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Food and Nutrition
A Science A–Z Life Series
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Food and
Nutrition
Written by Barb Davis
Visit www.sciencea-z.com
www.sciencea-z.com
Food and
Nutrition
Written by Barb Davis
www.sciencea-z.com
Key elements Used in This Book
The Big Idea: Humans are like other organisms in that we need food to
survive. Food is the fuel that powers us. Plants use photosynthesis to make
their own food, while animals eat plants, other animals, or both. Plants
and animals both use the process of respiration to convert food into energy.
In animals—including humans—food breaks down as it travels through the
digestive system, releasing nutrients and energy. To be healthy, we need
to consume a balance of various organic and inorganic nutrients. Knowing
which nutrients the body needs and in what proportions in our diet, as well
as which foods contain those nutrients, are all important for maintaining
our health.
Key words: agriculture, breathe, carbohydrate, carbon dioxide, carnivore, cell,
chlorophyll, cholesterol, consumer, cud, decomposer, diet, digestion, digestive system,
energy, enzyme, esophagus, fiber, food, food chain, glucose, herbivore, inorganic,
lipid, liver, mineral, molecule, nutrient, nutrition, omnivore, organic, organism, oxygen,
pancreas, photosynthesis, plants, producer, protein, respiration, ruminant, saliva, small
intestine, soil, stomach, stomata, sugar, sunlight, trans fat, transpiration, villi, vitamin,
water, water vapor
Key comprehension skills: Compare and contrast
Other suitable comprehension skills: Cause and effect; classify information; main idea
and details; identify facts; elements of a genre; interpret graphs, charts, and diagrams
Key reading strategy: Retell
Other suitable reading strategies: Ask and answer questions; connect to prior
knowledge; summarize; visualize; using a table of contents and headings; using
a glossary and boldfaced terms
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Linda Kloosterhof; title page: © iStockphoto.com/Andreas Prott; page 3: © iStockphoto.com/
Catherine Yeulet; page 4 (l): © iStockphoto.com/Jim Kruger; page 4 (tr): © iStockphoto.com/
Maria Gritcai; page 4 (br): © iStockphoto.com/Robert Plotz; page 5: © iStockphoto.com/Dane Steffes;
page 6 (top inset): © iStockphoto.com/Julie Macpherson; page 6 (bottom inset): © iStockphoto.com/
Karl Dolenc; page 6 (bottom main): © iStockphoto.com/Redmal; pages 6 (top main), 9 (c), 11 (l), 12,
18 (br), 19 (6, 7), 21 (tl): © Jupiterimages Corporation; page 8: © Learning A–Z; page 9 (t): © Xavier
Marchant/Dreamstime.com; page 9 (b): © iStockphoto.com/Klaas Lingbeek-van Kranen; page 11 (c):
© iStockphoto.com/Ivan Burmistrov; page 11 (r): © iStockphoto.com/Grafissimo; page 13 (t):
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MedicalRF.com/Getty Images; page 15 (c): © iStockphoto.com/Emrah Oztas; page 15 (b):
© iStockphoto.com/Marty Eby; page 16 (t): © iStockphoto.com/Robert Churchill; page 16 (b):
© Dorling Kindersley/Getty Images; page 17 (tl): © iStockphoto.com/Jesús Arias; page 17 (tr):
© iStockphoto.com/Peter Baxter; page 17 (bl): © iStockphoto.com/Katarina Drpic; pages 17 (br),
20 (tc): © iStockphoto.com/Kelly Cline; page 18 (tl): © iStockphoto.com/Michael Flippo;
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page 19 (2): © iStockphoto.com/Joe Potato; page 19 (5): © iStockphoto.com/Nataliya Peregudova;
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Gajda; pages 19 (1, 3, 4), 21 (bl): © Hemera Technologies/Jupiterimages Corporation; page 21
(br): © Olga Miltsova/123RF; page 22 (t): © Miltonia/123RF
Illustration Credits:
Pages 10, 13 (bottom), 14 (top), 15 (top): Cende Hill/© Learning A–Z
Food and Nutrition / © Learning A–Z / Written by Barb Davis
All rights reserved. / www.sciencea-z.com
lipids fats and oils (p. 19)
mineralsinorganic nutrients required
in small amounts for health
and normal growth (p. 22)
nutrientssubstances in food or soil that
organisms need to live, stay
healthy, and grow (p. 17)
omnivorean animal that eats both plants
and animals (p. 9)
oxygenan invisible, odorless gas essential
for life that makes up part of the
air (p. 7)
Table of Contents
photosynthesisthe process by which plants convert
energy from the Sun into food (p. 5)
What Needs Food?.................................................... 4
proteinorganic nutrients used by the body
to grow and to repair cells (p. 20)
How Do Plants Get Food?....................................... 5
respirationthe process by which cells produce
energy from stored sugars (p. 7)
How Do Plants Use Food for Energy?................... 7
vitaminsorganic nutrients required in small
amounts for health and normal
growth (p. 22)
Index
agriculture, 11
digestion, 12–16, 18, 19, 21
energy, 4–8, 10, 12, 14–20, 24
food chain, 10
photosynthesis, 5–8, 10
respiration, 7, 8, 12, 15, 18
ruminant, 16
26
small intestine, 13–15
stomach, 13, 14, 16
stomata, 5–7
villi, 15
water, 5–8, 23
water vapor, 7, 8, 12, 15
How Do Animals Get Food?................................... 9
How Do Animals Use Food for Energy?............. 12
Food’s Journey Through the Human Body......... 13
Food, Nutrition, and Health.................................. 17
Organic Nutrients................................................. 18
Inorganic Nutrients............................................... 22
Conclusion............................................................... 24
Glossary.................................................................... 25
Index......................................................................... 26
3
What Needs Food?
