Microorganisms PDF

# Microorganisms ## What are Microorganisms? - A wide variety of living organisms live among us and also inside us. - Some are large, while some are small enough to be seen only under a microscope. - The tiny ones include millions of single-celled organisms called microorganisms or microbes. - Som...

# Microorganisms ## What are Microorganisms? - A wide variety of living organisms live among us and also inside us. - Some are large, while some are small enough to be seen only under a microscope. - The tiny ones include millions of single-celled organisms called microorganisms or microbes. - Some of them are useful, while others are harmful and may cause diseases. ## Types of Microorganisms There are five major groups of microorganisms, they are: - Bacteria - Viruses - Protozoa - Fungi - Algae ## Bacteria - Bacteria were among the first living things to appear on the Earth. - They can be found in almost all environments and inside organisms. - Bacteria are of several shapes. - Some are spherical (cocci), some are spiral (spirilla) and some are rod-shaped (bacilli). - Examples of bacteria include Streptococcus and Lactobacillus. ## Viruses - Viruses infect all life forms. - They come in various shapes and sizes, and can be seen only with the help of powerful microscopes. - Some examples of viruses are the papillomavirus, which can cause cancer, and the varicella zoster virus (chickenpox virus). ## Protozoa - Protozoa are single-celled organisms that thrive in soil and aquatic environments. - Amoeba and Euglena are some examples of protozoa. ## Fungi - Fungi are plant-like organisms that do not contain chlorophyll. - Some examples of fungi are mushrooms and yeast. ## Algae - Algae include single-celled and multicellular organisms. - They are simple plant-like organisms found in water bodies, rocks and snow. - Spirogyra and Chlorella are some examples of algae. ## Milestones in the discovery of Microorganisms - Antonie van Leeuwenhoek (1632-1723), a Dutchman, first observed microorganisms with the help of his newly invented microscope. - Louis Pasteur (1822-1895), a Frenchman, discovered that microorganisms in the air spoil food. He concluded that they are the cause of fermentation and decay, and also the main cause of diseases. - Robert Koch (1843-1910), a German, designed techniques for handling bacteria that are used to this day. He studied the disease anthrax in cattle and proved that it was caused by specific microorganisms that spread the disease from infected animals to other healthy animals. - Joseph Lister (1827-1912), an Englishman, was a famous surgeon. He was the first to eliminate bacteria from the operating theatre by using carbolic acid, a disinfectant. This greatly improved the chances of a patient surviving an operation. ## Where are Microorganisms Found? - Microorganisms are found in almost every kind of environment, including inside other organisms! - A single gram of soil can contain anywhere from 100 million to 1000 million bacteria, while the collections of dead cells on your scalp contain 500 million or more bacteria. - The air you breathe, the clothes you wear, your skin, fingernails, and even your intestines, harbour microorganisms. ## Conditions for the Growth of Microorganisms - Different Microorganisms have different needs; they grow under a wide range of conditions. ### Oxygen - Many microorganisms require oxygen for respiration (are aerobic). - However, many others, like yeast and the tetanus-causing bacterium, do not require oxygen for respiration (are anaerobic). ### Water - Moisture is essential for most microorganisms to thrive. ### Suitable Temperature - Some microorganisms can tolerate and grow at extreme temperatures of –10 °C or above 100 °C. - But in general, microorganisms thrive between 25 °C and 38 °C. ### Dark Places - Many microorganisms thrive in dark places. - Direct sunlight often kills them. - However, photosynthetic microorganisms need light to grow. ### Suitable Food Supply - Microorganisms live and feed on a wide range of materials. - Some are saprophytes (most fungi and some bacteria) and are responsible for the decay and decomposition of dead organisms. - Others, like some bacteria, fungi and protozoa, are parasites and obtain food from the tissues of their host organisms. - Some bacteria, protozoa and algae can photosynthesise. ## Useful Microorganisms - Microorganisms are useful to us in many ways. ### Increasing Soil Fertility - Bacteria and fungi decompose dead organisms and organic matter like dung, straw and grass. - They thus enable the nutrients in dead organisms and organic waste to go back to the soil. - This not only prevents the accumulation of dead organic matter in the soil but also increases soil fertility. - Microorganisms have a very important role to play in the fixing of nitrogen. - Plants such as beans, peas and soya bean, belonging to the legume family, have swollen parts in their roots called nodules. - Different species of Rhizobium bacterium live in these swellings and convert nitrogen to ammonia. - This process is called nitrogen fixation. This helps to make the soil rich in nitrogen compounds, which are essential for the growth of plants. - Let us look at nitrogen fixation in detail. ### Nitrogen Fixation - Nitrogen is the most abundant element (makes up nearly 78% of the volume of air) in the Earth's atmosphere. - It is a vital element for living organisms since it is a component of important molecules such as proteins. - However, atmospheric nitrogen cannot be used directly by most organisms. - Plants can use nitrogen only in the form of nitrate ($NO_3^-$) or ammonium ($NH_4^+$) compounds. - But these compounds are available in limited quantity in the soil. - As crop plants generally require relatively large amounts of nitrogen for their growth, these compounds in the soil get used up. - Some bacteria convert atmospheric nitrogen to ammonia ($NH_3$). - Some nitrogen-fixing bacteria convert ammonia into nitrites, and others convert nitrites into nitrates. - This process is called nitrification. - The latter bacteria are called nitrifying bacteria or nitrifiers. - They make the soil rich in nitrates. - Many bacteria and fungi decompose organic matter and release fixed nitrogen for reuse by other organisms. - All these processes contribute to the nitrogen cycle. ### Nitrogen Cycle - As you have read, nitrifying bacteria fix ammonia in the soil in the form of nitrates. - In addition, small amounts of nitrogen and oxygen combine in the atmosphere during lightning to form nitrogen oxides. - The same happens during combustion in factories or in engines of motor vehicles. - These oxides react with rain water to form dilute nitric acid. - The nitric acid reacts with minerals in the soil to form nitrates. - Plants take in nitrates through their roots and assimilate them into proteins. - Animals obtain the proteins they need by eating plants or the flesh of other animals. - When plants and animals eventually die, the nitrogen compounds - proteins and so on—are broken down to give ammonia. - This process is known as ammonification. - The ammonia produced can enter different processes. - Some bacteria directly break down ammonia to release atmospheric nitrogen. - Nitrifying bacteria convert (fix) ammonia into nitrates. Nitrates may be stored in humus and taken up again by plants or leached from the soil and carried to lakes and streams. - They may also be converted to free nitrogen by denitrifying bacteria through a process called denitrification. - The nitrogen is returned to the atmosphere. - This process of circulation of nitrogen between the atmosphere, soil, plants and animals is called the nitrogen cycle. ## Cleaning the Environment - Raw sewage containing faeces and urine is a health hazard. - Bacteria break down raw sewage into harmless and even useful substances, which can be used in landfills. - They can also be used to replenish the soil with nitrates and phosphates, and also improve the soil’s water retention capacity. - In the villages of some countries like India and China, biogas fermenters are used to produce methane. - Human and animal faeces and leafy waste from crops are broken down by bacteria in the absence of oxygen (anaerobic conditions) to produce methane (biogas), a valuable fuel for cooking and lighting.