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Tab 2: Unit Overview and Goals i

Contents

Investigating Biodiversity and Interdependence Unit overview ..................................................................... 2

Concept storyline: Investigating Biodiversity and Interdependence ................................................................. 5

suggested Pacing Guide: Investigating Biodiversity and Interdependence ................................................................. 6

Investigating Biodiversity and Interdependence Unit Goals ... 7

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Unit overview and Goals

2 STC Unit: Investigating Biodiversity and Interdependence

InvestIgatIng BIodIversIty and Interdependence Unit overviewInvestigating Biodiversity and Interdependence gives students the opportunity for hands-on study of a variety of organisms. The unit focuses on the structure and diversity of three groups in particular—animals, protists, and fungi—and highlights several representative organisms.

Students discover that although these organisms may at first appear dissimilar, they share many features. Students also learn that humans are organisms—members of the kingdom Animalia. They discover that humans undergo many of the same life processes as smaller organisms, which gives the unit relevancy.

Students of all ages, but particularly those in secondary school, have a natural curiosity about living things and how they function. Investigating Biodiversity and Interdependence taps this curiosity by first helping students clarify what they already know about organisms, then having them perform a series of engaging, hands-on, thought-provoking activities that will enable them to expand their knowledge.

Investigating Biodiversity and Interdependence addresses the skills and concepts deemed appropriate for grades 5–8 by the National Science Education Standards. Through this unit, students become more acquainted with a variety of living organisms—including themselves. One of the major strengths of this unit is that it raises questions that invite further investigation. While suggestions for further study and inquiry are explored through reading selections and extensions, the NSRC encourages teachers to allow students time for further exploration, either individually or in groups.

Suggestions for the integration of technology are included—specifically, the use of the Internet for research and the application of computer technology where appropriate and economically feasible.

Part 1: strUCtUre and FUnCtion

Investigating Biodiversity and Interdependence is divided into two parts: Part 1: Structure and Function and Part 2: Diversity.

Part 1 consists of five lessons that set the stage for the entire unit. Lesson 1 is a pre-assessment. It gives students an opportunity to share what they already know about organisms as well as to demonstrate their skill at making observations. Students begin filling out their organism photo cards, which they will revisit and revise throughout the unit. After reading a selection about taxonomy, they use a list of Latin and Greek terms to assign genus and species names to the organisms on the photo cards.

Lesson 2 serves as an introduction to the compound light microscope and an interesting insect called the WOWBug™. Students learn and hone microscope skills while performing authentic scientific tasks—preparing slides of a live organism, observing the organism through the microscope under different magnifications, drawing the organism while following a set of guidelines, and peer-evaluating drawings of other group members. The “structure and function” theme, inherent throughout the unit, is introduced in this lesson.

In Lesson 3, students work with an organism called Lumbriculus variegatus, a relative of the common earthworm. More commonly known as the California blackworm, Lumbriculus affords students a relatively large specimen to observe. While students can easily observe various blackworm behaviors without magnification, they continue to enhance their microscope skills as they determine the pulse rate of the blackworm. Students observe the most common method of reproduction of the blackworm—asexual reproduction by means of fragmentation.

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Tab 2: Unit Overview and Goals 3

Students set up a pond in a 16-oz plastic cup in Lesson 4. They make macro- and microscopic observations of both the solid and liquid parts of the pond. They place five Lemna (duckweed) fronds in their ponds. (In Lesson 8, when they revisit their ponds to observe any changes that have occurred, they determine the average daily increase in the number of Lemna fronds when they perform a final count.)

Lesson 5 acquaints students with several types of cells—algal, plant, and animal—and their components. Students hypothesize about how the structures of the various cells and their organelles are suited to their functions.

Part 2: diversitY

In Lesson 6, students observe and draw four protists—Amoeba, Euglena, Paramecium, and Volvox. They identify and label the protists’ organelles and their methods of movement.

Lesson 7 introduces the Exploration Activity, a group research project on which students will continue to work for the remainder of the unit. In this activity, students research the structure and function of various parts of a vertebrate and identify and describe the components of its habitat. They present their findings to the class using a method approved by the teacher.

In Lesson 8, students revisit the ponds they constructed in Lesson 4 and document changes they observe, including the average daily increase in the number of Lemna fronds.

In Lessons 9 and 10, students work with two tiny freshwater organisms—Daphnia and Hydra. They explore the effects of cola and alcohol solutions on Daphnia and, using the remaining Daphnia and blackworm fragments for food, observe Hydra’s feeding habits.

In Lessons 11 and 12, students investigate the Fungi kingdom. They compare the rate of mold formation on freshly baked or homemade bread and brand-name bread and follow the progress of a fungal garden over several weeks. They design an inquiry in which they explore substances that affect yeast activity.

Lesson 13 is the first part of a final assessment. Students use the information on their organism photo cards, which they have revised and updated during the unit, to construct Venn diagrams. Students learn how to create Venn diagrams that show both shared characteristics and dissimilarities among examples of living things. Students also complete a set of selected-response items.

Appendix B is the assessment for Part 1 of the unit—Lessons 1–5. Appendix C presents two final assessment options: an assessment for Lessons 6–12 and a cumulative assessment of Lessons 1–12.

Several class periods are scheduled at the conclusion of the unit for students to practice and present their Exploration Activities. The teacher will decide whether to have students present their Exploration Activity projects prior to Lesson 13. This would give them more time to prepare for the final assessment in Lesson 13.

readinG seleCtions

The STC Program™ incorporates two types of reading selections into each unit to enhance and extend the lesson material. The first type is embedded directly into the procedure of the lesson. Called “Building Your Understanding,” these reading selections provide background information or further explanation of concepts that are critical to a student’s understanding of the inquiry at hand. A second type, “Extending Your Knowledge,” appears at the end of the lessons, extending the concepts of the lesson to the real world, highlighting the application of the concepts in such contexts as science and technology careers, current events, and the history of science and technology. Each of these reading selections is followed by two open-ended questions designed to help students apply the information from the text and extend their thinking.

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sCienCe notebooks

Students should have a science notebook in which to record their observations, data, conclusions, and answers to questions as well as their own ideas and thoughts as they progress through the inquiries in the unit. Students should come to view their notebook as a resource that they can use throughout the unit. Reviewing observations, data, and information will help them refine their understanding of key concepts and conceptual models. Teachers will find the science notebook to be a valuable assessment tool in tracking student progress in both content knowledge and inquiry skills.

