Algae Question 01

Evolution of Algae

• Algae evolved from a common photosynthetic ancestor.
• Estimates and models from fossil records place this event around 2 billion years ago (Tor).
• Oxygen became gradually available as a potent electron acceptor.
• This enabled aerobic organisms to evolve, have more productive ecosystems, and form complex ones.
• Photosynthesis is essential for algae, and the equation for this process is 2 H₂O + CO₂ ⇒ O₂ + CH₂O + H₂O

Origin of Plastids: Primary Endosymbiosis

• Debate exists about the exact mechanisms and order of events in the creation of the first eukaryotic cell.
• A prevailing hypothesis is that photosynthetic eukaryotes developed from a heterotrophic eukaryote engulfing a cyanobacterium.
• The cyanobacterium gradually became integrated into the cellular machinery as a plastid.
• This process is known as primary endosymbiosis.
• Photosynthetic eukaryotes have three main groups: green plants, red algae, and glaucophytes. These groups make up Archaeplastida.

Cyanobacteria (Blue-Green Algae)

• Cyanobacteria are photosynthetic prokaryotes.
• They are ancient life forms classified as bacteria.
• Prokaryotes lack a nucleus, chloroplasts, and mitochondria.

Prokaryotes vs. Eukaryotes

• Prokaryotes:
  • Nuclear materials are not contained within a nucleus.
  • Lack chromosomes or nuclear membranes.
  • Typically lack mitochondria and plastids.
  • Ribosomes are smaller (70S type).
• Eukaryotes:
  • Nuclear materials are contained within a nucleus.
  • Chromosomes are enclosed within a nuclear membrane.
  • Often contain mitochondria and plastids (e.g., in plant cells).
  • Ribosomes are larger (80S type).

Common Characteristic Features of Algae

• Algae range in size from tiny unicellular microalgae to large multicellular seaweeds over 50 meters.
• They are defined as photosynthetic organisms.
• Algae lack specialized root, stem, or vascular bundles.
• They do not have a diploid embryo stage.
• They lack sterile tissue surrounding their reproductive structures.
• Zygote development occurs via mitosis or meiosis, not embryo formation.

Rhodophyta (Red Algae)

• Abundant in warm tropical and subtropical areas, also in temperate and polar seas.
• Some are unicellular, others are complex.
• Critical to coral reef development (encrusting, calcified corallines), vital for consolidation.
• Carbohydrate deposits, sometimes containing calcium carbonate, in cell walls – important globally for carbon storage.
• Among the deepest photosynthetic eukaryotes, exceeding 210 meters deep.
• Recognized by their pink color, due to phycoerythrin and phycocyanin pigments.
• Phycoerythrin efficiently harvests blue and green light, often obscuring chlorophyll a.
• Freshwater red algae may exhibit more phycocyanin, appearing bluish.
• Rhodophyta species in high light conditions display coloration variability from yellow to brown.

Batrachospermum sp.

• Found in cold, clear, running fresh water streams.
• Deep water species are a reddish violet color.
• Shallow water species are olive green.

Thallus of Red Algae

• Thallus is more delicate than brown algae.
• Algae of this class lack motile forms.
• Reproductive cells are non-flagellated.

Multicellular Macroscopic Thallus in Algae

• Most red algae species have multicellular macroscopic thallus formations having various forms.
  • Uni-axial forms with an axis formed from a single row of filaments.
  • Multi-axial forms with multiple filaments forming an axis.
• Important for structural diversity.

Cell Wall Structure in Algae

• Cell walls consist of cellulose fibers (rigid) and gels of sugar polymers or polysaccharides (flexible).
• Cellulose fibrils, a structural component of plant cell walls, are composed of glucose polymers.

Rhodophyta Plastid Morphologies

• Two common types of plastid morphologies exist in Rhodophyta:
  • Axial/stellate plastids (e.g., Porphyridium): Large plastids with a central paranoid.
  • Parietal/discoidal plastids (e.g., Audouinella): Multiple smaller plastids lacking paranoids.

Storage Products in Algae

• Floridean starch, lacking amylose but containing highly branched amylopectin, is a storage product typically found in Floridean algae.
• This is an example of a storage polysaccharide.
• The chemical structure and properties distinguish Floridean starch from starch found in other plants.

Pit Connections in Algae

• In many algal cells, 90% do not completely divide but have open regions eventually filled with proteins.
• Ordinal level taxonomic features in the cells are displayed by the core morphology of the cap.
• Primary and secondary pit connections lend strength and provide connections between the cells.

Reproduction in Algae

• Reproduction occurs vegetatively (cell division, fragmentation), asexually (monospores), and sexually (gametes).
• Gametes are formed within gametangia.
• Most taxa use vegetative or asexual reproductive methods, which can vary vastly by species.
• Sexual reproduction occurs in gametangia.
  • Male gametes are spermatia produced in spermatangia
  • Female gametes are carpogonia (sessile, borne on carpogonial branches), composed of trichogyne + base

Class-Bangiophyceae

• Subclasses Bangioideae and Florideae are significant classifications.

