Microbes. By the end of this chapter you should be able to: explain what a microbe is classify microbes as fungi, bacteria, protists or viruses describe how big microbes are describe some of the ways in which microbes are studied explain how microbes reproduce
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Microbes By the end of this chapter you should be able to: explain what a microbe is classify microbes as fungi, bacteria, protists or viruses describe how big microbes are describe some of the ways in which microbes are studied explain how microbes reproduce identify ways in which microbes can be useful or harmful.
What is a microbe? • Microbe is a term for tiny creatures that individually are too small to be seen with the unaided eye. • Microbes include bacteriafungiprotists (back-tear-ee-uh) (fun-jeye) (pro-tists). • We can also include viruses (vye-rus-is) as a major type of microbe, though there is a debate as to whether viruses can be considered living creatures or not.
Bacteria • Bacteria consist of only a single cell. • Bacteria have been found that can live in temperatures above the boiling point and in cold that would freeze your blood. • They "eat" everything from sugar and starch to sunlight, sulfur and iron. • There's even a species of bacteria—Deinococcus radiodurans—that can withstand blasts of radiation 1,000 times greater than would kill a human being
Basic Bacteria • A bacterium is a simple cell that is made up of a cell wall, cell membrane and cytoplasm. • Bacteria do not have a nucleus like animal and plant cells. • Some bacteria have tails, known as flagella, for movement.
What Bacteria Look Like • There are thousands of species of bacteria, but all of them are basically one of three different shapes. • Some are rod- or stick-shaped and called bacilli (buh-sill-eye). • Others are shaped like little balls and called cocci (cox-eye). • Others still are helical or spiral in shape, called spirilla. • Some bacterial cells exist as individuals while others cluster together to form pairs, chains, squares or other groupings.
Where are bacteria found? • Bacteria live on or in just about every material and environment on Earth from soil to water to air, and from your house to arctic ice to volcanic vents. • Each square centimetre of your skin averages about 100,000 bacteria. • A single teaspoon of topsoil contains more than a billion (1,000,000,000) bacteria.
Fungi • Fungi come in a variety of shapes and sizes and different types. • They can range from individual cells to enormous chains of cells that can stretch for miles. • Mushrooms and toadstools are probably the best known fungi and come in many colours, shapes and sizes. • Some are edible while others are poisonous. • Moulds grow on decaying food and damp surfaces such as bathroom walls. • We use yeast to make foods and drinks like bread, cereals, wine and beer. • Although fungi often look like plants they are not. • They feed on dead and decaying material, helping to return nutrients to the natural cycles of the environment.
What Fungi looks like • Fungi include single-celled creatures that exist individually—the yeasts (A)—and multicellular bunches, such as moulds (B) or mushrooms. • Moulds are described as filament-like, because they form long thread-like, strands of cells called hyphae (high-fee). • These hyphae are what give mould colonies their fuzzy appearance. • They also form the fleshy body of the mushroom
Protists • Protists (sometimes called protozoa) are single celled organisms that live in water and areas of high moisture. • Protists are alive but they are not part of the plant or animal kingdoms. • About 40,000 protists are known, only a few cause disease. • Protists are the biggest microbes • Most protists live in moist habitats.
Viruses • Virus is the Latin word for ‘poison’—viruses cause many illnesses. • Viruses are much smaller than other microbes and must be viewed under the electron microscope. • Viruses are unlike other living things. • Viruses are not complete cells that can function on their own • Viruses depend on other organisms for energy, and cannot reproduce unless they get inside a living cell
SeeingMicrobes • Most microbes are too small to see with the human eye. • Microbiologists use the Light Microscope and the Electron microscope to view microbes. • Electron microscopes are used to view objects that are smaller than 0.2 millimetres, such as viruses or cell organelles. • They magnify in the range of 10 000 to 100 000 times. • The only problem is that the images made are black and white, and live specimens cannot be viewed. V. choleraeElectron micrograph of the bacterium
Observing Microbes • Single microbes are usually too small to be seen • As colonies they are visible to the naked eye. • Using a nutrient agar medium we can grow colonies of bacteria and fungi. • Bacterial colonies are small, shiny and coloured • Fungal colonies are large and fluffy
Binary Fisson • Bacteria and Protists reproduce by binary fission • The parent cell divides into two identical daughter cells.
Budding • Yeasts reproduce • by budding. • The parent cell forms a ‘bud’ on its outer surface and a copy of everything in the cell is moved into it. • A cell wall then forms between the bud and • the parent cell, and the bud breaks away.
Invasion • A virus is only able to reproduce inside a host cell. • A host cell is any cell that the virus invades and takes over. • When a virus comes into contact with a host cell, it hijacks the cell, forcing it to become a virus factory. • When the host cell is full of new viruses it bursts open, releasing the viruses, which then go on to infect more cells. • A virus can lay dormant—or asleep—for many years without a host cell