Protists

Protists size range

Most protists are microscopic, ranging from about 5 to 500µm.

Why is the term 'protist' taxonomically incorrect?

Protists are not a monophyletic group; they are being subdivided into multiple kingdoms based on evolutionary lineages.

Two major supergroups of protists

Archaeplastida (plant-like protists) and Unikonta (animal- or fungus-like protists).

Habitats of protists

Marine, freshwater, terrestrial, and symbiotic (including pathogenic) environments.

Three main types of locomotion in protists

Flagella, cilia, and pseudopodia.

Flagella movement

Flagella move with a whip-like motion, either pushing or pulling the cell forward.

Cilia movement

Cilia beat in a coordinated, breaststroke-like motion, propelling the cell forward.

Cirri in ciliates

Cirri are fused cilia that act like little legs, allowing the cell to 'walk' along surfaces.

Pseudopodia function

Pseudopodia extend through the flow of cytoplasm into a bulge, driven by microfilaments made of actin.

Plasmasol vs. plasmagel

Plasmasol is the liquid cytoplasm in the cell's core, while plasmagel is the thicker, gel-like cytoplasm beneath the cell membrane.

Water balance regulation in protists

Using contractile vacuoles, which collect and expel excess water.

Role of microtubules in contractile vacuoles

Microtubules contract around the vacuole, forcing water out through a pore on the cell surface.

Main nutritional modes in protists

Autotrophic (photosynthesis or chemosynthesis) and heterotrophic (ingesting food).

Phagocytosis

The process of engulfing solid food particles using extensions of the cell membrane.

Cytostome

A 'cell mouth' where food is ingested in some protists.

Survival in harsh environments

Some protists survive by forming protective cysts and becoming dormant until conditions improve.

Sensing environmental cues in protists

Using cilia, flagella, and chemical receptors for touch and chemotaxis.

Chemotaxis

Movement toward or away from chemicals in the environment.

Hunting strategy of predatory protists like Coleps

They use sharp, tooth-like projections to bore into prey and consume it.

Sensing light in photosynthetic protists

Using a light-sensitive flagellum and a light-blocking eyespot (stigma).

Function of the eyespot (stigma) in protists

It helps the cell determine the direction of light by blocking and unblocking light to the flagellum.

Phototaxis

Movement toward or away from light, advantageous for photosynthetic protists.

Description of foraminiferans

Foraminiferans are protists that can be visible to the naked eye, sometimes larger than small multicellular animals.

Characteristics of ciliates

Ciliates are protists that move using cilia and often have complex feeding structures like a cytostome.

Movement in amoebas

Amoebas move using pseudopodia and engulf food through phagocytosis.

Role of microfilaments in amoeboid movement

Microfilaments, made of actin, contract to push cytoplasm into pseudopodia, enabling movement.

Protection mechanism in Coleps

Coleps have calcium carbonate plates that act as armor and sharp projections for feeding.

Advantage of dormancy in protists

It allows protists to survive in harsh or dry environments by forming protective cysts.