12 Explain the concept of cardinal temperatures and their relationship to different groups of micro

Since bacteria grow in many environments from artic oceans to hot springs, it is not surprising that the optimum growth temperatures vary. Bacteria from the human gut grow well at body temperature (37 C) but bacteria from plants may be killed at that temperature. Hospital incubators are often set at 37 C. It is safer for the home experimenter to work with non-pathogenic bacteria from plants, fruit, soils, and water and these usually grow best at room temperature.

Temperatures: Optimum, Minimum, Maximum

Optimum = Temperature at which the bacterium grows most rapidly

Minimum = Temperature below which no growth occurs

Maximum = Temperature above which no growth occurs

Psychrophilic = Cold loving; optimum growth at 15 - 20C

Mesophilic = middle living; optimum growth at 30 - 37 C

Thermophilic = heat loving; optimum growth at 50 - 60 C

Psychrophiles are commonly isolated from cold waters and bottoms of lakes and oceans. Many grow well at 0 - 4C and some at -7 if solutes added to depress freezing point.

Mesophiles are the the most common bacteria. Saprophytes grow best around 30 and the parasitic species aaround 37C. Every species grows over a wide range. Saprophytic have a wider range than parasitic species. Two species may have an optimum at 37, but one may grow from 5 to 45 and the othr may only grow from 25 to 40.

Thermophiles were first found in hot springs and heating piles of hay and manure. They are fairly widespread in nature. They present a problem in pasteurizing milk because they grow at the temperatures intended to kill. Some cause canned foods to spoil because they produce highly thermo-resistant spores.

6.Describe the structure and function of valve. Av and sl

A heart valve normally allows blood flow in only one direction through the heart. The four valves commonly represented in a mammalian heart determine the pathway of blood flow through the heart. A heart valve opens or closes incumbent upon differential blood pressure on each side.[1][2][3]

The four valves in the heart are:[4]

The two atrioventricular (AV) valves, which are between the atria and the ventricles, are the mitral valve and the tricuspid valve.

The two semilunar (SL) valves, which are in the arteries leaving the heart, are the aortic valve and the pulmonary valve.

A form of heart disease occurs when a valve malfunctions and allows some blood to flow in the wrong direction. This is called regurgitation.

Atrioventricular or cuspid valves

These are small valves that prevent backflow from the ventricles into the atrium during systole. They are anchored to the wall of the ventricle by chordae tendineae, which prevent the valve from inverting.

The chordae tendineae are attached to papillary muscles that cause tension to better hold the valve. Together, the papillary muscles and the chordae tendineae are known as the subvalvular apparatus. The function of the subvalvular apparatus is to keep the valves from prolapsing into the atria when they close.

Mitral valve Also known as the "bicuspid valve" because it contains two flaps, the mitral valve gets its name from the resemblance to a bishop's mitre (a type of hat). It allows the blood to flow from the left atrium into the left ventricle. It is on the left side of the heart and has two cusps.

Tricuspid valve The tricuspid valve is the three-flapped valve on the right side of the heart, between the right atrium and the right ventricle which stops the backflow of blood between the two. It has three cusps.

Semilunar valves These are located at the base of both the pulmonary trunk (pulmonary artery) and the aorta, the two arteries taking blood out of the ventricles. These valves permit blood to be forced into the arteries, but prevent backflow of blood from the arteries into the ventricles. These valves do not have chordae tendineae, and are more similar to valves in veins than atrioventricular valves.

Aortic valve The aortic valve lies between the left ventricle and the aorta. The aortic valve has three cusps. During ventricular systole, pressure rises in the left ventricle. When the pressure in the left ventricle rises above the pressure in the aorta, the aortic valve opens, allowing blood to exit the left ventricle into the aorta. When ventricular systole ends, pressure in the left ventricle rapidly drops. When the pressure in the left ventricle decreases, the aortic pressure forces the aortic valve to close. The closure of the aortic valve contributes the A2 component of the second heart sound (S2).

Pulmonary valve The pulmonary valve (sometimes referred to as the pulmonic valve) is the semilunar valve of the heart that lies between the right ventricle and the pulmonary artery, and has three cusps. Similar to the aortic valve, the pulmonary valve opens in ventricular systole, when the pressure in the right ventricle rises above the pressure in the pulmonary artery. At the end of ventricular systole, when the pressure in the right ventricle falls rapidly, the pressure in the pulmonary artery will close the pulmonary valve.

As the heart muscle contracts and relaxes, the valves open and shut, letting blood flow into the ventricles and atria at alternate times. The following is a step-by-step illustration of how the valves function normally in the left ventricle:

After the left ventricle contracts, the aortic valve closes and the mitral valve opens, to allow blood to flow from the left atrium into the left ventricle.

As the left atrium contracts, more blood flows into the left ventricle.

When the left ventricle contracts, the mitral valve closes and the aortic valve opens, so blood flows into the aorta.