UsinG the annotated teaCher’s edition For stC-seCondarY

The Teacher’s Edition for STC–Secondary™ was developed to support the teacher in every aspect of the unit. Imagine having everything right at your fingertips, yet in an organized and intuitive design. In each lesson, you will find two types of content—pages that support the teacher, and pages that help the teacher support the students.

Teacher-only Content Pages: These pages have no Student Guide correlation, and appear at the beginning and end of each lesson. Here you will find overview and background information, planning and preparation, common misconceptions, homework and extension activities, and assessment guidelines. These pages guide teachers to obtain and prepare materials and highlight the concepts of the lesson.

Annotated Student Pages: These pages include inset full-color Student Guide pages right in the Teacher’s Edition. This way, you’ll always have the student instructions and reading selections right in front of you. The step numbers for each inquiry correspond one-to-one between the Student Guide step and

the annotated wrap of the Teacher’s Edition. The notes in the wrap provide anticipated or best responses, guide teachers in informal assessment, and offer classroom management tips. It is important to remember that the Student Guide explains the procedure while the annotation in the Teacher’s Edition wrap-around supports what is presented there.

teaCher’s tools Cd

The CD included with the kit includes all the reproducible sheets needed to teach this unit in PDF format. Blackline masters are grouped by lesson, so finding exactly what you need is fast and simple. If your unit uses chemicals, you’ll also find PDFs of all the Material Safety Data Sheets (MSDS) to print and have on hand in your classroom or the main office. Additional items include English and Spanish versions of the safety contract and any images or diagrams that need to be printed for use with overhead projectors or document cameras.

GlossarY

A glossary is included at the back of the Student Guide. It expresses scientific terms and concepts in a more formal language than students may initially use when they talk about or reflect on the inquiries and their observations. Before you introduce students to and have them use the more formal scientific terms, allow them to develop explanations and express their understanding in their own words.


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Grade-level ConCePtsUnit ConCePtsUniFYinG theMe

SUBCONCEPT 1Organisms have unique scientific names. Scientists name and classify organisms.

Lesson 1: What Are Organisms?Students list traits that are common to living things. Students learn how to assign each organism a genus and species name.

SUBCONCEPT 2Organisms have structures that perform specific functions.

Lesson 2: The WOWBug: Getting a Closer LookStudents learn and practice microscope skills in context with inquiries involving a tiny insect called the WOWBug™.

Lesson 3: Investigating LumbriculusStudents explore the structure and function of an invertebrate, segmented worm.

Lesson 4: Creating Your Own PondStudents create a pond ecosystem to study microorganisms and macroorganisms within.

SUBCONCEPT 3Different cells serve different functions. The cells of animals differ from those of plants.

Lesson 5: Exploring CellsStudents investigate the form and function of various cells: plant, animal, and algal.

SUBCONCEPT 4Some organisms are composed of a single cell.

Lesson 6: Exploring MicroorganismsStudents observe and identify four protists, recognizing animal-like and plantlike characteristics.

SUBCONCEPT 5An organism’s habitat influences its structure.

Lesson 7: Exploration Activity: Vertebrates and Their Habitats

Students research a vertebrate to discover how form and function interact.

SUBCONCEPT 6The structure of an organism’s parts is related to their function.

Lesson 8: Revisiting Your PondStudents make new observations of the pond and its organisms.

Lesson 9: Introducing DaphniaStudents observe, identify, and sketch Daphnia and its major structures.

Lesson 10: Exploring the HydraStudents observe a Hydra and its methods for obtaining food, reacting to touch, and reproducing sexually.

Lesson 11: Investigating Fungi I—The MoldsStudents observe mushroom spores and grow bread mold under different conditions. Students construct a fungal garden.

Lesson 12: Investigating Fungi II—YeastStudents explore yeast and yeast cell activity.

Lesson 13: Organizing Living Things— An Assessment

Students design Venn diagrams to show the similarities and differences among several kinds of organisms. Students also answer a series of selected-response items to demonstrate their knowledge of the concepts of the unit.

Concept storyline: Investigating Biodiversity and Interdependence

• Organisms have common traits. • The structure of each organism enables it to perform its function.

• Organisms are structured to carry out life tasks, such as getting food and using it to release energy.• All organisms are made of cells.

• Different kinds of living things obtain food and release energy in different ways. • Organisms can be classified based on their structure and function.


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1 Getting Started

Inquiry 1.1 Reading Selection

2 Inquiry 1.1. continued

Reflecting on What You’ve Done

Reading Selections

3 Getting Started

Inquiry 2.1 Inquiry 2.2

Reading Selection

4 Inquiry 2.3

Reflecting on What You’ve Done Reading Selection

5 Getting Started

Inquiry 3.1

6 Inquiry 3.2

7 Inquiry 3.3


8 Getting Started

Inquiry 4.1

9 Inquiry 4.2


10 Getting Started


11 Inquiry 5.2

12 Inquiry 5.3

13 Inquiry 5.4


14 Assessment—Part 1

(Appendix B) (optional)

15 Getting Started


16 Inquiry 6.2

17 Inquiry 6.3


Reading Selections

18 exPloration

aCtivitY Getting Started

19 exPloration

aCtivitY Getting Started continued

Part 1 Introducing the Exploration Activity

Reading Selection


Results (Appendix B)

(optional)

21 Getting Started

Inquiry 8.1

22 Inquiry 8.2


23 Getting Started

Inquiry 9.1

24 Inquiry 9.2


25 exPloration

aCtivitY Part 2 Choosing a

Vertebrate Part 3 Gathering Data

Reading Selection

26 Getting Started

Inquiry 10.1 Inquiry 10.2

27 Inquiry 10.3


Reading Selections

28 exPloration

aCtivitY Part 3 continued

29 Getting Started

Inquiry 11.1

30 Inquiry 11.2


31 exPloration

aCtivitY Part 4 Presenting Your

Research Project

32 Getting Started


33 Inquiry 12.1 continued


34 exPloration


35 exPloration


36 exPloration



37 Review for Assessment—

Part 2 (Appendix C) (optional)

38 Getting Started

39 Inquiry 13.1

40 Inquiry 13.2

41 Reflecting on

What You’ve Done Reading Selection


(Appendix C) (optional)

43 open 44 Assessment—Part 2

Results (Appendix C) (optional)

45 open

lesson 12

lesson 6

lesson 7

lesson 11

lesson 9

lesson 13

lesson 10

lesson 8

lesson 5lesson 4

lesson 2 lesson 3lesson 1

suggested Pacing Guide: Investigating Biodiversity and Interdependence Pacing Guide is based on 40- to 50-minute class periods.


