Download New Title - AIS IGCSE Science

0970_0989_bi_c06_te
3/9/06
1:46 PM
Page 971
38–1 Food and Nutrition
Section 38–1
1 FOCUS
H
Objectives
ow important is food in your life? Before you answer, think of
two American holidays: Independence Day and Thanksgiving
Day. What comes to mind? No matter where you live, chances are
that meals are the centerpieces of those special days. To most of
us, food is more than just nourishment—it is an important part of
our culture. Human societies throughout the world organize
meetings and family gatherings around food.
Key Concepts
• What are the nutrients your
body needs?
• Why is water such an important nutrient?
Vocabulary
Food and Energy
Have you ever wondered why you need to eat food? The most
obvious answer is to obtain energy. You need energy to climb
stairs, lift books, run, and even to think. Just as a car needs
gasoline, your body needs fuel for all that work, and food is your
fuel. Cells convert the chemical energy stored in the sugar glucose
and other molecules into ATP.
The energy available in food can be measured in a surprisingly
simple way—by burning the food! When food is burned, the energy
content of the food is converted to heat, which is measured in
terms of calories. The amount of heat needed to raise the temperature of 1 gram of water by 1 degree Celsius is 1 calorie. Scientists
refer to the energy stored in food as dietary Calories with a capital
C. One Calorie is equal to 1000 calories, or 1 kilocalorie (kcal).
The energy needs of an average-sized teenager are about
2200 Calories per day for females and about 2800 Calories per
day for males. If you engage in vigorous physical activity, however, your energy needs may be higher.
Chemical pathways in your body’s cells can extract energy
from almost any type of food. Why then does it matter which
foods you eat? Although most of the food you eat is used as fuel,
a certain amount of the food you eat has other important functions. Food supplies the raw materials used to build and repair
body tissues. Some of these raw materials are
used to manufacture new biomolecules. These
include the proteins that regulate cellular
reactions, the phospholipids in cell membranes, and DNA—your genetic material.
Food also contains at least 45 substances that
the body needs but cannot manufacture.
The science of nutrition—the study of food
and its effects on the body—tries to determine
how food helps the body meet all of its various
needs. Based on their research, nutritionists
recommend balanced diets that include many
different types of food. They also plan diets for
people with particular needs, such as diabetics.
Calorie
carbohydrate
fat
protein
vitamin
mineral
Reading Strategy:
Finding Main Ideas Before
you read, skim the section to
identify the key ideas. Then,
carefully read the section,
making a list of supporting
details for each main idea.
Tim
r
• Teaching Resources, Lesson Plan 38–1,
Adapted Section Summary 38–1, Adapted
Sav38–1,
Worksheets 38–1, Section Summary
e
e
Worksheets 38–1, Section Review 38 –1
• Reading and Study Workbook A, Section 38–1
• Adapted Reading and Study Workbook B,
Section 38 –1
Vocabulary Preview
Point out that five of the Vocabulary
terms are nutrients, or substances in
food that the body needs, and that
the other term is a measure of the
amount of energy in food. Ask:
Which term refers to the amount
of energy in food? (Calorie)
Reading Strategy
!
Figure 38–1 Holidays and
other celebrations often center
around food.
SECTION RESOURCES
Print:
38.1.1 Explain how food provides
energy.
38.1.2 Describe the nutrients your
body needs.
38.1.3 State why water is such an
important nutrient.
38.1.4 Explain how to use the food
pyramid.
• Issues and Decision Making, Issues and
Decisions 5, 35, 39, 49
Suggest that students create a table
as they read to compare and contrast
the nutrients that the body needs.
Possible column headings might
include: Type of Nutrient, Foods in
Which It Is Found, and Role It Plays in
the Body. Advise students to save
their tables for study guides.
2 INSTRUCT
Food and Energy
Make Connections
Chemistry Remind students that
ATP stands for adenosine triphosphate and that each molecule of ATP
contains one ribose molecule and
three phosphate molecules. Ask:
How is the energy in ATP released
so that cells can use it? (Energy is
released when chemical bonds are broken and ATP loses phosphate groups to
become, first, ADP, or adenosine
diphosphate, and then AMP, or adenosine monophosphate.)
