What is phoresis

The term phoresis is derived from the Greek word meaning “to carry.” In this type of symbiotic relationship, the phoront, usually the smaller organism, is mechanically carried by the other, usually larger, organism, the host. Unlike commensalism, there is no dependency in the procurement of food by either partner. Phoresis is a form of symbiosis in which no physiological interaction or dependency is involved. Both commensalism and phoresis can be considered spatial, rather than physiologic, relationships. Examples of phoresis arc the numerous sedentary protozoans, algae, and fungi that attach to the bodies of aquatic arthropods, turtles, and so on.

 

Posted by wolf on January 24th, 2012 | No Comments Posted in Parasitology

A few words about Commensalism

Commensalism does not involve physiologic interaction or dependency between the two partners, the host and the commensal. Literally, the term means “earing at the same table.” In other words, commensalism is a type of symbiosis in which spatial proximity allows the commensal to feed on substances captured or ingested by the host. The two partners can survive independently. Although at times certain nonpathogenic organisms (e.g., protozoa) are referred to as commensals, this interpretation is incorrect because they arc physiologically dependent on the host and are, therefore, parasites. An example of commensalism is the association of hermit crabs and the sea anemones they carry on their borrowed shells.

 

Posted by wolf on January 24th, 2012 | No Comments Posted in Parasitology

Infection in bacteria by lysogenic bacteriophages

An interesting mode of infection and transmission of viruses was found in bacterial system. Normally a bacterium infected with bacteriophage would lyse after some time and release a progeny of bacteriophages. In many experiments it was seen that the bacterium does not lyse and happily undergoes division. Analysis of such bacteria showed that the phage DNA becomes incorporated in the bacterial chromosome. In this case the phage  DNA is replicated along with the bacterial DNA, and is passed on to the daughter bacterial cells in the course of the cell division. The phage DNA retains its integrity and remains latent throughout many bacterial generations. Then, for some unknown reason, the phage DNA would detach from the bacterial chromosome and act as a lytic phage. The point of attachment for the lysogenic phage DNA to the bacterial chromosome is highly specific. It attaches in such a way that only one point of the phage DNA is attached and the rest forms two DNA arms on either side of the point of attachment. There are many questions that remain unanswered, such as what determines whether a phage will act in a lytic or lysogenic manner?

The phage infection in bacterial cultures can be demonstrated by simple experiments. The colonies of host bacterium may be allowed to grow on semi-solid agar-nutrient medium. A dilute suspension of phage particles is spread over the bacterial culture. After some time hole or plaques will appear on the bacterial colonies, indicating the process of lysis.

Posted by wolf on January 13th, 2012 | No Comments Posted in Cell Biology

Mode of viral infection

If a colony of bacteria is infected with bacteriophages, the bacteria undergo chance collision and ultimately the phages attach to the bacterial cell wall through tail fibres. The DNA of the phage is injected into the host cell by dissolving the cell wall at the point of attachment, and the protein shell remains outside. The phage DNA takes up the control of the bacterial cell and replicates several times. The DNA and RNA of the bacterial cell are depolymerised and the nitrogen bases are utilised during the phage DNA replication. Similarly, the proteins of the bacterial cell are hydrolysed and the amino acids, thus formed, are used for building up of the protein shells of the virus. The newly-formed phage particles are released from the infected bacterial cells after lysis within 20min. to 1 hr. The new viruses infect other bacteria and a fresh cycle of virus replication is repeated.

 

Posted by wolf on January 13th, 2012 | No Comments Posted in Cell Biology

Biological Units

Biologists occasionally need to examine some microscopic animals or plants. Microscopes magnify the specimens 1000 times or more larger than normal. So, understanding about the measurements is a must. In biology, the units of length commonly employed include the micron (abbreviated by µ) and the Angstrom (abbreviated by Å). A micron is equivalent to 10 -3 millimeters (mm). An Angstrom is equivalent to 10-4 µ or    10 -7 mm.

Weights are expressed in milligrams (10-3 grams) micrograms (10-6 grams), and nanograms (10-9 grams).

The unit of molecular weight employed is the dalton. A dalton is defined as the weight of a hydrogen atom. For example, one molecule of water (H20) weighs about 18 daltons . One dalton weighs 1.674 x 10-24 grams.

Posted by wolf on January 2nd, 2012 | No Comments Posted in General Zoology
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