1. Higher Biology
Unit 3
3.5- Symbiosis

2. 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

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

4. 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)

5. 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.

6. 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

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

8. 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

9. 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

10. 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

11. 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

12. Tapeworm Life Cycle

13. Types of symbiosis
Mutualism- both organisms benefit from the relationship

14. 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, non-photosynthetic prokaryotes
Chloroplasts were photosynthetic prokaryotes

15. 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