Protozoa

Domains and Kingdoms

Three Domains

  • Bacteria → Eubacteria.

  • Archaea → Archaebacteria.

  • Eukarya → Protista, Fungi, Plantae, Animalia.

Kingdom Protista

  • Very diverse group of eukaryotes.

  • Do not fit into plants, animals, or fungi.

  • Includes unicellular organisms and some multicellular forms (e.g., sea kelp).

  • First eukaryotes (~1.5 billion years ago).

General Characteristics of Protists

Habitat

  • Moist environments.

  • Water, soil, and inside organisms.

Cell Structure

  • Eukaryotic (membrane-bound nucleus).

  • Mostly unicellular.

  • Some colonial or multicellular.

Nutrition

  • Autotrophic → make own food (photosynthesis).

  • Heterotrophic → consume organic matter.

Reproduction

  • Asexual → binary fission.

  • Sexual → conjugation.

  • Some use both.

Endosymbiotic Theory (Lynn Margulis)

Definition

  • Eukaryotic organelles evolved from engulfed prokaryotic cells.

  • Symbiotic relationship → both organisms benefited.

Origin of Mitochondria

  • Anaerobic cell engulfed aerobic bacteria.

  • Aerobic bacteria produced energy → became mitochondria.

Origin of Chloroplasts

  • Cell engulfed photosynthetic cyanobacteria.

  • Cyanobacteria evolved into chloroplasts.

Evidence

  • Own DNA in mitochondria and chloroplasts.

  • Similar membranes to bacteria.

  • Similar size and structure to bacteria.

Significance

  • Major mechanism of evolutionary complexity.

  • Cells function like cooperative communities.

Major Types of Protists

1. Animal-like Protists (Protozoans)

  • Heterotrophic.

  • Usually unicellular.

  • Some parasitic.

2. Plant-like Protists (Algae)

  • Autotrophic.

  • Photosynthetic.

3. Fungus-like Protists

  • Decomposers or parasites.

  • Feed on dead or living matter.

Protozoans — Key Characteristics

  • Unicellular and microscopic.

  • Heterotrophic.

  • Live in moist environments.

  • Mostly reproduce by binary fission.

  • Some form protective cysts for survival.

  • Move using specialized structures.

Cyst Formation

  • Protective covering.

  • Prevents water loss.

  • Allows survival in harsh conditions.

Protozoan Movement and Classification

1. Zooflagellates

  • Move using flagella (whip-like tails).

  • Free-living or parasitic.

  • Example: Trypanosoma (sleeping sickness).

2. Sarcodines

  • Move using pseudopodia (“false feet”).

  • Irregular shape.

  • Feed by phagocytosis.

  • Example: Amoeba.

Subgroups:

  • Amoeboids → flexible cells.

  • Radiolarians → silica shells.

  • Foraminiferans → calcium shells.

  • Heliozoans → sun-like projections.

3. Ciliates

  • Move using cilia (hair-like structures).

  • Complex internal structures.

  • Two nuclei:

    • Macronucleus → cell function.

    • Micronucleus → reproduction.

  • Example: Paramecium.

  • Reproduction:

    • Binary fission.

    • Conjugation (genetic exchange).

4. Sporozoans

  • Non-motile.

  • Parasitic.

  • Complex life cycles involving multiple hosts.

  • Example: Plasmodium (malaria).

Protozoan Diseases

Malaria — Plasmodium

  • Spread by mosquitoes.

  • Infects liver and red blood cells.

  • Alternates between mosquito and human hosts.

Other Diseases

  • Trypanosoma → African sleeping sickness.

  • Giardia → digestive illness.

  • Entamoeba → amoebic dysentery.

  • Naegleria → brain infection (PAM).

Ecological Importance of Protozoans

  • Decompose organic matter.

  • Recycle nutrients.

  • Part of aquatic food chains.

  • Form symbiotic relationships.

Example of Symbiosis

  • Trichonympha in termites:

    • Produces enzyme to digest cellulose.

    • Helps termites digest wood.

Key AP Biology Concepts

  • Protists are extremely diverse and not a natural evolutionary group.

  • Endosymbiosis explains origin of mitochondria and chloroplasts.

  • Protists show evolutionary links between prokaryotes and multicellular eukaryotes.

  • Symbiosis is a major driver of evolutionary complexity.

  • Protists play important ecological and medical roles.