Prokaryotes, Protists, Plants, and Fungi: Structure, Function, and Ecological Roles

Prokaryotes: Bacteria and Archaea

General Characteristics

Prokaryotes are unicellular organisms lacking a nucleus and membrane-bound organelles. They include bacteria (with peptidoglycan cell walls) and archaea (without peptidoglycan).

• Bacteria: Possess peptidoglycan in their cell walls.

• Archaea: Lack peptidoglycan; often extremophiles.

• Roles: Nitrogen fixation, pathogenesis, production, decomposition, symbiosis.

Ecological Functions

• Decomposers: Release CO2, break down carbon into minerals or release it.

• Producers: Convert CO2 into O2; main food source for life.

• Nitrogen Fixers: Convert atmospheric N2 into usable compounds for plants.

• Pathogens: Cause diseases, affect species, and change environments.

• Symbiosis: Mutualistic (e.g., gut bacteria), pathogenic, bioremediation (removal of pollutants).

Genetic Exchange Mechanisms

• Transformation: Uptake of foreign DNA from surroundings.

• Transduction: Bacteriophages transfer DNA between bacteria.

• Conjugation: DNA transfer via temporary joining (sex pilus).

Cell Shapes and Gram Staining

• Coccus: Spherical

• Bacillus: Rod-shaped

• Spirillus: Spiral-shaped

• Vibrio: Comma-shaped

• Gram-positive: High peptidoglycan

• Gram-negative: Low peptidoglycan

Modes of Nutrition

Prokaryotes obtain energy and carbon in various ways:

• Photoautotroph: Light, CO2; photosynthetic prokaryotes, cyanobacteria, plants, algae.

• Chemoautotroph: Inorganic chemicals, CO2; certain prokaryotes.

• Photoheterotroph: Light, organic compounds; certain prokaryotes.

• Chemoheterotroph: Organic chemicals, organic compounds; many prokaryotes, protists, fungi, animals, some parasites.

Specialized Prokaryotes

• Thermophile: Archaea extremophile that tolerates high heat.

• Methanogen: Archaea extremophile that generates methane as a byproduct.

• Decomposer: Breaks down dead organisms and waste.

• Aerobic: Requires O2.

• Anaerobic: Does not require O2.

Types of Symbiosis

• Mutualism: Both species benefit.

• Commensalism: One species benefits, other unaffected.

• Parasitism: One species harmed, other benefits.

Protists

General Characteristics

Protists are eukaryotes that are not plants, animals, or fungi. Some are more closely related to plants, animals, or fungi than to other protists.

Endosymbiosis

• Primary Endosymbiosis: Eukaryotic cell engulfs a prokaryote (e.g., cyanobacterium → chloroplast).

• Secondary Endosymbiosis: Eukaryote engulfs another eukaryote.

• Tertiary Endosymbiosis: Host cell engulfs a eukaryotic alga that already contains a secondary plastid.

Life Cycles

• Gametic: Only diploid stage is multicellular (animals).

• Sporic: Alternation of generations; multicellular haploid and diploid stages.

• Zygotic: Only haploid stage is multicellular; meiosis occurs immediately after zygote forms.

Habitats and Motility

• Habitats: Phytoplankton (photosynthetic), zooplankton (heterotrophic), seaweed (photosynthetic).

• Motility: Flagellated, amoeboid (pseudopodia), ciliate.

Major Groups

• Excavata: Feeding groove, reduced mitochondria, diverse flagella.

• Stramenopiles: Hairlike projections on flagellum; includes diatoms, golden algae, brown algae.

• Alveolata: Sac (alveoli) under plasma membrane; includes dinoflagellates and ciliates.

• Rhizaria: Many amoebas with threadlike pseudopodia.

• Archaeplastida: Red and green algae, plants, charophytes.

Evolutionary Relationships

• Chlorophytes, Rhodophytes, and Plants: Photosynthetic, important habitats for fish.

Ecological Roles and Traits

• Diatoms: Unicellular, made of silica, reproduce sexually and asexually, produce 20-50% of oxygen.

• Brown Algae: Forms underwater forests, food source.

• Dinoflagellates: Single-celled, two flagella, forms red tide.

Plastids and Pseudopodia

• Plastid: Organelle in plant and algae cells that makes and stores food.

• Pseudopodia: Projection used for movement and capturing food.

Land Plants

Key Characteristics

Land plants have evolved adaptations for terrestrial life, including multicellular embryos, alternation of generations, and protective structures.

• Adaptations: Cuticle, stomata, vascular tissue, roots, lignin, tough-walled spores, alternation of generations, seeds, pollen, embryo protection.

