24 - Symbiosis*

Question 1

Host

Answer 1

the organism harbouring the other

Question 2

Symbiont

Answer 2

Usually microscopic or harboured partner

Question 3

mutualism

Answer 3

Both benefit, obligate association. Often based on protection and nutrient/waste exchange

Question 4

Cooperation/synergism

Answer 4

Both benefit, no obligatory. Often based on satisfaction of nutritional requirements

Question 5

Commensalism

Answer 5

One benefits, other is unaffected. Shelter, resources, habitat modification

Question 6

Predation

Answer 6

One engulfs the other

Question 7

Parasitism

Answer 7

Co existence, usually to detriment of one partner

Question 8

Amensalism

Answer 8

One produces an inhibitor of the other. E.g. antibiotics, alcohol formation by yeasts, acid formation

Question 9

Competition

Answer 9

Both compete for limited resource

Question 10

Consortia

Answer 10

Complex communities of diverse interacting
populations

Question 11

Ectosymbiosis

Answer 11

The symbiont is associated with host surfaces

Question 12

Endosymbiosis

Answer 12

Symbiont is internal to host

Question 13

Example of mutualism

Answer 13

• Reef building corals and zooxanthellae.
• Reef building corals satisfy most of their energy requirements using zooxanthellae
• Zooxanthellae receive nitrogenous compounds, phosphates, CO2 and protection.

Question 14

Syntrophism

Answer 14

Growth of one organism depends on or is improved by growth factors or nutrients provided by another organism growing nearby

Question 15

Marine food webs

Answer 15

depend on predation by predator protists on phytoplankton and bacteria

Question 16

Examples of predatory microbes

Answer 16

Bdellovibrio, Vampirococcus, Daptobacter

Question 17

What can parasitism lead to

Answer 17

genomic reduction and parasite dependence on host

Question 18

Benefit of parasitism

Answer 18

Population control

Question 19

Example of parasitism

Answer 19

Bacteriophages. Lysogenic cycle may add useful genes to host (mutualism?)

Question 20

Example of mutualism maintained by amensalism

Answer 20

• Fungus growing ants maintain fungal gardens as food source (mutualism)
• Gardens subject to infestation by parasitic fungus.
• Ants co-cultivate bacteria that produce inhibitors of the parasite (amensalism)

Question 21

Four likely outcomes of competition

Answer 21

1. Reduced growth: coexistance but neither achieves maximum potential growth (-/-)
2. Competitive exclusion: one is eventually eliminated from the habitat (+/-)
3. Niche separation: the competitors occupy different niches in the habitat (0/0)
4. Temporal resource sharing: the competitors occupy the habitat at different times (+/- and -/+ cycle)

Question 22

Competitive exclusion

Answer 22

The populations with the higher growth rate
ultimately exclude competitors from a niche

Question 23

Negative interactions of symbiosis as a driving force in evolution

Answer 23

• Limit population density
• Prevent individual dominance
• Drive increased genetic diversity

Question 24

positive interactions of symbiosis as a driving force in evolution

Answer 24

• Promote more efficient use of resources
• Enable organisms to colonise habitats they could not colonise alone
• Enhance **growth/survival **of benefiting populations