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InvestIgatIng BIodIversIty and Interdependence Unit Goals

An organism is a complete living thing.

Living things share certain characteristics.

Organisms are composed of one or more cells.

All living things undergo fundamental life processes.

Scientists name and classify organisms for identification and organizational purposes.

A compound light microscope uses two convex lenses to produce a clear, magnified image that is upside down and backward.

Different combinations of lenses provide a range of magnifications.

At different magnifications, the field of view changes size; the size is directly related to the total magnification.

The WOWBug™ is a tiny organism; like other organisms, it has distinct ways of moving around.

A WOWBug is an insect with typical insect characteristics as well as specialized features.

A dry-mount slide facilitates the observation of microscopic objects and organisms.

Organisms groom to maintain their bodies in prime condition.

Lumbriculus has a segmented body that is similar to that of the earthworm.

Organisms as small as Lumbriculus have structures that make up a circulatory system to transport food and oxygen through their bodies.

Some organisms, such as Lumbriculus, can reproduce asexually through fragmentation, followed by regeneration of new body parts.

An ecosystem includes living things and their physical and chemical environment, which function together as a unit.

A pond is an example of an ecosystem.

A macroorganism is an organism you can directly view; a microorganism is an organism you need magnification to see.

A pond ecosystem includes macroorganisms and microorganisms.

The cell is the basic unit of life.

Cells have a characteristic structure.

An organelle is a well-defined structure found in a cell.

Plant and animal cells have a cell membrane, a nucleus, and cytoplasm.

Plant cells have a nonliving cell wall and chloroplasts; animal cells do not.

Cells have many organelles, and only some can be seen without special tools, such as stains or an electron microscope.

When a plant cell loses water, the cell membrane becomes visible as the cytoplasm shrinks and pulls away from the cell wall.

In this unit, students investigate the structure and function of organisms from four different kingdoms. Their experiences introduce them to the following concepts, skills, and attitudes.

ConCePts


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Protists are organisms historically grouped together because of their wll-defined nuclei and unicellular or multicellular structure.

Microorganisms, or microbes, are organisms too small to be seen clearly without a microscope.

Protists have specialized features; some protists are somewhat like plants, while others are more animal-like.

Different kinds of protists move in different ways.

A body part’s structure is related to its function.

An organism’s home is called a habitat.

A habitat includes biotic and abiotic factors.

Vertebrates are animals with backbones.

Vertebrate structures are uniquely suited to performing their functions.

The body temperature of some vertebrates (“warm-blooded”) remains nearly constant, while the body temperature of others (“cold-blooded”) varies with environmental temperature.

Aquatic plants that reproduce by budding may have very high reproductive rates.

Daphnia, like other crustaceans, have an external rather than internal skeleton.

Daphnia’s characteristics include gills for gas exchange, two pairs of antennae, jointed appendages, and a transparent exoskeleton.

In Daphnia, as in humans, alcohol depresses heart rate and caffeine stimulates heart rate.

A Hydra is a long, cylindrical organism that, like its relative the jellyfish, has tentacles for capturing food.

The Hydra responds to touch, indicating that it has nerves.

Hydra are able to consume food larger than themselves by ejecting paralyzing poison from sting cells.

Like some plants, Hydra can reproduce asexually by budding.

Fungi comprise a kingdom of organisms that includes mushrooms, yeast, and molds.

Fungi reproduce by releasing spores that are produced both sexually and asexually.

A combination of warmth, moisture, and darkness is ideal for the development of most molds.

Fungi are decomposers, obtaining their food by breaking down living or dead organic matter.

Certain substances promote yeast cell activity; others do not.

Yeasts metabolize glucose into alcohol (ethanol) and carbon dioxide when oxygen is absent and into water and carbon dioxide when oxygen is present.

Yeast cells release carbon dioxide rapidly when they are active (metabolizing glucose).

Some species of yeasts are beneficial to humans; others are harmful.

A working definition is one that changes to accommodate new information.

Scientists communicate through scientific drawings that incorporate clear labels, magnification scale, and perspective.

Communicating procedures and explanations is an important part of the scientific process.

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Developing a list of characteristics common to all living things.

Assigning genus and species names to organisms.

Learning the parts of a microscope, and practicing manipulating them to obtain the best image.

Preparing scientific drawings that incorporate clear labels, magnification scale, and perspective.

Preparing dry-mount slides.

Devising data tables.

Measuring and recording a pulse rate.

Making and recording observations.

Observing, drawing, labeling, and measuring cells.

Observing and identifying plant and animal cell organelles.

Identifying animal-like and plantlike characteristics of protists.

Reading to obtain more information about the five kingdoms, evolution, and ecology.

Researching the relationship between body structure and function in a vertebrate.

Working collaboratively and sharing information.

Designing and creating a poster to show research results.

Sharing the results of research with the class.

Determining the heart rate of a Daphnia under various conditions.

Observing, sketching, labeling, and measuring a Hydra.

Designing and performing an inquiry.

Recognizing the relationship between yeast cell activity and various substances.

Creating Venn diagrams to show the similarities and differences among organisms.

skills

Developing an interest in structure and function in organisms.

Recognizing that successful species have evolutionary adaptations that make them well suited for their environments.

Developing a willingness to think creatively and logically to form scientific explanations.

attitUdes

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STC Life Science Strand: Life on Earth i

Lesson 1 What Are Organisms?

Lesson at a Glance ..................................................................... 1-A

Inquiry 1.1 Describing and Naming Organisms .............. 5

That’s Life! ...................................................................................... 7What’s in an Organism’s Name? ..................................................... 10

Taxonomy Taken a Step Further .................................................... 16

Lesson 2 The WOWBug: Getting a Closer Look


Through the Compound Eye ......................................................... 24

Inquiry 2.1 Corralling Your WOWBugs .............................. 26

Inquiry 2.2 Preparing a Dry-Mount Slide to View

WOWBug Grooming Behavior ......................... 27

Inquiry 2.3 Preparing Scientific Drawings

of the WOWBug .................................................. 29

Intriguing Insects ........................................................................... 32

Dr. Matthews and the WOWBug .................................................... 35

Microscope Pioneers ..................................................................... 37

Lesson 3 Investigating Lumbriculus


Inquiry 3.1 Drawing and Measuring a Blackworm ........... 43

Inquiry 3.2 Determining the Pulse Rate

of a Blackworm ........................................................................... 45

