Identifying Characteristics of Yeast, Mold, Protozoa and Rickettsia


Yeast are group of non-mycelial unicellular fungi belonging to the group Ascomycetes. They are cosmopolitian fungi which occur in almost all places of the world having organic matter, especially sugars. Most of the species are saprophytes. They grow on the nectar of flowers, surface of sweet fruits, sugarcane, milk and other food stuffs, animal excreta, humus of soil etc.

In general, yeast cells are longer than most bacteria. Yeast vary considerably in size ranging from one to five μm in width and from 5 to 30 μm or more in length. They are commonly egg shaped but are sometimes lemon shaped, pear shaped or elongated into false or true mycelium. Yeast have no flagella and other organelles of locomotion. Read more

Bacterial Structures Internal to Cell Wall and Reproduction

The bacterial structures internal to cell wall includes cytoplasmic membrane, protoplast, spheroplast, spores, plasmid and others.

Fig: Structure of bacteria ( uploads/2015/ 02/B9780323069380000062_gr2.jpg )

Cytoplasmic membrane: This is a thin structure that completely surrounds the cell. Its size is approximately 7.5 nm in thickness and is composed primarily of phospholipid (20 – 30 %), protein (60 – 70 %). The phospholipid form bilayered structure in which most of the protein are embedded tightly called integral protein. This protein can only be removed by destruction of the membrane with treatment such as with detergent. Other protein which are loosely attached are called peripheral protein. This peripheral protein can be easily removed mild treatment such as osmotic shock. Read more

Morphology of Bacteria and its Structures External to Cell Wall

The morphology of bacterial cell includes characteristics such as size, shape, structure etc. First of all, Leeuwenhoek revealed the gross appearance of microorganism including bacteria by light microscope. By the discovery of electron microscope in early 1940’s the study of structural bacterial cell has been made very easier. The morphological characteristic of a bacterial cell is as follows.

Size: Bacteria vary in size from cell to cell. It can be as small as 0.1 to 0.2 μm in width to as large as more than 50 μm in diameter. A few very large prokaryotes such as Epulopiscium fishelsoni [1] that inhabits the intestinal tract of Surgeon fish  are up to 50 μm in diameter and can be more than 0.5 mm in length. However, the dimension of an average rod cell prokaryotes E.coli are about 1×3 μm. Read more

Comparison of Refrigerants and its Ideal Properties

For refrigerants to be ideal, it should possesses following properties
1. Low boiling point
2. Low freezing point
3. High critical pressure and temperature (to avoid large power requirement)
4. Low specific heat (high specific heat decreases refrigerant effect per kg or refrigerant.
5. High latent heat (increases refrigerant effect per kg of refrigerant)
6. Pressure in evaporator and condenser should be low enough to reduce material cost and must be positive to avoid leakage of air into the system.
7. Low specific volume to reduce size of compressor.
8. High thermal conductivity to reduce area of heat transfer in evaporator and condenser.
9. Non-flammable, non-explosive, non-toxic and non-corrosive.
10. High miscibility with lubricating oil and should not have reacting property with lubricating oil in the temperature range of system.
11. High coefficient of performance (COP) to reduce cost of system
12. Readily available and cheap Read more

Refrigerants and its Types

Any substance that absorbs heat through expansion or vaporization may be termed a refrigerant. In broad sense, refrigerant is also applied to secondary cooling medium as brine solution or cold water. As commonly interpreted, however, refrigerant includes only those working medium which passes through cycle of evaporation, recovery, compression and liquefaction. Thus circulating cold mediums, ice and solid carbon dioxide are not primary refrigerants. The primary refrigerants directly take part in refrigeration system whereas secondary refrigerants are first cooled with the help of primary refrigerant and are further used for cooling purposes.

Fig: Refrigerants (

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Working Principle of Expansion Devices and its Types

Expansion devises are used in between evaporator and condenser in refrigeration system. These devices meters and regulates the flow of liquid refrigerant to an evaporator. The expansion device have following specific functions.
1. To reduce the pressure of liquid refrigerant coming from condenser.
2. To maintain desired pressure difference between high pressure and low pressure side of the system.
3. Capacity expansion devices are used to maintain the desired rate of flow and pressure drop across the system.
4. To control the flow of refrigerant according to variation of load on the evaporator. Read more

Working Principle of Condenser and its Types

High side equipment: The pressure of the refrigerant in the condenser is very little that at the compressor discharge. The pressure at compressor discharge is higher than at any other part of the system. Hence the condenser and other equipment in the system between compressor discharge and expansion valve are referred to as high side equipment.

Low side valve equipment: Since the refrigerant in the evaporator is at low pressure compared to that in the condenser, the evaporator and auxiliaries between the expansion valve and the compressor intake are often referred to as low side equipment. Read more