听听学科学/微生物
< 听听学科学
Microbes, are microorganisms. Single celled microorganisms, were the first forms of life, to develop on earth. This happened, 3 to 4 billion years ago. For 3 billion years, all organisms, in earth were microorganisms. So, during most of the history of our planet, the only form of life, was microorganisms. The first organisms, were single celled organisms. That is, the whole organism, had only one cell. Multicellular organisms, developed much later. Algae,a form of seaweed, is one of the earliest forms, of plant life. Other complex organisms, like plants and animals, evolved much later.
Till about the 17th century, we did not know of the existence, of microorganisms. Early scientist noticed, that small organisms and insects emerged, from decaying matter. When a plant or animal died, and decayed, they noticed small living things, coming out of it. They came to the conclusion, that decaying matter spontaneously gives birth, to new life. This was not surprising because, we could not study, what we could not see. Microorganisms, are a few microns in size. We cannot see them with a naked eye. But, things changed, with the discovery of the microscope. We could now see, what we could not see earlier. Antoine Van Leeuwenhoek's discovered microorganisms, in 1675. Louis Pasteur was a French chemist, and micro biologist, who lived in the 19th century. He extensively worked, on microbes. He made remarkable discoveries, of the cause, and prevention of diseases. He was the first to propose, the germ theory of diseases. The term, pasteurisation of milk, comes from him. He refined the concept, of vaccination. His discoveries, led to saving countless lives. He is known as the, father of micro biology.
The terms Microbes, is generally used to describe, any microscopic organisms. Microscopic organisms are a few microns, in size. The study of microorganisms is called, micro biology. Microbes, can be unicellular, or multi cellular. Most of them are usually, unicellular. They can be Prokaryotes, or Eukaryotes. Prokaryotes are cells, which don't have a nucleus. Eukaryotes are cells, which have a nucleus. Some eukaryotes, can be micro organisms. But, they are very small in number. In contrast, all prokaryotes are microorganisms. Bacteria and archaea, are prokaryotes. Viruses, are on the border of life. But micro biology, includes the study of viruses.
We usually, have a bad impression, about microbes. This is because, some micro organisms, causes us, to be ill. So, we tend to think that, all microbes cause diseases. This is not at all true. Most of the microbes, in our planet, are symbiotic to life. Most of the microbes are beneficial, to life. Microbes are found, in all the places, in the planet. Microbes are found in water, soil, air, inside rocks, in deep seas and also in plants. They are found, inside animals and human beings. Let us get an idea, of the amount of bacteria, that is present around us. There are typically, 40 million bacterial cells, in one gram of soil. There are, one billion bacterial cells, in one litre of, fresh water. This means, that there is bacteria all around us, but we cannot see it.
The number of microbes, on earth, is estimated to be, 5 million, trillion, trillion. This works out to be, 5 multiplied by, 10 to the power of 30, microbes in earth. If we weigh all the microbes, we will get the biomass of the microbes. Amazingly, the bio mass of microbes exceeds, the bio mass of all plants, and animals in earth.
Now we understand that, we have to give due weight, to the importance of micro organisms. Modern scientific thinking, understands the crucial role of microbes, in the bio sphere.
Most microbes, belong to the kingdom of, bacteria and archaea.
The disease Malaria, is caused by, a pathogenic protozoa. There are many microbes, in the kingdom of Protista. Amoeba, is a microbe in the kingdom, of Protista. It is a relatively bigger microbe, and can be observed. Amoeba, is usually found in water. Amoeba, has an interesting peculiar habit, of wrapping themselves around food, and eating it. This process is called, "phagocytosis".
There are many microbes, in the kingdom of Fungi. Yeast, belongs to the kingdom, of Fungi. Yeast is used, in baking and brewing, since ancient times.
There are not, many microbes in the kingdom of plants. Most plants have, large and complex structure. But, some green algae, are photosynthetic Eukaryotes, that exist in microscopic form. There are not many microbes, in the kingdom of animals. Microscopic anthropoids like, dust mites are rare examples of, microbes in the animal kingdom.
Viruses are, on the border of life. We will discuss viruses, along with other microbes.
