It was once believed that lower organisms do not have defense mechanisms. But this is not true. Even though a well-developed defense mechanism is present only in vertebrates, simple forms of defense mechanisms and immune systems are also available in lower forms of organisms. In vertebrates, as we move down from mammals to birds, to reptiles, to amphibians and to fish, the immune system becomes simpler. Lower organisms do not have a well-established defense mechanism or immune system as we have discussed in the case of vertebrates, but these organisms can also protect themselves from enemies and competitors by other types of defense mechanisms, some of, which are specific for a particular organism.
Defense mechanism in Microbes :
Bacteria and other microorganisms have various types of structural and physiological or biochemical means for defense against their enemies and adverse situations. A large number of bacteria and fungi produce digestive enzymes and toxic chemicals such as antibiotics and antimicrobial compounds. These compounds can kill or damage the cells of organisms in which they are in contact.
Many bacteria and other microorganisms are capable of producing capsules.
The phagocytic cells cannot engulf and destroy the capsulated bacterial cells. Phagocytes such as macrophages and neutrophils can easily engulf the noncapsulated bacterial cells and destroy them easily.
During unfavorable conditions, a large number of bacteria can be changed into spores, known as endospores. The cytoplasm of the cell is detached from the cell wall and changed into a spore in the middle of the cell. The spore has a very thick covering, and since it is formed within the cell, it is called an endospore. Endospores are highly resistant to heat, UV-radiations, and chemicals and antibiotics. Even though the formations of endospores are a mechanism to overcome the unfavorable conditions, the formation of such endospores can be considered a defense mechanism.
Defense mechanism in Insects :
There are different types of defense mechanisms in insects, which depends on the species of the insect. One of the main mechanisms is the production of antibacterial peptides. These toxic compounds are capable of killing bacteria. A large number of other insects also produce these types of toxic antibacterial peptides and are called cecropins. Bees produce a type of toxin called melittin, which is present in their venom and are able to do the hemolytic activity (lysing the RBC). In insects like the fruit fly (drosophila) the reproductive organs produce antibacterial peptides, the andropins. In certain other insects antibacterial pep tides are present in the hemolymph. Some of these antibacterial pep tides are produced in response to the bacterial infection in insects. In addition to these defense mechanisms, they also possess phagocytic cells. These cells can attack and destroy the invading microorganisms and pathogens.
Tags: Bio Technology, Bio Genetics, Defense Mechanisms
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