• Sporophyte: Dominant in seed plants and seedless vascular plants.

• Gametophyte: Dominant in nonvascular plants.

• Pollen and seeds: Allow reproduction without water.

Reproductive Structures

• Flower: Attracts pollinators.

• Fruit: Makes animals carry seeds.

• Seed: Well protected, pollen transferred by animals and wind.

Vascular and Nonvascular Plants

• Lignin and vascular tissue: Allow plants to grow tall and outcompete others.

• Seedless plants: Lead to a drop in CO2 and global cooling.

• Microphyll: Small leaves with a single unbranched vein.

• Megaphyll: Highly branched vascular systems.

Plant Organs and Tissues

• Sporophyte: Multicellular diploid spore-producing plant.

• Gametophyte: Multicellular haploid.

• Spore: Haploid reproductive cell.

• Gamete: Mature male or female reproductive cell (sperm or egg).

• Sporangia: Multicellular organ that produces spores.

• Gametangia: Multicellular organ that produces gametes.

• Phloem: Moves sugars.

• Xylem: Moves water and dissolved minerals.

• Lignin: Provides structural support, binds cellulose and hemicellulose.

• Roots: Absorb water and nutrients, act as anchor.

• Rhizoids: Root-like filaments in nonvascular plants.

• Vascular tissue: Transports water and nutrients.

Dispersal Methods

• Seedless vascular: Water only.

• Gymnosperms: Mostly wind, some water.

• Angiosperms: Wind, water, fruits, burrs, animals.

• Coniferophyte: Cone-bearing trees (cold climates).

• Cycadophyte: Palm plants (warm climates).

• Ginkgophyte: Fan-shaped leaves.

• Gnetophyte: Diverse; only gymnosperms to have elements in their wood.

Human Influence on Angiosperms

• Genetic modification, medicine, lumber.

Seed Structure

• Seed: Embryo and its food in a protective coat.

• Ovule: Female plant structure.

• Pollen: Male gametophyte, wall made of sporopollenin.

• Endosperm: Tissue in angiosperms that nourishes the embryo.

Fungi

General Characteristics

Fungi are heterotrophic eukaryotes with chitinous cell walls. They can be unicellular (yeast) or multicellular (molds, mushrooms).

• Chitinous cell walls: Provide structural support.

• Mycelium: Network of hyphae.

• Heterotrophic: Obtain nutrients by absorption.

• Nonvascular: Lack vascular tissue.

• Alternation of generations: Life cycle includes both haploid and diploid stages.

• Reproduce via spores.

Ecological Roles

• Decomposers: Break down dead organic matter.

• Mycorrhizal fungi: Form symbiotic relationships with plant roots, aiding nutrient and water absorption.

• Pathogens: Cause diseases in plants and animals.

• Lichen producers: Symbiotic association with algae.

Biotechnological Roles

• Production of cheese, bread, beer, wine, antibiotics.

Fungal Structures

• Hyphae: Thread-like structures forming the body.

• Yeast: Single-celled fungus.

• Mycorrhizae: Fungi that extend plant root systems.

• Lichen: Alga growth, symbiotic with fungi.

• Heterokaryotic: Cell contains two distinct nuclei.

• Dikaryotic: Two genetically distinct nuclei sharing cytoplasm.

• Mold: Fungus growing in damp or decaying matter.

Table: Comparison of Major Groups

Group	Cell Type	Cell Wall	Nutrition	Reproduction	Ecological Role
Bacteria	Prokaryotic	Peptidoglycan	Various (photoautotroph, chemoautotroph, etc.)	Asexual (binary fission)	Decomposer, producer, pathogen
Archaea	Prokaryotic	No peptidoglycan	Various (extremophiles)	Asexual	Decomposer, extremophile
Protists	Eukaryotic	Varied	Photoautotroph, heterotroph	Asexual/sexual	Producer, decomposer, pathogen
Plants	Eukaryotic	Cellulose	Photoautotroph	Alternation of generations	Producer
Fungi	Eukaryotic	Chitin	Heterotroph	Spores, sexual/asexual	Decomposer, symbiont, pathogen

Key Equations

• Photosynthesis:

$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$

• Cellular Respiration:

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy}$

• Nitrogen Fixation:

$N_2 + 8H^+ + 8e^- \rightarrow 2NH_3 + H_2$

• Alternation of Generations (Plants):

$\text{Sporophyte} \xrightarrow{meiosis} \text{spores} \xrightarrow{mitosis} \text{gametophyte} \xrightarrow{mitosis} \text{gametes} \xrightarrow{fertilization} \text{zygote} \xrightarrow{mitosis} \text{sporophyte}$