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

Chapter 27: Bacteria and Archaea

Evolutionary Relationships and Characteristics

Bacteria and Archaea are two major domains of prokaryotic life, each with distinct evolutionary histories and biological features. Understanding their differences and ecological roles is fundamental in biology.

• Differences between Bacteria, Archaea, and Eukarya: Bacteria and Archaea are both prokaryotes (cells lacking a nucleus), but differ in cell wall composition, membrane lipids, and genetic machinery. Eukarya includes all organisms with a true nucleus.

• Ecological Roles: Prokaryotes act as decomposers, producers, nitrogen fixers, and pathogens. Cyanobacteria are unique among prokaryotes for their ability to perform oxygenic photosynthesis.

• Horizontal Gene Transfer: The movement of genes between organisms, not by descent, is common in prokaryotes and accelerates evolution. Mechanisms include transformation, transduction, and conjugation.

• Nutrition Types: Prokaryotes exhibit diverse nutritional modes, including photoautotrophy, chemoautotrophy, and heterotrophy.

• Key Terms: Halophile (salt-loving), Extremophile (thrives in extreme conditions), Methanogen (produces methane), Decomposer (breaks down organic matter), Pathogen (causes disease).

• Symbiosis and Communication: Prokaryotes engage in mutualism, commensalism, and parasitism. They also exchange genetic material via conjugation.

Example: Thermophilic archaea thrive in hot springs, while cyanobacteria are crucial for oxygen production in aquatic environments.

Chapter 28: Protists

Characteristics and Diversity of Protists

Protists are a diverse group of mostly unicellular eukaryotes, occupying a variety of ecological niches. They play key roles in aquatic ecosystems and have complex life cycles.

• Protist Diversity: Protists include algae, protozoa, and slime molds. They can be autotrophic, heterotrophic, or mixotrophic.

• Evolutionary Relationships: Protists are paraphyletic, meaning they do not form a single clade. They are more closely related to plants, animals, or fungi than to each other.

• Endosymbiosis: The origin of mitochondria and chloroplasts in eukaryotes is explained by the endosymbiotic theory, where ancestral protists engulfed bacteria.

• Life Cycles: Protists may have complex life cycles, including alternation of generations and multiple hosts.

• Classification: Major groups include Excavata, SAR clade (Stramenopiles, Alveolata, Rhizaria), Archaeplastida, and Unikonta.

• Ecological Roles: Protists are primary producers, decomposers, and pathogens in aquatic environments.

• Key Terms: Flagella (whip-like structure for movement), Cilia (hair-like structures), Haploid (one set of chromosomes), Diploid (two sets), Gamete (sex cell), Sporophyte (spore-producing phase), Meiosis (cell division producing gametes).

Example: Plasmodium (causes malaria) has a complex life cycle involving both humans and mosquitoes.

Chapter 29: Plant Diversity I – How Plants Colonized Land

Adaptations and Life Cycles of Land Plants

Land plants evolved from green algal ancestors and developed adaptations to survive terrestrial environments. Their life cycles and structures reflect these evolutionary changes.

• Derived Characteristics: Land plants possess multicellular embryos, cuticles, and alternation of generations. They produce spores in sporangia and have multicellular gametangia.

• Adaptations: Features such as waxy cuticles, stomata, and vascular tissues help prevent water loss and support upright growth.

• Alternation of Generations: Plants alternate between haploid gametophyte and diploid sporophyte stages.

• Bryophytes: Nonvascular plants (mosses, liverworts, hornworts) rely on moist environments and lack true vascular tissue.

• Vascular Plants: Ferns and their relatives have vascular tissues (xylem and phloem) for transport and support.

• Key Terms: Sporangium (spore-producing structure), Gametophyte (haploid phase), Sporophyte (diploid phase), Cuticle (waxy layer), Stomata (pores for gas exchange).

Example: Mosses (bryophytes) dominate moist habitats and show a prominent gametophyte generation.

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

Seed Plant Adaptations and Reproduction

Seed plants, including gymnosperms and angiosperms, have evolved complex reproductive strategies and adaptations for terrestrial life. Their seeds and pollen allow them to thrive in diverse environments.

• Sporophyte vs. Gametophyte: Seed plants have a dominant sporophyte generation; gametophytes are reduced and protected within seeds or flowers.

• Seed and Pollen Adaptations: Seeds protect embryos and provide nutrients; pollen enables fertilization without water.

• Coevolution: Plants and animals (especially pollinators) have evolved together, influencing each other's traits.

• Angiosperms vs. Gymnosperms: Angiosperms produce flowers and fruits; gymnosperms produce naked seeds (e.g., conifers).

• Life Cycles: Seed plants show alternation of generations, with specialized reproductive structures.

• Human Impact: Agriculture and habitat changes have affected plant diversity and extinction rates.

• Key Terms: Ovule (structure that develops into a seed), Pollen (male gametophyte), Fruit (mature ovary), Endosperm (nutritive tissue), Double Fertilization (unique to angiosperms), Conifer (type of gymnosperm).

Example: Flowering plants (angiosperms) dominate most terrestrial ecosystems due to their efficient reproduction and dispersal mechanisms.

Key Terms Table

The following table summarizes important terms and their definitions for Chapters 27–30:

Term	Definition
Prokaryote	Cell lacking a nucleus; includes Bacteria and Archaea
Endosymbiosis	Origin of organelles by engulfment of other cells
Gametophyte	Haploid phase producing gametes in plants
Sporophyte	Diploid phase producing spores in plants
Alternation of Generations	Life cycle alternating between haploid and diploid stages
Seed	Structure containing plant embryo and nutrients
Double Fertilization	Process in angiosperms where two sperm fertilize egg and central cell
Flagella	Whip-like structure for movement
Stomata	Pores for gas exchange in plant leaves
Cuticle	Waxy layer preventing water loss in plants