General Biology Study Guide: Bacteria, Archaea, Protists, and Plant Diversity

Chapter 27: Bacteria and Archaea

Differences and Evolutionary Relationships

Bacteria and Archaea are two major domains of prokaryotic life, each with distinct evolutionary histories and characteristics. Understanding their differences is crucial for studying microbial diversity and evolution.

• Bacteria: Prokaryotes with peptidoglycan in their cell walls; diverse metabolic pathways; includes decomposers, pathogens, and nitrogen fixers.

• Archaea: Prokaryotes lacking peptidoglycan; often inhabit extreme environments; unique membrane lipids.

• Eukarya: Domain containing all eukaryotic organisms; evolved from prokaryotic ancestors.

• Evolutionary Relationships: Bacteria and Archaea diverged early in the history of life; Archaea are more closely related to Eukarya than to Bacteria.

Ecological Roles of Prokaryotes

Prokaryotes play essential roles in ecosystems as decomposers, producers, and nitrogen fixers. Cyanobacteria are notable for their role in oxygenic photosynthesis.

• Decomposers: Break down organic matter, recycling nutrients.

• Producers: Some prokaryotes, like cyanobacteria, produce oxygen via photosynthesis.

• Nitrogen Fixers: Convert atmospheric nitrogen into forms usable by plants.

• Pathogens: Cause diseases in plants, animals, and humans.

• Cyanobacteria: Only prokaryotes to perform oxygenic photosynthesis; crucial for Earth's oxygen supply.

Horizontal Gene Transfer

Horizontal gene transfer is the movement of genetic material between organisms, contributing to genetic diversity in prokaryotes.

• Mechanisms: Transformation, transduction, and conjugation.

• Importance: Facilitates adaptation and evolution; spreads antibiotic resistance.

Nutrition and Metabolism

Prokaryotes exhibit diverse nutritional strategies, classified by energy and carbon sources.

• Autotrophs: Use inorganic carbon (CO2) as a carbon source.

• Heterotrophs: Use organic compounds as a carbon source.

• Phototrophs: Obtain energy from light.

• Chemotrophs: Obtain energy from chemical compounds.

Key Terms

Understanding the following terms is essential for studying prokaryotic diversity:

• Halophile: Organism that thrives in high-salt environments.

• Extremophile: Organism adapted to extreme conditions (temperature, pH, salinity).

• Methanogen: Archaea that produce methane as a metabolic byproduct.

• Decomposer: Organism that breaks down dead organic material.

• Nitrogen Fixation: Conversion of atmospheric nitrogen to ammonia.

• Transformation: Uptake of free DNA from the environment.

• Transduction: Transfer of DNA via bacteriophages.

• Conjugation: Direct transfer of DNA between cells.

• Mutualism: Symbiotic relationship where both partners benefit.

• Commensalism: Symbiotic relationship where one benefits, the other is unaffected.

• Parasitism: Symbiotic relationship where one benefits at the expense of the other.

Chapter 28: Protists

Characteristics and Diversity

Protists are a diverse group of mostly unicellular eukaryotes. They exhibit a wide range of life cycles, habitats, and modes of nutrition.

• Unicellular and Multicellular Forms: Most are unicellular, but some (e.g., algae) are multicellular.

• Habitat: Aquatic environments, moist terrestrial habitats.

• Nutrition: Photoautotrophs, heterotrophs, mixotrophs.

Evolutionary Relationships

Protists are not a monophyletic group; they are classified based on evolutionary relationships and ecological roles.

• Paraphyletic Group: Protists do not include all descendants of their most recent common ancestor.

• Comparison with Other Eukaryotes: Protists differ from plants, animals, and fungi in their cellular organization and life cycles.

Endosymbiosis and Organelle Evolution

The endosymbiotic theory explains the origin of mitochondria and chloroplasts in eukaryotes.

• Primary Endosymbiosis: Ancestral eukaryote engulfed a prokaryote, leading to mitochondria and chloroplasts.

• Secondary Endosymbiosis: Eukaryote engulfed another eukaryote containing chloroplasts.

• Evidence: Double membranes, own DNA, similarities to prokaryotes.

Life Cycles and Classification

Protists exhibit diverse life cycles, including asexual and sexual reproduction. Classification is based on ecological roles and phylogeny.

• Major Clades: Excavata, Stramenopila, Alveolata, Rhizaria, Archaeplastida, Amoebozoa, Opisthokonta.

• Ecological Roles: Producers (algae), consumers (protozoa), decomposers.

Traits and Terminology

Key terms and traits help distinguish protist groups and their functions.

