Now, let us look at the physical and chemical factors that affect microbial growth. The physical factors that affect microbial growth are temperature, osmotic pressure, and Ph. Chemical factors are mainly chemical elements, Christ elements and oxygen. let us study each of these factors in detail. Shown here is the effect of temperature on the growth rate of microbes. microbes can therefore be grouped and named according to the temperature ranges in which they grow.

As one can observe each microbe has an optimal temperature as well as a minimum and a maximum temperature in which they can grow the sacrifice for example, shown here In a purple line have an optimal temperature of 10 degrees Celsius minimum around minus four degrees and a maximum of around 18 degrees centigrade. The side profiles have an optimal temperature of around 25 the mass of files around 35 the thermal files around 70 and hyper thermal files around 95. osmotic pressure is another physical factor that can affect physical growth rate of microbes. The cell cytoplasm tends to contain high solute concentration, whereas the environment contains low solid concentration Therefore, in order to bring a key briam between these two environments, water diffuses from higher solid concentration to lower solid concentration, this is known as osmosis. In a situation in which there is a higher concentration of solid outside the cell then the inside of the cell, the cell undergoes plasma cell is this.

In this case, the cell loses water in a hypertonic situation, or that is in a hypertonic solution. tonicity is the measure of osmotic pressure gradient of two solutions across a semi permeable membrane. Now, some cells like a cell wall in this diagram the cells in yellow are cells that lack a cell wall example of such cells. Are animal cells some microbial and some protozoan cells. When such a cell is placed in a hypertonic solution related to the cell cytoplasm, the cell swells up so much that it gets lized or in other words, bursts up. And so examples of hypertonic solution is freshwater.

When the same cell is placed in an isotonic solution such as blood plasma or normal sailing, it will neither swell nor shrink because there is no concentration gradient across the cell membrane. However, when such a cell is placed in a hypertonic solution, such as sea water, which has a lot of salt, these cells that have no cell walls get shriveled since water flows from The inside of the cell to the outside. Now, let us look at what happens to cells that have a cell wall. plant cells, fungi, most of the bacteria and archaea fit in this example. And those types of cells are shown in the bottom part of the panel. In a hypertonic situation, such as freshwater solution, the cell gains water from the outer environment and swells to the limits of the cell wall.

This cell does not get lized it is now turgid or normal. In an isotonic solution, such as blood plasma, or sailing, the flow of water coming inside the cell equilibrates with the flow outside of the cell. Thus the cell becomes placid in a hypertonic situation such as sea water Which is which has a high content of salt. Water flows out of the cell but as the cell retains its cell wall instead of becoming shriveled, it becomes plasma alized. These cell conditions are all due to the osmotic pressure on the cells that either have or do not have a cell wall. D hedge is another physical factor that affects microbial growth.

When it comes to pH, most microorganisms grow best at levels of neutral pH, which is around six and a half to seven and a half. A few microbes, however, require extreme pitches such as less than four, in which case they are known as acid profiles are more than 10 also known as beta files or basal philic. One thing to note in the lab is that with time the growth of microbes acidifies A medium that along with the eventual scarcity of nutrients causes an inhibition of further growth. Therefore, media in the lab needs to be changed frequently. The change of media can be done through aspiration in the case of an airborne cells shown in a or through centrifugation for non adherent cells as shown in B. Now, that we looked at physical factors, let us look at chemical factors that influence microbial growth.

Chemical elements such as carbon, nitrogen and phosphorus are needed for the nutrition and growth of microorganisms carbon in its source is usually organic materials or carbon dioxide. Carbon is the main constituent of cellular material. Nitrogen, the source of nitrogen can organic compounds are nitrogen gas. Nitrogen is involved in the synthesis of proteins amino acids DNA and RNA. phosphorus, its sources in organic phosphates. phosphorus is essential for nucleic acid synthesis and for biosynthesis of phospholipids and lippo polysaccharides LPs In short, and take like acids mainly.

Trace element a trace element as the name indicates is a chemical that is required only in minute amounts by living organisms for growth. It is usually part of a vital enzyme popper for example, is used by the enzyme which is involved in cellular respiration known as cytochrome oxidase. As I mentioned before, it's usually a metal examples of such our iron shown in a copper shown in B, and zinc shown in C, among other metals. Oxygen is another important chemical factor that affects microbial growth. When microbes are added to an urn inoculated tube of special medium, known as tired like a late medium which ends up over here. The location of the microbes within the media is based on the oxygen requirement of the microbes.

Let us look at that in detail. So, obligate on our robes will usually stay at the very top of the tire blacklight media where the oxygen levels are greatest Now, those organisms that strictly live in the absence of oxygen are earn aerobic and known as obligate anaerobes. These will be found usually at the very end of the culture too far away from the oxygen in the environment. Those are alike that like oxygen some water considered micro iro philic. These cells are located close to the top, but not at the very top of the media. Finally, those microbes that are earner robes but they can survive in aerobic conditions are called facultative anaerobes.

These cells are found spread throughout the medium. Summarize, macro organisms need physical and chemical facts for proper growth and nutrition, the physical factors are mainly temperature. And we have seen the type of thermal files and sacrifice are names of organisms that survive in extreme temperatures, osmotic pressure, and we have seen that phenomena such as licensed plasma analysis that is, and osmosis are phenomena that occur due to osmotic pressure. P hitch, we have seen that acid profiles are organisms that like low pH and then there are chemical elements such as carbon, nitrogen and phosphorus that are required for the survival and growth of the organisms. trace elements such as iron, copper and zinc which are essential for some enzymes to function and finally oxygen. So, which example we mentioned, obligate aerobes and obligate anaerobes that is, microorganisms that either strictly require oxygen or strictly do not require oxygen.

This concludes the lesson on physical and chemical factors that affect microbial growth.