Algae Terminology

What are algae?

• Mostly oxygen-producing, photosynthetic organisms found in aquatic habitats

• Include eukaryotic microscopic and macroscopic species, and prokaryotic cyanobacteria

How are algae distinct from land plants?

Lack key adaptations to terrestrial life that are found in plants

What are cyanobacteria?

• Prokaryotic algae

• Typically much smaller than eukaryotic cells

What does prokaryotic mean?

Lacks a nucleus and other membrane-bound organelles

How do cyanobacteria live?

• Some live alone as solitary cells or as pairs of cells formed after a recent cell division

• Other species form colonies

What is mucilage?

An extracellular coating mostly made up of polysaccharides, built from a mixture of sugars with and without nitrogen

Do cyanobacteria have flagella?

No

Why is vertical movement in the water column advantageous for cyanobacteria?

Helps them regulate their exposure to light for photosynthesis

List 3 different cellular mechanisms diverse cyanobacteria use to adjust their position.

• Pili

• Mucilage and protein fibrils

• Gas vesicles

What is the structure and function(s) of pili?

• Hair-like structures on the surface of the cell

• Can contract to pull the cell forward along a surface like a grappling hook in a small, intermittent twitching motion, with frequent changes in the direction of movement

• Can act like a parachute to slow down the vertical settling of free-floating cells

How do cyanobacteria use mucilage and protein fibrils to adjust their position?

• Pores in the cell surface create a mucilage, propelling the cell forward

• When the mucilage interacts with protein fibrils on the surface, they can introduce a swaying or rotating movement, depending on the orientation of the proteins

• Causes the cell to glide in a slow, uniform forward motion on a solid surface, in a direction parallel to the cell’s long axis

What is the structure and function(s) of gas vesicles/vacuoles?

• Aggregations of proteins in the cytoplasm

• Less dense than water, increasing buoyancy

• The cell can produce or collapse these vesicles to move closer to or further from the surface of the water

• Vertical positioning up and down the water column is controlled as cell density changes

What are filaments?

Long chains of cells

What is false branching?

Arises when filament growth occurs at a point of disruption

What are 2 types of false branching?

• When a heterocyte forms

• When a cell has died

What is true branching?

Produced by cell divisions perpendicular to the orientation of the main filament

What does multiseriate mean?

Filaments are more than a single cell in width

What does uniseriate mean?

Filaments are a single cell in width

Do cyanobacteria reproduce sexually using gametes and meiosis?

No

List 4 types of cyanobacterial reproduction.

• Binary fission

• Fragmentation

• Akinetes

• Spores

What is binary fission?

• Form of cell division

• Allows one cyanobacterium to form 2 daughter cells of equal size

• If these progeny become separated (do not form a filament or colony), the population increases

What is fragmentation?

Filamentous cyanobacteria can reproduce when filaments break apart into fragments

What are hormogonia?

• Short, motile fragments produced by many filamentous cyanobacteria

• Formed when separation disks (adjacent cells in the filament) undergo controlled death and collapse

Label structures a and b.

• a: hormogonium

• b: separation disks

What are akinetes?

• Specialized resting or dormant cells produced by heterocyte-forming filamentous cyanobacteria

• Vary in appearance

• Can better tolerate stress from temperature or nutrient levels than vegetative cells

• Higher density allows them to settle to the sediment where they remain dormant until conditions improve

• They then germinate, metabolize their storage compounds, produce gas vesicles, and rise through the water to produce new cyanobacteria

Label the structures indicated by the arrows.

Akinetes

How can akinetes be differentiated from heterocytes?

Akinetes generally have a larger size and more granular texture

How do akinetes have higher density than vegetative cells?

• Large size

• Thick cell wall

• Many storage granules

• Fewer gas vesicles

Label structures A and B.

• A: akinete

• B: heterocyte

What are spores?

