Symbiosis

A relationship between organisms of different species that show an intimate association with each other where at least one of the organisms gains a nutritional advantage

• Parasitism
• Commensalism
• Mutalism

Parasitism is a biotic interaction beneficial to one organism (parasite) which gains energy or nutrients and detrimental to another (host) due to direct loss of resources and use of energy in defense from the parasite

An endoparasite lives inside the body, eg tape worms and malaria parasite, whereas an ectoparasite lives outside the body eg tic, head lice, fleas

Specialised relatively stable relationships

An obligate parasite is an organism that can only function as a parasite (dependent on the host) eg viruses whereas a facultative parasite is an organism that can survive for periods of time without the host

• Through direct contact eg touch - virus on hands after sneezing, head lice and humans touching each other
• Resistant stage - a dormant resistant stage allows them to wait for another host to come along eg liver flukes on vegetation whilst waiting to be consumed by grazing animals
• Vectors - a carrier that is not affected by the parasite eg mosquito transmits malaria to humans

Commensalism is a biotic interaction which is beneficial to one species leaving the other host unnaffected eg hermit crabs carrying barnacles on their shells, clown fish protects itself from stings in sea anenome and collects food debris

Partnership which benefits both partners eg lichen - the algae recieves minerals from fungi and fungi recieves sugar from algae, nitrogen fixing bacteria and leguminous plants