symbiosis

Question 1

what is symbiosis?

Answer 1

an interaction between 2 different species of organisms

Question 2

what is mutualism and what is an example of it?

Answer 2

a symbiotic relationship where both the microbe and host benefit from the reaction
e.g. E. coli in our gut produces vitamins that we can’t synthesise and in return they gain nutrients

Question 3

what is commensalism and what is an example of it?

Answer 3

a symbiotic relationship where the microbe benefits from the interaction but there is no effect on the host
e.g. bacteria on the skin gain nutrients but it doesn’t alter the environment of our skin

Question 4

what is parasitism/predation/competition and what is an example of it?

Answer 4

a symbiotic relationship where the microbe benefits from the interaction at the expense of the host
e.g. intracellular pathogens that can only replicate by destroying the host cell

Question 5

what is endosymbiosis?

Answer 5

a symbiotic relationship where an organism lives within another organism

Question 6

what is ectosymbiosis?

Answer 6

a type of symbiotic relationship where an organism lives on the surface of another organism

Question 7

what is mixotrichia?

Answer 7

a unicellular eukaryote that forms symbiotic relationships with insects

Question 8

what symbiotic relationships does mixotricha form?

Answer 8

it forms endosymbiotic relationships with 2 types of bacteria that help it degrade cellulose and mitochondria
it forms ectosymbiotic relationships with 3 types of bacteria that help it move its 4 flagella

Question 9

what are bacteriocytes and how do they form bacteriomes?

Answer 9

bacteriocytes are structures that can contain bacteria within another organism such as an insect
bacteriomes are organs that form when bacteriocytes aggregate (clump together)

Question 10

what is L pneumonophila and how do they kill amoeba?

Answer 10

a fresh water intracellular bacteria that act as a parasite that infects amoeba
they replicate within the alveolar macrophages and produce specialised effectors that prevent lysosomes attacking them
they multiply in the macrophage causing the amoeba to die

Question 11

what are bacterial predators?

Answer 11

a small type of bacteria that attach to the membrane of gram-negative bacteria and invade the periplasm (space between inner and outer membrane) and feed on the host

Question 12

what is nodulation?

Answer 12

a symbiotic interaction between legume plants and rhizobia bacteria in the soil
it increases the growth rate and yield of the plants
the legumes use ammonium and nitrates

Question 13

what are rhizobia bacteria and what allows them to form symbiotic relationships?

Answer 13

gram-negative bacteria found in the soil that live in the rhizosphere (their niche) and they form in root nodules on legumes for nodulation
they have a complex genome containing lots of large plasmids

Question 14

what is the process of nodulation?

Answer 14

1. the legume produces root exudates (fluid) into the soil containing flavonoids that attract rhizobia
2. the rhizobia attach to the root activating nodulation genes in the rhizobia causing it to produce nod factors
3. receptors on root cells recognise the nod factors and the roots curl to entrap the rhizobia
4. the bacteria enters the tissue and forms infection threads in the root
5. the rhizobia is entrapped in symbiosomes in the membrane and differentiates into bacteroids that form nodules

Question 15

what are the 2 types of nodules that can form?

Answer 15

determinate nodules (have a meristem so can grow back again)
indeterminate nodules (no meristem so can’t grow back)