Inquiry 3.3 Investigating Regeneration of Blackworms .. 47

More Than Just Bait ....................................................................... 49

COnTenTs

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InvestIgatIng BIodIversIty and Interdependence

ii STC Unit: Investigating Biodiversity and Interdependence

Lesson 4 Creating Your Own Pond


Inquiry 4.1 Constructing Your Pond .................................. 57

Inquiry 4.2 Observing Your Pond ...................................... 58

Even a Habitat Has to Live Somewhere ......................................... 60

Lesson 5 exploring Cells


Inquiry 5.1 Observing, Drawing, and Measuring

an Algal Cell ....................................................... 67

Plant and Animal Cells: The Same, but Different ........................... 68


an Onion Leaf Cell ............................................ 70


Elodea Leaf Cells ............................................... 72

Inquiry 5.4 Exploring Animal Cells .................................... 73

Who Eats Whom? Heterotrophs Meet Autotrophs ........................ 76

Lesson 6 exploring Microorganisms


The Fine Art of Naming Organisms ............................................... 82

Inquiry 6.1 Exploring Living Protists ................................. 84

Inquiry 6.2 Observing and Drawing Protists from

Prepared Slides .................................................. 86

Inquiry 6.3 Creating a Protist Cartoon .............................. 88

Bacteria: Friends or Foes? .............................................................. 90

Mighty Microbes ............................................................................ 93

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STC Life Science Strand: Life on Earth iii

Lesson 7 exploration Activity: Vertebrates and Their Habitats


Part 1: Introducing the Exploration Activity:

Planning Your Research .............................................. 99

Part 2: Choosing a Vertebrate ................................................. 99

Animals with Backbones ............................................................... 100

Part 3: Gathering Data .............................................................. 102

Part 4: Preparing and Presenting Research Projects .......... 104

Daphnia’s Change of Appetite ...................................................... 106

Habitats As Homes ........................................................................ 109

Lesson 8 Revisiting Your Pond


Inquiry 8.1 Observing and Drawing My Pond

and Its Microbes ................................................ 117

Inquiry 8.2 Determining the Average Daily Increase

in the Number of Lemna Fronds ................... 119

The Changing Pond ....................................................................... 121

Lesson 9 Introducing daphnia


Inquiry 9.1 Preparing a Scientific Drawing

of a Daphnia ..................................................... 127

Inquiry 9.2 Exploring the Effect of Alcohol and Cola

Solutions on the Heart Rate of Daphnia ...... 129

The Transparent Water Flea ........................................................... 132

Lesson 10 exploring the Hydra


Inquiry 10.1 Observing and Sketching a Hydra ............... 137

Inquiry 10.2 Feeding the Hydra ......................................... 138

Inquiry 10.3 Sketching a Budding Hydra .......................... 139

Hydra: Up Close and Personal ....................................................... 140

Jellyfish Get a Bad Rap .................................................................. 144

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InvestIgatIng BIodIversIty and Interdependence

iv STC Unit: Investigating Biodiversity and Interdependence

Lesson 11 Investigating Fungi I—The Molds


Inquiry 11.1 Comparing Mold Formation on

Two Types of Bread ........................................ 151

Inquiry 11.2 Creating and Observing a Fungal Garden .. 152

There’s a Fungus Among Us ........................................................... 154

Lesson 12 Investigating Fungi II—Yeast


Inquiry 12.1 Exploring Yeast Cell Activity ........................ 160

Introducing Yeast ........................................................................... 161

Yeast: Rising to the Occasion ......................................................... 163

Lesson 13 Organizing Living Things—An Assessment


Inquiry 13.1 Making a Venn Diagram ................................. 169

Inquiry 13.2 Creating a Venn Diagram for

Three Organisms ............................................. 170

Tropical Rainforests: What’s All the Hype? ..................................... 172

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lessonIntroducIng Daphnia

GettinG Started inquiry 9.1 Preparing a Scientific Drawing of a Daphnia

ObjectiveS Summarize the characteristics shared by Daphnia, lobsters, and shrimp.

Observe, sketch, and measure a Daphnia and identify its major structures.

cOnceptS Daphnia, like other crustaceans, have an external rather than an internal skeleton.

Daphnia’s characteristics include gills for gas exchange, two pairs of antennae, jointed appendages, and a transparent exoskeleton.

Scientists communicate through scientific drawings that incorporate clear labels, magnification scale, and perspective.

Overview Students list characteristics shared by Daphnia, lobsters, and shrimp. In their science notebooks, students answer the questions found in the Student Guide.

Students make a scientific drawing of a Daphnia, including labeled structures and a measurement of its length.

Key termS Exoskeleton Antenna

Brood chamber

Intestine

time 0.25 period 0.75 period

cOrrelatiOn tO natiOnal

Science StandardS

Content Standard C • Structure and function in living systems• Populations and ecosystems• Diversity and adaptations of organisms

Content Standard C• Structure and function in living systems• Populations and ecosystems• Diversity and adaptations of organisms

123-A STC Unit: Investigating Biodiversity and Interdependence

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leSSOn at a Glance

inquiry 9.2Exploring the Effect of Alcohol and Cola Solutions on the Heart Rate of Daphnia readinG SelectiOn

Determine the heart rate of a Daphnia under various conditions.

Update the organism photo card for Daphnia.

The Transparent Water Flea Read about the characteristics of arthropods, the phylum to which Daphnia belongs.

In Daphnia, as in humans, alcohol depresses heart rate and caffeine stimulates heart rate. Daphnia’s characteristics include gills for gas exchange, two pairs of antennae, jointed appendages, and a transparent exoskeleton.

Students calculate the average heart rate of a Daphnia observed under the microscope. Students then determine the average heart rates of Daphnia individuals immersed in an alcohol solution or a cola solution.

“The Transparent Water Flea” describes the anatomy of Daphnia, which is almost transparent when viewed through the microscope.

Heart rate Arthropod Gill

Carapace Water flea

Crustacean

0.75 period 0.25 period

Content Standard A• Abilities necessary to do scientific inquiry

Content Standard C• Structure and function in living systems• Populations and ecosystems• Diversity and adaptations of organisms

Content Standard C•Structure and function in living systems• Populations and ecosystems• Diversity and adaptations of organisms

STC Life Science Strand: Life on Earth 123-B


intrOducinG Daphnia

Overview

In this lesson, students use a microscope to explore the characteristics of a crustacean called Daphnia. Daphnia often are called the “water flea” because of their appearance and jerky movements. As students discover, Daphnia are quite different from the fleas found on dogs and cats. As crustaceans, their closest relatives are aquatic organisms such as shrimp and lobsters. During “Getting Started,” students list characteristics shared by common crustaceans—lobsters, shrimp, and Daphnia. They decide on the type of skeleton these organisms have and its advantages and disadvantages over an internal skeleton.