All living things, or organisms, need energy
in order to live, complete their daily activities,
and remain healthy. This energy comes from
food. This book explains two life-sustaining
processes: how organisms get food and how
food goes through changes inside organisms
so they can use the food for energy.
Before reading on, think about how plants get
food and how they turn the food into energy.
Glossary
carbohydrates organic nutrients, including sugars
and starches, that can provide an
organism with energy (p. 18)
carbon dioxidean invisible, odorless gas that is
used during photosynthesis and
given off as a waste product during
respiration (p. 5)
carnivorean animal that only eats other
animals (p. 9)
chlorophyll a material in green plants that can
turn water, air, and sunlight into
food (p. 5)
digestion a series of chemical reactions that
break food down into forms that
the body can use (p. 12)
energy the power to do work, make a
change, or move objects (p. 4)
All living things need
food to survive.
enzymes proteins that speed up a chemical
reaction in the body (p. 13)
fibera food substance that cannot
be digested but which helps
the process of digestion (p. 21)
glucose a simple sugar made by plants
during photosynthesis that is
an important source of energy
for all living things (p. 5)
herbivorean animal that only eats plants (p. 9)
4
25
Conclusion
How Do Plants Get Food?
You have learned that both plants and animals
convert food into the energy they need. Plants
make their own food, while animals must consume
food. Luckily, you don’t have to control the process
of turning food into energy in your own body.
But you do have some important responsibilities
when it comes to deciding what to eat.
As you know, animals get the energy they need
to survive by eating many kinds of food found
in their environment. But plants don’t eat food.
Unlike other living things, they have the ability
to make their own food. Plants produce food
through a chemical process called photosynthesis.
Proteins, carbohydrates, lipids . . . your
body needs many things to produce energy
and to stay healthy. In fact, your body needs
a balance of nutrients. So how do you select
what to eat when you’re hungry? Choosing
foods by flavor, texture, or appearance will not
guarantee you a healthy diet. The most important
thing to do is to make sure you eat a variety of
foods. Try to avoid foods that have too much fat
and cholesterol. Limit the amount of red meat,
fried foods, butter, and artificial ingredients you
eat. Use healthier
fats and eat plenty
of great-tasting fruits
and vegetables, which
have the nutrients
your body needs.
24
During photosynthesis,
plants make a simple kind of
sugar, called glucose, which
becomes their food source. You
may have thought that plants
get their food from the soil, but
this is not the case. Green plants
contain chlorophyll, a pigment
that absorbs sunlight and converts the light energy
into glucose. During photosynthesis, plants also
use a gas called carbon dioxide, which is found in
the air. The carbon dioxide gets absorbed through
tiny holes called stomata, which are mostly found
on the underside of a plant’s leaves.
Although soil does not provide plants with
their food, it does supply plants with water and
minerals, both of which are absorbed through
the roots. Water and minerals aid in the process
of photosynthesis. The diagram on page 6 reviews
the process of photosynthesis.
5
Photosynthesis in Green Plants
5
4
3
6
2
Clearly, eating a good combination of foods is
extremely important. Actually, your body might
be able to go without any food for a month.
However, you could only survive for about a
week without water, and even less time in a hot,
dry place or while being active. Almost every
chemical reaction that takes place in your body
requires water. Your saliva is mostly water. Blood,
which is about 83 percent water, carries nutrients
to cells and carries away waste materials. More
than half your body mass is water. Experts say
you need about two liters (10.5 glasses) of water
a day to stay healthy. You get a lot of water from
the foods you eat. But there’s no better way to stay
hydrated than by simply drinking clean water,
especially when its hot and when you exercise.
