Territorial behavior

 A territory is an area held and defended by an organism or group of organisms of the same or different species. Territorial behavior is common to all vertebrates except amphibian but is rare in non-vertebrates.

The exact function of territory formation varies from species to species, but in all cases, it ensures that each mating pair of organisms and their offsprings are adequately spaced to receive a share of the available resources, such as food and breeding space. In this way, species achieves optimum utilization of the habitat.

The size of territories occupied by any particular species varies from season to season according to the availability of environmental resources. Birds of prey and large carnivores have territories several square miles in area in order to provide all their food requirements. Herring gulls and penguins have territories of only a few square metres, since they move out of their territories to feed and use them for breeding purposes only.

Territories are found prior to breeding, usually by males. Defense of the area is greatest at the time of breeding and fiercest between males of the same species. There are a variety of behavioral activities associated with territory formation and they involve threat displays between owners of adjacent territories. These threat displays involve certain stimuli which act as releasers. E.g. An adult male robin would attack another adult male displaying a red breast and a bunch of red feathers, but not a young male robin which did not have a red breast. The level of aggression shown by an organism increases towards the centre of the territory. The aggressiveness of males is determined partly by the level of testosterone in the body and this can affect territory size. E.g. the territory size of a red

grouse can be increased by injecting the bird with testosterone. Territories are acquired through threats, gestures and postures in place of actual fighting. Having obtained a territory, many species especially carnivores proceed to mark out the boundary by leaving a scent trail. This may be done by urinating or rubbing parts of the body against objects called scent posts along the boundary of the territory.

Altruistic behavior

Altruism is a form of social behavior whereby one organism puts itself either at risk or personal disadvantage for the good of other members of the species. In the case of activities associated with and parental care, altruism is not so difficult to comprehend since the action is clearly in the interest of the parents, offsprings and species. E.g. the female baboon protects and cares for its offspring for almost six years whilst most bird species feed and protect their demanding offprings until they are capable of fending for themselves. What is not so clear is the reason why some organisms give support to organisms which are not their offspring E.g birds and monkeys call out warnings to others in danger and female monkeys carry and care for the babies of other monkeys. In insects such as honey bees, wasps and ants, sterile female workers are prevented from producing offsprings, yet they spend their lives looking after their brothers and sisters. Hence, helping their sister (queen) to reproduce, they are effectively aiding in the production of queens, workers an drones with a genetic complement closer to their own than if they had offspring of their own. The conferring of a genetic advantage on closely related organisms forms the basis of altruistic behavior.

Altruistic behavior is very common amongst primates and varies from the extremes of social protection which exist between members of the same troop (monkeys), through acts of mutual grooming and food sharing (apes) to deliberate acts of self-sacrifice for family (God for humans). The extent of altruistic behavior appears to be related to close relatives (kin) such as offspring and siblings (brothers, sisters cousins) with whom they share certain alleles. Thus the adaptive significance of altruistic behavior is to increase the frequency of those alleles common both to the donor and recipient(s) of the altruistic behavior

Pathogenic Properties of Virus

• Viruses have mechanisms to evade host defenses viruses grow inside host cells to hide from immune defense.

• Kill immune cells e.g. HIV – TH Cells.

• Cytopathic effects: - The visible effects of viral infection on host cell. Some effects will kill the cell and some will just change the cells.

• Viruses stop DNA, RNA and/or protein synthesis e.g. Herpes virus block mitosis.

• LySOSomal autolysis of host cells e.g. Influenza: bronchiolar epithelium.

• Production of inclusion bodies (visible viral parts inside the cell) can identify a particular virus e.g. Rabies virus: Negri bodies.

•  Syncytium formation (neighboring cells fuse together) e.g. Varicella Zoster virus.

• Change in cell function e.g. Measles, production of interferons by host cell (triggers host immune response), induce antigenic changes on host cell surface (triggers destruction of infected cell by host immune response).

• Induce chromosomal changes, cell transformation: may activate or deliver oncogenes resulting in loss of contact inhibition (cancer) e.g. Papilloma virus.

Theories on membrane structures

• In 1902 it was thought that the membranes had only lipids (Overton). 
• In 1926 Gorter and Grendell proposed that lipids are capable of forming a double layer.
• In 1935 Danielli and Davson proposed the lipid bilayer model that includes proteins adhering to both lipid-aqueous interfaces.
• Artificial model systems such as the liposomes supported the idea of Danielli and Devson.
• A droplet of lipid made soluble in an organic solvent can be spread over a small hole on a septum that divides two chambers containing water.
• This set up is useful to study biophysical properties of a bilayer such as permeability and electrical resistance.
• Channels for ions can be formed by adding certain proteins or polypeptides.
• Liposomes act as excellent carriers for different molecules such as chemotherapeutic compounds, insulin and antibodies.

Fluid mosaic model

• Fluid mosaic model proposed by S.J. Singer and G.L. Nicolson (1972) was finally acceptable to most biologists.
• This model recognizes that lipids and proteins are in a mosaic arrangement.
• It also recognizes that there is translational movement of lipids and proteins within the lipid bilayer.
• Non covalent interactions ensure a fluid like state for the membranes.
• Integral proteins are intercalated into the continuous lipid bilayer.
• Polar/hydrophilic regions of proteins protrude from the surface while the nonpolar/hydrophobic regions are embedded inside.

Unit membrane model 

• Robertson in 1959 postulated the unit membrane model.
• This model stated that the central layer of plasma membranes is made up of hydrocarbon chains of lipids and the proteins constitute the dense surrounding layers on both sides when viewed through an electronmicroscope.
• Unit membrane model turned out to be an over simplification model as it can’t account for the number of protein molecules present across the membranes.