• Brown Algae: Multicellular, photosynthetic, includes kelp.

• Diatoms: Unicellular algae with silica cell walls.

• Dinoflagellates: Unicellular, often bioluminescent, some cause red tides.

• Flagella: Whip-like structures for movement.

• Cilia: Hair-like structures for movement.

• Haploid/Diploid: Refers to chromosome number in cells.

• Gamete: Reproductive cell (sperm or egg).

• Sporophyte/Gametophyte: Life cycle stages in algae and plants.

• Meiosis/Mitosis: Cell division processes; meiosis produces gametes, mitosis produces identical cells.

Chapter 29: Plant Diversity I – How Plants Colonized Land

Derived Characteristics of Land Plants

Land plants evolved unique adaptations to survive on land, distinguishing them from their algal ancestors.

• Multicellular Dependent Embryo: Embryo develops within parent tissue for protection.

• Walled Spores: Produced in sporangia; resistant to desiccation.

• Multicellular Gametangia: Structures for gamete production.

• Apical Meristem: Regions of cell division at tips of roots and shoots.

Adaptations to Terrestrial Life

Plants developed structures and life cycles to cope with terrestrial challenges.

• Cuticle: Waxy layer preventing water loss.

• Stomata: Pores for gas exchange.

• Support Structures: Lignin, vascular tissue for transport and support.

Alternation of Generations

Land plants exhibit alternation of generations, a life cycle with multicellular haploid and diploid stages.

• Sporophyte: Diploid, produces spores by meiosis.

• Gametophyte: Haploid, produces gametes by mitosis.

Bryophytes and Seedless Vascular Plants

Bryophytes (mosses, liverworts, hornworts) and seedless vascular plants (ferns, club mosses) represent early land plant lineages.

• Bryophytes: Nonvascular, dominant gametophyte stage.

• Seedless Vascular Plants: Vascular tissue, dominant sporophyte stage.

Key Terms

• Microphyll: Small leaf with a single vein.

• Megaphyll: Larger leaf with branched veins.

• Sporophyte, Gametophyte, Spore, Gametangia, Rhizoid, Vascular Tissue, Cuticle, Stomata, Bryophyte, Haploid, Microphyll, Archegonia, Antheridia

Chapter 30: Plant Diversity II – The Evolution of Seed Plants

Sporophyte vs. Gametophyte Generation

Seed plants show a dominant sporophyte generation, with reduced gametophytes protected within reproductive structures.

• Nonvascular Plants: Dominant gametophyte.

• Seedless Vascular Plants: Sporophyte and gametophyte both visible.

• Seed Plants: Dominant sporophyte; gametophyte reduced and dependent.

Adaptations for Dry Environments

Seed plants evolved pollen and seeds to reproduce without water, allowing colonization of dry habitats.

• Pollen: Delivers sperm to egg without water.

• Seeds: Protect and nourish the embryo; aid in dispersal.

Angiosperms and Gymnosperms

Seed plants are divided into gymnosperms (naked seeds) and angiosperms (seeds within fruits).

• Gymnosperms: Conifers, cycads, ginkgo; seeds not enclosed in fruit.

• Angiosperms: Flowering plants; seeds enclosed in fruit.

Coevolution and Diversification

Plants and animals have coevolved, influencing each other's diversification and adaptation.

• Pollination: Animals transfer pollen, increasing genetic diversity.

• Seed Dispersal: Animals aid in spreading seeds to new locations.

Human Impact and Extinction

Human activities affect plant diversity through habitat destruction, climate change, and introduction of invasive species.

• Extinction: Loss of plant species reduces ecosystem stability.

• Conservation: Protecting plant diversity is essential for ecosystem health.

Key Terms

• Seed, Homospory, Heterospory, Ovule, Pollen, Fruit, Endosperm, Double Fertilization, Secondary Metabolite, Conifer

Table: Comparison of Plant Groups

Group	Dominant Generation	Vascular Tissue	Seeds	Examples
Bryophytes	Gametophyte	No	No	Mosses, liverworts
Seedless Vascular Plants	Sporophyte	Yes	No	Ferns, club mosses
Gymnosperms	Sporophyte	Yes	Yes	Conifers, cycads
Angiosperms	Sporophyte	Yes	Yes	Flowering plants

Key Equations and Processes

• Photosynthesis:

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

• Alternation of Generations:

$\text{Sporophyte} \xrightarrow{meiosis} \text{Spores} \xrightarrow{mitosis} \text{Gametophyte} \xrightarrow{mitosis} \text{Gametes} \xrightarrow{fertilization} \text{Zygote} \xrightarrow{mitosis} \text{Sporophyte}$