Biology & Life Sciences Chapter 32 Homework The Answers Questions And Would Not Change

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224 Notes to Instructors

Notes to Instructors

Chapter 32 An Introduction to Animal Evolution

Chapter 33 Invertebrates

What is the focus of this activity?

In studying biodiversity, many students try to memorize each of the phyla and its

What is this activity designed to do?

Activity 32.1/33.1 What can we learn about the evolution of the animal kingdom by

examining modern invertebrates?

This activity is designed to help students understand how studying the existing traits

Activity 32.2/33.2 What factors affect the evolution of organisms as they

become larger?

Activity 27.2 addressed the difference in oxygen needs per ␮m2of membrane surface as

cells increased from about 10 ␮m in diameter (prokaryote) to 100 ␮m in diameter

Answers

Activity 32.1/33.1 What can we learn about the evolution of the

animal kingdom by examining modern invertebrates?

Fill in the chart on the next two pages to organize the major characteristics of key

invertebrate phyla.

Key invertebrate phyla

Characteristics Porifera Cnidaria Platyhelminthes Nematoda Annelida Mollusca Arthropoda Echinodermata

Examples of

organisms

Sponges Hydra, corals,

jellyfish

Planaria, flukes,

tapeworms

(flatworms)

Ascaris,

horsehair worms

(round worms

Earthworms,

leeches, fan

worms

(segmented

worms)

Clams,

oysters, snails

Insects, crabs,

lobsters,

crayfish

Starfish, sea

cucumbers, sea

urchins, sand

dollars

True muscle cells? No No; have

epithelio-

muscular cells

Yes Longitudinally

arranged muscles

only

Longitudinal

and circular

muscles

Increased

complexity of

muscle system

→ →

Key invertebrate phyla

Characteristics Porifera Cnidaria Platyhelminthes Nematoda Annelida Mollusca Arthropoda Echinodermata

Coelom?

Type?

None None None Pseudocoelom,

gut not lined

with mesoderm

embyonically

→ → →

Entercocoelom

formed by

outpocketing

off gut

Ciculatory

system?

Type?

None, primarily

diffusion

Diffusion and

some facilitation

of circulation via

fluid movement

in gastrovascular

Diffusion and some

facilitation of

circulation via fluid

movement in gastro-

vascular cavity.

Diffusion and

some

facilitation of

circulation via

fluid movement

Closed

circulatory

system,

heart(s),

arteries,

Some species

have an open

circulatory

system, and

some have a

All species

have an open

circulatory

system

Species have a

closed circulatory

system

Using the information in the chart and in Chapters 32 and 33 of Campbell Biology,

9th edition, answer the questions.

1. What set of characteristics is shared by all of the invertebrate animal phyla in the

chart?

2. What unique combination of characteristics defines each of the invertebrate phyla

as separate from the other phyla?

If you read down each column, you can determine the characteristics of each

combination of characteristics that is unique to and defines each phylum.

3. If you compare the characteristics of one phylum of the invertebrates with the next,

what key differences separate the groups from each other?

To answer this question, you need to compare the characteristics in a given

column/phylum with those in the next. Those characteristics that change from one

4. a. Looking across the rows, what major trends appear to occur in the evolution

of various organs or organ systems in these animal groups?

This chart is set up to allow you to visualize how the various systems changed in

the evolution of the various phyla. The arrangement also allows you to visualize

b. What developmental evidence is used to link Annelids, Arthropods, and Molluscs

evolutionarily?

Developmentally, Annelids, Arthropods, and Molluscs are all protostomes. They

Activity 32/33.1 227

c. What evidence is used to separate these phyla from the Echinoderms

and Chordates?

Echinoderms and Chordates are deuterostomes. This means that, develop-

d. Does this analysis provide evidence for or against the statement: “Evolution

adds onto or modifies what already exists”? Explain.

As is apparent in the chart, modifications are built upon what already exists. For

5. The chart organizes the major groups of animals based on grade, or shared body

plan features. What changes would you need to make in this organization to reflect

the possible phylogenetic relationships uncovered using molecular evidence?

