In the topic Classification I you learnt about the use of a hand lens. The hand lens is a device used to magnify objects in order to see them much more clearly.
Test yourself to see how much of the hand lens you can remember by naming the parts of the hand lens in the figure below.
By the end of this lesson you should be able to:
State the purpose of the light microscope.
Identify parts of the light microscope and state their functions.
Use and care for the light microscope.
Calculate magnification when using the light microscope
A Light Microscope
The Light Microscope
In Primary Science, you learnt about water-borne diseases which are caused by tiny living things in water. The tiny living things cannot be seen by the unaided eye or the hand lens. The microscope, an instrument with greater magnifying power, is used. A microscope gives finer details of tiny objects. The commonly used microscope in schools is the light microscope.
The light microscope uses light for illumination of the specimen to be viewed. It is therefore important to know the parts of the light microscope, functions of these parts and care for the microscope.
FUNCTIONS OF PARTS OF LIGHT MICROSCOPE
Eye piece lens: Used to magnify the specimen under view Coarse adjustment knob: Raises or lowers the body tube for focusing Fine adjustment knob: Raises or lowers the body tube for sharp focusing.
Body tube: Holds the eye piece lens and the revolving nose piece in position. Revolving nose piece: Holds the objective lens in position enabling changes from one objective lens to the other. Objective lens: Magnifies the specimen. Limb: Supports the body tube and the stage
Base/Stand: Provides steady support. Stage: Where specimen on a slide is placed. It has two clips to hold slide in position during viewing. Diaphragm: An opening which regulates the amount of light passing through condenser to illuminate the specimen. Mirror: Reflects light through condenser to the specimen.
Use of the Light Microscope
The microscope is used as follows:
Prepare the specimen to be observed.
Place the microscope on the bench, with the stage facing away from you.
Turn the low power objective lens into position. Ensure that the diaphragm is fully open.
Look through the eye piece lens with one eye while adjusting the mirror under the stage to allow enough light.
Place the slide with the specimen (already prepared) on the stage and clip the slide into position.
Look through the eye piece while ensuring enough light passes through the specimen.
Bring the low power objective lens to the lowest point using coarse adjustment knob until the specimen comes into focus.
Use fine adjustment knob to bring image into sharp focus.
Turn the medium power objective lens in position and adjust the focus using the coarse knob. For sharper images, use the fine adjustment knob.
If more details are required, turn the high power objective lens into position then use only the fine adjustment knob to bring the image into sharp focus.
Observe and draw what you see under the microscope. Work out and write the magnification beside the drawing
The videos next illustrate how to use and care for a light microscope.
You are able to see microscopic structures under the microscope because such structures are magnified. The extent of the magnification is a a product of eyepiece and objective lens magnifications.
Thus when using the microscope the magnification of the object/specimen viewed is given by multiplying the eyepiece lens magnification by the objective lens magnification.
Eyepiece lens magnification
X Objective lens magnification = Total Magnification.
However the term magnification is broader. It refers to the extent to which the specimen size has been changed. Image observed may be smaller or larger than the actual specimen. In either case, it is still a magnification.
CARE FOR THE MICROSCOPE
When using the microscope the following points should be observed:
Do not place the microscope too close to the edge of the bench/table.
When carrying the microscope, always use two hands.
To clean dirty lenses, special soft lens tissue paper or tissue paper moistened with ethanol is used.
The low power objective lens should click into position before and after use of a microscope. This helps to avoid damaging of objective lenses.
Clean and store the microscope in a safe place free from moisture and dust.
In Primary science you studied about water borne diseases such as typhoid and cholera. You learnt that such diseases are caused by tiny living organisms which cannot be seen using the unaided eye. These are therefore called microscopic organisms or microorganisms.
The microscope is used to observe such organisms.
By the end of the lesson you should be able to:
Identify the components of a cell as seen under the light microscope.
Identify the components of a cell as seen under the electron microscope and relate their structure to functions.
Compare plant and animal cells as seen under the microscope.
Cell Structure The basic unit of a living organism is the cell. A cell is a microscopic structure, that is, it can not be seen using the unaided eye. A microscope is used to observe cells.
Unicellular organisms, for example amoeba and bacteria are made up of only one cell. Multicellular organisms, for example humans, elephants and trees are made up of billions of cells. The main features of a plant and animal cell, as seen through a light microscope, is given next.
Cell Structure as Seen Under the Light Microscope
Under the light microscope only a few parts of the cell can be seen, as in the animal and plant cells below.
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