Level: U

DRA: 44
Science
Strategy:
Infer/Predict
Word Count: 1,542

6.2.8 Build Vocabulary

HOUGHTON MIFFLIN
Online Leveled Books

1033025
H O UG H T O N M IF F L IN
 by Nicholas Wetherbee

PHOTOGRAPHY CREDITS: Cover © Mike Abrahams / Alamy; 1 © Michael Rosenfeld; 2 © STOCKFOLIO / Alamy; 3 ©
Natural Visions / Alamy; 4 © Micro Discovery / Corbis; 5 © STOCKFOLIO / Alamy; 7 © Edd Westmacott / Alamy; 8 © ItStock
Free; 9 © Clouds Hill Imaging Ltd. / Corbis; 10 © Bettmann / Corbis; 12 © Michael Rosenfeld; 14 © Mike Abrahams /
Alamy; Bkgrnd © Studio Montage
Copyright © by Houghton Mifflin Harcourt Publishing Company
All rights reserved. No part of this work may be reproduced or transmitted in any form or by any means, electronic or
mechanical, including photocopying or recording, or by any information storage and retrieval system, without the prior
written permission of the copyright owner unless such copying is expressly permitted by federal copyright law. Requests
for permission to make copies of any part of the work should be addressed to Houghton Mifflin Harcourt School Publishers,
Attn: Permissions, 6277 Sea Harbor Drive, Orlando, Florida 32887-6777.
Printed in China
ISBN-13: 978-0-547-02888-0
ISBN-10: 0-547-02888-1
1 2 3 4 5 6 7 8 0940 18 17 16 15 14 13 12 11

If you have received these materials as examination copies free of charge, Houghton Mifflin Harcourt School Publishers
retains title to the materials and they may not be resold. Resale of examination copies is strictly prohibited.

Possession of this publication in print format does not entitle users to convert this publication, or any portion of it, into
electronic format.
 Table of Contents

Mold Can Be Good or Bad. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

How Mold Grows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Mold Likes Dark and Dampness . . . . . . . . . . . . . . . . . . . . . . . . . 5

Useful Molds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Mold as Medicine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

A Moldy Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Saving Lives with Mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

At Home with Mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6_028880_VR2_3BL_Mold.indd 2 1/17/08 8:56:01 AM

 Mold Can Be Good or Bad
Have you ever seen gray, furry spots on the sandwich
meat that stayed in your lunch box over the weekend? Or fuzzy,
green dots on the bread that got left out? And what about the
big, round circle on a bruised peach that looks like a small piece
of soft cloth? They’re all types of mold.
Yuck! They’re ugly on food. They look like they’d make
you sick, and many do. But did you know that some kinds of
molds are used in medicines? Instead of making you sick, they
make you well.
Scientists think there are more than 100,000 kinds of mold.
With that many kinds, it’s easy to imagine that some are good
for people — and some aren’t.

Mold on bread

6_028880_VR2_3BL_Mold.indd 3 1/17/08 8:56:04 AM

 How Mold Grows
When molds begin to grow, they are too tiny to see with
your eyes. But if you use a microscope, you may think you are
seeing elegant flowers.
The roots of the “flower” grow in soil, which is actually the
food. The stem grows up and out from the food. The seeds form
a fuzzy blanket on top. These seeds are called spores.
The detached spores can travel through the air like
dandelion seeds on the wind. Or they can travel on water or
insects. If they land in a place where they can grow, they start
the process over again. The roots grow into the food, a stem
grows up, and spores grow at the top.
This process can happen very quickly. Many mold
“flowers” grow near each other and soon they can be seen
without a microscope. A small spot of mold can double or triple
its size overnight.

This is how one type of mold

looks through a microscope.

6_028880_VR2_3BL_Mold.indd 4 1/17/08 8:56:07 AM

Mold Likes Dark and Dampness
Plants need some basic things to grow. They need food,
water, air, and sunlight. But molds are different. They need
food, water, and air like plants. But they don’t like sunlight
nearly as much as plants do. Most molds actually grow better in
dark, damp places. Sunlight would dry up the moisture.
A cut or a bruise on a piece of fruit is another great place
for mold to grow. Fruit has a lot of moisture — and mold likes
damp places! As the mold grows on the fruit, the fruit rots.
This process is called decomposition.
Food growers know how to protect foods from mold.
For example, some growers will cut up apples and dry them
in the sun until they are shriveled. Dried apples can last for
a long time.

Rotting apples

5
 Look Out for Mold!
Some food molds can be very dangerous. Most grow
on the surface where you can see them. But their
roots can extend deep into the food. In most cases,
it’s best to throw away food if you see mold on it.

Most molds like warmer temperatures, but some

grow in the refrigerator. They can grow on salty foods
like bacon, ham, or salami. Others like sugars in jams
and jellies.

The best way to prevent food from growing mold is

to keep the kitchen clean. This includes the inside of
the refrigerator, sponges, and dish towels. Here are
some more tips:

• Store leftovers in clean containers.

• Cover leftovers so mold spores don’t land

on them.

• Use leftovers within three or four days.

6_028880_VR2_3BL_Mold.indd 6 1/17/08 8:56:14 AM

 Useful Molds
For the most part, it’s best not to eat anything that is moldy.
Molds can cause health problems. But there are a few molds
that actually turn out to be tasty.
For example, some cheeses are made by adding mold to
them. The mold gives the cheese a sharp, special taste. These
cheeses are often called “blue” cheeses because the mold makes
blue lines through the middle.
There’s also a mold that was the key to one of the most
famous discoveries in medicine. Could mold really save lives?

Blue cheese is
made with mold.