To answer this:

a. On a separate sheet of paper, redraw the chart to reflect the new phylogenetic

relationships based on molecular evidence.

The new chart should show that recent DNA analyses indicate that, among the

b. What specific molecular characteristics/data are being used to determine

evolutionary relationships among animal phyla?

As noted in the text, the new molecular phylogenies “are based on mitochondrial

228 Activity 32/33.1

6. How would your answers to questions 2, 3, and 4 differ (if at all) when the chart is

redrawn and filled in to reflect changes in relationships based on molecular

evidence?

The answers to questions 2 and 3 would not change. Some of the evolutionary trends

7. In biological terms, a group of organisms is said to be successful if it is represented

by a large number of species or if the mass of all the organisms in the group is large.

(In both cases, “large” is determined relative to other groups or organisms.) Given

this definition of success, which of the major groups of animals would you argue is

the most successful? Be sure to provide evidence for your argument.

Answers may vary depending on the criteria chosen. For example, did you choose

success based on the total mass of organisms, the total number of organisms, or the

Activity 32.2/33.2 What factors affect the evolution of organisms

as they become larger?

In the evolution of life on Earth organisms have evolved from single celled to multicelled;

small to large; simpler to more complex. Keep in mind, that this apparent increase in

complexity occurs because evolution adds on to or modifies what already exists.

As you discovered in Activity 27.2, surface-area-to-volume ratios and the need for

organisms to gain or lose substances across their surface areas have put constraints on the

evolution of cell structure and function. These same constraints affect the ability of

multicellular organisms to survive. Given their small size, most of the evolution in

unicellular organisms has involved changes in cell chemistry and/or internal cellular

structure. In contrast the evolution of larger and larger multicellular organisms is

evidenced primarily as changes in both external and internal morphology.

1. A quick review and extension of Activity 27.2: How has small size affected

prokaryotic diversity?

Activity 32.2/33.2 229

a. How do surface-area-to-volume (SA/V) ratios change as the size and shape of

cells and organisms change? To answer this, calculate the SA and Vof a cube

1 mm on a side. Then do the same for cubes that are 2 mm and 4 mm on a side

and compare their SA/V ratios.

230 Activity 32.2/33.2

b. What do the ratios mean?

As linear dimensions increase by 2 times, SA increases by 4 times, but volume

c. Is this graph of the change (in surface area compared to volume) linear or

exponential?

To answer this question, complete the following table and then graph the surface

areas and volumes from this table and the previous table.

Cubes: 1 mm square 2 mm square 4 mm square Ratios

Linear dimension 1 mm 2 mm 4 mm 1:2:4

Cube linear

dimension:

8 mm 16 mm 32 mm 64 mm

Suface area 6  6  6

6  16  16

6  32  32

6  64  64

Activity 32.2/33.2 231

Data:

SA (mm2)V(mm3)

24 8

300000

250000

200000

150000

100000

50000

0 10000 20000

Surface area

Volume

30000

y = 0.068x1.5

R2 = 1

d. What effect does this relationship between surface area and volume have on the

ability of larger and larger multicellular organisms to support the metabolic needs

of all parts of their bodies, for examples, to supply oxygen needed for cell

respiration?

It is obvious that as organisms become larger, the SA/V ratio decreases

2. In the previous examples, as the “organism” sizes changed, their shapes remained

constant (as cubes). How would changing the shape of the organism affect SA/V

ratios? Use modeling clay or playdough to make a cube that is 2.5 cm (1 inch) on a

side. The cube will obviously have a constant mass or volume.

232 Activity 33.2/33.3

The answers will depend on the methods each student uses to change the shape. For

3. Review the chapters on fungal, animal and plant diversity in your textbook. For each

of the models that you developed to increase SA/V ratios, find an example of a

fungus, plant and/or animal, or a particular organ system, that uses the same method

to increase SA/V ratios and describe it below.

Shape change Effect on SA/V ratio

Model 1

Model 2

Model 3

Proposed model–increase SA/V by:

This type of increase in SA/V ratios can be

found in the following organism(s)/organ

systems:

Activity 33.2/33.3 233