THE MICROSCOPE Summarized

This Should Take Just An Hour To Study, But Don't  Worry If It Takes More Than Expected As We All Learn At A Different Pace.

THE LIGHT MICROSCOPE

The microscope is used to see tiny objects that are invisible to the naked eye. It uses lenses to magnity the object to tocus (display) it in greater detail. A very good light microscope can magnity about 1500 times, and can show many of the important structures in animal and plant cells. The discovery and the introduction of the microscope have significantly contributed (more than any other instrument) to the development and understanding of Biology as a science. There are two types of microscopes named after the source of illumination: the light microscope and electron microscope. The light microscope is the one that you are going to use in your Biology laboratory, it's the one suitable at your level for now. Most cells are too small to be seen even if you use a magnifying glass or a hand lens, a cell would only appear as big as a full stop. You need a microscope to see the detailed structure of cells. The most common type of microscope used in schools and colleges is called a light microscope, as shown in the following figure below,  The name 'light microscope' means that light is passed through the specimen that is being studied

The Functions Of The Parts Of The Microscope (You only need to know 11 parts and functions of the microscope at your level,  which we'll discuss below)

1) Tube

the microscope image is viewed through the tube with the aid of an eyepiece (one in a monocular microscope and two in a binocular microscope)

2) Eyepiece  

the image projected by the objective is further magnified when viewed through this lens

3) Arm

the central element integrating all the mechanical and optical components to form the complete microscope, it supports the body tube and is the part you can grasp to carry the microscope

4) Base  

acts as a stand for a microscope and gives the microscope eafirm, steady support

5) Objective lenses 

form a magnified image of the objective in the intermediatei image plane, there are three objective lenses to choose from: lovw power objective, medium power objective and high power objective

6) Stage 

supports the slide that is clamped into position by means of clips, the stage has a hole in it that allows light to shine up through the specimen

7) Coarse adjustment 

moves the tube and lenses up and down to approximately the right position so that the specimen is in focus, this knob is used only with the low power objective lens

8)Fine adjustment

moves the tube and lenses up and down to put the specimen at the right position so that the specimen is perfectly focused, it is used to achieve fine focus with the high power and medium power objectives

9) Light source 

a bulb that supplies light, it is situated inside the base of the microscope

10) Iris diaphragm 

a hole under the stage that regulates the amount of light that goes through a specimen on the stage, it collects light and illuminates the specimen

11) Mirror  

has a flat surface on one side and concave surface on the other side that it is used to reflect light up through the specimen on the stage

Biological Drawing

In the written alternative to the practical examination, you are sometimes provided with a photograph of an organism and asked to make an accurate drawing of it. You can practise drawing in your notebook, using animals or plants that occur in and around where you live. You should try to concentrate on the features that adapt the organism to its surroundings, such as reduced leaf size or a protective shell. When you draw the features of any organism, you should draw accurate proportions and accurate numbers of subunits. Your drawing should be large - at least half of the available space on your paper. Use a sharp pencil and a clean rubber. It must also be accurate and clear. One way to draw accurately is to measure the important features of the organism, so that the features will be in proportion. "Note it! What does accurate mean? For example the human foot normally has five toes. A drawing showing more or fewer toes would be inaccurate, and could mean a loss of marks"

Size And Magnification

Someone looking at your drawing should be able to find the real or actual size of the organism from information given on your drawing. It the organism is large enough, you could use a ruler to measure its size. Measure each feature, such as body length or height, then measure this distance on your paper. You can measure features, such as the diameter of an eye, or the length and width of a leaf. The more measurements you take from a specimen, the more accurate your drawing will be. if the organism is about the same size as the paper, you could draw it the actual size. The number of times the drawing is bigger or smaller than its actual size is known as magnification. It is shown on drawings as, for instance, x2, if your drawing is twice as big as the organism, or x0.5, if it is half the actual size. You may use any other magnification that is appropriate, but you must state it to your drawing. For example, if the organism you are drawing is bigger than the paper, you must reduce or scale down your drawing from life size. If the organismis is 1 m high, you could represent each metre in real life with 100 mm on your drawing. The resulting drawing would be one-tenth the size of the organism, and would be represented as a magnification of one-tenth (x0.1). If the organism you are drawing is very small (for example, a fly that is 10 mm long), you could choose to represent every millimetre in real life by 10 mm on your drawing. Then the fly in your drawing would be 100 mm long. You could write on your drawing that the magnification is ten times (x 10).

Tips For Drawing

• Make your drawing as large as possible to fill the available space

• You Will be rewarded marks for accurate observations, correct proportiols, clear, sharp outines and labels

• If you are drawing a feature, such as the outline of a cell, the lines should be clear, sharp and join up smoothly

• Do not shade or colour your drawing, as this can cover up detail and make the drawing less accurate

• If you are drawing an organism with a complicated, repetitive structure, sucn as the branches and twigs on a tree, you do not need to draw them all-only one or two to show detail. Indicate the general outline of the entire tree, and then draw accurate details ot individual structures, such as leaves, flowers, fruit and bark in greater detail. Do not forget to label the features on your drawing and give it a title

• Label lines:
must be inpencil
must touch the part you want to identify
may not cross
should be on one side of the drawing only, if possible
must be straight lines no arrows

• Labels must be:
printed
in pen

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