1
1Roots absorb water and
minerals, and transport
them to the plant’s cells.
2A green pigment in plant
cells, called chlorophyll,
captures the Sun’s light
energy and turns it into
chemical energy.
3Carbon dioxide from air
enters the leaf through
tiny holes called stomata.
6
4The energy from the Sun
helps carbon dioxide
molecules react with
water molecules to
make a simple sugar
called glucose.
5The plant uses some
of the glucose it makes
and stores the rest.
6Oxygen, a waste product
from the food-making
process, passes out of
the leaf and enters the air.
23
Vitamins assist with
many jobs in your body.
They can support good
eyesight, strong teeth, and
healthy skin. Many foods
and drinks contain vitamins.
Carrots, for example, contain
vitamin A, while oranges
supply you with vitamin C.
Although you don’t need large amounts
of vitamins, you can become ill without
adequate amounts.
Inorganic Nutrients
The left side of the formula below explains
what plants use during photosynthesis. The
right side explains what plants produce during
photosynthesis.
Photosynthesis Formula
water + carbon dioxide + light → sugar (food) + oxygen
How Do Plants Use Food for Energy?
Minerals are inorganic nutrients that are
important to your health. Calcium is one of
the many minerals your body needs. A lack
of calcium can cause bone problems. Other
minerals found in foods include salt, zinc, iron,
copper, magnesium, and potassium. Your blood
uses iron to carry oxygen, and salt is used in
your sweat, blood, and tears.
Your body only needs
small amounts of these
minerals for good health.
However, your body does
not manufacture minerals,
Some people take
so you must get them
pills to add extra
vitamins and minerals
from the food you eat.
to their diet.
22
Photosynthesis takes place inside the smallest
parts of a plant—its cells. Much like bricks in a
building, cells join together to make up most
living things.
Some of the glucose (sugar) that a plant makes
during photosynthesis remains stored in its leaves,
fruit, stem, roots, and other parts. To use the rest
of the food for energy, the plant must break down
the glucose in its cells. This involves a different
chemical process, called respiration.
During respiration, glucose reacts with
oxygen to release energy that plants need to
live. Respiration also forms carbon dioxide and
water vapor as waste products. These waste
products exit the plant through the stomata.
The left side of the next formula explains
what plants use during respiration. The right side
explains what plants produce during respiration.
7
Respiration Formula
sugar (food) + oxygen → energy + carbon dioxide + water vapor
To review, photosynthesis is how plants
make their own food. Respiration is how plants
use that food for energy. While photosynthesis
occurs in sunlight, respiration can occur in the
dark or the light. All organisms use respiration,
but plants also use photosynthesis. Use the chart
below to compare these two important processes.
Photosynthesis
Respiration
produces food
uses food
stores energy
releases energy
uses water
uses glucose
uses carbon dioxide
uses oxygen
produces glucose
produces water vapor
produces oxygen
produces carbon dioxide
occurs in sunlight
occurs in the dark or light
used primarily by plants
used by all organisms
When plants lose water
vapor through their leaves,
it is called transpiration. To prove
that plants give off water, try
sealing a few leaves of a living
plant in a bag for a few days
and watch what happens!
8
There are many kinds of protein, and your
body needs a variety. You can get some of these
proteins from foods such as eggs, cheese, milk,
meat, and fish. You can get other proteins from
nuts, seeds, dried peas, beans, and grains such
as wheat, rice, and oats. Vegetarians, who don’t
eat meat, rely on foods from plants to get the
protein they need.
Eat meat, cheese, milk,
eggs, and nuts for protein.
Another important part of a healthy diet is
fiber. Fiber is a substance that your body cannot
digest. Why would you need something you
cannot digest? Fiber helps food pass through
your intestines quickly and easily. Fresh fruits
and vegetables, beans and peas,
and whole-grain cereals are all
good sources of fiber. Scientists
believe that eating a diet high in
fiber helps prevent cancer and
other health problems.
21
How Do Animals Get Food?
Animals get food in three ways. Before you
read on, can you guess what these ways might be?
These foods are tasty, but they
are often high in unhealthy fats,
and they do not provide many
healthy nutrients.
Lipids also create the fat under your skin
that keeps you warm as well as the oil that
makes your hair shiny. All healthy bodies need
a certain amount of fat. However, too much fat
is unhealthy. Certain fats are good for you if
eaten in the right balance, including omega-3
and omega-6 fatty acids. Some foods contain a
particular type of fat, called trans fat, which can
increase the amount of cholesterol in the blood.
