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Electric animals.

Background

Our senses aid our survival and feed us critical information about our environment. Humans perceive their world with the five senses of touch, taste, smell, hearing, and sight. Some animals use additional senses, one of which is the sense of electricity.

All animals emit weak electrical charges, via their muscles, just by moving, but electric animals also have special electric organs. Some emit strong charges, some sense the charges, and some do both. Because electricity is easily conducted in water, most electric animals are fish. They use electrical signals to protect themselves, attract mates, find prey, and navigate.

Electric fish, like the electric eel, its cousin the electric catfish, the electric ray, and the elephant fish in Africa, are electrogenic: they emit charges from electric organs in their bodies. They are also electroreceptive and can detect electricfields. The weak electric signal from each species of electric fish is specific, allowing it to distinguish its own species from another.

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Most electric fish live in dark, murky waters and rely on their extra sense. The electric eel has poor vision and depends on its weak electric charge to navigate. Its electric organ is made up of plates of musclefibers connected in a series down its long body. Each electric plate generates less than a volt of electricity, but when combined together--like batteries in a flashlight--they generate a stronger charge used to stun and kill prey.

Other fish, some salamanders, and at least two mammals (the platypus and the echidna), are also electroreceptive. Sharks, skates, and rays all use electroreception to locate prey and navigate--especially sharks like the hammerheads that exist in darker environments.

Electroreceptive animals have a special network of gel-filled sensors called the Ampullae of Lorenzini. The shark's sensors are located in its head, between its snout and its eyes, and are connected to visible pores on the skin. Scientists believe the gel transmits incoming electrical signals from the pores to the brain. The pores

are key to electroreception. The more pores an animal has, the finer its sense of electroreception.

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Level Pre-A

Main Concept: Students will learn that some animals can "feel" and "give off" electricity.

Initiating Questions Level Pre-A

1. Where does electricity come from? (Electricity is a form of energy. The bodies of animals and humans produce small amounts of electricity naturally. It helps our bodies to work.)

2. Can animals feel electricity?

Follow-up Questions Level Pre-A

3. Do you think animals use electricity like we do?

4. How do animals "give off" electricity?

Vocabulary

Students will trace the blue letters in "electricity," "electric" and "animals."

Weekly Lab

The Power of Size--For this activity, provide one empty pocket flashlight with two "AA" batteries, and one empty flashlight with three "C" batteries. Before beginning, remove the batteries. Students are encouraged to touch and analyze small and big batteries. Students will circle the big batteries in the picture. Demonstrate how the small batteries fit into the small flashlight, and how the big batteries fit into the big flashlight. Students will draw lines matching the batteries with the correct flashlight. This WEEKLY LAB allows students to consider how battery size can matter in making electricity. Put the batteries in each flashlight (the positive end always goes in first). Turn off the overhead lights, and turn on the flashlights. Ask, "Which flashlight is brighter?" Explain that "just like flashlights," bigger eels have more electricity too. Encourage the students to share their thoughts with the class.

Math

Students will count the batteries in the picture and write in the numbers. Students can also count the batteries used in the WEEKLY LAB. Ask, "Is it the same as in the picture?"

Storytelling

Encourage students to look at the cartoon panel and to tell a story about what happened to the eel.

Challenge

Students observe a picture of an electric eel and are asked to color the eel and color his electric organs red.

Bringing It Home

Students will draw their own picture of an electric eel. It should show the electric organs.

Level A

Main Concept: Students will understand that some animals can "feel" electricity. Some animals can also "give off" electricity. They have body parts that work like batteries. They also learn about batteries and battery ends.

Initiating Questions

1. How can body parts work like batteries?

2. Have you ever seen or touched batteries?

Follow-up Questions

3. How and why do you think an animal could "give off" electricity?

4. How do you think an animal could "feel" electricity?

5. How do batteries work? Do bigger batteries make more electricity? How are the ends of a battery different from each other?

Vocabulary

Answers: electric, electricity, batteries

Discuss the word electricity and how it means one thing to humans and another to animals.

Weekly Lab

Are Bigger Batteries Brighter?- Provide batteries and two empty tube-style flashlights that are close in size and length. One should take "C" batteries and the other "D" batteries. Leave the batteries out. Ask, "Do you think bigger batteries are brighter?" They will mark "yes" or "no." Ask, "Which batteries are bigger?," They will mark "C" or "D". Let students handle the batteries and compare the ends to the ends shown in the pictures. Identify the "positive" ends and the "negative" ends. Demonstrate how the bigger batteries go into the bigger flashlight (positive ends in first). Turn out the overhead lights and turn on the flashlights. Ask, "Which one is brighter?." Students will check the correct box. Explain to students that bigger flashlight batteries carry more electricity than smaller ones. Also, explain that just like batteries, longer eels carry more electricity than shorter eels.

