lecture 12 (rhodophyta)

Question 1

what is the role of encrusting red algae in coral reef ecosystems

Answer 1

they help support the reefs, hold them together

Question 2

a crust-like coralline algae has been found deeper than any other photosynthetic eukaryote, explain how this alga can grow where there is only 0.0005% of surface light intensity

Answer 2

due to the accessory pigments which are effective at capturing light (phycoerythrin, phycocyanin and allophycocyanin)

Question 3

how deep is the deepest algae?

Answer 3

268m deep in the bahamas -> a crustose coralline algae

Question 4

indicate two commercial uses of red algae

Answer 4

pharmaceuticals, human food

Question 5

describe the extracellular matrix in red algae

Answer 5

composed of cellulose microfibrils, and amorphous gel-like mixture (made of agar and carrageenan, and mucilages)
some deposit CaCO3

Question 6

do red algal cells have intercellular connections that allow exchange of solutes and gasses between cells such as plasmodesmata?

Answer 6

no plasmodesmata

Question 7

what type of alga are parasitic and what do they look like

Answer 7

some red alga, white in colour

Question 8

what is the organization of red algae

Answer 8

branched filaments or multiaxial filament aggregations (pseudoparenchymatous)

Question 9

what are pit plugs? how many kinds are there?

Answer 9

proteinaceous plugs, they have no intercellular connections (no solute transfer)
two types: primary and secondary

Question 10

how many cell layers of red algae are there?

Answer 10

two, cortex and medulla (lacks meristoderm)

Question 11

describe primary and secondary pit plugs

Answer 11

primary = between sister cells, structural link between cells
secondary -> between non-sister cells (forms for gene recombination, plugs once DNA transfers) or between parasite and hosts (transfers parasite DNA into host then plugged)

Question 12

describe the 5 unique features of the red algae cell biology (excluding triphasic life cycle)

Answer 12

1. lack centrioles
2. lack flagella from all life stages
3. pit plugs
4. cell-cell fusion on cells other than gametes
5. cell elongation and repair
6. development of multinucleate cells and polyploid nuclei

Question 13

describe the triphasic life cycle of a florideophycean red alga (eg. polysiphonia)

Answer 13

male gametophyte (N) with N spermatium releases spermatia
this lands on the female gametophyte (N) carpogonium (N) (via the trichogyne), and fertilizes the egg.
once fertilized, the zygote becomes the 2N carposporophyte which releases 2N carpospores. these settle and become the 2N tetrasporophyte which has 2N tetrasporangium. Meiosis occurs and releases four N tetraspores which become the male and female gametophytes.

Question 14

what is the evolutionary advantage of a triphasic life cycle?

Answer 14

potential for dramatic amplification of a single fertilization event since each zygote nucleus can give rise to billions of gametophytes

Question 15

what of the following multicellular stages are free-living? gametophyte, carposporophyte, tetrasporophyte

Answer 15

the gametophyte and the tetrasporophyte are free living

Question 16

draw the biphasic life cycle of bangiophyceans (eg. pyropia)

Answer 16

blade-like N gametophyte have spermatium and carpogonium which release sperm(N) and eggs (N) that fertilize and become a zygote (2N).
the zygote undergoes mitotic division to produce several carpospores (2N) that grow into 2N microscopic filamentous sporophytes. these undergo meiosis and release N spores

Question 17

Bangiophyceans vs Florideophyceans

Answer 17

2 classes of red algae
bangiophycea = unicels, filaments and simple blades. single plastid per cell, biphasic sexual reproduction and pit plugs in some taxa only (eg. pyropia)
florideophycea = most diverse, sexal reproduction is triphasic, pit-plugs present (eg. corallinales, gracilariales, polysiphonia)