Too much cholesterol can lead to heart disease.
While carbohydrates are
the main source of your body’s
energy, protein is useful in
another way. Your body uses
protein to build and repair
cells. Protein is essential for
building and strengthening
your bones, muscles, skin,
and the rest of your body.
20
Milk is a good source
of protein.
Some animals only
eat plants; a zebra
is considered an
herbivore because
it only eats plants.
Some animals eat
other animals; a lion
that eats zebras and
other animals is a
carnivore, or meat
eater. Finally, an
animal may eat both
plants and animals,
which makes it an
omnivore; warthogs
are omnivores.
Think
of ten
wild animals. How
would you classify
them as herbivores,
carnivores, or
omnivores?
herbivore
carnivore
omnivore
9
A Desert Food Chain
primary
consumer
secondary
consumer
producer
decomposer
tertiary
consumer
All living things are part of one or more food
chains. Almost all food chains begin with food
producers. This group includes green plants—
which produce energy through photosynthesis—
as well as algae, and other organisms that can make
their own food. Primary consumers (herbivores and
omnivores) eat the producers, getting energy in the
process. Then secondary consumers (carnivores
and omnivores) eat primary consumers. Tertiary
consumers (mostly carnivores) eat secondary
consumers. Finally, decomposers break down any
leftover living matter. This step completes the food
chain. In this way, energy flows through the food
chain. Since plants are organisms that make food,
they are where most of the food production begins.
10
Complex carbohydrates
consist of long chains
of glucose molecules,
called starches. Foods
such as potatoes, rice,
whole grains, beans,
corn, and some other
vegetables are starches.
These complex “carbs”
take longer for your body
to digest, so they keep
your energy steadier
throughout the day than
simple carbohydrates
do. Which category of
carbohydrates do you
suppose doctors suggest
you eat more of?
Vegetables, cereal,
whole-grain breads,
and rice are
carbohydrates.
Lipids, which are fats and oils,
are another type of nutrient.
Rub a peanut on a paper bag
and you get an oily stain.
Nuts, meats, and other
foods contain lipids. Your
body uses lipids to store energy.
Ounce for ounce, lipids supply
more than twice as much energy
as carbohydrates do.
Some foods, like
these, contain
healthy fats.
19
Organic Nutrients
Your body gets most of its energy from
carbohydrates. These important organic nutrients
are found in many common foods. How do they
give you energy? Just as in plants, animals use the
process of respiration to convert food into energy.
After you eat foods that contain carbohydrates,
your body breaks them down into glucose
molecules (a simple sugar) and combines them
with oxygen. Do you remember what happens
next? Energy is released! Refer to the formula
on page 8 to review the process of respiration.
Carbohydrates are generally described as
one of two types: simple or complex. Simple
carbohydrates are small molecules of sugars that
come in foods such as doughnuts, candy, fruit,
and soda pop. You can digest them very quickly
to get a short-term spike in energy.
But if you don’t use this energy
by being active, it often gets
stored as fat. Eating too much
sugar for many years may also
result in disease.
18
Agriculture
How do you get the foods you eat? Do you go
into nature to collect plants and hunt wild animals?
Probably not. Someone else has grown the plants
and raised the animals for you, and then they sold
the food to you in a nearby store or restaurant.
Agriculture is the science of growing crops and
raising livestock. For most of human history,
agriculture involved backbreaking labor. People
planted seeds by hand and harvested the crops with
handheld tools. Harnessing animals to pull a heavy
plow was extremely hard work, too. In 1830, it took
250 to 300 hours of labor to produce 100 bushels of
wheat. By 1890, mechanical planters, tractors, and
other inventions had cut that time to about 50 hours.
Today, advanced technology helps farmers harvest
that same100 bushels of wheat in much less time.
Plus, the wheat requires fewer acres of land now
because scientists have found ways to alter plants
so they yield more food than they used to. In other
words, agriculture has become much more efficient
since the time when people used handheld tools
to dig holes in the soil and plant one seed at a time.
11
How Do Animals Use Food for Energy?
There it sits—a nice, juicy
apple loaded with energy, ready
to help you walk, run, and breathe.
How does your body get the energy
contained in that apple? Remember
the plant and its chemical-processing factory?
Animals also process chemicals to make energy.
This process is called digestion.
The digestive system in animals works like
a “disassembly line.” It takes food apart, piece
by piece, in a series of chemical reactions that
break food down into tiny particles. These
particles, called molecules, are distributed to
the body’s cells by blood, which circulates
throughout the body.
