Chapter 27 Review

Which of the following statements is false? Eumetazoans have specialized tissues and parazoans don't. Lophotrochozoa and Ecdysozoa are both Bilataria. Acoela and Cnidaria both possess radial symmetry. Arthropods are more closely related to nematodes than they are to annelids.

Acoela and Cnidaria both possess radial symmetry.

How have Hox genes contributed to the diversity of animal body plans?

Altered expression of homeotic genes can lead to major changes in the morphology of the individual. Hox genes can affect the spatial arrangements of organs and body parts. If a Hox gene was mutated or duplicated, it could affect where a leg might be on a fruit fly or how far apart a person's fingers are.

Which of the following is not a feature common to most animals? development into a fixed body plan asexual reproduction specialized tissues heterotrophic nutrient sourcing

asexual reproduction

The time between 542-488 million years ago marks which period? Cambrian period Silurian period Ediacaran period Devonian period

Cambrian period

Which of the following periods is the earliest during which animals may have appeared? Ordovician period Cambrian period Ediacaran period Cryogenian period

Cryogenian period

Describe and give examples of how humans display all of the features common to the animal kingdom.

Humans are multicellular organisms. They also contain differentiated tissues, such as epithelial, muscle, and nervous tissue, as well as specialized organs and organ systems. As heterotrophs, humans cannot produce their own nutrients and must obtain them by ingesting other organisms, such as plants, fungi, and animals. Humans undergo sexual reproduction, as well as the same embryonic developmental stages as other animals, which eventually lead to a fixed and motile body plan controlled in large part by Hox genes.

Using the following terms, explain what classifications and groups humans fall into, from the most general to the most specific: symmetry, germ layers, coelom, cleavage, embryological development.

Humans have body plans that are bilaterally symmetrical and are characterized by the development of three germ layers, making them triploblasts. Humans have true coeloms and are thus eucoelomates. As deuterostomes, humans are characterized by radial and indeterminate cleavage.

How is it that morphological data alone might lead scientists to group animals into erroneous evolutionary relationships?

In many cases, morphological similarities between animals may be only superficial similarities and may not indicate a true evolutionary relationship. One of the reasons for this is that certain morphological traits can evolve along very different evolutionary branches of animals for similar ecological reasons.

How is it that most, if not all, of the extant animal phyla today evolved during the Cambrian period if so many massive extinction events have taken place since then?

It is true that multiple mass extinction events have taken place since the Cambrian period, when most currently existing animal phyla appeared, and the majority of animal species were commonly wiped out during these events. However, a small number of animal species representing each phylum were usually able to survive each extinction event, allowing the phylum to continue to evolve rather than become altogether extinct.

Briefly describe at least two theories that attempt to explain the cause of the Cambrian explosion.

One theory states that environmental factors led to the Cambrian explosion. For example, the rise in atmospheric oxygen and oceanic calcium levels helped to provide the right environmental conditions to allow such a rapid evolution of new animal phyla. Another theory states that ecological factors such as competitive pressures and predator-prey relationships reached a threshold that supported the rapid animal evolution that took place during the Cambrian period.

Plant life first appeared on land during which of the following periods? Cambrian period Ordovician period Silurian period Devonian period

Ordovician Period

Consulting the modern phylogenetic tree of animals, which of the following would not constitute a clade? deuterostomes lophotrochozoans Parazoa Bilateria

Parazoa

If a Hox 13 gene in a mouse was replaced with a Hox 1 gene, how might this alter animal development?

The animal might develop two heads and no tail.

Why might the evolution of specialized tissues be important for animal function and complexity?

The development of specialized tissues affords more complex animal anatomy and physiology because differentiated tissue types can perform unique functions and work together in tandem to allow the animal to perform more functions. For example, specialized muscle tissue allows directed and efficient movement, and specialized nervous tissue allows for multiple sensory modalities as well as the ability to respond to various sensory information; these functions are not necessarily available to other non-animal organisms.

Describe at least two major changes to the animal phylogenetic tree that have come about due to molecular or genetic findings.

Two new clades that comprise the two major groups of protostomes are called the lophotrochozoans and the ecdysozoans. The formation of these two clades came about through molecular research from DNA and protein data. Also, the novel phylum of worm called Acoelomorpha was determined due to molecular data that distinguished them from other flatworms.

Approximately how many mass extinction events occurred throughout the evolutionary history of animals? 3 4 5 more than 5

more than 5

As with the emergence of the Acoelomorpha phylum, it is common for ____ data to misplace animals in close relation to other species, whereas ____ data often reveals a different and more accurate evolutionary relationship. molecular : morphological molecular : fossil record fossil record : morphological morphological : molecular

morphological and molecular

Which of the following is thought to be the most closely related to the common animal ancestor? fungal cells protist cells plant cells bacterial cells

protist cells

Until recent discoveries suggested otherwise, animals existing before the Cambrian period were believed to be: small and ocean-dwelling small and nonmotile small and soft-bodied small and radially symmetrical or asymmetrical

small and soft-bodied

Which of the following phenotypes would most likely be the result of a Hox gene mutation? abnormal body length or height two different eye colors the contraction of a genetic illness two fewer appendages than normal

two fewer appendages than normal

Explain some of the advantages brought about through the evolution of bilateral symmetry and coelom formation.

The evolution of bilateral symmetry led to designated head and tail body regions, and promoted more efficient mobility for animals. This improved mobility allowed for more skillful seeking of resources and prey escaping from predators. The appearance of the coelom in coelomates provides many internal organs with shock absorption, making them less prone to physical damage from bodily assault. A coelom also gives the body greater flexibility, which promotes more efficient movement. The relatively loose placement of organs within the coelom allows them to develop and grow with some spatial freedom, which promoted the evolution of optimal organ arrangement. The coelom also provides space for a circulatory system, which is an advantageous way to distribute body fluids and gases.

Which of the following statements about diploblasts and triploblasts is false? Animals that display radial symmetry are diploblasts. Animals that display bilateral symmetry are triploblasts. The endoderm gives rise to the lining of the digestive tract and the respiratory tract. The mesoderm gives rise to the central nervous system.

The mesoderm gives rise to the central nervous system.

An animal whose development is marked by radial cleavage and enterocoely is ________. a deuterostome an annelid or mollusk either an acoelomate or eucoelomate none of the above

deuterostome

Which of the following is not possible? radially symmetrical diploblast diploblastic eucoelomate protostomic coelomate bilaterally symmetrical deuterostome

diploblastic eucoelomate

What type of data is primarily used to determine the existence and appearance of early animal species? molecular data fossil data morphological data embryological development data

fossil data

During embryonic development, unique cell layers develop into specific groups of tissues or organs during a stage called ________. the blastula stage the germ layer stage the gastrula stage the organogenesis stage

gastrula stage

Which of the following organisms is most likely to be a diploblast? sea star shrimp jellyfish insect

jellyfish