Exam 5 chapter 32

Question 1

General features of all animals include:

Answer 1

• heterotrophy
  
  • multicellularity
  • no cell walls

Question 2

Some, but not all, animals have or are capable of:

Answer 2

• the ability to actively move
• sexual reproduction
• specialized tissues – muscle and nerve
cells central to animal lifestyle

Question 3

Five key innovations in animal evolution:

Answer 3

1) symmetry
2) tissues that allow for specialized
structures or functions
3) body cavity
4) various patterns of embryonic development
5) segmentation or repeated body units

Question 4

Most animals exhibit radial or bilateral symmetry.

Answer 4

• Sponges are asymmetrical.
• Radial symmetry = longitudinal plane
through the central axis divides the
animal into two halves that are mirror
images of each other (examples are
members of phylum Cnidaria)

•  Bilateral symmetry = body has right and 	   left halves that are mirror images of 	  	   each other (examples are most other 	  	   animals that are not sponges or 	 	  	 	   cnidarians)

•  Advantages of bilateral symmetry –
	1)  move in a consistent direction with
	     head end leading
	2)  associated with brain, sensory 				     structures such as eyes and ears = 		     cephalization

Question 5

The evolution of tissues allowed for specialized structures and functions.

Answer 5

• Zygotes (fertilized eggs) are totipotent.
They can give rise to any and all cells in the animal’s body. Cells specialize during embryonic development. Specialization is irreversible in all animals except for sponges.

Question 6

Early Embryonic Development in Animals

Answer 6

• cleavage = succession of mitotic cell divisions without cell growth between the divisions
  
  • blastula = hollow ball of cells produced by cleavage; cavity inside is the blastocoel
  • gastrula = formed from the blastula when one end of the embryo folds inward, expands, and fills the blastocoel
  • archenteron = pouch inside the gastrula; opens to the outside via the blastopore

Question 7

A body cavity made possible the development of advanced organ systems.

Answer 7

Three germ layers:

	1) ectoderm (outer layer) gives rise to
			- outer covering of body
		- nervous system
	2) endoderm (inner layer) gives rise to
		- digestive system including 					   intestines, and organs like liver, 			   and lungs of vertebrates
	3) mesoderm (middle layer) gives rise 		     to
		- skeleton
		- muscles

Question 8

Three germ layers:

Answer 8

1) ectoderm (outer layer) gives rise to
- outer covering of body
- nervous system
2) endoderm (inner layer) gives rise to
- digestive system including intestines, and organs like liver, and lungs of vertebrates
3) mesoderm (middle layer) gives rise to
- skeleton
- muscles

Question 9

Three germ layers:

Answer 9

•  Animals having all three layers are
	   triploblastic and are members of the
	   Bilateria.  
	•  Cnidarians have only two layers 	 	 	   (ectoderm and endoderm) and are
	   diploblastic.  They have no organs.
	•  Sponges have no tissues or organs.

Question 10

Three body plans for bilaterally symmetrical animals.

Answer 10

1) Acoelomate = no body cavity between digestive tract and muscle layer (Ex. flatworms)
2) Pseudocoelomate = have body cavity that develops between mesoderm and endoderm
(Ex. roundworms)
3) Coelomate = body cavity develops entirely within the mesoderm
(Ex. annelids)

Question 11

The circulatory system functions to carry nutrients and oxygen to tissues and removes wastes, including carbon dioxide, by diffusion between the circulatory fluid and other cells in the body.

Answer 11

• Open circulatory system – blood passes from vessels into sinuses, mixes with body fluid that bathes the cells or tissues, and then reenters vessels in another location
  * Closed circulatory system – blood is entirely confined to vessels and is physically separated from other body fluids

Question 12

Bilaterians have two main types of development.

Answer 12

1) Protostome = “first mouth” – mouth develops from the blastopore
(Ex. flatworms, nematodes, mollusks,
annelids, arthropods)

2) Deuterostome = “second mouth” – 	 	    anus develops from the blastopore
	(Ex. echinoderms and chordates)

Question 13

Other terms to know:

Answer 13

• archenteron = “primitive gut”

* blastopore = opening into the archenteron

Question 14

Cleavage patterns

Answer 14

1) Spiral cleavage – new layer of cells nestles into the space between the older cells (Ex. annelids, mollusks, nemerteans, other protostomes)
2) Radial cleavage – pairs of new cells are positioned directly above the older cells (Ex. all deuterostomes)

Question 15

Determinate vs. Indeterminate Development

Answer 15

1) Protostomes have determinate development in which the type of tissue that each embryonic cell will form is determined early.
2) Deuterostomes have indeterminate development in which each cell remains totipotent and each cell’s fate is not determined for several cleavages.

Question 16

Segmentation – the advantages

Answer 16

1) efficient and flexible movement

2) redundant organ systems

Question 17

The Classification of Animals

Answer 17

There are 35-40 phyla based on shared characteristics. All animals share a common ancestor.

* Metazoa – includes the sponges that do 	not have embryonic germ layers or 	differentiated cells that form tissues
* Eumetazoa – includes animals that do 		have embryonic germ layers and 	differentiated cells that form tissues

Question 18

Molecular data help reveal evolutionary relationships.

Answer 18

.

Question 19

Morphology- and molecule-based phylogenies agree on many major groupings.

Answer 19

• Sponges – monophyletic; shares common ancestor with other animals
  
  • Cnidarians evolved before bilaterally symmetrical animals
  • Annelids and arthropods were thought to be closely-related based on segmentation, but the arthropods are now grouped with animals (ecdysozoans) that molt their cuticles at least once during their life

Question 20

Morphology-based phylogeny focused on the state of the coelom.

Answer 20

•  The protostomes and deuterostomes 		   differ in embryology.
	•  All acoelomates and pseudocoelomates
	   are protostomes.
	•  Some coelomates are protostomes;
	   some are deuterostomes.

Question 21

Protostomes consist of spiralians and ecdysozoans.

Answer 21

• Spiralian animals gradually add mass to
the body and exhibit spiral cleavage.
(Annelids and mollusks, rotifers, platyhelminthine worms, ectoprocts, and brachiopods are Lophotrochozoa)

•  Ecdysozoans grow by molting external 	   skeletons.  (Examples include many 	  	   species, but among these are the 	  		   nematodes and the arthropods.)

Question 22

Deuterostomes include chordates and echinoderms.

Answer 22

• Patterns of development indicate that
echinoderms and chordates evolved
from a common ancestor.

Question 23

The Roots of the Animal Tree of Life

Answer 23

• Metazoans appear to have evolved
from colonial protists. The Eumetazoa
most likely evolved from colonial
flagellates.
• Molecular analysis may explain the
Cambrian explosion. Rapid
diversification may be result of evolution of Hox genes.