5 2 cells to systems (life science)

5.1 Classifying Organisms (Life Science) 5.2 Cells to Systems (Life Science) 5.3 Human Body Systems (Life Science) 5.4 Plants (Life Science) 5.5 Interactions in Ecosystems (Life Science) 5.6 Changes in Ecosystems (Life Science) 5.7 Water on Earth (Earth Science) 5.8 Weather Patterns (Earth Science) 5.9 Earths Changing Surface (Earth Science) 5.10 Protecting Earths Resources (Earth Science) 5.11 Matter and Its Properties (Physical Science) 5.12 Changes in Matter (Physical Science) 5.13 Forces in Motion (Physical Science) 5.14 Changing Forms of Energy (Physical Science) 5.15 Electricity (Physical Science) 5.16 Stars and Galaxies (Space and Technology) 5.17 Earth in Space (Space and Technology) 5.18 Technology in Our Lives (Space and Technology)

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by Erika Alexander

Scott Foresman Science 5.2

Genre Comprehension Skill Text Features Science Content

Nonfi ction Draw Conclusions • Labels

• Captions

• Diagrams

• Glossary

Cells to Systems

ISBN 0-328-13919-X ì<(sk$m)=bdjbje< +^-Ä-U-Ä-U

Life Science

Scott Foresman Science 5.2

Genre Comprehension Skill Text Features Science Content

Nonfi ction Draw Conclusions • Labels

• Captions

• Diagrams

• Glossary

Cells to Systems

ISBN 0-328-13919-X ì<(sk$m)=bdjbje< +^-Ä-U-Ä-U

Life Science

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cell membrane

cell wall

chloroplast

cytoplasm

nucleus

organ

organ system

tissue

vacuole

What did you learn?

1 What are some things that cells need that you need too?

2 Why do nerve cells have long, branching shapes?

3 Name three important jobs that your bones do.

4 Every cell in your body needs food

On your own paper, write to explain how the food gets to each of your cells

let you move What do you think would happen if you didn’t have any bones? or if you didn’t have any muscles?

Illustrations: Title Page, 5, 7, 9, 12, 15 Leonello Calvetti

Photographs: 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 Unless otherwise acknowledged, all photographs are the property of Scott

Foresman, a division of Pearson Education Photo locators denoted as follows: Top (T), Center (C), Bottom

(B), Left (L), Right (R) Background (Bkgd)

Opener: ©Dr Fred Hossler/Visuals Unlimited 2 (BR) ©Dr Fred Hossler/Visuals Unlimited, (Bkgd)

©Michael Webb/Visuals Unlimited; 6 (BL) ©Dr Dennis Kunkel/Visuals Unlimited, (BC, BR) ©David

Phillips/Visuals Unlimited; 7 (CL) ©Susumu Nishinaga/Photo Researchers, Inc., (CR) ©RDF/Visuals

Unlimited, (CL) ©Dr Dennis Kunkel/Visuals Unlimited; 8 (BL) ©Quest/Photo Researchers, Inc., (CR)

©Veronika Burmeister/Visuals Unlimited; 11 (TL) ©Dr Fred Hossler/Visuals Unlimited, (CC) ©Dr Richard

Kessel & Dr Randy Kardon/Visuals Unlimited, (BL) ©Dr Donald Fawcett/Visuals Unlimited

ISBN: 0-328-13919-X

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 permissions, 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

Cells to Systems

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What is inside a cell?

Cells and Their Functions

A cell is the smallest living part of any living thing Some

organisms have only a single cell Animals and plants may

have trillions Most cells are so small they can’t be seen without

a microscope

Cells have the same needs as all life forms, and they contain

tiny parts to help them meet their needs Cells need food to

survive, just like you All cells have parts that move inside of

them, and some cells can even move on their own Cells can

respond to changes around them, and can even communicate

with other cells to get a job done

Cells use materials in food to grow and to repair wounds

Cells also need energy They mix food with oxygen to get energy This process is called respiration Carbon dioxide and water are also made by this process The energy that cells make

is used for growing, moving, and dividing into new cells

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The Parts of Cells

All cells have some of the same parts Each part has a special

job to do Many of the jobs are similar to the jobs our larger

body parts do For example, you have skin to protect you, a

digestive system to process food, and a system of nerves to

control everything

The cell membrane, which surrounds the cell, acts like a

gate It opens to let food and oxygen in and to let wastes out

The nucleus of a cell contains chromosomes Chromosomes

are made of DNA, a chemical that is shaped like a twisted

ladder The chromosomes carry the information a cell needs

to do its job Each chromosome has sections called genes that

carry units of information Almost every cell in your body has

the same genes These genes pass from one generation to the

next in a process called heredity

Plant cells have some special parts that animal cells do

not have They have a tough cell wall surrounding their cell

membrane This gives plants extra support They also have

chloroplasts, which plants use to make food Chloroplasts

use sunlight to turn water and carbon dioxide into sugar and

oxygen The plant gets its energy from the sugar

5

The Size of Cells

Cells must be big enough to hold all their parts, but not too big If a cell is too big, food and oxygen are not able to reach the middle of the cell fast enough to keep it alive

Almost every cell nucleus in your body has 46 chromosomes

Vacuoles sometimes break down and store material In plant cells, they may store water

Mitochondria combine oxygen and food to produce energy in the process of cellular respiration

The cell membrane can be compared

to your skin.

Cytoplasm is all the material of the cell between the cell membrane and the nucleus.

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How do cells work together?

