Biological Responses

Response of Organisms to the Abiotic World Biological Timing Responses All organisms, except those living in deep caves or in the depths of the ocean, respond to night and day, the seasons, the tides and even the phases of the moon. These organisms can have: Annual cycles – yearly changes of the seasons Daily cycles – night and day Lunar – monthly cycles often related to the moon Tidal – related to the ebb and flow of the tides.

Biological Timing Responses Cont It is advantageous to an organism to synchronise its activities with the rhythms in its environment. There are 3 basic ways of synchronising the physiology and behaviour of organisms to these cycles. An exogenous Rhythm this is a direct response to an environmental response, i.e. the rhythm is controlled by the external environmental stimuli detected by an organism (the surge in plant growth in the wet season)

Biological Timing Responses Cont Endogenous Rhythm an internal biological clock that programs the organism’s behaviour to synchronise with the external environment. A combination of exogenous and endogenous rhythms.

How do we know some rhythms are Endogenous They continue in a constant environment. These are said to be free-running. The rhythm has a frequency that is not the same as the period of an external environmental factor. e.g.the human circadian rhythm is not 24 hrs but 24hrs and 42 mins

How do we know some rhythms are Endogenous? The rhythm may persist when the organism is moved from one part of the world to another. e.g. periwinkles move up and down the rock face in response to the tides. If placed in a tank miles away from the sea, they still move up and down the tank in the same rhythm as the ocean tides.

Find these definitions… Biological clock Period of rhythm Phase shift Free running period Entrainment Zeitgeber Circa Photoperiod Anthropomorphism Ethology Stimulus Receptor Effector

Biotic Factors Coping with the physical factors in the environment is only one aspect of survival. Equally important are: For animals – obtaining food For all organisms – avoiding being used as food by other organisms eg predators and parasites.

Biotic Factors Competition – this exists when demand for a resource exceeds its supply. This may be interspecific – between species Or intraspecific – within a species.

Biotic Factors Exploitation – one organism benefits at the expense of another which is harmed to a certain degree. This includes predation, grazing and parasitism. Cooperation – both organisms benefit, could be mutualism i.e. between species or within a species, as in reproduction in many animals.

Biotic Factors Commensalism – the members of one species benefits and the other is not affected in any way. e.g. epiphytes (perching plants), these take no nutrients from the tree on which they perch, they are there purely to gain light

Biotic Factors Mutualism – both organisms benefit from their association with each other. Antibiosis – one member of the partnership is inhibited and the other is unaffected. e.g. fungi give out a substance which inhibits bacterial growth.

Biotic Factors Succession – the replacement of one species by another over time. Stratification – vertical relationships in space with other organisms e.g. layers of animals as you go down the depth of the ocean to the bottom of the sea.

Summary of Interspecific Relationships Ref pg 9 Designs of Life