Almost all bacteria are, invisible to the naked eye. Bacteria usually are, a few microns in size. As of now, we have no idea of the total number, of bacterial species, that exists in earth. Estimates vary widely, from 10 million to 1 billion. We have classified about, 1000 species of bacteria. Prokaryote bacteria, do not have a nucleus, but they do have D N A. This is typically, a circular chromosome, located in a body, called Nucleoid. This Nucleoid, is in the cytoplasm of, the bacterial cell. The bacterial cell, is surrounded, by a cell membrane. The cell membrane, is also called, as a plasma membrane. This membrane encloses, the contents of the cell, in the cytoplasm. Bacteria do not usually have, membrane bound organelles, in their cytoplasm. They also do not have, a mitochondria, or chloroplast. But they have ribosomes. In most bacteria, the plasma membrane, is surrounded by a, cell wall. The cell walls are, like the fortress walls. Scientists give a lot of importance, to the cell walls of bacteria. This is because, fighting a bacteria, is usually done by, weakening the cell wall. Once the cell wall, is weakened, it makes it easier, for antibacterial agents, to attack the bacterial cells.
Some bacterial species, are spherical. They are called, cocci. Some are, rod shaped. They are called, bacilli. Some are, comma shaped. They are called, vibrio. Some are, spiral shaped. They are called, Spirilla. We may wonder, why all this fuss, about how bacteria looks. The shape of the bacteria, is one way by which, micro biologists identify a bacteria, when viewing them through a microscope. Of course, there is more than one criteria, to identify a bacteria. There are other steps to, uniquely identify them. Example of one such test, is a gram test.
Most bacteria exist, as single cells. Some form pairs, and are called diploids. Others form, a cluster, like a bunch of grapes. The bacteria staphylococcus, is an example of this cluster type.
Bacteria reproduce asexually. One bacterial cell, divides into two daughter cells. This is called, binary fission. Bacterial cells, can experience, exponential growth.
The Microbes, that cause diseases, is called as pathogens. In common terminology, we call them as germs. In our discussion, in this module, we will use the term, germs also. In this context, germs can be taken to mean, pathogenic microbes. Some examples of major diseases, caused by pathogenic bacteria, are. Plague. Tuberculosis or TB. Cholera. Syphilis. Leprosy. Tetanus. Typhoid. Diphtheria. These diseases, were the cause, of millions of deaths. Bacteria also cause, some minor illness, which we are familiar with. Examples are. Sinusitis. Gastritis. Food Poisoning. Urinary tract infection.
Some illnesses are caused by The disease Malaria, is caused by a pathogenic protozoa, called plasmodium. An example of a disease, caused by microbial fungi, is ring worm.
Virus is a microbe, which is in the border of life. The crucial difference between, viruses and other microbes is, Viruses cannot, reproduce on their own. They need a host cell, to replicate themselves. The host for a virus could be a plant or animal, including human beings.
Many viruses are pathogenic. One such example, of a pathogenic virus, is the smallpox virus. Millions of people have died, due to smallpox infection.
Viruses are, even smaller than bacteria. They are about, a few nano meters, in size. They cannot be seen, with an optical microscope. They do not have, nuclei, mitochondria, or ribosomes. But, they do have, a small strand of D N A, or R N A. This strand of nucleic acid, D N A or R N A, is the core, of the virus. It has a protein coating on it, called the capsid.
Some viruses can, even infect good bacteria. A virus, which infects bacteria, is called a bacteriophage.
Usually, viruses infect, only one type, of host. Viruses that infect plants, are harmless to animals. Viruses that infect animals, are harmless to humans. Some examples of serious illness, caused by viruses are. Aids. SARS. Hepatitis C. Rabies. Meningitis.
Pathogenic microbes can be transmitted, in multiple ways. Some microbes are, transmitted through air. These microbes enter our system, when we breathe. Many common cold viruses, are transmitted this way.
Some microbes get, injected into our blood. For example, a mosquito carrying a virus, can inject it in our blood, when it bites us. When a hair dresser, uses a pre used razor, it can potentially transmit, a virus. The needle used, to give an injection, or even a tattoo, is a potential source for, transmitted viruses.
Harmful microbes can be present, in infected foods. When we eat these foods, we can get infected. Microbes can also be transmitted, by contact with infected people, or objects. Infections caused by microbes, like viruses, can spread, very rapidly. When some people, get infected, the infection gets passed on, to other people. These other people, in turn pass it on, to more people. When there is a large scale infection, of a population, we call it an epidemic. If it spreads worldwide, we call it a pandemic.
There are many ways, we can protect ourselves, from pathogenic microbes, or pathogens. Some are, natures own methods. Some are, by human intervention. We will take our human body, as an example, for discussions.
The skin of the body, is the excellent first line of defence. It provides, an almost impenetrable biological barrier, for our internal environment.