Types of Cells and Their Work

The shapes of cells help them do different jobs Some cells

have special parts to help them do their job

Very long cells are called branching cells Nerve cells have

branching shapes to help them send messages through the

body Their great length allows signals to be sent very quickly

between different parts of the body

Cells that have a smooth round shape are called round cells

Red blood cells are round They act like saucers to pick up and

carry oxygen Their smooth shape helps them move through

blood vessels

A third kind of cell is called a flat cell These cells join

together to cover a surface A layer of flat cells is very strong yet

flexible Your skin is made of flat cells

This nerve cell is a

branching cell.

This red blood cell is

a round cell.

This skin cell is a flat cell

7

Special Cell Structures

Cilia are some other tiny hairlike structures Cilia wave back and forth to sweep dirt and germs out of your airways.

There are hairlike structures in your ears that bend when sound waves make vibrations When they bend, nerve signals travel to your brain

Muscle cells contain long fibers These fibers can move

to make the cell shorter The fibers are not very strong by themselves But they work together in each cell Then many cells work together to make the muscle strong.

7

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Cells Form Tissues

Often the same kind of cells work together to do the same

job When cells work together, they form a tissue Nerve cells

work together to form nerve tissue A group of bone cells make

up bone tissue

Tissues Form Organs

Tissues join with other tissues to form organs Your body’s

organs do many important jobs Your heart, eyes, ears, and

stomach are all organs Your skin is the largest organ you have

Plants have tissues and organs too Plant organs include stems,

roots, leaves, and flowers

Hair follicle Hair forms inside cells in hair follicles As new cells form, old ones are pushed out The hair you see is dead tissue.

Sweat gland pore

Sweat leaves your skin

through pores It then

evaporates from your

skin, helping to keep

you cool.

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Skin Cell Tissue

Skin cells form in many layers The top section alone has about

25 layers! New cells form in the bottom layer and push the other cells outward and away from the blood supply Cells are dead when they reach the surface Dead cells simply fall off, but they are always being replaced by new cells from below It takes about one month for skin cells to be pushed

to the surface

Other Tissues in the Skin

Your skin is more than just layers of flat skin cells Skin has many tissues working together to do many jobs Your skin prevents germs from entering your body It also keeps too much water from leaving Nerve tissue allows your skin to sense touch, pressure, and temperature Oil glands make oil that keeps your skin soft The hair on your skin stands up when you get cold, trapping air next to the skin to keep you warm This

is what we call goosebumps It is caused by muscles in the skin pulling the hair upright

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How do organs work

together?

Organ Systems

In your body, many cells work together in tissues Many

tissues work together in organs An organ system is a

group of organs that work together to perform important

jobs for your body

Bones Form a System

Each of your bones is an organ About two hundred

bones work together in your skeletal system This system

supports your body It also protects other organs from being

damaged

Muscles Work as a System

Your muscles are part of a system too The job

of your muscles is to move your body Your body

has about 640 muscles in it Different muscles

work together when your brain tells them you

want to run or jump Sometimes muscles

work without your brain telling them to

For example, if you are cold, your muscles

might shiver, helping to keep you warm

You shiver without even thinking about it

Bones work together.

This is a cutaway view of where the bone in your leg meets the bone in your hip.

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Bone cells

Between the bone cells is a hard material that has lots of calcium

This material makes bones hard

Other parts of the body, such as muscles, also use calcium from blood to do their work Bones store calcium until the level of calcium in the blood is low.

Muscles work together.

Squeeze your fist tight Several muscles work together to make your fingers form a fist Can you feel the muscles get tight in your lower arm?

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Organ Systems Work Together

Sometimes organ systems need to work together to do more

difficult jobs Your skeletal system and muscle system need to

work together so you can move Your bones provide support,

and your muscles move your bones You need both systems to

move your arm or any other part of your body

Two or more muscles have the job of moving a bone in

opposite directions Muscles move bones by pulling on them

They never push

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Other Systems Work Together

In your body, many systems must work together For example, you know that your muscles work with your bones to make you move But the muscles would not work if they didn’t receive messages telling them what to do Your nervous system carries these messages from the brain and spinal cord

Some organs might belong to two organ systems Your heart pumps your blood, so it is part of the circulatory system But

it is also a muscle, so it is also part of your muscle system

Your bones make up your skeletal system, but they also do an important job for the circulatory system A soft material called marrow is found inside some of your bones Marrow makes red and white blood cells for the circulatory system

Bone marrow

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Muscles Flex and Extend

When you bend your elbow, your biceps muscle pulls your

arm up When you straighten your arm again, your triceps

muscles are pulling Muscles work in pairs to bend your wrist

and rotate your arm too

Triceps

Biceps

Triceps

Biceps

15

It is amazing to think about all the work that cells do in your body Tiny cells work together to form tissues Tissues team up and make organs Your organs work with each other and form organ systems This teamwork is what makes it possible for your body to do all the things you need it to do

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Glossary

in and out

for plant cells

from sunlight to turn water and carbon dioxide into oxygen and sugar

the nucleus

together to do a main job in the body

an important job

together doing the same job

materials

Vocabulary

cell membrane

cell wall

chloroplast

cytoplasm

nucleus

organ

organ system

tissue

vacuole

What did you learn?

1 What are some things that cells need that you need too?

2 Why do nerve cells have long, branching shapes?

3 Name three important jobs that your bones do.

4 Every cell in your body needs food

On your own paper, write to explain how the food gets to each of your cells

let you move What do you think would happen if you didn’t have any bones? or if you didn’t have any muscles?

Illustrations: Title Page, 5, 7, 9, 12, 15 Leonello Calvetti

Photographs: 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 Unless otherwise acknowledged, all photographs are the property of Scott

Foresman, a division of Pearson Education Photo locators denoted as follows: Top (T), Center (C), Bottom

(B), Left (L), Right (R) Background (Bkgd)

ISBN: 0-328-13919-X

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 permissions, 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

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