In Inquiry 9.1, students observe, sketch, label, and measure a Daphnia, following the rules for scientific drawings. In Inquiry 9.2, students measure the average heart rate of a Daphnia in spring water. Then, one pair in each group measures the effect of a weak alcohol solution on the heart rate of a Daphnia while the other pair in each group measures the effect of a weak cola solution. They speculate about whether these two substances have similar effects on humans.

bacKGrOund

Daphnia are aquatic, freshwater crustaceans of the order Cladocera. A Daphnia’s body is enclosed almost entirely in a bivalved, transparent exoskeleton called a carapace. The carapace forms a large, flexible sheet that folds along the dorsal midline to form two valves, one on either side of the Daphnia. A Daphnia’s body is compressed laterally, appearing much broader from the side than from the front. Its body has three main parts—an anterior head, a thorax, and a posterior abdomen. The thorax and abdomen are enclosed by the carapace. The head extends in front of the carapace.

There are many more female than male Daphnia in a culture. In fact, it is unusual even to find a male. Female Daphnia may produce up to 400 eggs in their lifetime. Females produce two kinds of eggs. The first, called summer eggs, develop parthenogenetically, or without fertilization. These eggs are carried in the brood

chamber (shown in Figure 9.1) until they hatch. In some species, Daphnia are already sexually mature when they hatch and can immediately produce young of their own.

The second kind of eggs, called winter eggs, are produced only after fertilization by a male. They are larger, fewer in number, and more “yolky” than summer eggs. Winter eggs are not kept within the brood chamber. They are released when the female molts and may then sink or float, depending on the species. These eggs, which hatch the following spring, always contain female Daphnia that reproduce without fertilization.

Daphnia have two pairs of antennae. The first pair is tiny, but is larger in males than in females, and has a sensory function. The second pair is much larger than the first and is the same size in males and females. One antenna from the second pair extends from each side near the middle of the head. The branches of these antennae bear feathery setae. On the larger setae are rows of much smaller setae, which produce a featherlike appearance. These antennae function like oars and move downward quickly to propel the organism upward in a jerky motion. After the upward movement, the antennae, with their great surface area, act like parachutes, allowing Daphnia to sink slowly through the water until they jerk upward again.

Daphnia have a single compound eye, which is usually in motion. The muscles that control the eye’s movement can be seen through a compound microscope. Daphnia also have a tiny naupliar eye, ventral to the larger compound eye and embedded in the edge of the brain. (A naupliar eye is a tiny eye found in the larvae of most crustaceans.)

Five to six pairs of flattened, biramous (two-branched) appendages extend from Daphnia’s thoracic region. These appendages bear setae, which act as filters to remove algae and other phytoplankton from the water. These filtered organisms are passed from appendage to appendage until they reach the mouth, which is located in a groove between the head and the carapace. The intestine, or digestive tube, extends from Daphnia’s mouth to its anus and is often green because of the large quantity of phytoplankton the organism ingests.

Daphnia’s heart is located in the dorsal region of the anterior thorax, behind the large compound eye. The heart is easily observed through the organism’s transparent carapace. Daphnia have an open circulatory system, which means blood is not confined within vessels. The heart beats rapidly to send blood throughout the body to the inner wall of the carapace, where an exchange of oxygen and carbon dioxide

lesson

123-C STC Unit: Investigating Biodiversity and Interdependence


rEAdIng SELEctIon

“The Transparent Water Flea” provides the background information necessary for students to complete this lesson. Students will learn that Daphnia are members of a class of arthropods called crustaceans. The selection describes the anatomy and physiology of Daphnia.

occurs. (Gas exchange also occurs along bulbous portions of its appendages, called epidods, which serve as gills.) The blood collects from these areas and reenters the heart.

The average heart rate of Daphnia varies with the species but ranges from 230 to 300 beats per minute. Environmental conditions can greatly affect Daphnia’s heart rate. For example, the heart rate increases with the intensity of light or an increase in the temperature of the water. Depressants such as alcohol lower the heart rate, while stimulants such as caffeine or nicotine increase it.

nOte Daphnia’s heart rate is too rapid to measure simply by counting—most people cannot count that quickly. Therefore, in this lesson students are

asked to make a mark with their pencils on a piece of paper each time they see the heart beat. This is more of a reflexive response, and students usually can master this technique fairly well with practice. They count the pencil marks they make in a given period of time and adjust that number mathematically to reflect beats per minute.

STrucTure oF an adulT DaphniaFiguRE 9.1

cOmmOn miScOnceptiOnS

Students often mistake a Daphnia’s appendage movements for its heartbeat. You can correct this misconception by using a microvideo system to identify the heart for students.

Second antenna

Compound eyeintestine

Heart

Eggs in brood chamber

First antennaFiltering setaeEpipods (legs)

CarapaceAnus

STC Life Science Strand: Life on Earth 123-D


lesson


Daphnia’s transparent outer shell makes it easy to observe its internal structures. PHOTO: Paul Hebert/Gewin V (2005) Functional Genomics Thickens the Biological Plot. PLoS Biol 3(6): e219. doi:10.1371/journal.pbio.003029/Creative Commons Attribution 2.5 License

INTRODUCTION

In this lesson, you will explore some features and behaviors of an organism called Daphnia. You will observe the organism through a microscope and prepare a scientific drawing of a Daphnia and some of its structures. Finally, you will measure a Daphnia’s heart rate before and after the organism has been treated with two different chemicals.

IntroducIng DaphniapreparatiOn

1. Title a transparency or piece of newsprint “Lobsters, Shrimp, and Daphnia—Characteristics.” About halfway down, in the middle of the page, print “Skeleton: _________________.” Make two columns below the word “skeleton.” Title the first column “Advantages” and the second column “Disadvantages.”

2. Make one copy of Student Sheet 9.1: Template for Daphnia Drawing, Student Sheet 9.2a: Table for Recording Heartbeats of Daphnia, and Student Sheet 9.2b: Effect of Alcohol and Cola Solutions on the Heart Rate of Daphnia for each student.

3. With a black marker, print “Alcohol Solution” on a 4-oz plastic cup, “Cola Solution” on a second cup, and “Spring Water” on a third.