Mucus and cilia, found in the nose and throat, can catch foreign microbes. The digestive system, of the human body, is completely insulated, from the rest of the body. Though, we have billions of bacteria, in the digestive system, The internal organs, of the body, and blood, are sterile. That is, they do not have microbes, in normal conditions. Only when we get infected, and get ill, that these parts, of the body, have germs.
The natural human immune system, can be considered as, the second line of defence. The blood in our body has, red blood cells, and white blood cells. The white blood cells, play a big role, in the immune system, of the body. There are five types, of white blood cells. 1. Neutrophil. 2. Eosinophil. 3. Basophil. 4. Lymphocyte. 5. Monocyte.
When you see the results of a blood test, you can look out for these friendly cells. These cells, are like an army, of friendly Doctor Soldiers, of our body. These white blood cells, recognise foreign bodies like, pathogenic microbes. They also attack, and kill these pathogens. They employ, different strategies, for doing this. One simple strategy, is simply, to eat the pathogenic cell. These cells are, called phagocytes. Phagocytes, eat or ingest the, pathogens. The meaning of macrophages, is big eaters. Macrophages also ingest, harmful microbes, or pathogens. In the process of ingesting harmful microbes, the friendly doctor soldier white blood cells, might die. They literally give their life, to protect us.
Sometimes, we have a mild infection. These are easily handled by, the immune system. In most cases, we will not even be aware, that we have been infected. When there is a severe infection, it is like a large scale invasion. Germs cells are capable of, replicating and multiplying, very fast. When the severe infection takes place, more white blood cells are created, to combat it. This results in a large scale battle, between the friendly soldier white cells, and the invading pathogens. In the heat of the battle, the temperature of the body, might go up. This is commonly referred to, as fever. Within limits, fever is actually a good sign, that the immune system, is doing its job. When the infection is too severe, for the immune system to handle, it requires human intervention. It is always a good idea, to consult a doctor to know, when this is required.
There are many immune cells, which we inherit. Some are passed on, from mother to baby. Some immune cells, are manufactured by the body. Since There are some immune cells, which are specific, to a particular pathogen, or illness. There are hundreds, even thousands, of types of germs, that could infect us. Each type of germ, can cause a different type of illness. It is amazing to know that the body, can manufacture specific cells, to combat every type of germ, it encounters. They are called, antibodies. The body can literally remember, most of the germs, that infected it once. If the same germ infects us again, the immune system responds much faster, to create antibodies for it. For example, if we had chicken pox infection, when we were young, it is unlikely, that we will ever get it again. We need to be thankful, to our immune system, and friendly doctor soldier cells, for our good health. In fact, having a strong immune system, is one of the good ways, to be healthy.
There are many simple ways, by which we can protect ourselves, from harmful pathogens. We will discuss, only a few of them. Many germs spread, through contact. Washing our hands frequently, specially before meals, is one simple hygienic practice. Personal cleanliness, and a clean environment, is another important hygienic practice. Not exposing food, to germs or insects, is another good hygienic principle. Food exposed to insects, like mosquitoes, are specially prone, to be infected. If we eat infected food, we are likely to become ill.
Safe drinking water is called, potable water. Germs do not tolerate, high temperatures. We can make best use of this. Boiling water, gets rid of most germs. Ultra violet or U V light, also kills germs. We can treat water, by exposing to U V light. This and other methods, are readily available, to make water safe, for drinking. Since many diseases are water borne, this is a very important, hygienic precaution.
The practise of cooking, naturally destroys germs. This is because, germs cannot live in high temperatures. Pressure cooking is specially effective, against germs.
When something is germ free, we call it sterile. Doctors and hospitals, take special precautions to maintain, a sterile environment.
In a simple sense, vaccination is a way of stimulating the bodies, natural immune system. In vaccination, we actually inject, germs into our body. However, these germs are neutralised, or weakened before injecting. What we inject, is called as a "vaccine". These inert or weak germs in the vaccine, are capable of inducing the body to produce, antibodies for the germs. These antibodies, then in turn protect the body, from infection of the same germs. Vaccination, is an inexpensive, and very effective way of guarding, against many infections. Vaccination, is normally administered, to children, at an young age. This practice is very critical, to prevent many diseases. Louis Pasteur, was one of the people, who developed, the vaccination technique. Since then, vaccines have been developed for, most of the major commonly occurring infections. This is a significant good news for all of us. You might be surprised, and saddened, to know that, 300 to 500 million people, died due to a single disease, called smallpox. You also would be glad to know that, smallpox has now been eradicated, worldwide. Similarly, thanks to wide spread vaccination, hundreds of millions of lives, have been saved. Thanks to vaccination, many of us are still alive today.
