Key Area 3.5 - Symbiosis

What is symbiosis?

A co-evolved intimate relationship between members of 2 different species

Why are the co-evolutions of adaptations essential?

A change in one partner is likely to affect the survival of the other

What are the 2 types of symbiosis?

Parasitism

Mutualism

What is parasitism?

A parasite benefits in terms of energy or nutrients, whereas the host is harmed by the loss of these resources (+,-)

Who benefits in parasitism?

The parasite as it derives its nutrition from the host, which it exploits

Who is harmed in parasitism?

The host

What does the host lose in parasitism?

Some energy and/or nutrients to the parasite

Why are parasites dependent on their host?

They often have a limited metabolism & means that they cannot survive if they lose contact with their host

What are the most effective parasites?

Those who do not cause their host to die (or at least not until the completion of the parasite's life cycle is ensured)

What are the three mechanisms of transmission of parasites?

Direct contact

Release of resistant stages

Use of a vector

What is direct contact for parasites?

When the parasite is passed from host to host during physical contact

What's an example of direct contact?

Head & body lice

What is the release of resistant stages for parasites?

Means they are able to survive adverse environmental conditions for long periods until they come into contact with a new host

What's an example of the release of resistant stages?

Resistant larvae & pupae of the cat flea

What is the use of a vector for parasites?

Vectors ore organisms which carry the parasite from one host to another, but the vector does not cause the disease itself, it transfers pathogens from a host to another

What's an example of a vector carrying a parasite?

The mosquito carrying the pathogen which causes malaria

What are the 2 parasitic life cycles?

Direct & indirect lifecycles

What is a parasitic direct life cycle?

Simple ones involving only one host

What are indirect parasitic life cycles?

More complex ones which involve a primary & secondary hosts

The primary host is used as the site of the sexual stage of reproduction

The secondary host is also used in its life cycle

The primary host becomes infected when it's invaded by or consumes the infected secondary host

What is an advantage of having multiple parasitic hosts?

Hugely increases reproductive capacity & chance of survival as a single host relies on food contamination

What is mutualism?

Both mutualistic partner species benefit in an interdependent relationship (+,+)

What is the mutualistic relationship between herbivores & cellulose digesting microbes?

Herbivores obtain energy & sugar form the digestion of cellulose by the microbes

The microbes receive protection, warmth & a constant supply of food

What is the mutualistic relationship between coral polyps & unicellular algae?

Polyp uses carbohydrate made by algae as food

Algae are provided with a secure habitat & supply of polyp's nitrogenous waste which they convert to protein

What is the mutualistic relationship between plant & bees?

Bees pollinate plants

Plants provide nectar which is a food source for the bees

What is the mutualistic relationship between humans & microbes?

Humans benefit from fermented unused energy substrates, production of vitamins, prevented growth of pathogens & regulated gut developments

Micro-organisms living in the gut receive a steady supply of food