Topic 12

Question 1

What is the cell structure and specialization of animals?

Answer 1

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

Question 2

What are characteristics of animals?

Answer 2

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

Question 3

What are the key innovations in animal evolution?

Answer 3

1. Patterns of embryonic development
2. Development of different tissues
3. Type of body symmetry
4. Presence or absence of a body cavity

Question 4

What is the homeobox?

Answer 4

highly conserved nucleotide sequence

regulatory genes (that produce proteins)

turn other genes on and off

Question 5

What are hox genes?

Answer 5

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

Question 6

What is reproduction and embryonic development in animals?

Answer 6

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

Question 7

What is protostomia?

Answer 7

first invagination of the gastrula (blastopore) becomes the mouth

Question 8

What is deuterostomia?

Answer 8

second invagination becomes the mouth

first opening becomes anus, or closes up

Question 9

What does cell cleavage in protostomes look like?

Answer 9

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)

Question 10

What does cell cleavage look like in deuterostomes?

Answer 10

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)

Question 11

What is direct development?

Answer 11

embryo continues gradually on towards adult form (humans)

Question 12

What is indirect development?

Answer 12

intervening stages (larvae) whose morphology and behavior differs greatly from sexually mature adult stage

Question 13

What is the group eumetazoa?

Answer 13

animals with true tissues

specialized cells aggregated into distinct tissues, more advanced designs

Question 14

What was the origin of embryonic tissue layers and muscle?

Answer 14

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)

Question 15

What are germ layers?

Answer 15

endo- (digestive tract)

ecto- (outer covering, skin and nerves)

meso- (muscle and other organs)

Question 16

What is radial symmetry?

Answer 16

no front and back, or left and right

radial animals are often sessile or planktonic (drifting or weakly swimming)

Question 17

What is bilateral symmetry?

Answer 17

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

Question 18

What is cephalization?

Answer 18

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)

Question 19

What are body cavities?

Answer 19

most triploblastic animals possess a fluid-filled body cavity

a true body cavity is called a coelom, derived from mesoderm

Question 20

What are coelomates?

Answer 20

animals that possess a true coelom

Question 21

What are pseudocoelomates?

Answer 21

animals lack complete mesodermal lining, possess a pseudocoelom

Question 22

What are acoelomates?

Answer 22

lack a body cavity

Question 23

What is the function of the coelom?

Answer 23

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)

Question 24

What are the key concepts surrounding animals?

Answer 24

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