5 2 inside sea creatures (life science)

5.1 The Cat Family (Life Science) 5.2 Inside Sea Creatures (Life Science) 5.3 Staying Healthy (Life Science) 5.4 Food and Farming (Life Science) 5.5 Build an Aquarium (Life Science) 5.6 Changing World (Life Science) 5.7 Underwater Explorers (Earth Science) 5.8 Drought (Earth Science) 5.9 Mountains of the World (Earth Science) 5.10 Green Gardening (Earth Science) 5.11 Pioneers of Physics (Physical Science) 5.12 Baking Chemistry (Physical Science) 5.13 Building Science (Physical Science) 5.14 Generating Power (Physical Science) 5.15 The Light Bulb (Physical Science) 5.16 Telescopes (Space and Technology) 5.17 Moon Landings (Space and Technology) 5.18 Cars Present, Past, and Future (Space and Technology)

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Scott Foresman Science 5.2

Nonfi ction Draw Conclusions • Captions

• Labels

• Diagrams

• Glossary

Cells to Systems

ISBN 0-328-13921-1

ì<(sk$m)=bdjcbh< +^-Ä-U-Ä-U

Scott Foresman Science 5.2

Nonfi ction Draw Conclusions • Captions

• Labels

• Diagrams

• Glossary

Cells to Systems

ISBN 0-328-13921-1

ì<(sk$m)=bdjcbh< +^-Ä-U-Ä-U

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1 What do sea urchins use their tube feet for?

2 Jellyfi sh are a type of cnidarian What does this name mean, and why is it a good name for jellyfi sh?

3 Describe how the chambered nautilus grows

interesting ways of moving around Write to explain a few of them Use examples from this book

5 Draw Conclusions A giant blue clam and

a squid are both mollusks, but only the clam has a shell Why do you think this is?

What did you learn?

Extended Vocabulary

bivalves cartilage cephalopods cnidarians echinoderms funnel

mantle mollusks propel

Vocabulary

cell membrane

cell wall

chloroplast

cytoplasm

nucleus

organs

organ systems

tissues

vacuole

Picture Credits

Every effort has been made to secure permission and provide appropriate credit for photographic material

The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.

Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).

4 Bill Curtsinger/NGS Image Collection; 12 (BL) Andre Seale/Alamy Images.

Scott Foresman/Dorling Kindersley would also like to thank: 11 (TR) Natural History Museum/DK Images.

ISBN: 0-328-13921-1

This publication is protected by Copyright, and permission should be obtained from the publisher prior to any

prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,

mechanical, photocopying, recording, or likewise For information regarding permission(s), write to

Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.

3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05

by Laura Johnson

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What You Already Know

Your whole body is made from tiny parts called cells

The cells work together to form tissues, and the tissues

form organs These organs work together in organ

systems, and two or more systems may work

together to let you do all the things you do

Your cells, as tiny as they are, have even

smaller parts These parts help the cell take

in oxygen, process food, and get rid of

wastes A cell has all the same needs

as you do There are many

different kinds of cells in your

body, with different shapes

to do different jobs Some

are long and thin to carry

messages, while others are fl at

to make up tough surfaces

Others are dish-shaped to

carry oxygen through your body

Cells join together to form

tissues Muscle, bone, and nerve

are three kinds of tissue More

than one kind of tissue can

form an organ Your heart,

skin, and eyes are all organs

2

human skeletal system

Groups of organs working to do the same job are called organ systems Each of your bones is an organ, and they all work together to form the skeletal system

Your systems carry out the major work that needs to be done in your body, such as digesting food, taking in oxygen, and sending messages from your brain to the rest of your body

Your systems work together too For example, you need both your skeletal system and your muscular system to move around The bones support the muscles, and the muscles supply the motion

As you can see, the parts of your body are very complicated and interesting Now we’ll look to see what’s inside sea creatures These animals may be very different from you, but you’ll fi nd that they can be interesting too

scallops

3

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Jellyfi sh are not made of

jelly and they are not fi sh!

