Book cover for Biology

Biology

Sylvia S. Mader, Michael Windelspecht

ISBN #9780078024269

12th Edition

687 Questions

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153,501 Students Helped

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

Chapter 28 delves into the evolution of invertebrates, emphasizing the characteristics that define animals and the evolutionary processes leading to the vast diversity observed today. It introduces major hypotheses like the colonial flagellate hypothesis and explores differences in body plan organization and development (radial vs. bilateral symmetry, protostome vs. deuterostome). The chapter also shows how combining morphological and molecular data has advanced our understanding of invertebrate phylogenies, highlighting the evolutionary continuum from simple sponges to more derived groups such as arthropods, lophotrochozoans, ecdysozoans, and invertebrate deuterostomes.

Learning Objectives

1

Explain the key characteristics that define the animal kingdom, including lack of cell walls, heterotrophy, multicellularity, and specialized tissues.

2

Describe and compare major evolutionary hypotheses such as the colonial flagellate hypothesis and understand their implications in the evolution of invertebrates.

3

Differentiate between various body plan organizations (radial vs. bilateral symmetry) and embryological development processes (protostome vs. deuterostome).

4

Analyze the evolutionary relationships among invertebrate groups, including ancient lineages like sponges and derived groups such as arthropods, echinoderms, lophotrochozoans, ecdysozoans, and invertebrate deuterostomes.

Key Concepts

CONCEPT

DEFINITION

Invertebrates

Animals that do not possess a backbone, displaying a wide range of body plans and developmental strategies.

Heterotrophy

A mode of nutrition where organisms obtain organic molecules by consuming other organisms instead of producing them internally.

Multicellularity

The organization of an organism into multiple cells that work together, often specializing in different functions.

Specialized Tissues

Groups of cells that perform specific functions within an organism, contributing to its overall biological processes.

Colonial Flagellate Hypothesis

An evolutionary theory suggesting that animals evolved from colonies of flagellated unicellular organisms that gradually specialized and formed multicellular assemblies.

Radial Symmetry

A body plan where body parts are arranged around a central axis, common in some primitive and simple invertebrates.

Bilateral Symmetry

A body plan characterized by a single plane of symmetry that divides the organism into mirror-image halves, frequently associated with more complex organisms with defined anterior and posterior ends.

Protostome

A group of animals in which the blastopore (the first opening in embryonic development) becomes the mouth; these organisms typically exhibit spiral cleavage during embryogenesis.

Deuterostome

A group of animals where the blastopore forms the anus and the mouth develops later, often exhibiting radial cleavage in early development.

Example Problems

Example 1

Which of these is not a characteristic of animals? a. heterotrophic b. ingest their food c. cells lack cell walls d. have chlorophyll e. multicellular

Example 2

The phylogenetic tree of animals shows that a. rotifers are closely related to flatworms. b. both molluscs and annelids are protostomes. c. some animals have radial symmetry. d. sponges were the first to evolve from an ancestral protist. e. All of these are correct

Example 3

Which of these does not pertain to a protostome? a. spiral cleavage b. blastopore is associated with the anus c. coelom, splitting of mesoderm d. annelids, arthropods, and molluscs e. mouth is associated with first opening

Example 4

Which features of a sponge are mismatched? a. buds—asexual reproduction b. collar cells—flagellated c. osculum—upper opening d. spicules—sexual reproduction e. spongin—support

Example 5

Comb jellies are most closely related to a. cnidarians. b. sponges. c. flatworms. d. roundworms. e. rotifers.
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Step-by-Step Explanations

QUESTION

How does the colonial flagellate hypothesis explain the evolution of multicellularity in animals?

STEP-BY-STEP ANSWER:

Step 1: Recognize that unicellular flagellates are capable of movement and have specialized structures like flagella for locomotion.
Step 2: Understand that under certain environmental pressures, these unicellular organisms may form colonies where individual cells remain attached.
Step 3: Realize that within these colonies, cells begin to specialize based on their position and function, leading to more efficient cooperation and division of labor.
Step 4: Conclude that this gradual specialization and cooperation among colony members provides a plausible pathway for the evolution of permanent multicellularity in the animal kingdom.
Final Answer: The colonial flagellate hypothesis suggests that multicellularity emerged from colonies of flagellated unicellular organisms that specialized and coordinated their functions, leading to the complex structure of modern animals.

Colonial Flagellate Hypothesis

QUESTION

What are the key differences between protostome and deuterostome embryological development?

STEP-BY-STEP ANSWER:

Step 1: Examine the cleavage patterns during early embryonic development; protostomes often exhibit spiral cleavage while deuterostomes display radial cleavage.
Step 2: Identify the fate of the blastopore: in protostomes, it develops into the mouth, whereas in deuterostomes, it becomes the anus.
Step 3: Consider other developmental differences, such as the formation and specialization of tissues and organs.
Final Answer: The fundamental differences between protostome and deuterostome development lie in their cleavage patterns and the fate of the blastopore – protostomes form their mouth first, while deuterostomes form the anus from the initial opening.

Protostome vs. Deuterostome Development

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Common Mistakes

  • Overlooking the importance of multicellularity and specialized tissues in defining the animal kingdom.
  • Confusing radial symmetry with bilateral symmetry and not understanding their evolutionary implications.
  • Misinterpreting the colonial flagellate hypothesis as applicable to all multicellular organisms rather than a specific evolutionary pathway for animals.
  • Neglecting the differences between protostome and deuterostome embryological development, leading to errors in phylogenetic classifications.
  • Underestimating the role of molecular data in modern phylogenetic studies and its integration with traditional morphological analyses.