Download Ch. 6 Multicellular Primary Producers

Ch. 6 Multicellular Primary Producers: Seaweeds and Plants
I.
Multicellular Algae: The Seaweeds
A. Sometimes called macrophytes or macroalgae
1. All are multicellular
2. Classified by structure, pigments, food products stored
3. Eukaryotic
a. More complex than unicellular algae
b. Lack specialized structures and reproductive mechanisms of terrestrial plants
B. General Structures
1. Thallus – complete body
2. Blades – flattened, leaf-like portions of thallus
a. Main photosynthesis area
b. Not true leaves – have no veins and the upper and lower sides are identical
c. Pneumatocysts – gas-filled bladders keep blades afloat
3. Stipe
a. Stem-like structure, provides support
b. Blades originate at stipe
4. Holdfast
a. Root-like structure attaches thallus to bottom
b. No significant absorption of water or nutrients
c. Does not penetrate sand or mud
d. Stipe and holdfast lack specialized tissues for water and nutrient transport
C. Types of Seaweed
1. Green Algae (phylum Chlorophyta)
a. 90% are freshwater or terrestrial
b. Have a simple thallus
c. Pigments and food reserves are the same as plants (plants may have evolved
from green algae)
d. Chlorophyll gives bright green color
e. Filamentous green algae may be branched or unbranched
f. May have many nuclei per cell
2. Brown Algae (phylum Phaeophyta)
a. Color varies from olive-green to dark brown
b. Yellow-brown pigments, especially fucoxanthin, overshadow chlorophyll
c. Almost always marine
d. Often dominant primary producer on temperate and polar rocky coasts
e. Some live on rocky slopes exposed at low tide
f.
Kelps – most complex, largest brown algae
1. Some consist of single blade up to 3m long
2. Blades can be harvested for food
3. Along Pacific coast, largest kelp may have blades 3m long
4. Can grow 5 inches per day
5. May form dense kelp beds or forests
6. Kelp beds among the most productive marine environments
3. Red Algae (phylum Rhodophyta)
a. There are more species of red algae than green and brown combined
b. The red pigment, phycobilins, masks chlorophyll
c. Mostly marine
d. Inhabit most shallow-water environments
e. Some are parasites of other algae
f. Coralline algae deposit calcium carbonate in its cell walls
D. Life History
1. Asexual reproduction is common
2. Fragments of thalli can grow into new individuals
3. Some produce spores
a. Disburse to new locations
b. Some spores, called zoospores, have flagella
4. Sexual reproduction produces gametes
a. Gametes from different individuals fuse, mix genes
b. Gametes can form in the same thallus
c. Gametes form by meiosis to give haploid cells
d. 4 types of life histories
1. First: Most common: 2 types of thalli
a. Diploid (2n) sporophyte generation undergoes meiosis to give
haploid (1n) spores (motile in green and brown algae)
b. Spores develop into haploid gametophyte thallus
c. Gametophyte thallus produces haploid gametes
d. Some species have male and female thalli; some produce both
male and female on same thallus
e. Gametes fuse to form diploid thallus
f. Alternation of Generations – one generation is the sporophyte,
the other is the gametophyte
g. In some species, sporophyte and gametophyte are identical, in
other, the sporophyte is large and the gametophyte is small
2. Second type: unique to red algae
a. 3 generations alternate
b. Sporophyte (2n) undergoes meiosis to form gametophyte (1n)
c. Gametophytes (1n) fertilize to form carposporophyte (2n)
d. Carposporophyte (2n) forms 2n spores that grow into sporophyte
3.
Third type: mo alternation of generations
a. Only one type of thallus (2n)
b. Produces haploid gametes
c. Fertilization takes place forming a 2n zygote that becomes a
Diploid thallus (2n)
d. some brown and green algae do this
4. Fourth type: some green algae
a. Dominant thallus is haploid
b. Produces haploid gametes
c. Fertilization forms a 2m zygote
d. Zygote undergoes meiosis to form haploid spores
e. Haploid spores grow to form haploid thallus
5. Development of gametes or spores can be influenced by temperature,
amount of nutrients in the water, temperature, or day length
II.
E. Economic Importance
1. Mariculture – farming of seaweed
2. Phycocolloids – gelatinous chemicals made by seaweeds
a. Used in food processing and other products
b. Algin – stabilizer and emulsifier
c. Carrageenan from red algae is an emulsifier
d. Agar – from red algae forms jellies
3. Seaweed used as fertilizer, food additive and wound dressings and possible biofuels
Flowering Plants
A. Have true leaves, stems, and roots
B. Only seagrasses are truly marine plants
1. Seagrasses are not real grasses, they are closer to lilies
2. Roots and erect shoots grow from horizontal stems (rhizomes)
3. Pollen carried by water, does not need insect carriers
4. Tiny seeds develop in small fruits and are dispersed
5. Seagrasses also provide food and shelter for animals
C. Salt Marsh Plants
1. Cordgrasses – true grasses tolerant of salt, primary producers provide habitat and
breeding grounds
2. Protect against erosion and purify water
3. Inhabit zone above mudflats
4. Salt glands excrete excess salt
5. Halophyte – a salt-tolerant plant
D. Mangroves
1. Trees and shrubs adapted to live along tropical and subtropical shores
2. Can tolerate salt
3. Mangal – mangrove forest
4. Adapted to high water loss through leaves and soft soil low in oxygen