Prokaryotes

I. Prokaryotes — Overview

Prokaryotes = Bacteria + Archaea

Key Characteristics

  • Unicellular

  • No nucleus (DNA in nucleoid region)

  • No membrane-bound organelles

  • Size: 1–5 µm

  • First life forms on Earth (billions of years ago)

  • Reproduce rapidly

  • Major portion of Earth’s biomass

II. Classification of Life (Evolution of Classification)

Early Systems

  • 1700s: Plantae, Animalia

  • 1800s: Protista added

  • 1950s: Five kingdoms → Monera (prokaryotes), Protista, Fungi, Plantae, Animalia

Modern System (Most Important for AP Bio)

3 Domains

  1. Bacteria

  2. Archaea

  3. Eukarya

Prokaryotes = Bacteria + Archaea

III. Domains of Prokaryotes

A. Bacteria (Eubacteria)

Characteristics

  • Most common organisms

  • Live in normal environments

  • Have cell walls (peptidoglycan)

  • Many cause disease

Major Groups

  • Cyanobacteria → photosynthetic, produce oxygen

  • Spirochetes → spiral-shaped

  • Proteobacteria → very diverse

  • Gram-positive bacteria → thick cell wall

B. Archaea (Archaebacteria)

Characteristics

  • Ancient organisms

  • Live in extreme environments

  • No peptidoglycan cell walls

  • Unique cell membranes

Types

  • Methanogens → produce methane, live in intestines

  • Extreme halophiles → high salt environments

  • Thermoacidophiles → high heat + acidity

IV. Identifying Prokaryotes

A. Shape

Shape

Description

Example

Cocci

spherical

Streptococcus

Bacilli

rod-shaped

E. coli

Spirilla

spiral-shaped

Treponema

B. Movement

  • Use flagella

  • Flagellum rotates → propulsion

C. Cell Wall Structure

Gram Staining

  • Gram-positive: thick peptidoglycan

  • Gram-negative: thin wall + outer lipid layer

D. Energy Use

Carbon Source

  • Autotrophs → make own food

  • Heterotrophs → consume other organisms

Oxygen Use

  • Obligate aerobes → need oxygen

  • Obligate anaerobes → oxygen kills them

  • Facultative anaerobes → can live with or without oxygen

V. Nutrition

Heterotrophs

  • Depend on other organisms

  • Types:

    • Chemoheterotrophs

    • Photoheterotrophs

Autotrophs

  • Produce own food

  • Types:

    • Photoautotrophs (light energy)

    • Chemoautotrophs (chemical energy)

VI. Reproduction in Prokaryotes

Asexual Reproduction

Binary Fission

  • DNA replicates

  • Cell splits → identical daughter cells

  • Very rapid growth

Spore Formation

  • Dormant survival structures

  • Survive extreme conditions

  • Example: endospores

Sexual Genetic Exchange

Conjugation

  • DNA transfer through cell bridge

  • Increases genetic diversity

VII. Importance of Prokaryotes

A. Ecological Roles

Decomposers

  • Break down dead organisms

  • Recycle nutrients

  • Used in sewage treatment

Nitrogen Fixation

  • Convert nitrogen → usable form for plants

  • Example: Rhizobium in roots

B. Benefits to Humans

  • Produce vitamins in intestines

  • Food production (yogurt, fermentation)

  • Medicine and biotechnology

  • Environmental cleanup

C. Harmful Effects

  • Cause disease

  • Food spoilage

  • Infections

VIII. Research & Applications

  • Studied in:

    • Microbiology

    • Biotechnology

    • Immunology

  • Used in:

    • medicine

    • industry

    • environmental science

IX. AP Bio Key Concepts to Memorize

  • Prokaryotes lack nucleus.

  • Binary fission = rapid reproduction.

  • Gram staining distinguishes bacteria.

  • Archaea live in extreme environments.

  • Nitrogen fixation supports ecosystems.

  • Conjugation increases genetic diversity.

  • Bacteria essential for nutrient cycles.