Assignments to do:

I Remember:

1. Letter combinations qu are pronounced as [qw]: quickly

2. – ant, - ent are suffixes of adjectives: elegant, different

II Read the words paying attention to their pronunciation:

Requirement, quality, question, quantity, quest, quite, square, squirrel.

III Read and translate to the following words:

Impotent, distant, present, significant, different, important, opponent.

IV Learn the names of chemical elements and compounds:

Carbon, nitrogen, sulfur, phosphorus, oxygen, hydrogen sulfide, phospholipids,

phosphorus, potassium, magnesium, calcium, iron, copper, molybdenum, zinc.

V Read and translate the text about classification of organisms:

Chemical Requirements for Growth of microorganisms

Chemical requirements include sources of carbon, nitrogen, sulfur, phosphorus, oxygen, trace elements, and organic growth factors.

Besides water, one of the most important requirements for microbial growth is carbon. Carbon is the structural backbone of living matter; it is needed for all the organic compounds that make up a living cell. Half the dry weight of a typical bacterial cell is carbon. Chemoheterotrophs get most of their carbon from the source of their energy organic materials such as proteins, carbohydrates, and lipids. Chemoautotrophs and photoautotrophs derive their carbon from carbon dioxide.

Some important bacteria, including many of the photosynthesizing cyanobacteria, use gaseous nitrogen directly from the atmosphere. This process is called nitrogen fixation. Some organisms that can use this method are free-living, mostly in the soil, but others live cooperatively in symbiosis with the roots of legumes such as clover, soybeans, alfalfa, beans, and peas. The nitrogen fixed in the symbiosis is used by both the plant and the bacterium.

Sulfur is used to synthesize sulfur- containing amino acids and vitamins such as thiamine and biotin. Important natural sources of sulfur include the sulfate ion, hydrogen sulfide, and the sulfur-containing amino acids. Phosphorus is essential for the synthesis of nucleic acids and the phospholipids of cell membranes. Among other places, it is also found in the energy bonds of ATP. A source of phosphorus is the phosphate ion. Potassium, magnesium, and calcium are also elements that microorganisms require, often as cofactors for enzymes.

Microbes require very small amounts of other mineral elements, such as iron, copper, molybdenum, and zinc; these are referred to as trace elements. Most are essential for the functions of certain enzymes, usually as cofactors. Although these elements are some- times added to a laboratory medium, they are usually assumed to be naturally present in tap water and other components of media. Even most distilled waters contain adequate amounts, but tap water is sometimes specified to ensure that these trace minerals will be present in culture media.

Microbes that use molecular oxygen (aerobes) produce more energy from nutrients than microbes that do not use oxygen (anaerobes). Organisms that require oxygen to live are called obligate aerobes.

Essential organic compounds an organism is unable to synthesize are known as organic growth factors; they must be directly obtained from the environment. One group of organic growth factors for humans is vitamins. Most vitamins function as coenzymes, the organic cofactors required by certain enzymes in order to function. Many bacteria can synthesize all their own vitamins and do not depend on outside sources. However, some bacteria lack the enzymes needed for the synthesis of certain vitamins, and for them those vitamins are organic growth factors. Other organic growth factors required by some bacteria are amino acids, purines, and pyrimidines.