A microscope is an instrument used to produce enlarged images of small objects. The most common kind of microscope is an optical microscope, which uses lenses to form images from visible light. The optical microscope has been a standard tool in life science as well as material science for more than one and a half centuries now. The optical microscopes are of two main types:
a) Simple Microscope b) Compound Microscope
Figure 1. Parts of a simple microscope
The simple microscope is generally considered to be the first microscope. It was created in the 17th century by Antony van Leeuwenhoek, who combined a convex lens with a holder for specimens, magnifying between 200 and 300 times.
The structure of a simple microscope is very simple. It has a body, a stage made of thick glass for placing slides, two clips to fix the slides, a handle, an eyepiece placed with the handle and a mirror. There is an adjustment knob by which the eye piece may be moved upward and downward. The entire body stands on the base or foot.
How to handle the simple microscope?
At first the slide is to fix on the stage with the help of clips. The light should be focused on the slide by moving the mirror. Then keeping the eye in the eye piece the adjustment knob should move in such a way that the eyepiece comes to a position from where the object on the stage can be seen most clearly. At this position, keeping the eye in the eyepiece, the specimen is to be observed carefully, or if required be dissected with the help of forceps or needle whichever is convenient.
Principle: A simple microscope works on the principle that when a tiny object is placed within its focus, a virtual, erect and magnified image of the object is formed at the least distance of distinct vision from the eye held close to the lens.
Figure 2. Working of a simple microscope When an object is placed between the principle focus and the optical centre of a convex lens a virtual, erect and magnified image is formed. The ray diagram is given here explains how an object looks enlarged when viewed through a bi-convex lens. Observe that the object and the image are on the same side of the lens. Image is formed at the least distance of distinct vision from the eye i.e., the distance from the object is approximately equals to 25 cm.
Magnification of Simple Microscope
The magnifying power of a simple microscope is given by:
m = 1 + D/f
D = least distance of distinct vision
F = focal length of the convex lens
The focal length of the convex lens should be small because smaller the focal length of the lens, greater will be its magnifying power. Also, the maximum magnification of a simple microscope is about 10, which means that the object will appear 10 times larger by using the simple microscope of maximum magnification.
Limitations of using a light microscope: Visible light restricts the amount of resolution achieved with a light microscope. Magnification may range from 500x to 1500x. In general, light microscopes require specimens to be thin, small and transparent for optimum viewing. The diffraction limits the resolution to approximately 0.2 µm.
Uses of a simple microscope:
2. A light microscope is also referred to as a?
a) Electron microscope
b) Compound microscope
c) Scanning problem microscope
3. On the microscope stage, what is used to hold the glass slide in place and prevent it from moving?
a) Stage clip
c) Fine adjustment knob
4. Ocular lens
a) Is used to regulate the amount of light on the specimen
b) You look through to see the specimen
c) Projects light upwards through the diaphragm, the specimen, and the lenses
5. What happens when light passes through a condenser lens?
6. What does the objective lens do?
7. What is the maximum magnification of a light microscope?
8. What is the maximum resolution of a light microscope?
9. What are the advantages of a light microscope?
We all know that in autumn and/or fall season, the leaves start to change color from green to red, yellow, and brown. The mixture of red, purple, orange and yellow is the result of chemical processes that take place in the tree as the seasons change from summer to winter. My 5-year-old kid always ask me “Why and how do leaves change colors during fall?”
To explain this, let us first understand the function of leaves. The food-making process takes place in leaves in numerous cells containing chlorophyll, which gives the leaf its green color. Chlorophyll has a vital function: it captures solar rays and uses the resulting energy in the manufacture of the plant’s food — simple sugars which are produced from water and carbon dioxide. These sugars are the basis of the plant’s nourishment — the sole source of the carbohydrates needed for growth and development. In their food-manufacturing process, the chlorophyll break down, thus are being continually “used up”. During the growing season, however, the plant replenishes the chlorophyll so that the supply remains high and the leaves stay green.
How plants make food during fall season without chlorophyll pigments?
During fall, because of changes in the length of daylight and changes in temperature, the leaves stop their food-making process. The chlorophyll breaks down, the green color disappears, and the yellow to orange colors become visible.
The steps below describe how the leaves change color during fall/autumn season:
Growing season of plants
Color of leaves are green due to chlorophyll pigments
Lack of sunlight energy
Degradation of chlorophyll pigments
The pigments carotenoids and anthocyanins that have been present (along with the chlorophylls) in the cells all during the leaf’s life begin to show through. These provide colorations of yellow, brown, orange, and purple colors, respectively.
A fun and educational video by SciShow Kids explains why do leaves change color in fall?
I have mentioned below a science experiment that describe the leaf color changing phenomenon in detail.
