Lab #6: Rhodophytes, Chlorophytes and Streptophytes

Question 1

Characteristics of Rhodophytes

Answer 1

Cell: Eukaryotic

Cell covering: Cell wall of cellulose and hemicelluloses with an outer mucilage
layer. Economically important mucilages include agar &
carrageenan. Some species deposit CaCO3 and MgCO3

Flagella: Lack of any flagellated stages

Chloroplas: Double membrane with no chloroplast ER, thylakoids unstacked,
primary pigment is chlorophyll a, accessory pigments include
carotenes, phycobilins (phycoerythrin-red and phycocyanin-blue)
and xanthophylls

Food storage: Floridean starch

Level of organisation: Unicellular to multicellular (branched filamentous,
pseudoparenchymatous sheets

Reproduction: Asexual by means of spores. The life cycle has alternation of
generations, which may be biphasic (Bangiophyceae) or triphasic
(Florideophyceae) with an extra sporophyte generation
dependent on the gametophyte. Sexual reproduction is all
oogamous

Habitat: Some terrestrial and fresh water forms, but most are common in
marine habitats from the intertidal zone down to ~200 meters

Question 2

Genus Polysiphonia

Answer 2

Small and finely branched
Grows in tufts on rocks
Pseudoparenchymatous
Isomorphic alternation of generations

Question 3

Polysiphonia Triphasic Life Cycle

Answer 3

Male gametophyte forms several spermatangia on special side branches called trichoblast

Spermatangia bear non-motile spermatia

Female gametophyte short lateral branch tip forms pericarp
Inside a 4 celled carpogonium is formed
Distal cell has long extension called trichogyne for sperm reception

After fertilization diploid nucleus passed to auxiliary cell

Mitosis begins and small mass of cells called carposporophyte
This grows and the pericarp grows into a cystocarp.
The carposporophyte then produces many carposporangia each releasing one large carpospore

Each spore produces a free living tetrasporophyte
This produces a tetrasporangium, here meisosis occurs to produce a tetrad of spores the tetraspores that create the gametophytes

Question 4

Genus Mazaella

Answer 4

Intertidal
Purple colour and iridescent sheen

Question 5

Characteristics of Chlorophytes

Answer 5

Cell: Eukaryotic

Cell covering: Cell wall of mainly cellulose, some calcification may exist

Flagella: Flagella are present in many genera. In others, flagella exist only
in the reproductive cells (zoospores or gametes). Usually two or
four anterior flagella per cell except in Oedogonium. Some
species have lost a flagellated stage

Chloroplast: Double membranes; no extra chloroplast ER; thylakoids in stacks
of two to six; primary pigment is chlorophyll a; accessory
pigments are chlorophyll b, carotenes and xanthophylls

Food: storage ‘True’ starch, often formed by structures in the chloroplasts called
pyrenoids. Green algae are edible but their small size makes
them an impractical major food source

Level of organisation: Highly variable. Form can be unicellular, aggregates, filamentous,
foliose, pseudoparenchymatous, parenchymatous or siphonous
(coenocytic)

Reproduction: Asexual reproduction is often via spores. A wide variety of sexual
reproductive strategies (isogamous, anisogamous, oogamy) and
all life cycle types exist (zygotic meiosis, gametic meiosis,
isomorphic and heteromorphic alternation of generations)

Habitat: Most are found in freshwater, but some are marine and a few are
terrestrial

Question 6

Genus Chlamydomonas (Order Chlamydomonadales)

Answer 6

Biflagellate unicellular organism
Freshwater lakes or ponds
Zygotic meiosis
Asexual zoospores

Question 7

Genus Volvox (Order Chlamydomonadales)

Answer 7

Most elaborate freshwater motile colonies
Whole colony enclosed in gelatinous matrix
Cells joined by cytoplasmic strands
Zygotic meiosis oogamous

Question 8

Genus Ulva (Order Ulvales)

Answer 8

Bright green
vegetative form has a small holdfast and sheet-like thallus
Isomorphic alternation of generations

Question 9

Genus Cosmarium (Order Desmidiales)

Answer 9

Special family of phytoplankton called Desmids
Single-celled with each cell made up of two semi-cells
Each has a chloroplast and a nucleus lies in between them
Sexual reproduction by conjugation

Question 10

Genus Spirogyra (Order Zygnematales)

Answer 10

freshwater filamentous green alga is
bright green colour
coarse filaments
do not get tangled

Question 11

Genus Chara (Order Charales)

Answer 11

characteristics that are more like those of higher plants

nodal-internodal construction

• lateral appendages
• an apical meristem
• formation of a phragmoplast during cell division
• protonema
• reproduction: sexual organs are multicellular with many sterile support cells surrounding
  oogonia and antheridia. No other alga has a protective layer of vegetative cells
  surrounding the reproductive cells. This is also a feature of land plants. The sperm cells are similar to the sperm of the Bryophytes.