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Chapter 33-56

BIO SCI 94 Chapter Notes - Chapter 33-56: Symmetry In Biology, Cambrian Explosion, Blastomere

Biological Sciences
Course Code
Robin Bush

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Lecture 14 Reading
Chapter 33
33.1 Review:
- Multicellular, heterotrophic eukaryotes- that lack cell walls - & ingest (eat) their prey
- Largest consumers in Earth
- 30-35 phyla & many number (approx 8 million or more) species
- Cambrian Explosion : The rapid diversification of animals body types & lineages
- Animals: member of Eukaryotic lineage.
- Complex, large, multicellular body. Eats other organisms & are mobile
- Key Traits of Animals
-Multicellular. ECM ( includes proteins specialized for cell-cell adhesion &
-Heterotrophs ( get their Carbon compounds from other organisms)
- Ingest or “eat”
- Move under their own power
- Has neurons & muscle cells (except for sponges)|| enables movement
- Fungi & animals similarity: multicellular heterotrophs & digest & absorb nutrients
-Animals are the only multicellular heterotrophs to ingest their food before digestion
- Animals are the largest: Herbivores, detritivores, & predators on Earth
- Animals: monophyletic group that originated from a protist similar to Choanoflagellates
- Basic “tool kit” emerged for multicellular organisms- root of animal lineage
- Sponges lack organized & complex tissues other than: rudimentary epithelium
-Most ctenophores & cnidarians: radial symmetry
- 2 embryonic germ layers
- Neurons organized into a nerve net
- Some of the genes responsible for bilateral symmetry came up before the split of ctenophores &
-Most animal species bilaterians
- Bilateral symmetry: 3 embryonic tissues & coelom: tube-within-tube
- Bilaterians: centralized nervous system & cephalized bodies
- Head region: mouth, sensory organs, & brain
- Bilaterian tube-within-tube (built 1 of 2 ways)
- Protostome or Deuterostome patterns of embryonic development
- Segmentation: annelids, arthropods, & vertebrates
- 3 types of data:
- Fossils

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- Comparative Morphology
- Body Plan: Basic architecture of animal’s body (limbs, body segments, & tissues)
- Comparative Genomics
- Animals are monophyletic group
- Multicellularity originated from a sponge-like animal
- Sponges & Choanoflagellates: (Similarities)
- Sessile: Permanently attached to substrate; immobile
- Choanocyte: flagellated feeding cell found in Choanoflagellates & sponges
- Choanoflagellates form colonies
- Epithelium: layer of tightly joined cells that cover interior and or exterior surface of animal
- Tool kit of genes: key set of developmental genes that establishes body plan in plants &
animals. Includes Hox genes
- Specialization of cell types
- Regulation of cell cycling & growth
- Adhesion among cells, between cells & extracellular matrix
- Regulation of self & nonself, innate immunity
- Programmed cell death
- Subsequent duplication & diversification of (^^) these genes contributed to animal
- Tissues: Group of cells that function as a unit
- Diploblasts:Body develops from 2 basic embryonic cell layers or tissues (ectoderm &
- Triploblast: Body develops from 3 embryonic cell layers or tissues : ectoderm,
mesoderm, & endoderm
- Germ Layer: ⅓ of the basic tissues formed during gastrulation- gives rise to all other
- Ectoderm: outermost layer; skin & nervous system
- Endoderm: innermost layer; (lining)digestive tract & organs connecting to it
- Mesoderm: middle layer; Circulatory system, muscles, & internal structures
(bones & most organs)
- Diploblasts:

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- Muscle simpler organization (ectoderm); Reproductive (endo)
- Radial Symmetry: 2 planes of symmetry; body formation is usually cylinder
- Bilateral Symmetry: 1 plane of symmetry (right vs left) w/ long & narrow body
- Bilaterians: Member of Bilateria. Bilaterally symmetrical @ some point in their life
- Protostomes & deuterostomes are bilaterians
- Nerve Net: organization of nerve cells into large ganglia or tracts (Ctenophores & cnidarians)
- Central Nervous System: Neurons collected into clusters called ganglia
- Ganglia: Mass of neurons in CNS
- Cephalization: formation of anterior region (head); mouth & sensory organs found
- Brain: aka cerebral ganglion
- Locating & capturing food is efficient if directed by head region and powered by body
- Basic Bilaterian body shape: “tube within a tube”
- Coelom: fluid-filled cavity between inner & outer tubes
- Circulation of O2 & nutrients
- Can act as a Hydrostatic skeleton
- Coelomates: Has coelom fully lined with mesoderm
- Acoelomates: no coelom
- Pseudocoelomates: Partially lined with mesoderm
- Protostomes: Mouth before anus; blocks of mesoderm forms the coelom
- Deuterostomes: Anus before mouth; pockets of mesoderm pinch off for coelom
- Lophotrochozoans: Grows continuously when conditions are good
- Ecdysozoans: grows: shedding of external skeleton (outer covering) & expands body
- Segmentation: vertebrates & invertebrates
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