Symbiosis Symbiosis Learning outcomes Learning outcomes To know the following interspecies To know the following interspecies relationships and examples of each: relationships and examples of each: 1. 1. parasitism parasitism 2. 2. mutualism. mutualism.
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Symbiosis Learning outcomes To know the following interspecies relationships and examples of each: 1. parasitism 2.mutualism.
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SymbiosisSymbiosis
Learning outcomesLearning outcomes
To know the following interspecies relationships and To know the following interspecies relationships and examples of each:examples of each:1. 1. parasitismparasitism2.2. mutualism.mutualism.
Detailed learning outcomes
Symbiotic relationships are co-evolved and specific intimate Symbiotic relationships are co-evolved and specific intimate relationships between members of two different species.relationships between members of two different species.
1.1. ParasitismParasitismA parasite benefits in terms of energy or nutrients, whereas a A parasite benefits in terms of energy or nutrients, whereas a host is harmed by their loss. Parasites often have a limited host is harmed by their loss. Parasites often have a limited metabolism so cannot survive out of contact with a host.metabolism so cannot survive out of contact with a host.
2.2. MutualismMutualismBoth mutualistic partner species benefit from the relationship. Both mutualistic partner species benefit from the relationship. One example is that of cellulose-digesting protozoa/bacteria One example is that of cellulose-digesting protozoa/bacteria living in the guts of many herbivores. living in the guts of many herbivores.
Symbiotic relationships
Symbiosis
MutualismParasitism
Symbiosis
Symbiosis is the close relationship between two different species, eg the relationship between nitrogen-fixing soil bacteria (Rhizobia) and leguminous plant roots (peas, beans and clover).
There are two types of symbiosis:
• parasitism
• mutualism.
Parasitism
Harmed
A B
Benefits
A parasite lives on another organism (the host) from which it obtains food. This:• benefits the parasite• harms (or kills) the host.Some parasites (ectoparasites) live on the outer skinof the host:
ticks fleasleech
Parasitism
Some parasites (endoparasites) live inside the host (usually in vertebrates):
tapeworm
Living with parasites
Only poor parasites kill their host as this is not to their advantage, especially for obligate parasites.
There is a balance between parasitic damage and host defence, so the relationship is relatively stable.
Diseases often occur in cycles as parasite and host co-evolve.
Secondary host species or vectors
Vectors are organisms that transmit parasites, usually insects and ticks. These vectors are essential for the development of the infectious stage of the lifecycle of some parasites before they are transmitted to the next host (eg mosquitoes transmit the malarial parasite).
Some of these vectors therefore have a double aspect of parasitism.