Topic 12 Flashcards
What is the cell structure and specialization of animals?
animals are multicellular eukaryotes
they lack cell walls (unlike plants and fungi)
their bodies are held together by an extracellular matrix (ECM), structural proteins such as collagen
nervous tissue and muscle tissue are unique, defining characteristics of animals (ability to move)
tissues are groups of cells that have a common structure, function, or both: true tissues are separated by membranous layers
What are characteristics of animals?
chemoheterotrophic: cannot make own carbon-based food source, must consume other organisms
sexual reproduction (mostly): motile haploid sperm fertilizes larger non-motile haploid egg to make diploid zygote
capable of movement: at least one stage of life cycle
What are the key innovations in animal evolution?
- Patterns of embryonic development
- Development of different tissues
- Type of body symmetry
- Presence or absence of a body cavity
What is the homeobox?
highly conserved nucleotide sequence
regulatory genes (that produce proteins)
turn other genes on and off
What are hox genes?
control anterior to posterior developmental sequence of embryo
order of Hox genes along chromosomes similar among different groups of animals
but number of repetitions can differ
number of Hox genes varies among animal phyla (absent in sponges, few in jellyfish, many in vertebrates)
result of several gene duplication events over envolutionary
What is reproduction and embryonic development in animals?
most animals share similar pattern of early embryonic development
have haploid gametes of different sizes (small motile sperm, large non-motile eggs)
diploid zygote undergoes a number of mitotic cell divisions = cleavage
cleavage leads to formation of a multicellular, hollow blastula
the blastula undergoes gastrulation forming a gastrula with different layers of embryonic tissues
during development, germ layers give rise to the tissues and organs of the animal embryo
What is protostomia?
first invagination of the gastrula (blastopore) becomes the mouth
What is deuterostomia?
second invagination becomes the mouth
first opening becomes anus, or closes up
What does cell cleavage in protostomes look like?
the new row of cells is twisted slightly off centre
spiral cleavage
determinant: new cell is destined to form some part of the later embryo (removal of some cells results in embryo missing organs)
What does cell cleavage look like in deuterostomes?
each cell division stacks the new cells directly above the previous ones
radial cleavage
indeterminate: early embryonic cells not differentiated (could split young embryo and get two complete later embryos –> identical twins)
What is direct development?
embryo continues gradually on towards adult form (humans)
What is indirect development?
intervening stages (larvae) whose morphology and behavior differs greatly from sexually mature adult stage
What is the group eumetazoa?
animals with true tissues
specialized cells aggregated into distinct tissues, more advanced designs
What was the origin of embryonic tissue layers and muscle?
while sponges have the genetic tool kit needed for cell-cell and cell-ECM adhesion (most do not have complex tissues, lack Hox genes)
animals other than sponges are divided into two groups (based on the number of embryonic tissue layers they have)
What are germ layers?
endo- (digestive tract)
ecto- (outer covering, skin and nerves)
meso- (muscle and other organs)
What is radial symmetry?
no front and back, or left and right
radial animals are often sessile or planktonic (drifting or weakly swimming)
What is bilateral symmetry?
two-sided symmetry (lobster, human)
bilateral animals often move actively and have a central nervous system (CNS)
bilaterally symmetrical animals have a right and left side, a dorsal (top) side and a ventral (bottom) side
anterior (head) and posterior (tail) ends
What is cephalization?
the development of the head (CNS)
concentration of sensory organs in head
adapted for forward and direction movement (quicker response to stimuli in environment, better able to search of food, better defenses capabilities)
What are body cavities?
most triploblastic animals possess a fluid-filled body cavity
a true body cavity is called a coelom, derived from mesoderm
What are coelomates?
animals that possess a true coelom
What are pseudocoelomates?
animals lack complete mesodermal lining, possess a pseudocoelom
What are acoelomates?
lack a body cavity
What is the function of the coelom?
cushions internal organs from blows to outside body
allows internal organs to shift without deforming outside of body
fluid-filled cavity can be used as hydrostatic skeleton (by tensing muscles around incompressible fluid)
What are the key concepts surrounding animals?
animals are a monophyletic group, with sponges as the basal animal
the evolution of animals is more complicated than a smooth transition from simple to complex
many key innovations did not arise all at once, evolution did not stop within any of the lineages
body symmetry is a key morphological aspect of an animal’s body plan