• Sub-class Bangioideae mostly feature freshwater/terrestrial environments; multicellular and unicellular forms occur in their species; they typically have only one nucleus per cell; and they have steallate chromatophores. They also commonly have one pyreniod and no pit connections

• Sub-class Florideae predominantly occupy marine environments; they are relatively complex, uniaxial or polyaxial; they often have more than one nucleus per cell; discoid chromatophores are common; they usually have pyranoid and pit connections

Life Cycle of Rhodophyta

• A variety of life cycle patterns are observed in Rhodophyte algae.
  • Biphasic life history (2 phases) - common in Bangiophycidae.
  • Triphasic life history (3 phases) - more common in Florideophycidae.
• Life cycles vary, but a common theme is distinct morphological and reproductive phases.

Phaeophyta (Brown Algae)

• Found in equatorial to subpolar regions, but they have their greatest diversity in cold and temperate areas.
• Their bodies typically have holdfast, stipe, and blade segments.
• The color and the texture of the algae can determine their location and general characteristic features.
• They contain fucoxanthin (golden brown xanthophyll pigment), which causes the color variation in the algae.
• Pigment coloration and cell structure are closely related.
• They have uninucleate cells.
• Mannitol and laminarin are reserve food source.
• They have a tough, leathery, or rubbery texture.

Cell Structure of Brown Algae

• Brown algae cell walls consist of cellulose, pectin substances, and algin/fucoidin compounds, leading to a gelatinous texture.

Cell Structure of Brown Algae

• Brown algae cells have mitochondria, ribosomes, endoplasmic reticulum, and Golgi bodies.
• Food reserves (e.g., laminarin) are stored within these cells.
• Mannitol is another photosynthesis product, serving as an alcohol.
• Chromatophores are plastids that store chlorophylls a and c, and fucoxanthin.

Reproduction in Brown Algae

• Brown algae exhibit various reproduction methods, including vegetative, asexual, and sexual reproduction.
• Vegetative reproduction involves fragmentation and propagules.
• Asexual reproduction involves zoospores.
• Sexual reproduction includes isogamy, anisogamy, and oogamy. Notably isogamy ranges from simple forms to more complex anisogamy.

Chlorophyta (Green Algae)

• Eukaryotic organisms with membrane-bound organelles.
• Thallus is typically green due to chlorophyll pigments.
• Chloroplasts are plastids containing chlorophylls a and b (typical of plants, not just algae).
• Pyrenoids are structures associated with starch formation.
• Starch is the major storage product; starch is stored within the cells.
• Motile forms possess eyespot (stigma) and other organelles.
• Unicellular, colonial, and multicellular filamentous forms occur.

Classification of Green Algae

• Unicellular thallus (e.g., Chlamydomonas, Chlorella, Chlorococcum).
• Colonial thallus (e.g., Gonium, Pandorina, Volvox, Chlorococcales, Pediastrum, Hydrodictyon).
• Multicellular filamentous thallus (e.g., Spirogyra, Ulothrix, Oedogonium, Chaetophora, Bulbochataete, Cladophora, Ulva, Stigeoclonium, Fristschiella).
• Siphonaceous/coenocytic thallus (e.g., Acetabularia, Characium).

Diatoms (Bacillariophyceae)

• Diatoms are eukaryotic algae with a unique, two-part silica cell wall called the frustule.
• They are mostly planktonic and occur in a variety of marine and freshwater environments.
• The frustule is composed of two overlapping parts (e.g., like petri dish halves).
• Two major orders: Centrales and Pennales are the chief divisions in Diatom morphology.
• Important as a primary food source.
• They have a biphasic life cycle that is important for understanding the algae’s genetic and reproductive patterns.
• They also have auxospores and different pigments (chlorophyll a, c, and fucoxanthin).
• Storage products are important for metabolic functions.

Differences between Bangioideae and Florideae

• Bangioideae: Primarily freshwater or terrestrial; simple cells; one nucleus per cell; and characteristic features of green algae
• Florideae (e.g., Gracilaria): Primarily marine; complexity of cell structure; many nuclei per cell, and the characteristic features of red algae.

General Differences in Algal Types (Summary)

• Pigments: Red algae (phycoerythrin/phycocyanin), brown algae (fucoxanthin), green algae (chlorophyll a&b), and diatoms (chlorophyll a, c, and fucoxanthin).
• Storage Carbohydrates: Red algae (floridean starch), brown algae (laminarin), green algae (starch), and diatoms (chrysolaminarin).
• Cell Wall Composition: Red algae (cellulose), brown algae (pectin & algin), green algae (cellulose and pectin), diatoms (hydrated silica).

Additional notes provided by the pages

• Organelles are present in all of the cells described (mitichondria, ribosomes, endoplasmic reticulum, Golgi).
• Differences in algal reproduction and life cycles are also important features to consider when making distinctions between the types.
• Various algae exhibit motile forms.
• Algae are ubiquitous in their general distribution to water sources, cold water to hot springs.
• Algae can cause significant economic loss to crops like tea and coffee.
• Detailed explanation and diagrams of algal thallus and types are also presented.