They are 98 percent water

The rest of them is a jellylike

material stiff enough to support

their body structure They belong to

a group of animals called cnidarians,

which means “stinging creatures.”

All cnidarians have tentacles with stinging cells

in their tips These stinging cells contain springlike

threads called nematocysts When shrimp or other

prey touch a tentacle, the nematocysts inject a poison

into the victim and paralyze it

Some jellyfi sh just drift in the water Others propel

themselves by fi rst expanding, then quickly squeezing,

their bag-shaped bodies This action forces water out

of an opening under their bodies As they move, they

keep their tentacles spread out to catch food

Jellyfi sh

Have you ever seen a jellyfi sh, a sea urchin, or a

squid? These animals are strange and amazing-looking

on the outside In this book you’ll learn that these

animals, and a few others, are even more

interesting on the inside!

Introduction

jellyfi sh

4

The jellyfi sh releases its venom into the fi sh

Tentacles can

be more than

10 feet in length.

Inside each tentacle are thousands of nematocysts

how the box jellyfi sh paralyzes its prey

5

Barbed tubes pierce the fi sh’s scales.

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Scallops belong to a group of animals

called mollusks Mollusks have soft bodies

without skeletons to support them A layer

of fl esh, called a mantle, covers their bodies

The mantle makes a very thin chemical

layer This chemical hardens and

slowly builds up to form a shell

that protects the animal’s organs

Scallops are bivalves This

means they have two shells

that are connected by a hinge

The hinge is actually a strong

muscle Scallops swim by

fl apping their shells

great scallop

Most bivalves don’t swim—

they remain attached to

objects The scallop’s ability to

swim makes it quite unusual

Tiny eyes in the mantle detect light and dark.

6

Gills absorb oxygen from the water.

The mantle controls the fl ow of water into the shell.

The heart pumps blood

to the tissues and gills.

When the shell opens, water fl ows in the front When the shell snaps shut, water shoots out the back and the scallop swims forward

As they swim, scallops feed on microscopic food, such as algae and plankton, that fl oat in the water

Around the edge of the mantle

is a row of blue eyes Although they can’t see very well, these eyes can sense movement and tell when enemies, such as sea stars, are near

Common scallops are about two to three inches wide However, the giant scallop, or great scallop, can grow to be eight inches wide

Giant Blue Clam

The largest bivalve, the giant blue clam, can weigh more than fi ve hundred pounds! The blue pigment,

or coloring, in the clam’s mantle protects it from too much sunlight

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All sea urchins have

a fi ve-fold symmetry

This means that their bodies have fi ve sections that are all the same, like the sections of an orange

Sea urchins belong to a group

of animals called echinoderms

Echinoderms are spiny-skinned

invertebrates that move slowly

across the ocean fl oor Sea urchins

have a round body that is divided

into fi ve equal segments Close-fi tting,

bony plates under their skin form a shell

Most sea urchins have long, movable

spikes on their shells They can push

themselves along fl at surfaces with these

spines Between the spines are rows of

tube feet with suction cups They are used

to climb, to grab on to surfaces, and to catch

food Some sea urchins use tube feet to

gather shells and seaweed and cover

themselves to hide from predators Sharp

spines are the sea urchin’s best defense

Sea Urchin

Sea urchins can be black, brown, green, purple, red, or white

8

Teeth can move in different directions

Muscles move the teeth.

Ball-and-socket joints allow the spines to move in all directions.

sea urchin

Sea urchins eat plants that grow on rocks and on the ocean fl oor A powerful jaw on the underside of their bodies can scrape up food Their mouths have fi ve teeth that can move in different directions

Sea urchins have no brain They have a very simple circulatory system of water-fi lled channels that fl ow through their body

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The chambered nautilus

has irregular brown and

white stripes It can grow

to a width of 10 inches

Chambered Nautilus

Another mollusk, the chambered nautilus, begins life

in a shell with seven small sections, or chambers Like the

scallop, it has a mantle that helps it form a shell As the

soft body of the animal grows, it adds new, larger

chambers to its shell Each chamber is sealed off as the

nautilus moves into a new chamber A full-grown nautilus

may have up to thirty-eight chambers A cone-shaped

head, surrounded by sixty to ninety short tentacles,

can stick out of the open chamber

The closed chambers are fi lled with

nitrogen and other gases A narrow tube

called a siphuncle winds through all the

chambers Depending on the mixture of

fl uids and gases in the

chambers, the nautilus

either rises in the

water or sinks

When the nautilus retreats into its shell,

a fl eshy shield covers the entrance.