• Small, round cells produced by division of vegetative cells

• Typically better at surviving unfavourable conditions than normal vegetative cells

List 2 types of spores.

• Endospores/baeocytes

• Exospores

What are endospores/baeocytes?

Spores that are produced internally within a vegetative cell, which then breaks open

Label the structures indicated by the arrows.

Endospores/baeocytes

What are exospores?

Spores that bud off one end of the parent cell

Label the structures indicated by the arrow.

Exospores

What is nitrogen fixation?

Conversion of nitrogen gas (N₂) from the atmosphere into ammonia (NH₄⁺)

Why is nitrogen fixation important?

• Ammonia (NH4+) can be used to build amino acids, DNA or RNA nucleotides, ATP, and other nitrogen-containing molecules essential for life

• Cyanobacteria can continue to grow in conditions that would otherwise have too little nitrogen

What does nitrogen fixation require?

An anoxic environment (without oxygen)

What are heterocytes/heterocysts?

Cyanobacterial cells with adaptations to reduce oxygen and increase energy production

• Not photosynthetic

• Thick cell walls reduce diffusion of oxygen into the cell

• Can import carbohydrates from neighbouring cells to provide fuel for energetically expensive nitrogen fixation

• Respiration produces energy in the form of ATP and also consumes oxygen, further reducing oxygen levels

What is the most common way for cyanobacteria to fix nitrogen?

Heterocytes

How can some cyanobacteria lacking heterocytes fix nitrogen?

• Under anaerobic conditions

• At night

List 7 functions of mucilage.

• Colony formation

• Nutrient absorption

• Improved buoyancy

• UV protection

• Herbivore deterrence

• Movement

• Improved nitrogen fixation

What is an ocular micrometer?

• A lens in the eyepiece of the microscope

• Used to measure the size of a structure in ocular units (OU)

What is the calibration ratio for the 4x objective lens?

250 um/OU

What is the calibration ratio for the 10x objective lens?

100 um/OU

What is the calibration ratio for the 40x objective lens?

25 um/OU

What are green algae?

• Known for their typically bright green colour, which they share with their close relatives the land plants

• Individual lineages of green algae will contain species with and without flagella, with branching or unbranching filaments, and that are unicellular, colonial, or multicellular

What are the main differences between the green algal lineages?

• Cellular

• Metabolic

• Ecological

Which 2 sister groups are green algae found in?

• Streptophytes

• Chlorophytes

Which group includes land plants and green algae?

Streptophytes

How were green algae historically classified?

According to their structure

What is convergent evolution?

Features evolved multiple times in different lineages

What is meiosis?

When cells go from diploid (2n) to haploid (n)

What is syngamy?

When cells go from haploid (n) to diploid (2n)

What is a dominant life stage?

Where mitosis creates a multicellular organism or increases population size

What is a haplontic life cycle?

A life cycle characterized by the presence of a dominant haploid (n) stage

What is a diplohaplontic life cycle?

A life cycle which alternates between dominant haploid (n) and diploid (2n) stages

What is a diplontic life cycle?

A life cycle characterized by the presence of a dominant diploid (2n) stage

What is a gametophyte?

• A haploid (n) organism in diplohaplontic species

• Undergoes mitosis to produce gametes

• Germinates from spores

What is a sporophyte?

• A diploid (2n) organism in diplohaplontic species

• Undergoes meiosis to produce spores

• Formed by fertilization of gametes

What does isomorphic mean?

In diplohaplontic organisms, when the diploid (2n) and haploid (n) forms are very similar in appearance

What does heteromorphic mean?

In diplohaplontic organisms, when the diploid (2n) and haploid (n) forms are morphologically distinct from each other

What does isogamous mean?

• When gametes are more or less identical in size and shape

• There are no male or female gametes, but there are different “mating types”, which can fuse

What does anisogamous mean?

• When 2 gametes are produced with different sizes and/or motility

• The small and motile gamete is usually the male

• The larger, non-mobile gamete is female

What are placoderm desmids?

