Algae and fungus-like protists

Biology · Kingdom Protista. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

Test this topic free All Biology topics

The idea

Algae are the plant-like protists. They have chlorophyll a and make food by photosynthesis, but they have no true roots, stems or leaves, and their sex organs are not protected by sterile cells. They are grouped by their pigments, stored food, cell wall and flagella.

Euglenoids, dinoflagellates and diatoms are mostly single cells. Green, brown and red algae include large seaweeds. Green algae share so many features with plants that they are thought to be the ancestors of land plants.

Slime moulds and water moulds (oomycetes) are the fungus-like protists. They feed like fungi, but their cell structure and life cycle show they are not true fungi.

Rules to remember

Euglenoids (Euglena): flexible protein pellicle, no cell wall, eyespot, chlorophylls a and b; can also absorb organic food in the dark.
Dinoflagellates: cellulose plates, two flagella in grooves; blooms cause red tides.
Diatoms: silica shell in two overlapping halves; chlorophylls a and c; important producers; remains form diatomaceous earth.
Green algae (Chlorella, Spirogyra, Ulva): chlorophylls a and b, starch, cellulose walls.
Brown algae (kelps, Fucus, Laminaria): fucoxanthin, food stored as laminarin, algin in walls.
Red algae (Polysiphonia): phycoerythrin absorbs the blue and green light of deep water; source of agar.
Plasmodial slime mould: a multinucleate mass of cytoplasm with no walls. Water moulds: cellulose walls and flagellated spores; Phytophthora infestans causes late blight of potato.

Common mistake

Do not write that red algae absorb red light. A pigment looks red because it reflects red light; phycoerythrin absorbs blue and green light.

Worked example

Sea water near a coast turns reddish-brown and many fish die. The water is full of single cells covered by cellulose plates, each with two flagella in grooves. Identify the organism and the event.

Cellulose plates rule out diatoms (silica) and euglenoids (pellicle only).
Two flagella lying in grooves, one around the cell and one along it, are typical of dinoflagellates.
A sudden population explosion of dinoflagellates colours the sea and releases toxins that kill fish.

Answer: Dinoflagellates; the event is a bloom called a red tide.

Ask about this

Type what you are stuck on. The helper finds the explanation, worked examples and the notes to read, free and instant.

Keep going

← Protozoa: animal-like protists Body, nutrition and reproduction of fungi →Take a Biology test