Food, Nutrition, and Health
Foods contain chemicals that provide you—
and all organisms—with the energy to move,
grow, and heal. These chemicals and substances
in food are called nutrients. You need a variety
of nutrients to maintain good health. Not all foods
contain the same nutrients, so it is important to eat
foods that give you the right balance of nutrients.
There are six main types of nutrients. We classify
them into two main groups: organic and inorganic.
Organic nutrients—essential chemicals found in
living things—come from foods such as meat,
fruits, grains, and vegetables. Inorganic nutrients
are chemicals not produced by living things. As
you read on, think about whether the foods you
eat provide all of these important nutrients.
You’ve learned that plant cells use the
respiration process to convert glucose to energy.
A similar thing happens inside the cells of animals.
During breathing, oxygen is delivered to blood
cells. Then glucose molecules from the animal’s
food combine with oxygen in the animal’s cells.
When glucose and oxygen combine in a chemical
reaction, they release—you guessed it—energy!
Just as plants do, animals give off water vapor
and carbon dioxide during respiration. The water
vapor is what makes an animal’s breath feel wet.
12
17
So Many Stomachs!
What do cows, camels, and
giraffes have in common? They
all have very unusual stomachs!
These animals, called ruminants,
have up to four chambers in
their stomach that each act
as a separate stomach. Why
so many?
Whether it is three chambers or four, the main
purpose of these stomachs is the same: eat now,
digest later. Ruminants eat on the run, grabbing
as much food as they can before some hungry
predator starts to chase them. The ruminants store
a large quantity of food in the first chamber of
their stomach. Here, it begins the breakdown
process with the help of digestive enzymes.
Later on, the animal can bring up the partially
digested food, called cud, from the first stomach
and chew it some more. Have you ever seen cows
comfortably lying around, looking as though they’re
chewing gum? That’s not gum they’re chewing!
This second chewing helps break down grasses
that are hard to
digest. Then the
cud passes into
the other chambers
of the stomach, where
enzymes continue to launch
chemical reactions to extract
Stomach
energy from the food.
chambers
16
Food’s Journey Through the Human Body
Now let’s look at the
digestive system of the human
body. When you eat an apple,
the food begins a long journey.
It starts with your teeth, which
tear off a piece of the apple. The
saliva in your mouth adds moisture and enzymes.
Enzymes are chemicals found throughout your
digestive system. They speed up the chemical
reactions that take place during digestion. At this
stage of your food’s journey, the enzymes soften
the apple as your teeth grind it into smaller bits
of food so you can swallow it.
Next, your tongue
pushes the softened
apple bits to the back
of your mouth, and
you swallow. The
food travels down
your esophagus, the
long tube that connects
your throat to your
stomach. The circular
muscles in this tube
contract to push the
food down toward
your stomach.
mouth
esophagus
stomach
liver
pancreas
large
intestine
small
intestine
13
What was once a bite
of a tasty apple has reached
your stomach. The lining
of your stomach makes
two types of chemicals:
gastric juices and enzymes.
Did you ever eat a piece of
lemon? It’s so sour! Gastric
juices in your stomach are acidic, like lemon juice,
but much stronger. As the apple bits reach your
stomach, gastric juices mix with the food and
break it down even further.
Stomach enzymes launch chemical reactions
that break down the food into even tinier pieces.
Then your stomach moves the food around. Your
food is unrecognizable at this point. It is being
turned into energy.
Even though your
stomach mixes food and
enzymes, most digestion
takes place in your small
intestine. As the food
travels from your stomach
to the small intestine,
other organs, such as
the liver and pancreas,
add more enzymes and
other digestive chemicals.
14
In some people, the
pancreas doesn’t
work. So they use
manufactured
enzymes from a
pig’s pancreas to
help break down
their food for them!
The digested molecules
of food are now in a form
that the body can use for
energy. They leave the
small intestine through
villi—tiny fingerlike
structures lining its walls.
Blood moves through the
villi to pick up the molecules
so they can circulate to other
cells in your body.
villi
Now you have completely digested that apple
you ate hours ago. Digestion has turned the fruit
into molecules of sugar. The sugar molecules carry
stored energy from the apple. These molecules are
transported by the blood to your body’s
cells, where respiration changes most
of the molecules into energy. You use this
energy for all of your body’s activities.
The blood carries the
waste products of water
vapor and carbon dioxide
to your lungs, where you
breathe them out. Any
leftovers from the food
you ate will leave the
body as waste.
The small intestine is
only called “small”
because it’s narrow.
It can be 7 meters
(23 ft.) long—as long
as a truck!
15