Higher Biology Unit 3 3 5 Symbiosis Symbiosis

Higher Biology Unit 3 3. 5 - Symbiosis

Symbiosis • Symbiosis refers to the relationship between 2 organisms of different species that live in direct contact with one another • They are relationships that have evolved over millions of years • This coevolution is essential as a change in one would affect the other

Types of symbiosis • Parasitism- one organism (the parasite) benefits at the expense of the other (the host)

Parasitism • A parasite gains its nutrition from the host organism • The host is harmed or at least loses some energy/materials to the parasite • In many cases a balance has evolved between the parasite and host • Parasites often require a limited metabolism and must maintain contact with their host • Effective parasites do not cause their host to die (at least until completion of its life cycle)

Parasitic feeding The liver fluke is a parasite that lives and feeds inside its host. Mosquitos are parasites that live and feed outside their host.

Parasite Transmission • Transmission of a parasite to a new host can occur in 3 main ways • Direct contact • Release of resistant stages • Use of a vector

Direct contact • Direct contact involved transmission of a parasite form one host to another through direct physical contact • Examples include head and body lice

Release of resistant stages • Different stages of the parasites development area able to withstand adverse conditions until they come into contact with a suitable host • Examples include cat fleas

Use of a vector • A vector is a carrier of a pathogen such as bacteria or viruses • An example is mosquitoes carrying Plasmodium the unicellular organisms that causes malaria from human to human

Parasitic Life Cycles • In a direct life cycle eggs are shed and pass to a new member of the host species • This involves one species of host only and is common in parasites that feed outside of their host

Parasitic Life Cycles • Indirect life cycles are more highly evolved • In addition to a primary host species used as the site of sexual reproduction the parasite uses a secondary host species • A new primary host becomes infected when it is invaded by or consumes the infected secondary host • This type of life cycle is more common in parasites that live and feed inside their hosts

Tapeworm Life Cycle

Types of symbiosis • Mutualism- both organisms benefit from the relationship

Origin of mitochondria and chloroplasts • Mitochondria and chloroplasts are believed to have evolved from 2 types of prokaryote that had become resident in larger cells • Mitochondria were aerobic, nonphotosynthetic prokaryotes • Chloroplasts were photosynthetic prokaryotes

Evidence to support this theory • Mitochondria and chloroplast have their own circular DNA • Both organelles features ribosomes more similar to those found in prokaryotes than eukaryotes • A strong similatiry exists in structure and size between prokaryotes and these organelles • Molecular studies of ribosomal RNA indicate these organelles originated in bacteria