An Antibiotic, is an agent which kills harmful pathogens, or inhibits their growth. Antibiotics are man made. Penicillin, was the first antibiotic, to be discovered, by Alexander Fleming. Penicillin was effectively used, to treat gonorrhoea, strep throat, and pneumonia. Since then, scientists have developed many more antibiotics. They are effective, in treating many illness and diseases, that we encounter. Scientists are still developing, many more antibiotics for other illness, and diseases. When we take antibiotic, both the harmful bacteria, and some of the beneficial bacteria, are killed. This is normally a good trade off, since, the harmful bacteria, may be dangerous to us.
But, there is one more major criteria, to be considered. Germs are, living organisms. Like any other living organisms, they evolve. Life span of a germ, is very short. But, it replicates very fast. Every new generation of the germ, is a little more evolved, than the previous generation. Not surprisingly, germs learn to develop resistance, to antibiotics. Over a period of time, a germ might become totally resistant, to antibiotics. This has already started happening. Some germs have developed full resistance, to antibiotics. Scientists call them, "super bugs". So antibiotics, need to be used, with responsibility.
Most of us have a disease, called Germophobia. Germophobia, is a fear of germs. It is natural, that all of us, have a fear for germs. Good news is most microbes, are not harmful, to us. In fact many microbes, are beneficial to us.
The human body, has ten times more bacteria cells, than human cells. These bacteria cells are present, even when we are, in perfectly good health. These bacteria are symbiotic, or beneficial to life. They help in digesting, the food, that we eat. There are many other ways, that bacteria is useful, to the human body.
For many centuries, we knew how to use microbes. Though we did not know, that they were microbes, we knew how to make use of them. Microbes have been used in baking, pickling, and brewing. We are familiar, with a fermentation process, that happens when milk is made into curds. This bacteria, that is involved in fermenting milk into curds, is called lactobacillus.
Yeast is a microbe, belonging to the kingdom of Fungi. Yeast is used in baking bread. It is also used to ferment the dough, for making our favourite, edly and dosa. This is, one of the many beneficial microbes, that we normally eat, in our food. Beneficial bacteria, is also called as, probiotics.
Microbes, play a vital role, in our ecological system. For example, Microbes present in the soil, play a crucial role, in the nitrogen cycle. Microbes decompose organic matter, and help produce nitrogen compounds. Nitrogen fixing bacteria, present in roots of plants, convert nitrogen, into nitrogen based organic compounds. These nitrogen compounds, are used by plants, as nutrition. Other bacteria, like denitrifying bacteria, convert nitrates into nitrogen, which is released into the atmosphere. The Nitrogen cycle, plays a key role in ecology.
We are aware that, chemical pesticides can be harmful, to animals, insects, and human beings. Example, Honey Bee, is an important insect. It acts as, a pollinator. Pollinators, are required by many plants, for reproduction. Pesticides have been killing, honey bees. This has resulted in shortage, of honey bees, in many countries. Some types of Bacteria, can also be used, as a pesticide. Using bacteria, for pest control, is called biological pest control. Scientists, are still working on this. Biological pest control, is environment friendly, and does not harm animals, insects, and human beings.
We know that, water is a precious commodity. We need to recycle waste water, and reuse it. Waste water can contain, many organic substances. Bacteria, can be used to breakdown, the organic matter. The residue created, can be used as, fertiliser. Waste water treatment plants, using this principle, are already widely used.
Bacteria can be used, to convert various forms of agriculture and urban waste, into usable fuels. These bio gas reactors, can produce methane. Methane, is a combustible gas. Methane can be used, as a fuel. Bio gas plants, can be set up in a small village, or even in an apartment.
Microbes are used to produce, many organic chemicals. Some examples are. Acetic acid or vinegar. Butyric acid. Lactic acid. Citric acid.
Recent developments, allows us to study, microbes in great detail. Using an electron microscope, we can literally see the insides, of a microbe. We are now, beginning to understand, how they work, at the molecular level. Microbes, also have genes. These genes are, relatively simple. Scientist use microbes, to study genetic properties. Scientist are exploring, many more possibilities, for beneficial use of microbes. Example. Medical scientists are researching, whether drugs, can be delivered to specific cells, in the human body, using microbes. There are many uses of microbes, which are being researched. The field of micro biology, is still very very young. There is a Lot more to discover, than the little, what we already know.