Biodiversity Midterm 2

the evolution of multicellularity

1) Aggregation of individual cells. 2) Division of a single cell

traits of complex multicellularity

Three dimensional body plan, multiple cell types, developmental program involving cell division and differentiation.

what year did the Cambrian explosion occur?

542 million years ago

what year did the Permian extinction occur?

251 million years ago

Pannotia

the supercontinent in the south at the start of the Paleozoic era

Pangea

the supercontinent at the end of the Paleozoic era that spanned between both poles

Ediacaran Explosion

the period before the Paleozoic era. Soft bodied, non predatory organisms.

Ediacaran Biota

earliest known complex organism

causes of the Cambrian explosion

1) Changing environment- increase in oxygen levels, warm shallow marine areas, increased Ca+ in the ocean allows for skeletons to develop

2) Predators and bio-engineering species emerge

3) Evolution of developemental systems- Hox genes emerge

Body plan

assemblage of morphological features shared among members of a phylum.

features of a body plan

1) Grade of organization

2) Body symmetry

3) Number of germ layers

4) Body cavities

5) Segmentation

Cephalization

evolutionary trend of mobile organisms developing a head with sensory organs.

Coelom

fluid filled body cavity surrounded by mesodermal tissue

animal-vegetal axis

establishes polarity in embryo. vegetal pole= yolk rich (less active), animal pole= more active

Schizocoely

Coelom arises from the splitting of mesodermal tissue. (Protostomes)

Entercoely

Coelom forms at the same time as the mesoderm. (Deuterostomes)

Morphogens

Gradient of small, diffusible, signaling molecules that direct development. (external instructions, cells “talking to each other)

Choanoflagellates

the sister group of animals

Phylum Porifera

earliest diverging animals (sponges). Cellular grade of organization (pinacocytes, amoebocytes, choanocytes). Have a gelatinous “tissue” = mesophyl (not a true tissue)

Phylum Cnidaria (jellyfish and coral)

diploblastic (gat cavity) allows for extracellular digestion. appendages with nerve cells (nerve network)

True tissue

1) cells with a polarity (apical-basal), 2) basal lamina to anchor cells, 3) intercellular junctions between cells

Cnidocytes

unique stinging cells (Cnidaria)

Clade Bilateria

clade of animals defined by there bilateral symmetry.

Urbilateria

The last common ancestor of the bilaterian clade. Was likely marine, soft bodied ciliated organism with a small central brain.

Nephrozoa

The animals with kidneys (Protostomes and Deuterostomes)

Clade Lophotrochozoa

grouping of protostome animals. Some have trochophore larva and others have lophophore feeding structures.

Phylum Platyhelminthes

The flatworms. mostly parasitic organisms that produce yolkless eggs. yolk cells (Vitellaria) added later.

Phylum Annelida

The segmented worms.