Math

From the WEEKLY LAB, have the students first count the batteries they worked with, and then count the positive (+) and negative (-) ends they touched.

Writing In Science

Encourage students to describe the difference between the positive (+) and negative (-) battery ends. Point out that every battery has two ends, and one end is always positive (+) and one end is always negative (-). They will draw their own picture of each end and write one complete sentence about each end.

Challenge

Students get more practice identifying the positive (+) and negative (-) ends on illustrated batteries.

Bringing It Home

Students are asked to create a 2-panel cartoon by telling a story with pictures in the existing panels. It may help to discuss some ideas first.

Level B

Main Concept: Students will understand that some animals have special electric organs and use electricity as a sixth sense. Some emit charges, some sense the charges, and some do both.

Initiating Questions

1. Do all animals "give off" electricity? (All animals emit small amounts of electricity just by moving.)

2. Do you think some animals might be better equipped to emit electricity than others?

3. Do you think some animals can sense electricity better than others?

Follow-up Questions

4. Why do you think animals sense electricity?

5. How do you think they are able to sense electric charges?

6. How do you think emitting electricity and sensing electricity are different?

Vocabulary

Answers: Some animals can sense electricity. Some animals can emit charges.

Weekly Lab

Positive, Meet Negative!--You will need a fresh "C" or "D"-size flashlight battery, 20-gauge copper wire (two 13-cm lengths), a D&C upgrade flashlight bulb, electrical tape (or masking tape) and scissors. Discuss the concept of conductivity with students. Explain that in order for electricity to work, the positive (+) and negative (-) electric charges have to "meet" each other. Explain how certain materials (such as wire and water) conduct (carry) electricity well and help the different charges to meet. Other materials (such as wood and rubber) do not work as well. (See also Level A.)

Math

Have students measure the generic batteries in the picture with a ruler using centimeters.

Answers: 1 battery is 4 cm; 3 batteries lined up are 12 cm; 4 batteries lined up are 16 cm.

You may also have students measure actual batteries, but that will involve working with fractions or decimals. "C" size batteries measure 4.5 cm long each and "D" size batteries measure 5.5 cm.

Writing in Science

Students are asked to think of items that use electricity to work and to make a list in the left box. In the right box, students should write down what the electricity helps that item to do. An example is provided.

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Challenge

Students are asked to think about what life would be like without electricity. They will draw a cartoon of themselves talking to a friend about it.

Puzzle

Students are asked to search for the new vocabulary words. (Solution to the right.)

Level C

Main Concept: Students will understand that some animals have special organs and use electricity as a sixth sense, as a mode of protection, and to hunt.

Students learn that some animals can sense electric charges, some can emit electric charges, and some can do both. Students learn about the meaning of the term "electroreceptive."

Initiating Questions

1. Are all animals able to emit electricity? (All animals emit small amounts of electricity.)

2. How do you think animals are able to emit electricity? (Some animals have electric organs that work like batteries.) Why do they do it? (communication)

Follow-up Questions

3. Why is the sense of electricity important to animals? (protection, communication)

4. Why do you think electroreception is important to the shark? (detect prey, navigation)

5. How do you think batteries work?

Vocabulary

Answers: 1) electricity; 2) sense; 3) electric; 4) batteries; 5) emit; 6) prey

Comprehension

Students learn about the meaning of the term "electroreceptive." They are asked to circle the animal which is electroreceptive, but doesn't emit or give off electricity (the shark). Direct students' attention to the pores on the shark's snout which are used to sense electric charges. Next, they are asked to copy the names of each animal in the picture. (shark, electric ray, electric catfish and electric eel).

Weekly Lab

Positive, Meet Negative!--(See Level B.) Discuss the concept of conductivity with students. Certain materials (wire, water) are good electrical conductors, because they contain more free electrons than materials that do not (wood, rubber). To make electricity, batteries need to have a good conductor for the positive (+) and negative (-) electric charges to meet. A good conductor helps that to happen. Copper wire is an excellent conductor.

Math

Students learn about math tables and practice organizing information in one. Actual answers may vary.

Writing in Science

Students will consider their WEEKLY LAB activity and how some materials are better conductors of electricity than others. They are asked to guess what would happen with a battery if there were no good conductors available. They should write down their thoughts.

Level D

Main Concept: Students will understand that because water is a good conductor of electricity, most electric animals are fish. They have special organs and use electricity as a sixth sense, as a mode of protection, and to hunt. Some animals are electrogenic and emit charges, some are electroreceptive and sense the charges, and some do both. The electric eel emits electricity the same way flashlight batteries do.

Initiating Questions Levels D and E

1. Why do you think animals would be electric?

2. How do you think some animals are able to emit electricity? (See Level C--INITIATING QUESTIONS.)

Follow-up Questions Levels D and E

3. Why do you think some animals are electrogenic? (communication, mating)

4. Why do you think electroreception is important to the shark? (detect prey, navigation)

5. How do electric organs work? How do you think the battery in your flashlight works?

Vocabulary

Answers: 1) electricity; 2) emits; 3) senses; 4) conductor; 5) electrogenic; 6) electroreceptive

BONUS: Each electric plate of the eel measures about 1/10th of a volt.