4. Prepare an alcohol solution by adding 1 mL of ethyl alcohol to 60 mL of water in a graduated cylinder. Pour the alcohol solution into the appropriately labeled cup and insert a pipette. Have the lid available for storage.

5. Prepare a cola solution by adding 1 mL of a caffeinated cola drink to 60 mL of water in a graduated cylinder. Pour the solution into its labeled cup and insert a pipette. Have the lid available for storage.

6. Fill the third cup with spring water. Insert a pipette. Have the lid available for storage.

7. Pull apart a cotton ball into individual strands. Each group will need two cotton strands.

8. Set up a materials station with the Daphnia culture and a pipette, the cola solution, the alcohol solution, the cup of spring water, 16 depression slides, 16 coverslips, cotton, and the class sets of organism photo cards.

9. Set up the microvideo system, if one is available. You can use it to point out the location of a Daphnia’s heart. If you do so, have a coverslip and a depression slide available for yourself.

10. Place the lesson materials and the sets of organism photo cards in a convenient place for students.

lesson



STC Life Science Strand: Life on Earth 125

MATERIALS FOR LESSON 9For you Your copy of Student Sheet 2.3a:

Guidelines for Scientific Drawings

1 copy of Student Sheet 9.1: Template for Daphnia Drawing

1 copy of Student Sheet 9.2a: Table for Recording Heartbeats of Daphnia

1 copy of Student Sheet 9.2b: Effect of Alcohol and Cola Solutions on the Heart Rate of Daphnia

For your group 1 set of organism photo cards 2 compound light microscopes 2 depression slides 2 strands of cotton 2 coverslips 4 Daphnia (2 per class period) 2 metric rulers, 30 cm (12 in.) 2 transparent rulers 4 pencils or fineline markers

Determine the heart rate of a Daphnia under various conditions.

Update your organism photo card for Daphnia.

Observe, sketch, and measure a Daphnia and identify its major structures.

OBJECTIVES FOR THIS LESSON

1 mL ethyl alcohol 120 mL spring water* 1 mL caffeinated cola drink*

For each student 1 copy of Student

Sheet 2.3a: guidelines for Scientific Drawings*

1 copy of Student Sheet 9.1: Template for Daphnia Drawing*

1 copy of Student Sheet 9.2a: Table for Recording Heartbeats of Daphnia*

1 copy of Student Sheet 9.2b: Effect of Alcohol and Cola Solutions on the Heart Rate of Daphnia*

For each group of 4 students 1 set of organism photo

cards 2 compound light

microscopes* 2 depression slides 2 coverslips 2 strands of cotton from a

cotton ball* 4 Daphnia (2 per class

period) 1 paper towel* 2 metric rulers, 30 cm

(12 in)* 2 transparent rulers 4 pencils or fineline

markers* *Needed but not supplied

MATERIALS FOR LESSON 9For the teacher 1 transparency or piece of

newsprint* 1 microvideo system

(optional)* 1 depression slide (optional) 1 coverslip (optional) 2 Daphnia cultures 2 graduated cylinders,

100 mL* 3 clear plastic cups, 4 oz 3 clear plastic lids, 4 oz 4 plastic pipettes 1 cotton ball* 1 black marker*

nOte Lesson 10 requires some advance preparation. Refer to page 131-B for

further information.



lesson xx

gettIng Started

1

Daphnia are related to lobsters and shrimp. List in your science notebook some of the characteristics you think these three organisms share. Use Figures 9.1 and 9.2 and the Introduction photo on page 124 for reference.

spiny lobster FiGURE 9.1 PHOTO: Courtesy of Carolina Biological Supply Company

shrimp FiGURE 9.2 PHOTO: Courtesy of Carolina Biological Supply Company

2

Record your answers to the following questions. Be ready to share them with the class.

A. What kind of skeleton do Daphnia, lobsters, and shrimp have?

B. What are the advantages and disadvantages of this kind of skeleton over the type of skeletons humans have?


IntroducIng Daphnialesson 9

gEttIng StArtEd

1. While groups are recording their ideas, follow these steps to transfer cotton strands, a Daphnia, and a drop of spring water to the depression on each of the 16 slides:

a. Place a few cotton strands on the depression on each of the slides.

b. Squeeze the bulb of the pipette. Keeping the bulb squeezed, move the tip of the pipette close to a Daphnia in the culture container. Release the bulb quickly to suck a Daphnia into the pipette.

c. With the tip of the pipette facing down toward the culture container, squeeze the bulb gently until you see the Daphnia move close to the opening of the pipette. Quickly move the tip of the pipette to the slide and squeeze until a drop of water and the Daphnia fall into the depression in the slide. Lay a coverslip over the depression. Do not press on the coverslip or you will crush the Daphnia.

d. Carefully place the slides at the materials station for students to pick up.

nOte Since the inquiries in this lesson will take more than one day, you will need to

set up the slides in the same way for each class on the second day.

2. Have students share their responses with the class, and record them on the transparency you prepared. (Students will revise their responses during “Reflecting on What You’ve Done.”)

lesson



STC Physical Science Strand: Energy in our World 127

InQuIrY 9.1

PREPaRINg a SCIENTIFIC DRawINg OF a Daphnia

PROCEDURE

1

You will work in pairs for this inquiry. Have one student from your pair go to the materials station to obtain a slide with a Daphnia in a drop or two of spring water. One or two strands of cotton under the coverslip will have isolated the Daphnia in a small area for viewing. Do not press down on the coverslip.

2

Use your microscope to focus on the Daphnia under the highest power at which you can see the entire organism.

3

Draw the Daphnia in as much detail as you can on Student Sheet 9.1: Template for Daphnia Drawing. Follow the guidelines for scientific drawings listed on Student Sheet 2.3a. Title your drawing “Daphnia: The Water Flea.” Refer to “The Transparent Water Flea” on pages 132–133 for information about how to label your drawing.

4

Use your transparent ruler to measure the length of the Daphnia. Record the length, following the guidelines for scientific drawings.

