Topic 13 Flashcards
What is the common ancestor of animals?
common ancestor resembled Choanoflagellates
heterotrophic protist
single flagellum surrounded by collar of microvilli (fingerlike projections of cell membrane)
cell morphology very similar to that of sponges (Porifera)
What is the hypothesis of evolution of multicellularity?
hypothesis: ball-shaped colony of choanoflagellates may have evolved into a simple animal with endo- and ectodermal layers
What is the role of natural selection in the evolution of multicellularity?
if cooperative aggregations of cells are able to survive better and produce more offspring than their unicellular counterparts
What the advantage of multicellularity?
coordination among cells
specialized cells for different functions (protective skins, enzyme secretion for trapping food, coordinated movement, specialized cells for reproduction)
What was the Paleozoic Era?
Cambrian explosion marks the earliest fossil appearance of many major groups of living animals
suddenly complex life-including many forms with skeletons
most major phyla appeared
Why did animal diversification occur so late?
Earth’s environment (oxygen in oceans and atmosphere was low until Cambrian)
need oxygen to support larger animals
What are the variables hypothesized to play a role in animal diversification?
higher oxygen levels (extrinsic)
the evolution of predation (intrinsic)
new niches beget more new niches (intrinsic and extrinsic)
modified genes, modified bodies (intrinsic)
What was the Mesozoic Era?
dinosaurs were the dominant terrestrial vertebrates
the first mammals emerged
flowering plants and insects diversified
What was the Cenozoic Era?
the beginning of the era followed mass extinctions of both terrestrial and marine animals
extinctions included the large, nonflying dinosaurs and the marine reptiles
mammals increased in size and exploited vacated ecological niches
the global climate cooled
What is the phylum porifera?
sponges
lack hox genes
range from a few mm to a few m in height
except for larval stage, are sessile
attached to one spot, do not move
do not go through ontogeny
no symmetry
What is mesohyl?
gelatinous acellular layer between the outer “skin” and the choanocyte layer
meso = middle, hyl = “stuff”, because it is acellular it is not a tissue
overall body plan of a sponge can range from a simple vase to a very complicated network of many flagellated chambers
What is suspension feeding?
can extract very tiny particles
the food particles are engulfed by phagocytosis at base of choanocyte cell
amoebocytes nudge up and take up food passed on by choanocyte
amoebocytes then carry food/nutrients to other cells, or use energy to make spicules or other structural materials
What is sponge reproduction?
mostly hermaphroditic (simultaneous: male and female at the same time, or sequential: first one sex, then change to the other)
do not have ovaries or testes (eggs arise from modified amoebytes, sperm arise from modified choanocytes)
external (some) or internal fertilization (mostly)
What is eumetazoan design?
specialized cells aggregated into distinct tissues, more advanced designs, tissues combine –> organs
What is the phylum cnidaria?
eumetazoa: have true, differentiated tissues
diploblastic: two layers (ecto- and endoderm)
organs: collections of tissues specialized for different tasks
most have radial symmetry and simple body plan
