Cellularity, Body Size, Germ Layers, and Body Cavities Flashcards
What is a tissue?
aggregations of morphologically and physiologically similar cells that perform a specific function
When did diplobastic germ layers arise?
arose in Cnidaria and Ctenophores
Where are the middle layers derived in diploblasts?
not embryologically
What does triploblastic development allow?
allows for more building material
When did triploblastic development airse?
Bilataria
Why can’t a cell become too large?
because cells require transport across membrane
Simple mechanisms for cells to transport easier?
fold, flat, or thread shape
What is the solution to the surface-to-volume dilemma? (5)
increase number of cells constituting a single organism
Metazoa that lack specialized tissues and organs rely on diffusion (needs cell to be in contact with environment)
some arrange cellular material to get diffusion is a shorter distance
pack internal bulk with nonliving material
assume different body geometry
What is an example of packing internal bulk with nonliving material?
jellylike mesoglea of medusae and ctenophores
Four different body geometry
increase in 1d is a vermiform plan (ctenophores)
increase in 2d is a flat, sheetlike body (Platyhelminthes)
sponges branch and fold internal and external body
internal transport and exchange systems (3d increase) like circulatory systems and organs
What are germ layers?
embryonic tissue layers of metazoa
What develops from each germ layer?
ectoderm (outer body wall) and endoderm (digestive tube)- outer and inner sheets of embryonic cells
What is the mesoderm?
fluid-filled cavity
Three functions of the mesoderm
frees inner tube (gut and some organs) from being attached to the body wall
serves as a mechanical buffer
allows development of new structures (storage chamber for gametes, circulation medium, and hydrostatic skeleton)
How is genetics and body cavity organization correlated?
Organization of body cavity is only loosely correlated to phylogeny
What is an acoelomate, and an example?
(Xenacoelomorpha, Platyhelminthes, Entoprocta, Cycliophora, Gnathostomulida, Micrognathozoa, Nematomorpha, Gastrotricha, some Loricifera, some Nematoda)-
mesoderm forms a slightly solid mass with small open spaces (sometimes)
What is a true coelom?
cavity arising from the mesoderm itself and is lined by peritoneum
What is a peritoneum?
thin lining from the mesoderm that encloses the cavity in annelids and echinoderms
How are organs found in the coelom?
organs are not truly free, but separated by the peritoneum
What is a pseudocoelom, and examples?
(Rotifera, some Nematoda, some Loricifera, most Priapula, Tardigrada, and some Kinorrhyncha)
body cavities that are neither from the mesoderm nor fully lined by the peritoneum
How are organs found in a pseudocoelom?
organs lie free and is bathed directly in its fluid
What does the space in a pseudocoelom represent?
space represents remnants of the blastocoel
