Even when using monocular (one eye piece) microscopes, learn to keep both eyes open.
Magnification: The image seen under the microscope is larger than the specimen on the slides; so the specimen has been magnified.
Magnification is a number that express the number of times that a specimen has been increased in size.
For example: The egg of frog is 1.25mm and when viewed under the microscope, the diameter of the image was 5cm. Calculate the magnification.
Magnification = size of specimen ¸size of image
5cm ¸ 1.25mm
50mm ¸ 1.25mm = 40
\Magnification = X40
Magnification power of a microscope equals to the magnification power of the eye piece X the magnification power of the objective lens used.
For example: If the objective lens used is X4 and the eye piece lens is X10, then total magnification is 4X10 = X40.
Other magnifying lenses or glasses may be used when studying larger specimens in details for example the leg of an insect. The lens is moved up to a point when the image is most clear. The magnification on these magnifying glasses is usually indicated on the lens.
Very tiny organisms are measured in micrometers (µm). 1000µm = 1mm i.e. 1,000,000µm = 1m.
A student completes her biology research work with a microscope, a book and a computer.
Other types of microscopes utilize the wave nature of various physical processes, the most important being the electron microscope, which uses a beam of electrons in its image formation. Electron microscopes have magnifying powers of 1,000 to 1,000,000 magnitudes possible, with resolutions ranging from 0.001 to 0.000 000 01 mm. Special microscopes, such as acoustic microscopes or scanning tunneling microscopes, use other physical effects, further extending the range of objects that can be viewed. Indeed, with a scanning tunneling microscope, even individual molecules and atoms can be seen. Some of these specialized microscopes, as well as the more common optical and electron microscopes, are described in this article. A brief history of microscopy is also included.
Activity
Name the parts of the Microscope below
Study Activity
OBJECTIVE QUESTIONS.
Circle the correct answer.
1.
The scientist who introduced a binomial system of classification is:
(a) Darwin.
(b) Linnaeus.
(c) Pasteur.
(d)
Aristotle.
2.
Animals with backbones are called:
(a) invertebrates.
(b) arthropods.
(c) vertebrates.
(d) phylum.
3.
Scientific classification sorts organisms into very large groups and then
sub-divides these groups into smaller units. Which is the correct sequence?
(a) Phylum (or division), genus, kingdom, family, species, class.
(b) Class, species, family, kingdom, genus, phylum (or division).
(c) Phylum (or division), kingdom, genus, class, species, family.
(d) Kingdom, phylum (or division), class, family, genus, species.
4. Which of the following groups consists entirely of arthropods in Figure I?
(a) Q, P, N and M.
(b) M, N, P and 0.
(c) N, P, 0 and Q.
(d) M, P, 0 and Q.
5.
Which of the animals in Figure 1 is a mammal?
(a) M.
(b) N.
(c) P.
(d) Q.
6.
Which of the following keys correctly identifies animal M in Figure 1?
(a) Fins present.
(b) Shell present.
(c) Legs present (8 legs).
(d) Antennae present.
7.
Which of the following is a feature of the echinoderms?
(a) Smooth exoskeleton:
(b) Radial symmetry.
(c) Jointed legs.
(d) Soft segmented body.
8.
Which of the following features distinguish mammals from other vertebrates?
(a) Sweat glands.
(b) Internal fertilization.
(c) Pentadactyl limb.
(d) A notochord.
Figure 2.
9. Which of the following groups consists entirely of coelenterates in Figure 2?
(a)R,
S and T.
(b)
R,TandU:
(c)S, T and U.
(d) R, U and S.
10. In Figure 3 which of the foI1wirg groups consists entirely of echinoderms?
(a)
K, Land M.
(c) K, I, and N.
(b)
K, M and N.
(d) L, M and N.
11. In Figure 3 which of these animals is a true worm?
(a) K.
(b) M.
(c) L.
(d) M.
12. Which of the following is not a crustacean?
(a) Barnacle (c) Crab
(b) Lobster. (d) Sea anemone.
13. Which of the following is not a fish?
(a) Skate.
(b) Barnacle
(c) Crab
(d) Lobster.
(e) Sea anemone.
14.
Which of the following is not a bird?
(a) Bat.
(b)
Duck.
(c) Penguin.
(d)
Heron.
15.
Which of the folIosing is not an insect?
(a) Grasshopper
(b)
Cyclops.
(c) Dragonfly
(d) Butterfly
16.
Which of the following is not a flat worm?
(a) Plananan,
(b)
Coral.
(c) Tapeworm.
(d) Liver-fluke.
17.
Which of the following is not a mammal?
(a) Antelope.
(b)
Kangaroo.
(c) Bat.
(d)
Leech.
18.
Which of the following is not a inolluse?
(a) Land snail.
(b)
Slug.
(c) Sea-cucumber.
(d) Oyster.
19.
Which of the following is not a reptile?
(a) Tortoise.
(b)
Beetle.
(c) Lizard.
(d) Snake.
20,
Which cellular bodies are concerned with protein synthesis?
(a) Centrosomes.
(b) Ribosomes.
(c) Nucleoli.
(d) Mitochondria.
21.
Protein material of cells is a polymer of:
(a) amino-acids. (b) hexoses,
(c) peptides. (d) glycine.
22.
The organs concerned with photosynthesis are:
(a) vacuoles. (b) chloroplasts.
(c) chlorophyll. (d) mesophyll.
23.
Which one of the following structures would you not find in cytoplasm?
(a) Centrioles. (b) Chromosomes.
(c) Kinetosomes. (d) Mitochondria,
24.
Which structures in the cell are the sites where respiratory energy
transformations are carried out?
(a) Centrioles. (b) Chioroplasts.
(e) Golgi bodies. (d) Mitochondria.
25.
Which of the following structures is not present in the cells oi higher plants?
(a) Centrosome. (b) Golgi bodies.
(e) Endoplasmic reticulum, (d) Mitochonciria.
26.
The nucleolus in a cell nucleus is a spherical body concerned with:
(a) transport of food materials within the cell.
(b) Maintaining the shape of the nucleus.
(c) Synthesis of DNA.
(d) Protein synthesis in the cell.
27.
Which of the following structures has only been found in animal cells when
viewed with an electronic microscope?
(a) Lysosomes. (b) Nucleoli.
(c) Chioroplasts. (d) Mitochondria.
28.
A biologist discovered a new living cell in a culture with a distinct cell wall
but one definite nucleus. The cell is likely to be that of:
(a) a bacterium. (b) an animal.
(c) a protozoa. (d) a plant.
29. Which of the following is made of mainly non-myelinated nervous tissue?
(a) White matter of the central nervous system
(b) Cranial nerves:
(c) Spinal nerves.
(d) Automatic nerves.
30.
Which is the major component of bone tissue?
(a) Calcium fluoride.
(b) Calcium carbonate.
(c) Magnesium chloride.
(d) Calcium phosphate.
31.
The correct order of increasing complexity in an organism is:
(a) Organ cell system.
(b) Cell organ tissue.
(c) Tissue organ system.
(d) System tissue cell.
32. Which of the following is the least unspecialised plant tissue?
(a) Sclerenchyma.
(b) Chlorenchyma
(c) Collenchvma.
(d) Parenchyma.