Biofilm  

A thin, slimy community of microorganisms living together on a moist surface.

Bilateral

Having a left‑and‑right symmetry - a shape that can be split into two matching halves.

Birefringence

A light‑splitting effect in crystalline cell walls (especially in desmids) that makes them glow with colour under polarised light.

Bright field illumination

Standard microscope lighting with a bright background and natural colours.

Brownian motion

The constant, jittery movement of tiny particles caused by collisions with water molecules; its biological role in algae is still uncertain.

Chloroplast

The green organelle that performs photosynthesis, turning sunlight and CO₂ into sugars.

Crystalline

Made of highly ordered, repeating molecular structures that interact strongly with light.

Cyanobacteria  

Ancient blue‑green bacteria that first evolved oxygen‑producing photosynthesis.

Cytoplasmic strands

Thin internal fibres that hold the nucleus and other organelles in place.

Dark field illumination

A microscopy technique that redirects light so the background stays black while only scattered light from the specimen is seen, making the subject appear brightly lit.

Desmid

A group of freshwater green algae with ornate symmetry; among the closest living relatives of land plants. 

Diatom

A microscopic algae enclosed in a patterened silica shell called a frustule. Diatoms are major photosynthesisers in both fresh and marine waters and form a key foundation to aquatic food webs.

Diatomaceous earth

Powdery deposits formed from millions of accumulated diatom shells.

Endosymbiosis  

A major evolutionary event where one cell permanently incorporated another, eventually giving rise to chloroplasts in plants and algae.

Extracellular polysaccharide

A sticky, sugar-based substance released outside the cell that helps algae stick together or attach to surfaces. 

Filamentous algae  

Algae that grow as long chains of connected cells.

Flagella  

Whip‑like structures that beat to move a cell or colony through water.

Frustule  

The glass‑like silica shell of a diatom.

Fucoxanthin  

A brown pigment inside diatom chloroplasts that helps them absorb light efficiently.

Gonidia  

Large reproductive cells inside a Volvox colony that develop into new daughter colonies.

Isthmus  

The narrow waist between semicells where growth and division begin.

Mucilage  

A slippery gel used by algae for movement, attachment, or protection.

Nematocysts  

Stinging cells used by hydra to capture prey.

Nucleus  

The cell’s central organelle containing its DNA.

Oil deposits

Energy‑rich stores inside algae that also help control buoyancy.

Pennate diatom

A long, boat‑shaped diatom with bilateral symmetry.

Polarised light

Light filtered so it vibrates in a single direction; in microscopy it reveals colours and patterns in crystalline structures that are invisible under normal light.

Pyrenoids

Small organelles inside chloroplasts that concentrate carbon and enhance photosynthesis.

Raphe  

A slit in some diatoms that releases mucus for gliding movement.

Semicells  

The two mirror‑image halves that make up a desmid cell.

Somatic cells

The smaller cells on the outer surface of a Volvox colony that coordinate movement toward light and also perform photosynthesis.

Striae  

Rows of tiny grooves or pores on a diatom’s shell.

Vacuoles  

Fluid‑filled organelles that regulate pressure, store materials, and help maintain internal balance.