Monophyletic group found within the Zygnematophyceae

Where are placoderm desmids found?

• Common in freshwater lakes and ponds

• Particularly abundant in highly-coloured or low-nutrient waters

What are semi-cells?

Placoderm desmid cells constricted into 2 parts

What is the isthmus?

A narrow region that joins semi-cells in placoderm desmids

Label structures A and B.

• A: semi-cell

• B: isthmus

How do placoderm desmids move?

• Secrete mucilage through pores in the cell walls

• Some species secrete mucilage alternately from each tip of the cell, resulting in a tumbling movement

• Other species screte mucilage from only one half of the cell, so when the mucilage abosrbs water, it swells and pushes the cell forward

How does asexual reproduction occur in placoderm desmids?

• Mitosis

• Each semi-cell receives one daughter nucleus and then produces new symmetrical semi-cells

How does sexual reproduction occur in placoderm desmids?

• Haploid (n) vegetative cells produce gametes by mitosis

• Gamete fusion produces a diploid zygospore, which undergoes meiosis to produce new haploid germlings

What type of life cycle do placoderm desmids have? How do you know?

Haplontic: dominant haploid stage

What are the Charophyceae?

Monophyletic group of freshwater green algae

Why is Chara among the best studied algae?

Close relationship to land plants

What is the thallus?

Vegetative body

What are oogonia?

Egg-producing reproductive structures

What are antheridia?

Sperm-producing reproductive structures

What type of life cycle does Chara have? How do you know?

Haplontic: dominant haploid stage

Is Chara isogamous or anisogamous? How do you know?

Anisogamous:

• Gametes differ in size and motility

• Large, immotile eggs

• Small, motile sperm

List 3 different ways microscopic green algae can live.

• Unicellular

• Colonial

• Multicellular

What does colonial mean?

Physically coordinated cells

What does multicellular mean?

Physical coordination and specialization of cell structure/function

List 2 types of colonies.

• Flattened colonies

• Spheroidal colonies

What are the Chlamydomonadales?

Algal order in the Chlorophyceae

Why are the Chlamydomonadales actively studied?

To better understand how multicellularity can evolve

How many flagella do most Chlamydomonadales have?

2

How many plastids do most Chlamydomonadales have? What shape are they?

Single cup-shaped plastid

What type of life cycle do the Chlamydomonadales have? How do you know?

Haplontic: dominant haploid stage

What regulates colony formation in Scenedesmus?

In the presence of a chemical produced by a zooplankton herbivore, Scenedesmus is stimulated to form colonies that are bigger, and therefore harder for the small zooplankton to eat

What are the Oedogoniales?

• Monophyletic group within the Chlorophyceae

• Includes Oedogonium and related genera

• Freshwater species that grow on substrates in shallow waters

• Can form large blooms, especially in nitrogen-rich wastewater

How does asexual reproduction occur in Oedogonium?

Motile zoospores form and are released from zygosporangium cells along the filament

How does sexual reproduction occur in Oedogonium?

• The egg in a spherical oogonium is fertilized by sperm produced by smaller antheridium cells near the oogonium (macrandrous species) or on dwarf male filaments (nannandrous species)

• The diploid (2n) zygote then undergoes meiosis to produce new individuals

Label structures A-C.

• A: vegetative cell

• B: dwarf male filament

• C: oogonium

What are the Ulvophyceae?

• Polyphyletic group of green algae

• The phylogeny has not been resolved

What is a dissecting microscope?

Important tool in the observation of biological specimens, especially for structures and features too small to observe easily by eye, but too large or bulky for a compound microscope

How does Hydrodictyon reproduce?

• Each cell in the colony can produce a new colony

• Leads to explosive population growth when nutrients are abundant

• Huge blooms can clog waterways and accumulate in rotting masses on the shore

What does coenocytic mean?

Cells contain multiple nuclei