Plant Biology: Hormones and Symbiotic Relationships

Plant Hormones

• Gibberellins (GAs) stimulate shoot elongation, seed germination, and fruit/flower maturation
• Auxins control meristem differentiation and are responsible for cell elongation in phototropism and gravitropism

Mycorrhizae

• Symbiotic fungi associated with plant roots
• Fungi are integrated into the root's physical structure
• Plants obtain essential elements from the soil
• Fungus obtains nutrients from plants

Epiphytes

• Plants that grow on other plants
• Not dependent on a host plant for nutrition
• Two types of roots: clinging aerial and aerial
• Clinging aerial roots absorb nutrients from humus accumulated in trees
• Aerial roots absorb moisture from the atmosphere

Saprophytes

• Lack chlorophyll
• Obtain food from dead organic matter
• Enzymes break down organic food materials into simpler forms
• Many parasitize fungi that digest dead matter or are mycorrhizal

Choanoflagellates

• Sessile protists, some colonial

Sponges

• Multicellular, sessile animals

• Major animal characteristics: multicellular, heterotrophs, and move at some point in their lives

Body Plans

• Asymmetry: Sponges
• Radial symmetry: Body parts arranged around a central axis, allowing organisms to experience the environment equally in all directions (e.g., Cnidarians)
• Bilateral symmetry: Body parts arranged along a single plane (e.g., most animals)

Body Cavities

• Coelom: A fluid-filled body cavity surrounded by mesoderm; found in some animals
• Diploblasts lack a coelom; coelom is enclosed, fluid filled body cavity in some animals

Blastula & Gastrula

• Blastula: Rapidly dividing cells that transition to gastrula, which develops specialized cells.
• Gastrula comprises of three primary germ layers: ectoderm, endoderm, and mesoderm.

Hydrostatic Skeletons

• Allow limbless animals to move via coordinated muscle contractions

Tube-within-a-tube body plan

• Protostomes or deuterostomes
• Outer tube forms body wall and inner tube forms digestive tract
• Digestive system formed from endoderm
• Body wall formed from ectoderm
• Muscles and organs formed by mesoderm

Protostomes and Deuterostomes

• Protostomes: Mouth develops first
• Deuterostomes: Anus develops first

Epithelial Tissues (Summary)

• Squamous: Flattened, overlapping cells (e.g., skin, mouth)
• Columnar: Long and wide cells (e.g., nose, trachea)
• Transitional: Elongated, compacted cells (e.g., urinary bladder)

Animal Body Plan Features

• Number of embryonic tissue layers
  • Diploblasts: 2 tissue layers (endoderm and ectoderm).
  • Triploblasts: 3 tissue layers (endoderm, ectoderm, mesoderm).
• Presence/absence of fluid-filled body cavity (coelom)
• Nervous system, body symmetry, and cephalization (development of a head region)
• Earliest events of embryonic development

Triploblasts

• Animals with three tissue layers

Animal Development Gastrulation

• Process that develops blastopore (hollow) from zygote (fertilized egg).
• Germ layers form during this process (ectoderm, endoderm, and mesoderm)
• These layers develop into organ systems (tissues, organs, etc).

Mouth Development (Summary)

• Two major groups
• Protostomes
  • Mesoderm separates to form body cavity in schizocoely process
• Deuterostomes
  • Mesoderm pinches off (enterocoely process) body cavity

Animal Phylogeny

• Specialized tissue
• Symmetry
• Coelom
• Protostome vs. deuterostome

Animal Phylogeny: Defining Features of Groups

• Porifera: Sponges, mostly marine, no true tissues. Suspension feeders, filtering water through their porous bodies. Reproduction: (asexual budding, sexual – eggs + sperm).
• Cnidaria: Jellyfish, corals, anemones. Primarily marine. Diploblastic. Radial symmetry. 2 body forms (polyp and medusa). Stinging cells (nematocysts) for predation
• Lophotrochozoa: Bilateral symmetry. Coelom present in some. Not all undergo a larval stage. Flatworms, annelids, and mollusks.
• Platyhelminthes: (Flatworms) – dorsoventrally flattened bodies. Most are free-living, some are parasitic. No coelom, but have a simple digestive system.
• Annelida: (Segmented worms) – Bodies subdivided into repeating segments. True coelom, complex digestive and circulatory systems.
• Mollusca: Snails, clams, octopuses. Soft-bodied animals, often with a hard shell (calcium carbonate). Well-developed muscular foot, visceral mass, mantle.
• Ecdysozoa: Grow by shedding their external covering. Bilateral symmetry. Segmented bodies and jointed legs. Protostomes. Nematodes (roundworms), and arthropods.
• Nematoda: (Roundworms) – Unsegmented, tubular bodies with a pseudocoelom. Most are free-living, some are parasitic.
• Arthropoda: Insects, crustaceans, arachnids. Segmented bodies, exoskeleton made of chitin, jointed appendages, well-developed sensory organs. Bilateral symmetry. Complex digestive, respiratory, and circulatory systems.
• Echinodermata: Starfish, sea urchins, sea cucumbers. Primarily marine. Bilateral symmetry as larvae, radial symmetry as adults. Water vascular system for movement and feeding. Endoskeleton. Unique deuterostome lineage.