Biology 1A    Oct 8, 1998
Lecture 12 - Algae II

Page Contents :

• Reading Assignment
• Overview of Lecture
• Overview of Lab
• Lecture Outline
• Vocabulary
• Study Questions
• Related Websites

Stern: Chapter 18

Overview of Lecture:

Multicellularity has evolved many times in many ways.
Rhodophyta: the red algae.
Chromista
     haptophytes
     diatoms
     brown algae
Chlorophyta: the green algae.

Overview of Lab:

(A bullet indicates a handout.)
• Algal Morphology (cont'd).

A. Multicellularity has evolved many times.
1. The ancestors of animals & of fungi were unicellular.
2. The ancestors of the reds, greens, and chromists were all unicellular.
3. Each group developed multicellularity independently of the others.
B. How do you create a multicellular organism from a unicellular one?
1. Cellular division
2. Cellular cohesion
C. Multicellularity in algae.
1. colony - loose association of few to 1,000 of cells
2. coenocytes - multinucleate tubes
3. filaments - chains of cells (end-to-end)
a. unbranched filaments
b. branched filaments
4. membranes - flat sheet of cells; one to two cells cells thick
5. parenchyma - "blocks" of cells with divisions in three directions
D. Introduction to meristems
1. Some cells remain meristematic - retain ability to divide.
2. apical meristems
3. basal meristems
4. intercalary meristems

A. What are the red algae?
1. Over 4000 species
2. Principal seaweeds of tropical marine waters
3. Live at greatest depths of any algae
B. Distinguishing traits
1. cell wall - celloluse & mucilaginous substances (alginates)
2. flagellae - none
3. pigments
a. chlorophylls a & d
b. phycobilins
i. water-soluble pigments
ii. found only in reds and cyanobacteria
iii. phycoerythrin - red pigment; absorbs blue light
iv. phycocyanin - bluish pigment

4. photosynthate - floridean starch
5. life cycles
a. isomorphic alternation of generations
b. complex triphasic life history - two diploid phases
C. Economic importance
1. Porphyra - nori; vital to Japanese sushi industry; used as wrap or in soups
2. Gracilaria - source of agar for culturing
3. Gelidium - source of alginates for chocolate syrup, mayonnaise
4. Chondrus crispus (Irish "moss") - carageenan, emulsifier in pudding
5. some encrusted by calcium carbonate - create many tropical reefs and beaches

A. Distinguishing traits
1. cell wall
a. cellulosic compounds
b. usually contains other compounds; variable between groups
2. flagellae
a. in most groups, present only in the gametes
b. two dissimilar flagellae; attached laterally
3. pigments
a. chlorophyll a & c
b. fucoxanthin - golden-brown carotenoid
4. photosynthate - laminarin, mannitol, oils
5. relationships
a. Major groups: Haptophytes, Diatoms, Brown algae
b. Several non-photosynthetic groups: e.g. Oomycota
c. Most of the rest are lumped together as chrysophytes
B. Haptophytes
1. unicellular phytoplankton
2. coccoliths - CaCO3 plates secreted from Golgi apparatus
3. important fossil group
C. Diatoms
1. What are the diatoms?
a. unicellular or colonial
b. no flagellae
c. most are diploid
d. phytoplankton - most important source of food in aquatic ecosystems
2. Diatoms have a rigid frustule
a. located inside the cell membrane
b. made of crystalline silica
c. minute pores may be involved in locomotion
d. pennate or centric - defines the two major diatom groups
e. two halves like a petri dish or box
3. diatomaceous earth
a. dead diatoms accumulate on bottom of ocean, and are pressed into rock
b. mined for economic uses
D. Brown algae
1. What are the brown algae?
a. About 1000 species
b. Principal seaweeds of cool and temperate waters
c. kelps versus rockweeds
d. Most have alternation of generations, usually heteromorphic
e. Often have complex morphology
2. Example of complex morphology: Macrocystis
a. holdfast - attaches to substrate
b. stalk
c. blade - main organ of photosynthesis
d. float - keeps blades near the surface
3. Variations in morphology:
a. Fucus (rockweed) - receptacles, conceptacles; brown with a diploid life cycle
b. Nereocystis (bull kelp)
4. Importance of kelps
a. kelp forests
b. economic uses

A. What are the green algae?
1. 65,000 species, large percentage are freshwater desmids
2. Perhaps the most diverse group of algae morphologically
B. Distinguishing traits
1. cell wall - cellulose & cellulosic compounds
2. flagellae
a. 2, 4, many, or absent
b. number and symmetry of attachment distinguishes major groups
3. pigments
a. chlorophylls a & b (same as in plants)
b. carotenoids & xanthophylls
4. photosynthate
a. starch (same as in plants)
b. stored in organelles called pyrenoids
5. other characteristics
a. sexual reproduction - all three kinds found
b. life cycles - all three kinds found
c. morphology - unicells, colonies, filaments, membranes, etc.

• How many times has multicellularity evolved? Which algal groups have multicellular species?
• What must happen to produce a multicellular organism? How do meristems help solve this problem?
• How did fungi become multicellular? Is this kind of multicellularity found in other groups?
• How are colonies different from other kinds of multicellularity?
• What are the similarities between coenocytes and filaments? What are the differences?
• Explain the connection between meristems and indeterminate growth.
• What is the only multicellular group to completely lack meristems?
• Which group of seaweeds is most common in cool and temperate oceans? in tropical oceans?
• Why are red algae able to survive at greater depths than other algae?
• How is the life cycle of a red alga different from the typical alternation of generations?
• Why was the discovery of this life cycle important?
• What are some economic uses of red algae? of brown algae? of diatoms?
• Compare and contrast the cell wall composition of the six major algal groups. Do the same for flagellae, pigments, and photosynthates.
• Which group of algae contains chlorophyll d? chlorophyll b? mannitol? starch? floridean starch?
• What are the three major groups of phytoplankton? How are they important? How are they similar? How are they different from each other?
• Distinguish between kelps and rockweeds.Which would you expect to have larger floats and why?
• Diagram and label the parts of a typical kelp. Explain how each part functions.
• Describe the intertidal zone. How are alginates important to the survival of algae that live there?
• Draw and explain the structure of a typical flagellated chromist cell.
• What is a coccolith? What controversy started when coccoliths were first discovered?
• How was this controversy resolved?
• What kind of sexual life history do diatoms have? When is meiosis initiated and why?
• Diagram and explain the structure of a typical diatom frustule. What is it made of? How is its structure relevant to diatom asexual reproduction?
• What is diatomaceous earth? How is it formed? How can it be used economically?

• UCMP - Introduction to the Eukaryota
• UCMP - Introduction to the Rhodophyta
• UCMP - Introduction to the Chromista (Haptophytes, Diatoms, & Kelps)
• UCMP - Introduction to the Green Algae