STC Physical Science Strand: Energy in our World 127 STC Life Science Strand: Life on Earth 127

InQuIrY 9.1

prOcedure

1–5. Go over Procedure Steps 1–5 in the Student Guide. Use a microvideo system, if available, to point out the heart to students and to differentiate the hearbeat from the movements of its appendages. Alternatively, have students refer to the labeled illustration of Daphnia on page 133 in “The Transparent Water Flea.” Then have each pair of students pick up a slide from the distribution center. Point out that the liquid in the culture container is spring water.

nOte if there is too much water on the slide, the Daphnia will swim about rapidly, and the students will be unable to observe its internal

structures. Help students adjust the amount of water in the depression by using the tip of a corner of a paper towel to absorb some of the water from the depression. Removing too much water will get air under the carapace and kill the Daphnia. Be careful not to remove the Daphnia as well.



inquiry 9.1 continued

5

Take the following steps to observe and identify specific structures to include in your drawing. (Refer to Figure 9.3 and the illustration in “The Transparent Water Flea.”)

A. Look for the intestine, which runs from the mouth to the anus. Notice its color. Discuss with your partner why you think it is this color.

B. Locate the Daphnia’s heart. Notice how rapidly it beats.

C. Find the “brood chamber,” a sac located just below the heart of the female Daphnia. Discuss with your partner what might be found inside a brood chamber.

D. Focus on your Daphnia’s eye. Switch the microscope to a higher power to observe the eye in greater detail. Discuss with your partner how its structure differs from that of a human eye.

E. Focus on one of the antennae under high power. Discuss with your partner one possible function of the antennae.

F. Focus on one of the legs under high power. Notice the bristles. Discuss with your partner what you think the function of the bristles may be.

6

When you and your partner have completed your drawings, move to Inquiry 9.2 if instructed to do so by your teacher. Use the same slide but get a fresh Daphnia for this inquiry if you will be completing the inquiry during the same period. Follow your teacher’s instructions for returning the Daphnia to the culture container.

you can easily see the digestive tube, heart, and brood chamber in the Daphnia at the center of this photo.FiGURE 9.3 PHOTO: Courtesy of Carolina Biological Supply Company



6. Tell students they can move on to Inquiry 9.2 if they complete Inquiry 9.1 early enough in the period. Otherwise, have students return the Daphnia to the culture containers, using the same procedure they used at the end of Inquiry 6.1.

lesson



InQuIrY 9.2

ExPLORINg THE EFFECT OF aLCOHOL aND COLa SOLuTIONS ON THE HEaRT RaTE OF Daphnia

PROCEDURE

1

Read all of the Procedure Steps carefully. They will give you the information necessary to prepare a data table in the box provided on Student Sheet 9.2b: Effect of Alcohol and Cola Solutions on the Heart Rate of Daphnia. You will record your data and your partner’s data on this table.

2

Observe the Daphnia closely. Practice measuring its heartbeat using the following technique:

A. Place a pencil or fineline marker in your writing hand and hold the tip just above the middle of the top left box on Student Sheet 9.2a: Table for Recording Heartbeats of Daphnia.

B. For 10 seconds, tap the point of your pencil in the first box, making a mark each time the Daphnia’s heart beats as shown in Figure 9.4. Have your partner time you and call “Stop” when 10 seconds are up. if you need more practice, make your marks in the right box in the top row.

each dot represents one beat of the Daphnia’s heart.FiGURE 9.4


InQuIrY 9.2

prOcedure

1. Explain to students that in this inquiry they will measure the heart rate of Daphnia under three different conditions—in spring water, in an alcohol solution, and in a cola solution. Then review Steps 1–13 of the Procedure in the Student Guide. As students prepare their data tables, advise them to include enough rows or columns to record all of their data.

2–6. Explain that, because the Daphnia's heart beats so rapidly, students will not be able to simply count the number of beats per minute as they could do with a human. Inform students that this is why they use the pencil-tapping technique in this inquiry.



inquiry 9.2 continued

3

When you have finished practicing, move your pencil so that you are holding the tip above the middle of the first box in the second row. Have your partner time you for 10 seconds while you mark each heartbeat.

4

Count the number of marks to determine the number of times your Daphnia’s heart beats in 10 seconds. Decide with your partner how to use this figure to calculate the Daphnia’s heart rate per minute. Record this calculation in the appropriate place on your data table.

5

Repeat Steps 3 and 4, using a different box for your marks. Use your data from the two trials to calculate the average heart rate of the Daphnia in spring water.

6

Switch roles with your partner and repeat Steps 2–5.

7

Watch and listen as your teacher demonstrates how to add an alcohol or cola solution to the Daphnia slides.

8

One pair in your group will measure a Daphnia’s heart rate while the organism is immersed in a weak alcohol solution. The other pair will do the same while its Daphnia is immersed in a weak cola solution. Before you begin, write one-sentence answers to the following questions on Student Sheet 9.2b:

A. How do you think alcohol will affect the heart rate of Daphnia? Why?

B. How do you think cola will affect the heart rate of Daphnia? Why?

9

Have one pair in your group add a drop of weak alcohol solution to its Daphnia in the manner demonstrated by your teacher. Have the other pair in your group add a drop of weak cola solution to its Daphnia. Let the slides sit for about 2 minutes.



7–12. Demonstrate how to add a drop of alcohol or cola solution to the slide using the following technique:

a. Remove the coverslip.

b. Use a pipette to suck up a drop of the solution.

c. Place a drop of solution into the depression. Replace the coverslip.

d. Allow the slide to sit for about two minutes. If there is too much liquid, show students how to use the corner of a paper towel to absorb some of it from the slide.

lesson



10

Have one partner in each pair record the Daphnia’s heartbeats in a box on Student Sheet 9.2a, while the other partner keeps time for 10 seconds.

11

Switch roles and repeat Step 10. Calculate the average number of heartbeats per minute for the two trials and record it on the data table.

12

Exchange information with your group members.

13

Follow your teacher’s directions for returning the Daphnia to its container. With your group, update your organism photo card for Daphnia.

reFlectIng ON WHAT YOU’VE DONE

1

2

3

Based on what you have learned in this lesson, answer the following questions in your science notebook:

A. What effect does cola have on the heart rate of Daphnia? Explain.

B. What effect does alcohol have on the heart rate of Daphnia? Explain.

C. How would you expect a person’s heart rate to change if he or she drank a large quantity of cola or alcohol?

Refer to the reading selection “The Transparent Water Flea” on pages 132–133 to respond to the following in your science notebook:

A. List three ways in which Daphnia are similar to other crustaceans.

B. Explain why Daphnia are referred to as “water fleas.”

C. Explain one function of the bristles on a Daphnia’s legs.

Revise as necessary the responses you made during “Getting Started.” Discuss your changes with the class.