Suggested science experiment books
Water is essential for life. It covers 2/3 of the earth’s surface and every living thing is dependent upon it. The human body is comprised of over 70% water, and it is a major component of many bodily fluids including blood, urine, and saliva. Water – with its formula H2O – is the only inorganic compound existing in its solid, liquid and gaseous physical state under natural conditions. Water serves as a medium for the transformation of highly complex organic molecules that form the basis for life processes. The solid state of water is known as ice; the gaseous state is known as water vapor (or steam). The units of temperature (formerly the degree Celsius and now the Kelvin) are defined in terms of the triple point of water, 273.16 K (0.01 °C) and 611.2 Pa, the temperature and pressure at which solid, liquid, and gaseous water coexist in equilibrium.
The above video explains the important properties of water
Two important properties of water are discussed below:
What does it mean to say the water molecules is polar and is a “universal solvent?”
Water has high surface tension, what does this mean?
At an interface between air and water, a water molecule on the surface forms hydrogen bonds with other molecules around and below it, but not with air molecules above it. The unequal distribution of bonds produces a force called surface tension; this causes the water surface to contract and form a surprisingly tough film or ‘skin’.
Examples of surface tension:
Walking on water: Small insects such as the water strider can walk on water because their weight is not enough to penetrate the surface.
Floating a needle: A carefully placed small needle can be made to float on the surface of water even though it is several times as dense as water. If the surface is agitated to break up the surface tension, then needle will quickly sink.
Surface tension disinfectants: Disinfectants are usually solutions of low surface tension. This allow them to spread out on the cell walls of bacteria and disrupt them.
Soaps and detergents: These help the cleaning of clothes by lowering the surface tension of the water so that it more readily soaks into pores and soiled areas.
Washing with cold water: The major reason for using hot water for washing is that its surface tension is lower and it is a better wetting agent. But if the detergent lowers the surface tension, the heating may be unneccessary.
Why bubbles are round: The surface tension of water provides the necessary wall tension for the formation of bubbles with water. The tendency to minimize that wall tension pulls the bubbles into spherical shapes.
Surface Tension and Droplets: Surface tension is responsible for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a spherical shape by the cohesive forces of the surface layer.
Let us explore some properties of water at surfaces with 2-3 activities. The materials needed are:
Fill a cup all the way to the top with water.
What do you think would happen if you were to add pennies to it?
Try adding pennies one at a time. What happens to the water in the cup?
How many pennies can you add without causing the water to overflow?
The video below demonstrates cohesion and surface tension in water. We add pennies into a full glass of water to show how surface tension will create a convex dome of water that rises above the rim of the glass. Surface tension is generated by cohesion and keeps an elastic tension between all the molecules in a liquid. The water has one of the highest surface tension.
Take some water with a straw and put a few drops on plastic wrap.
(a) What is the shape of the drop?
(b) Move a drop around with your straw. Does the drop change?
“Scientific inquiry starts with observation. The more one can see, the more one can investigate.” What are you waiting for, share with us your observations through comments.
Are you familiar with the chemical processes that govern our lives? Let us try to solve the questions about the study of the chemistry of living things and seek to understand the roles these play in developing and sustaining life.
What is Biochemistry?
The term biochemistry, which is the chemistry of life or the study of the processes behind all living organisms, was first coined in 1903 by Carl Neuberg, the father of biochemistry. Biochemistry is everywhere. General topics in biochemistry include: medicine, nutrition, molecular biology, and plant and animal biology. It deals with the structures and functions of cellular components such as proteins, carbohydrates, lipids, nucleic acids and other biomolecules.
Video: A brief and concise introduction to biochemistry. What is it? What does it involve? And why is it important?
Career prospects in Biochemistry
Although each occupation a biochemistry degree holder might work for has its own employment outlook, the statistics bureau predicts the employment of biochemists will increase 31 percent from 2010 to 2020, much faster than the average for all occupations. But as biochemists are in a small field, the growth will create only 7,700 new jobs over that time. The growth will be due to the demand for new medicines and medical procedures, cleaner energy, better crop yields and effective ways of protecting the environment.
2017 Salary Information for Biochemists
Biochemists earned a median annual salary of $82,180 in 2016, according to the U.S. Bureau of Labor Statistics. On the low end, biochemists earned a 25th percentile salary of $58,630, meaning 75 percent earned more than this amount. The 75th percentile salary is $117,340, meaning 25 percent earn more. In 2016, 31,500 people were employed in the U.S. as biochemists. The salary details of the year 2017 can be studied at https://www.payscale.com/research/US/Job=Biochemist/Salary.
As a scientific discipline in its own right, biochemistry has a major impact on all areas of the life sciences and biochemists are in high demand among employers. Keep following my website for next blog article on basics of biochemistry.