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Blue-Green Algae (Cyanophyta)

• Includes a large number of algae, characterized by a specific cellular organization.
• Cells lack a well-defined nucleus.
• Characterized by a blue-green coloration from pigments like chlorophyll, carotenoids, and xanthophylls.
• Photosynthesis product is glycogen.
• Tolerant of varied conditions.
• Some species form symbiotic relationships with fungi (lichens).
• Have a relationship with bacteria.
• Classified as a separate phylum (Schizophyta).
• Lack of nuclei, sexual reproduction, and plastids.

Cell Structure (Cyanobacteria)

• Cell wall composed of two layers: thin inner and thick outer gelatinous layer (cell sheath).
• Internal structure includes a peripheral pigmented region (chromatoplasm) and a central colorless region (centroplasm).
• Possess plasma membrane, protein granules, and circular DNA (nucleoid).
• Ribosomes, photosynthetic lamellae, and phycobilisomes (cyanosomes).
• Reproduction through hormogonia.

Resting Spores or Kinetes

• Relationship between heterocysts' position and kinete formation location is evident.

Economic Importance

• Some species, like Nostoc, Oscillatoria, Scytonema, and Spirulina, are used to improve soil fertility.
• Certain species produce toxins that pollute water.

Eukaryotic Cells

• Protists are microscopic, unicellular organisms.
• Not classified in other kingdoms.
• Some are unicellular, colonial, or multicellular.
• Eukaryotic—possessing a true nucleus.
• Categorized according to nutrition modes.
• Include protozoa, algae, and fungus-like protists.
• Toxins can attack the liver or nervous system, or irritate the skin.
• Toxins released when cells die.

Animal-like Protists (Protozoa)

• Single-celled organisms with animal-like characteristics.
• Commensalistic—living in association with or in other organisms.
• Diverse habitats, including freshwater and marine ecosystems, frequently found in plankton.
• Ingest food through phagocytosis (some have mouthlike structures for consuming prey, others using pseudopods).
• Possess structures for movement and feeding (e.g., food vacuoles, contractile vacuoles).

Plant-like Protists (Algae)

• Photosynthetic; their nutrition is plant-like.
• Possess chlorophyll a (and some have chlorophyll b, c)
• Derive energy through oxygenic photosynthesis.
• Acquire carbon from dissolved bicarbonates.
• Eukaryotic organisms with internal structures like mitochondria, endoplasmic reticulum, ribosomes, and Golgi bodies, and in most cases, chloroplasts.
• Cell walls are primarily composed of cellulose (in most cases) with variations in other polysaccharides (pectin and alginic acids).
• Examples of algal phyla: Euglenophyta, Bacillariophyta, Chlorophyta, Phaeophyta, and Rhodophyta.

Phylum Euglenophyta

• Semirigid pellicle composed of protein strips.
• Size range from 10-500 µm.
• Predominantly freshwater, found in various environments including high organic content water and even soil, brackish, or salt waters.
• Storage product of photosynthesis is a β-1,3-linked glucan called paramylon.
• Reproduction through fission and cyst formation.

Division Bacillariophyta (Diatoms)

• Members are commonly known as diatoms.
• Single-celled or colonial, found in various waters (both fresh and salt).
• Cell walls are composed of silica (silicified).
• Characterized by overlapping halves (valves) that form a unique structure.
• Store photosynthetic products as lipids or oils, and protein-like substances (chrysolaminarin).
• Motile stage, sometimes seen in some species, involves a single flagellum.
• Can produce unique spore types known as autospores.
• Cell walls contain photosynthetic pigments like chlorophyll a and c, along with fucoxanthin.
• Cell structure described in valve and girdle views.

Cell Division of Diatoms

• Initial volume increase in the frustule (cell wall) results in slight valve separation.
• Nuclei undergo mitotic division.
• The resulting spindle is parallel to the cell's short axis.
• Longitudinal division of the chloroplast forms two daughter protoplasts.
• Each daughter protoplast receives half of the old cell wall (the hypotheca for one and epitheca for the other).
• The formed cell (with the old epitheca) retains the same size as the original cell, while the cell with the old hypotheca is slightly smaller.
• Repeated cell division leads to a decrease in the overall size of diatoms.