REFLECTING ON WHAT YOU’VE DONE1. Students should respond to the questions in complete sentences in their science notebooks.

a. Cola, which contains caffeine, a stimulant, increases Daphnia’s heart rate.

b. Alcohol, a depressant, slows the heart rate of Daphnia.

c. These substances, consumed in sufficient quantities, have the same effect on the heart rate of humans as they do on that of Daphnia.

possible by the movements of their large antennae.

c. The bristles on a Daphnia’s legs filter out suspended food particles and they pass the particles from one appendage to the next until the food enters the mouth.

3. Have students revise their responses from “getting Started,” and ask them to share their revisions with the class.

2. Ask students to refer to the reading selection “The Transparent Water Flea.” Then have them record their answers to the questions in their science notebooks.

a. Daphnia have an exoskeleton, gills, many jointed appendages, and two pairs of antennae.

b. Daphnia resemble fleas because of their appearance and jerky movements, which are made

13. Explain the cleanup procedures. Tell students that there is a plastic cup with spring water at the materials station. To avoid contaminating the Daphnia that remain in the culture container, advise students to return their Daphnia to the cup of spring water using the procedures outlined at the end of Inquiry 6.1 in the Student Guide.

Ask students to take a few minutes after cleaning up to update their organism photo cards for Daphnia.



intrOducinG Daphnia

hOmewOrK

period 1Ask students to review “The Transparent Water Flea” on pages 132–133.

period 2Ask students to read the Introduction to Lesson 10.

extenSiOnS

Science1. Have students repeat Inquiry 9.2 using solutions of other stimulants such as tea, coffee, or nicotine (obtained by soaking cigarette tobacco in water). Have them submit a lab report of their findings. The tobacco from one cigarette mixed with one cup of spring water should be sufficient for the nicotine solution. Prepare and provide the nicotine solution yourself.

language arts2. Have students read the following examples (loose translations of a poem by Jonathan Swift and a limerick by an unknown author) and then create their own poems about Daphnia and submit them to you.

poem 1Big fleas have little fleas Upon their backs to bite ’em. And little fleas have lesser fleas And so on, ad infinitum.

poem 2A flea and a fly in a flue Were imprisoned, so what could they do? “Let us flee,” said the fly. “Let us fly,” said the flea. So they flew through a flaw in the flue.

Science3. Have students bring in pill bugs or roly polys (isopods), which are among the few terrestrial crustaceans. These bugs are easily found under rocks and logs in damp areas. Have students examine the structures on a pill bug through the microscope and compare the bug’s characteristics with those of Daphnia. Pill bugs live only in damp habitats because they breathe with gill-like structures that require water to work properly.

Science/Social Studies4. Have students research how crustaceans are used for food around the world. Have them submit their findings along with, perhaps, a recipe for a dish with a tasty crustacean as the main ingredient.

mathematics5. Have students check the prices of lobster meat at a local supermarket and calculate the cost of a lobster dinner for five. Ask them to assume that each person would require 6 oz of lobster meat for the main course. Have them list the lobster and side dishes in menu form with prices to the right of each item. The total cost should be at the bottom of the price column.

lesson

131-A STC Unit: Investigating Biodiversity and Interdependence


aSSeSSment

Assessment for this lesson should be based on the student’s ability to:

• Participate in the inquiries and adhere to the directions.

• Observe and sketch Daphnia, label its major structures, and measure its length with a transparent ruler.

• Determine the heart rate of Daphnia in spring water, in an alcohol solution, and in a cola solution, and use those results to explain how alcohol and cola may affect the heart rate of humans.

• Update the organism photo card for Daphnia.

preparatiOn FOr leSSOn 10

1. In Lesson 10, students will observe the feeding habits of Hydra. In preparation for this, choose a student from each of your classes to help you obtain the Hydra from the culture containers and distribute them to students during that lesson. Before the lesson, demonstrate for these students how to obtain the Hydra, using the following technique:

a. Stick the pipette into the culture container until its tip is almost touching a Hydra.

b. Quickly release the bulb so that the suction dislodges the Hydra and sucks it into the pipette.

c. Squirt the water and the Hydra into the depression on a plastic slide. Do not use a coverslip.

2. Prepare food for the Hydra. One pair in each group will feed its Hydra a blackworm fragment; the other pair will feed its Hydra a Daphnia. Follow the procedures you used during the preparation for Lesson 3 to prepare one blackworm fragment for each group in each of your classes. The Hydra fragments should be no larger than 0.5 cm. Save enough Daphnia so that each group in each of your classes has one.

STC Life Science Strand: Life on Earth 131-B


readIng SeLectIon extendIng your knowledge

ike the WOWBug, Daphnia belong to the phylum of jointed-limbed organisms called Arthropods. Like shrimp, crabs, and lobsters, Daphnia are members of a class

of Arthropods called crustaceans. Crustaceans are characterized by an external skeleton, gills for gas exchange, two pairs of antennae, and numerous jointed appendages. Different species of Daphnia range in length from around 0.2 millimeters (0.008 inch) to more than 5 millimeters (0.2 inch).

Daphnia are particularly interesting animals to study because their exoskeletons, or carapaces, are transparent. This makes it easy to observe and identify their internal organs with a hand lens or a microscope. Their hearts beat very rapidly, pumping blood throughout their bodies. Their intestine, tubular in shape, extends from mouth to anus. Female Daphnia have a large brood chamber just below their heart. The brood chamber holds the female’s eggs.

Daphnia have been called “water fleas” because they move with a jerky motion that resembles the way a flea jumps. They do this by quickly flipping their antennae downward. They control their depth in the water by adjusting the movement of their antennae like a parachute.

Daphnia can survive in almost any freshwater environment—lakes, ponds, streams, swamps, and marshes. They feed on microscopic organisms such as bacteria, algae, and protozoa. Daphnia propel food toward their mouths using water currents they generate with their leg movements. They filter out food particles with the bristles on their legs, then pass the food from the bristles to their mouths.

In their lifetime, female Daphnia produce up to 400 eggs. Reproduction in Daphnia follows an unusual process—the eggs develop in the female’s brood chamber without being fertilized. Offspring are fully developed when they hatch.



lesson



extendIng your knowledge

1. Why are Daphnia easy to study and what has it allowed us to learn about them?

2. Why don’t we study only organisms that are easy to study?

1.

dIscussIon QuestIons

Second antenna

Eye intestine Heart

Eggs in brood chamber

Carapace

Legs

First antenna

Because Daphnia reproduce so rapidly, they are an important source of food for many other organisms, especially fish. They provide an important link in the food chain between the microscopic organisms upon which they prey and the larger organisms that prey upon them. ■




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