6_028880_VR2_3BL_Mold.indd 7 1/17/08 8:56:18 AM

 Mold as Medicine
Before the 1940s, doctors had few drugs that could help
them treat infections. For many years, they didn’t understand
the principle that germs caused the infection. Once they did,
they didn’t have a way to stop the germs from growing.
A small cut could turn into something very dangerous.
Germs in the cut could move into the bloodstream. Some people
got very sick. Some even died.
Scientists searched for a medicine that they could use
to heal an infection. The medicine would kill the germs that
caused the infection. It could save the person’s life.

Germs can cause infections.

6_028880_VR2_3BL_Mold.indd 8 1/17/08 8:56:21 AM

 Doctors had been trying to find ways to treat infections for
thousands of years. More than 3,000 years ago, doctors in China
placed a type of moldy food on some skin infections to help
them heal. Others in history used warm earth as a treatment.
The doctors didn’t know it, but the dirt probably had mold in it
that killed germs.
Doctors in Europe and the United States first began to
understand germs in the late 1800s. They began experiments to
see how germs grew and how they could be controlled.
In 1897, a French medical student noticed that one type of
mold killed a germ that caused serious diseases. He thought it
would be good to do more tests. But he didn’t have a way to do
them himself. Several others noticed the same mold over the
years, but not much came of it. People were reluctant to believe
that a fuzzy mold could be so important.

A close-up of grey and

brown molds on cheese

6_028880_VR2_3BL_Mold.indd 9 1/17/08 8:56:29 AM

 Sir Alexander Fleming discovered penicillin,
a mold that could kill germs.

10

6_028880_VR2_3BL_Mold.indd 10 1/17/08 8:56:34 AM

 A Moldy Discovery
By the 1920s, many scientists were studying germs
— sometimes called bacteria. They grew germs that caused
diseases in flat dishes. Then they tried different ways to kill
the germs.
In 1928, a British scientist went on vacation. He forgot to
clean the germ dishes before he left. When he returned, most of
the dishes were covered with germs.
But he was surprised by one dish. It had a large spot of
mold growing in it. The germs all around it had been killed.
He studied the mold and named it penicillin.
Scientists studied penicillin for several years. Then came
the big question. Would it work on people?
The scientists tested penicillin on a patient in England
in 1941. He had a small cut that had become infected.
When he was near death, scientists suggested treating him
with penicillin.
The patient quickly got better. But there wasn’t enough
penicillin to keep treating him. He got sick again and died.
Now the scientists knew penicillin worked. But they
needed to change their equations for growing the mold.
They had to produce much larger amounts of penicillin.
The British scientists faced a complex problem. World War II
had begun. Their country was being bombed by Germany
every day. Most of the money and energy in the country was
being used for defense.

11

6_028880_VR2_3BL_Mold.indd 11 1/17/08 8:56:39 AM

 12

6_028880_VR2_3BL_Mold.indd 12 1/17/08 8:56:43 AM

 Saving Lives with Mold
The British scientists asked the United States for help.
The United States had not yet entered the war. But U.S. doctors
knew that many soldiers would die from infections. Finding a
way to produce large amounts of penicillin would save lives.
The British talked to American scientists in Illinois. These
Americans had been working with molds, too. The two teams
of scientists decided on a compromise. Instead of trying to
compete, they would work together.
They found a way to grow penicillin much faster. Before,
their mold would only grow on the surface of a food. If they
added air to the middle of a moldy food, they could get it to
grow even more.
The scientists also wanted to find a new penicillin mold
that grew better in big tanks. They asked people in the area to
bring them moldy foods to test. A lab worker brought in one of
the specimens. She had a cantaloupe with a large spot of mold
growing on it. It produced about 200 times as much penicillin
as the mold tested in Britain.
Soon, there was enough penicillin to go around. It would
save the lives of many soldiers. Doctors used penicillin to treat
infections and many illnesses. Penicillin seemed to be the
perfect cure.

Penicillin is now made

in large amounts.

13

6_028880_VR2_3BL_Mold.indd 13 1/17/08 8:56:57 AM

 At Home with Mold
Scientists believe mold has been around for over three
billion years. So it’s a pretty safe bet that mold is here to stay.
It has played a role in some important discoveries. But scientists
say the best place for mold is outdoors. If you see mold inside
your home, get rid of it.
Mold can grow on walls, ceilings, and even rugs — as well
as on food. It appears any time things get wet and stay wet.
Mold can damage the parts of the house where it grows. Most
importantly, mold can cause health problems. Keep the surfaces
in your house dry, and you won’t have to worry about mold.
Remember not all mold is bad. In fact, mold is an amazing
living thing. Take a closer look at mold the next time you spot it,
and think about all it can do!

Mold can grow

in damp houses.

14

6_028880_VR2_3BL_Mold.indd 14 1/17/08 8:57:08 AM

 Responding
TARGET VOCABULARY Word Builder Make
a chart like the one below. List words that mean
the opposite of complex.

Complex
Same Meaning Opposite Meaning

difficult ?

complicated ?

Write About It
Text to World Molds are complex. Write a
paragraph explaining how you would teach a
second grader about mold. Use two words from
the Word Builder in your paragraph.

15

6_028880_VR2_3BL_Mold.indd 15 1/17/08 8:57:17 AM

 TARGET VOCABULARY

complex equations
compromise principle
decomposition reluctant
detached shriveled
elegant specimens

TARGET STRATEGY Infer/Predict Use text clues

to figure out what the author means or what might
happen in the future.

Which word is made up of a smaller word

that means you have sworn to do something?

16

6_028880_VR2_3BL_Mold.indd 16 1/17/08 8:57:19 AM

Level: U
DRA: 44
Science
Strategy:
Infer/Predict
Word Count: 1,542

6.2.8 Build Vocabulary

HOUGHTON MIFFLIN
Online Leveled Books

1033025
H O UG H T O N M IF F L IN