Meet The Scientist

Students meet Dr. Carl Hopkins, Professor of Neurobiology and Behavior at Cornell University.

Weekly Lab

Does Bigger Mean More?--(See Level B regarding materials needed. Use "C" size batteries.) Discuss the concept of current with students. Bigger batteries carry more current (expressed in amps) and result in more power. Current multiplied by voltage equals power.

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Writing in Science

Students are asked to write up their WEEKLY LAB according to correct scientific method.

Math

Answers: A) estimated 5 volts; B) 3 x 1.5 volts = 4.5 volts; C) 5 x 1.5 volts = 7.5 volts; D) 4.5 cm; E) 5 x 4.5 cm = 22.5 cm

Level E

Main Concept: (See Level D.) Some electroreceptive animals sense electric charges with sensors called Ampullae of Lorenzini. Electric animals emit charges specific to their own species.

Vocabulary

Answers: 1) emit; 2) sense; 3) conducted; 4) electrogenic; 5) electroreceptive; 6) volt

BONUS: The shark, ray, and skate have sensors called Ampullae of Lorenzini that are connected to pores in their skin and transmit electrical signals to their brains.

Meet The Scientist

(See Level D.)

Weekly Lab

More Electric?--(See Level D.) Discuss the Big Question and potential hypotheses with the students. Discuss the concept of current with students. Bigger batteries carry more current (expressed in amps) and result in more power. The current multiplied by the voltage equals power. Explain that, just like larger batteries, longer eels emit a greater electric charge.

Math

Students are asked to estimate the amount of energy produced or emitted in their WEEKLY LAB trials using a "BRIGHTNESS SCALE" of 0 to 4. Answers: A) estimated 6; B) (2 x 1.5 volts) + (2 x 1.5 volts) = 6 volts; C) (3 x 1.5 volts) + (3 x 1.5 volts) = 9 volts, (or 6 x 1.5 volts = 9 volts)

To extend this activity: have students practice measuring and adding (or multiplying) various lengths and diameters, using the batteries pictured or actual batteries.

Writing in Science

(See Level D.)

DID YOU KNOW

Electric eels are not true eels, but long-tailed knifefish. They are related to catfish!

DID YOU KNOW?

The electric eel produces more electricity than any other living creature.

DID YOU KNOW??

An electric eel can be as thick as a human when it reaches maturity?

DID YOU KNOW??

The heaviest eel recorded weighed 20 kilograms. That's about the same as a medium-sized dog!

DID YOU KNOW??

The hammerhead shark has a wider head than other sharks, and therefore it has more I pores for electroreception!

DID YOU KNOW??

The shark can detect prey under sand, even if the other senses like sight and smell are obscured.

DID YOU KNOW??

The Ampullae of Lorenzini are made up of salt and Protein gel-clusters.

DID YOU KNOW??

Some people call the jelly in the shark's Ampullae of Lorenzini shark snot!

New Words:

animals

electricity

electric

batteries

Some animals (an-i-mals) feel electricity (e-lec-tric-i-ty).

Some animals give off electricity. Zap!

Some animals are electric animals.

Some animals have body parts like batteries (bat-te-ries).

Vocabulary

Trace the words.

electricity batteries electric

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Some animals are electric.

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Some animals give off electricity.

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They have body parts like batteries.

Weekly Lab

Adult Supervision Required

Do you think bigger batteries are brighter? yes [] no []

Step 1" Which batteries are bigger? [] "C" or [] "D"

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Step 2: Look at the battery ends, Touch the ends.

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This end is (+) positive (pos-i-tive).

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This end is (-) negative (neg-a-tive).

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Step 3: Put the big batteries in the big flashlight (flash-light).

Put the small batteries in the small flashlight.

Step 4: Which batteries are brighter--[] "C" or [] "D" batteries?

Math

How many batteries did you use in the LAB?

1. I used--batteries.

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2. How many battery ends did you touch?

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I touched--positive (+) ends. +

I touched--negative (-) ends. =

I touched--total battery ends.

Writing in Science

Draw a picture, Write a sentence.

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Write a sentence about positive ends.

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Write a sentence about negative ends.

Challenge

Look at the batteries, Look at the battery ends.

Draw a "+" in the box by the positive end,

Draw a "-" in the box by the negative ends,

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Bringing it Home

Make a cartoon (car-toon) about an electric eel.

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Publication:Science Weekly
Geographic Code:1USA
Date:Nov 4, 2008
Words:2681
Previous Article:Erosion.
Next Article:Weekly resources: helpful sources for planning your Science Weekly classroom activities.
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