# A-level Biology/Microbiology and Biotechnology
## Introduction to Microbiology

Microbiology is the study of the organisms in the surrounding environment which are too small to be clearly visible with our naked eye when observed individually. These organisms are called '"microorganisms"' and can only be observed through microscopes. Microorganisms are less than 0.1mm in size, which means that they are smaller in size than the visual range of humans. Microorganisms can be found everywhere on the planet Earth. They are the most abundant and diverse group of organisms on Earth. Many different groups of microorganisms currently inhabit the Earth. They possess different adaptations, specialized and differentiated functions, various forms and structures, different shapes and sizes, and numerous habitats to ensure their survival and existence on Earth. Some of the different groups of microorganisms are Bacteria, Archaea Bacteria, Cyanobacteria or Blue Green Bacteria, Protists, Algae, Fungi, Mollicutes (Mycoplasmas and Phytoplasmas), Viruses, Viroids, and Prions.
The units which are used to measure the microorganisms and their structural components are nanometers and micrometers. Due to the larger sizes of some microorganisms, they are more readily visible than the other smaller types of microorganisms. Microorganisms are found everywhere on the earth including in soil, water, air, in interior surfaces and on exterior surfaces of the earth.
Most of the microorganisms act as the primary producers of the food chains in the fresh and marine water habitats, as most of them possess the ability to perform photosynthesis. Therefore, they form the basis of the food chains in the aquatic water bodies.

### Saprotrophs and Saprophytes

The microorganisms that live in the soil, which are commonly known as the soil microorganisms possess the ability to decompose and digest the waste products and materials in the environment and also assist in the recycling of the chemical elements and compounds in between the soil, water, air and the living organisms. These soil microorganisms decompose complex organic matter into simple organic matter and then into simple organic and inorganic molecules and after that, into their constituent most basic elements either by physical breakdown or by biochemical transformation of these complex compounds. These organisms, called Saprotrophs or Saprophytes, cannot produce their own food and instead feed on the non-living, dead, organic, decaying and waste matter in order to survive. Most of the Fungi such as Rhizopus, Mucor, Agaricus, Penicillium, Aspergillus, Morchella and Saccharomyces (Yeast), some bacteria such as soil bacteria, some protozoans and some algal species such as photosynthetic algae, like green algae, exhibit saprophytic mode of nutrition.

### Bioaerosols and Pathogens

Some microorganisms are suspended and released into the atmosphere as bioaerosols, possessing the capability to travel and spread long distances with the help of the wind current and precipitation. These bioaerosols are composed of bacterial cells, their cellular fragments and remnants, fungal spores and their hyphae, viral particles, viroids, mollicutes, prions, their metabolic waste and by-products. Therefore, the pathogenic bioaerosols are capable of transmitting and spreading of most of the infectious diseases in living organisms. Only a trace number of microorganisms which are associated with the other living organisms such as plants, animals and human beings are pathogenic and cause infectious diseases. The majority of the microorganisms are beneficial and harmless to other organisms, but some are very harmful, causing infectious diseases.

### Extremophiles

Some of the microorganisms are well adapted to inhabit the extreme environmental conditions which are unfavourable and can even be lethal for the other living organisms. These microorganisms are known as extremophiles. These extremophiles can be discovered inside the crust of the Earth, in the deepest seas at high pressures, in extremely acidic or in extremely basic conditions, in hydrothermal and alkaline vents, in frozen sea water, in volcanoes, in hot water springs, in the upper atmosphere and in outer space.