Algae

Question 1

define algae

Answer 1

a group of organisms (not a clade) that all derived chloroplasts from the same endosymbiotic event but are now very varied
Almost all aquatic

Question 2

importance of pigments in algae

Answer 2

-Algae are named by colour
-A range of pigments means more wavelengths can be used for photosynthesis
-What pigments an algae has determines its ecological niche and what colour it is

Question 3

what is chlorophyll and its types?

Answer 3

Colour is produced when chlorophyl a absorbs light - absorbs blue and red light best and reflects green light
Chlorophyl b and c differ in the wavelengths of light they absorb but all reflect green
Chlorophyl produces green colour associated with plants

Question 4

what are the accessory pigments?

Answer 4

Carotene and Xanthin - absorb blue and green and so appear yellow/red/orange
Phycoerythrin and phycocyanin - absorb green, yellow, orange

Question 5

types of algae: cyanobacteria
- how many species?
- description?
- pigments?
- ecology?
- fossil evidence?

Answer 5

200 species of bacteria
Unicellular or form filaments of cells (largely independent still) - some even form mats
Contain many internal folded membranes which is where photosynthesis occurs
Chlorophyll a with carotenoids and phycobilins (phycocyanin) - produces blue-green colour which gives them their other name blue-green algae
Terrestrial, freshwater, marine
Stromatolites: mounds of cyanobacteria that grow in tidal flats (rare)
Lower cyanobacteria layers die with no light but provide a foundation for other layers to grow to a macroscopic size
Fossilised stromatolites have very similar cyanobacteria to what we have together (3.5 billion yo)
Nitrogen fixation: anabeana forms filaments with interspersed heterocysts which do not photosynthesise but fix atmospheric nitrogen into an organic form that can be used by other organisms
Humans exploit this - rice paddies are flooded and blooms of cyanobacteria appear, then the paddies are drained killing the cyanobacteria and allowing the plants to use the nitrogen increasing yield

Question 6

types of algae: dinoflagellate (cerozoan)

Answer 6

Marine habitats but also freshwater
Chlorophyll a and c plus carotenoids (reg, brown, gold colour)
Single-celled with an equatorial groove with one flagellum inside and one outside which produces a rolling movement
Symbiotic with animal groups like corals, sponges, jellyfish and flatworms
Often toxic and their blooms produce “red tides”

Question 7

types of algae: discicristates and euglenoids

Answer 7

Single celled with flagella
Predators, parasites and only few are photosynthetic autotrophs
Chlorophyll a and b

Question 8

types of archaeplastid algae

Answer 8

glaucophytes, red algae, green algae,

Question 9

describe glaucophytes

Answer 9

retain some cellular features of endosymbiotic origin of chloroplasts
Not very diverse: three genera
Chlorophytes retain two features of cyanobacteria: chlorophyl a with phycocyanin and phycoerythrin)
Chloroplast walls are similar to cell walls of cyanobacteria (made of peptidoglycan) which is absent in red and green algae as those chloroplasts are protected by the eukaryote and don’t need a wall - fossil of endosymbiosis

Question 10

describe red algae (rhodophytes)

Answer 10

Some unicellular but most are complex multicellular organisms
Some freshwater but most are tropical marine
Cell walls are made cellulose fibres in a agar or carrageenan matrix
Pigments: chlorophyl a and phycobilins which usually mask chlorophyl a and make algae red (allows them to be deep water specialists where blue light is present)
Complex and unusual sexual life cycle with 1 multicellular haploid phase and 2 multicellular diploid phases
Why not colonise the land? Accessory pigments are ecologically advantageous in deep waters where blue light predominates and there is not enough blue light on land

Question 11

describe green algae (viridophytes)

Answer 11

Pigments: chlorophyl a and b
Two main groups: chlorophytes and streptophytes diverged 1200-725 million years ago

Question 12

what are the viridophytes? when did they diverge and what are their pigments?

Answer 12

Pigments: chlorophyl a and b
Two main groups: chlorophytes and streptophytes diverged 1200-725 million years ago

Question 13

describe the chlorophytes

Answer 13

• freshwater and marine
• single celled and multicelled
• photosynthesise

Question 14

describe the streptophytes

Answer 14

• green algae and land plants
• single celled to multicelled
• many still live in aqueous habitats
• some have evolved to land

Question 15

important adaptation of streptophyte charales:

Answer 15

zygote is often a resting stage as it has a protective coat (sporopollen) and is retained on the parent plant to receive nutrients

Question 16

why did streptophytes and zygnematales colonise land and not another algal group?

Answer 16

Opportunity: ecological gradient of freshwater to land is less steep than ocean to land (what water there is on the land in rain and pools is fresh)
Sporopollen: forms zygote coat and land plants use this mechanism to coat their spores
Synthetic pathways for protective biochemicals such as phenylpropanoids: protects from UV (much harsher on land than in water)

Question 17

pigments in cyanobacteria

Answer 17

chl a and phycobillins

Question 18

pigments in glaucophytes

Answer 18

a and phycobillins

Question 19

pigments in rhodophytes

Answer 19

a (sometimes c), phycobillins and carotenoids

Question 20

viridophyte pigments

Answer 20

a + b and caretenoids