Exam 3 Review General Biology Study Notes: Eukaryotic Diversity, Plants, Fungi, and Animal Evolution (Chapters 27–32)

Chapter 27 – Diversification of Eukaryotes

Protists and Their Diversity

Protists are a diverse group of eukaryotic organisms that are not classified as plants, animals, or fungi. They exhibit a wide range of forms and functions, typically inhabiting aquatic environments.

• Defining Features: Protists lack defining features that unite them into a single group.

• Paraphyletic Group: Protists do not share a single common ancestor exclusive to them; they are grouped based on shared ancestral traits.

• Microscopy: Used to study cell structure and distinguish organelles and cell diversity.

• Synapomorphies: Shared derived traits used to identify evolutionary relationships.

Plasmodium and Disease

• Plasmodium spp.: Cause malaria, a major chronic infectious disease transmitted by mosquitoes.

• Life Cycle: Complex, involving both human and mosquito hosts.

Species	Disease
Plasmodium spp.	Malaria: affects over 3.4 billion people globally

Endosymbiosis and the Origin of Mitochondria

The endosymbiosis theory explains the origin of mitochondria and chloroplasts in eukaryotic cells.

• Mitochondria: ATP-generating organelles, believed to have originated from engulfed proteobacteria.

• Supporting Evidence:

  • Similar size to α-proteobacteria

  • Replicate by fission (like bacteria)

  • Have their own ribosomes and circular genomes

  • Phylogenetic data: Mitochondrial genes are closely related to bacterial genes

  • Lateral gene transfer: Genes from endosymbiotic bacteria moved into host nuclear genome

Endosymbiosis and the Origin of Chloroplasts

• All photosynthetic protists have chloroplasts.

• Chloroplasts have circular DNA and peptidoglycan in their cell walls.

• Endosymbiosis leading to chloroplasts first occurred in the ancestor of Plantae.

• Chloroplasts in other lineages are surrounded by more than two membranes, suggesting secondary endosymbiosis.

Key Themes in Eukaryotic Diversification

• Why protists are paraphyletic

• Origin of mitochondria and chloroplasts

• Leading hypotheses for the origin of the nucleus and membrane-bound organelles

• Major protist groups with medical/ecological significance (e.g., Plasmodium, dinoflagellates, shellfish poisoning)

Chapter 28 – Green Algae and Land Plants

Major Plant Groups and Key Features

Group	Vascular Tissue	Seeds	Dominant Generation
Nonvascular plants	No	No	Gametophyte
Seedless vascular plants	Yes	No	Sporophyte
Seed plants	Yes	Yes	Sporophyte

Key Features of Land Plants

• Vascular tissue: Allows transport of water and nutrients

• Seeds: Enable reproduction without water

• Flowers and fruits: Found in angiosperms

• Cuticle and stomata: Adaptations to prevent water loss and allow gas exchange

Seed Plants

• Angiosperms: "Encased seeds" (flowering plants)

• Gymnosperms: "Naked seeds"

• Fossil record for land plants begins about 475 million years ago

• Reproduce without water (pollen, seeds)

Preventing Water Loss: Cuticle and Stomata

• Cuticle: Waxy, waterproof layer covering aboveground parts, prevents water loss and limits CO2 uptake

• Stomata: Pores surrounded by guard cells that open/close to allow gas exchange while minimizing water loss

Alternation of Generations

• Life cycle alternates between multicellular haploid (gametophyte) and diploid (sporophyte) generations

• Dominant generation varies among plant groups

Chapter 29 – Fungi and Their Ecological Roles

Fungi as Decomposers and Mutualists

• Fungi are major decomposers, recycling nutrients from dead plants and animals

• Some fungi form mutualistic relationships with plants (mycorrhizae) and animals

Fungal Morphology

• Yeasts: Single-celled fungi

• Mycelia: Multicellular, filamentous forms composed of hyphae

• Some species can switch between yeast and mycelial forms

The Nature of Mycelium and Hyphae

• Hyphae: Long, narrow filaments that make up mycelium

• Hyphae divided by septa (cross-walls) with pores for material flow

• Some fungi are coenocytic (lack septa)

• Adaptations: High surface area for absorption, resistance to drying

Fungal Reproduction

• Fungi reproduce via diverse structures, both sexually and asexually

• Sexual reproduction involves four main types of structures:

  1. Swimming gametes and spores: Chytrids produce flagellated gametes and spores

  2. Zygosporangia: Zygomycetes form distinctive spore-producing structures

  3. Basidia: Basidiomycetes produce spores from club-like cells

  4. Asci: Ascomycetes form sac-like cells at hyphal ends

• Asexual reproduction involves production of conidia, spores dispersed by wind or water

Major Themes in Fungal Diversification

• Absorptive Nutrition and Symbiosis: Fungi absorb nutrients from their surroundings and form symbiotic relationships with other organisms

• Types of Plant-Mycorrhizal Interactions:

  • Ectomycorrhizal Fungi (EMF): Form sheaths around plant roots, do not penetrate root cells

  • Arbuscular Mycorrhizal Fungi (AMF): Grow into root tissue, increasing surface area for nutrient exchange

Fungi as Decomposers: Adaptations

• Fungi digest food outside their bodies and absorb the resulting simple compounds

• Secrete enzymes to break down complex substances such as lignin and cellulose

• Lignin peroxidase: Catalyzes oxidation of lignin

• Cellulases: Convert cellulose into glucose for absorption

Chapter 30 – An Introduction to Animals

Major Animal Groups

• Lophotrochozoa: Include mollusks and annelid worms

• Ecdysozoa: Include nematodes and arthropods

Animal Body Plans and Evolution

• Animal kingdom is monophyletic

• Diploblasts vs. triploblasts (number of embryonic tissue layers)

• Radial symmetry vs. bilateral symmetry

• Bilateral symmetry associated with the evolution of the central nervous system

• Body cavity (coelom) evolution: Advantages for movement and organ function

Chapter 31 – Protostome Animals

Protostome Diversity and Adaptations

• Protostome development compared with deuterostomes

• Lophotrochozoans vs. ecdysozoans

• Major protostome phyla: Mollusks, annelids, arthropods, nematodes

• Arthropod segmentation, exoskeletons, jointed appendages, and wings

• Evolutionary strategies for occupying diverse habitats

Chapter 32 – Deuterostome Animals

Major Deuterostome Groups

• Deuterostomes: Include chordates and echinoderms

• Chordate characteristics: Notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail

• Major vertebrate innovations: Jaws, limbs, lungs, amniotic egg

• Evolution of endothermy in birds and mammals

• Basic timeline and patterns in hominin evolution (bipedalism, brain size, earliest Homo sapiens fossils, Out of Africa model)