Water is expelled through the funnel

to provide thrust.

10

To swim, the nautilus forces water through a movable funnel below its head This funnel is called

a siphon As it forces water through the siphon, it swims backward

During the day the chambered nautilus lives at great depths

At night it rises to feed among the coral reefs in shallow water

chambered nautilus

The nautilus lives only in the outer chamber.

As the nautilus grows it constructs new chambers.

11

Fossils like this provide valuable information about the nautilus During prehistoric times, there were 10,000 kinds of nautilus

Only a few species still live today.

Nautilus Fossil

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Squid belong to a group of mollusks called cephalopods

Cephalopods have large heads and long arm structures

that look like many feet Their name comes from

Greek words that mean “head” and “foot.”

A squid’s head is in the middle of its body

Behind the head is a bullet-shaped sac

covered by a special layer

called a mantle The space

inside the sac, called the

mantle cavity, holds the squid’s organs,

including its ink sac A squid can squirt

ink from this organ to hide itself from

predators Unlike a nautilus, a squid’s

mantle doesn’t make a hard shell

Squid

The tentacles have suckers on their ends.

Many squid can change color to hide from enemies or attract mates Some can even light up.

12

At the other end of the head are eight sucker-lined arms and two extra-long feeding arms When hunting, a squid sneaks up on its prey and quickly grabs it with its two long tentacles The arms can taste food If the squid likes the taste, it pulls the victim into its mouth There,

a hard beak crushes or tears the food apart

To swim, a squid sucks water in through holes between its head and mantle Then it squirts jets of water out of a tube called a funnel Squid prefer to swim backwards But by pointing this funnel in different directions, squid can also swim forward

or sideways to catch prey

eye

The position of the fl exible funnel controls the direction

of the squid’s travel.

ink sac

squid

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Sharks are cartilaginous fi sh Their skeletons

are not made of bones, but of a rubberlike material

called cartilage Sharks have a large liver fi lled with

oil Because oil is lighter than water, the oil keeps

the shark from sinking Sharks’ fi ns also

keep them fl oating Two pectoral,

or side, fi ns act like airplane wings

A powerful tail acts like an engine

Together, they provide lift that keeps the

shark from sinking The only problem is

that this only works when sharks are

swimming So, they have to swim

constantly—even when they

are sleeping!

Spinner Shark

Sharks have several rows

of teeth When a tooth in the

front falls out, one from the row

behind it takes its place

The spinner shark is a fast-moving shark that

often leaps right out of the water It charges into schools,

or groups, of fi sh and spins very quickly, snapping its

mouth open and closed to catch food

liver

14

The largest known shark is about forty feet long The smallest is about fi ve inches Scientists are not sure how many different kinds of sharks there are—

perhaps as many as 350

Sharks and the other creatures of the sea you’ve read about may look as strange to us as animals we might see in movies or comic books

But their odd outsides are just the beginning

These creatures are amazing on the inside too!

spinner shark

Leopard sharks use their coloring as camoufl age among rocks and coral.

Most sharks have streamlined bodies that help them move quickly through the water

15

pectoral fi n

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Glossary

bivalves invertebrates that have two connected

shells that can close like a mouth

cartilage tough, rubberlike material found in animals

cephalopods invertebrates with soft bodies, large heads,

and tentacles

cnidarians simple invertebrates with tentacles around

their mouths

echinoderms invertebrates that are round and have shells

and tube feet

funnel a body part that some invertebrates use to

get around

mantle a layer of fl esh that covers some invertebrates

mollusks an invertebrate with a soft body with only one

section, often covered with a shell

propel to move one’s self