Key area 5: Symbiosis

1. Key area 5: Symbiosis

2. Symbiosis LI: • Define what is meant by “symbiosis”. • State that symbiotic relationships are co-evolved and intimate.

3. Symbiosis Symbiosis is a co-evolved intimate ecological relationship between organisms of two differentspecies that live in direct contact with one another. These are relationships that have evolved over millions of years (co-evolution). TWIG - Symbiosis

4. There are two types of symbiosis: • Parasitism • Mutualism

5. Parasitic relationships LI: • Define what is meant by a parasitic relationship • Describe the benefits to the parasite of the relationship. • Describe how parasites are transmitted. • Describe the role of intermediate (secondary) hosts for some parasites.

6. Parasitism In parasitism one organism, the parasite, derives its energy and nutrition from another organism, the host, which it exploits. The host is harmed or at least loses some energy and/or nutrients to the parasite. TWIG - Parasitism

7. Parasites often have a limited metabolism and cannot survive outside the body. e.g. Tapeworms do not have a digestive system since the host has already digested the food.

8. Transmission of parasites Parasites can be transmitted to new hosts in a variety of ways: • Direct contact – passed from person to person by physical contact e.g. head lice.

9. Release of resistant stages – able to survive adverse environmental conditions until they come into contact with a new host e.g. cat fleas.

10. 3. Use of a vector – (for example mosquitoes carry Plasmodium, the unicellular organism that causes malaria, from human to human).

11. Parasitic life cycles There are two types of parasitic life cycle: • Direct life cycle – where eggs are shed and pass on to a new member of the host species.

12. Indirect life cycle – in addition to using a primary host species as the site for its sexual reproduction, the parasite becomes adapted by evolution to employ a secondary host species in its life cycle.

13. Life cycle of Schistoso-miasis

14. Work as a group to produce a poster describing the lifecycles of parasites. Tapeworm Plasmodium falciparum Ophiocordyceps unilateralis Ixodes ricinus Cuscuta

15. Mutualism LI: • Define what is meant by mutualism. • Explain the theory of mutualism in the evolution of chloroplasts and mitochondria. • Describe the benefits of mutualism.

16. Mutualism In a mutualistic symbiotic relationship both organisms involved benefit from the relationship.

17. These can be: 1. relationships where both organisms provide a service e.g. Clown fish and anemomes The anemones provide the fish with protection from predators (which cannot tolerate the stings of the anemone's tentacles) and the fish defend the anemones against butterflyfish which eat anemones.

18. 2. Relationships where one organism provides a service and another receives a resource e.g. Flowering plants and bees. The bees pollinate the plants – spreading the pollen. While the plant provides nectar which is a food source to the bees.

19. The human gut is full of many species of bacteria, fungi etc. which perform a host of useful functions, such as fermenting unused energy substrates, training the immune system, preventing growth of harmful, pathogenic bacteria, regulating the development of the gut, producing vitamins for the host, such as biotin and vitamin K. The microbes in return receive a steady supply of food. 3. Relationships where both organisms receive a resource e.g. human gut microflora.

20. Symbiotic origin of chloroplasts and mitochondria It is thought that chloroplasts and mitochondria evolved from two different types of prokaryotic cells that had initially become residents in larger anaerobic cells.

22. Endosymbiosis Mitochondria: An anaerobic ancestral eukaryotic cell engulfed an aerobic ancestral prokaryotic cell – producing an aerobic eukaryotic cell. This aerobic ancestral cell evolved into the mitochondria.

23. Endosymbiosis Chloroplasts: Some of the newly evolved eukaryotic cells then absorbed an ancestral photosynthetic cell. This became the chloroplast producing an ancestral plant cell.

24. Evidence for endosymbiosis Research the evidence for endosymbiosis and make a bullet point list of the main pieces of evidence. Good links are: • http://evolution.berkeley.edu/evolibrary/article/_0_0/endosymbiosis_04 • http://endosymbionts.blogspot.co.uk/2006/12/evidence-for-endosymbiosis.html

25. Metabolism and Survival Questions KEY AREA 5 – Symbiosis • Testing Your Knowledge 1 Page 297 Q 1-3 • Applying your knowledge page 337 Q 6 • Problem Solving page 81-82 Q 1-4