Technology:
• iText, Section 38 –1
• Transparencies Plus, Section 38 –1
Digestive and Excretory Systems
971
0970_0989_bi_c06_te
3/9/06
1:46 PM
Page 972
38–1 (continued)
Nutrients
Nutrients
Nutrients are substances in food that supply the energy and raw
materials your body uses for growth, repair, and maintenance.
The nutrients that the body needs are water, carbohydrates, fats, proteins, vitamins, and minerals.
Demonstration
Ask: What are the sources of water
in our diets? (Students are likely to
mention drinking water and other beverages, but they might not mention the
water contained in food.) Explain that
some foods are mostly water, whereas other foods contain almost no
water. Demonstrate how much water
is contained in a variety of foods,
such as a slice of apple, a slice of
potato, a slice of bread, and a cracker.
Measure the masses of the foods
when they are fresh. Then, leave the
foods out to dry on paper plates for a
few days and measure their masses
again. Have students compare the
dry masses with the fresh masses and
infer which food contained the most
water and which contained the least.
! Figure 38–2
Every cell in
the body needs water because
many of the body’s processes
take place in water. On hot days
or when you exercise, you need to
drink more water to replace the
water that is lost in sweat.
How does sweat help to maintain homeostasis?
Carbohydrates Simple and complex carbohydrates are the
Build Science Skills
Designing Experiments Relate
that populations with high-fiber diets
have been found to have low rates of
colon cancer. Add that people who
eat high-fiber diets usually also have
low-fat diets, which are known to
lower colon cancer rates. Thus, it is
not clear if fiber alone lowers colon
cancer rates. Challenge students to
design an experiment to help resolve
this issue. (Students should say they
would compare colon cancer rates in
people on high-fiber, low-fat diets with
the rates in people on low-fiber, low-fat
diets.)
Water The most important nutrient is water.
Every cell
in the human body needs water because many of the
body’s processes, including chemical reactions, take
place in water. Water makes up the bulk of blood, lymph, and
other bodily fluids. On hot days or when you take part in strenuous exercise, sweat glands remove water from your tissues and
release it as sweat on the surface of your body. As the water in
sweat evaporates, it cools the body. In this way, sweating helps
maintain homeostasis. Water vapor is also lost from the body
with every breath you exhale and in urine.
Humans need to drink at least 1 liter of water each day. If
enough water is not taken in to replace what is lost, dehydration
can result. This condition leads to problems with the circulatory,
respiratory, and nervous systems. Drinking plenty of clean
water, as the woman is doing in Figure 38–2, is one of the best
things you can do to help keep your body healthy.
! Figure 38–3 Breads, pastas,
and cereals are foods rich in
carbohydrates. Simple carbohydrates do not have to be digested
or broken down. Complex carbohydrates must be broken down before
they can be used by the body.
Inferring Which type of carbohydrate—simple or complex—provides
the body with quick energy?
main source of energy for the body. Figure 38 –3 shows some of the
foods that contain carbohydrates. The sugars found in fruits,
honey, and sugar cane are simple carbohydrates, or monosaccharides and disaccharides. The starches found in grains,
potatoes, and vegetables are complex carbohydrates, or
polysaccharides. Starches are broken down by the digestive
system into simple sugars. These molecules are absorbed
into the bloodstream and carried to cells throughout the
body. Sugars that are not immediately used to supply
energy are converted into the complex carbohydrate glycogen, which is stored in the liver and in skeletal muscles.
Many foods contain the complex carbohydrate cellulose,
often called fiber. Although the human digestive system
cannot break down cellulose, you need fiber in your diet. The
bulk supplied by fiber helps muscles to keep food and wastes
moving through your digestive and excretory systems. Foods
such as whole-grain breads, bran, and many fruits and vegetables are rich in fiber.
Fats Fats, or lipids, are an important part of a healthy diet.
Fats are formed from fatty acids and glycerol. Your body needs
certain fatty acids, called essential fatty acids, to produce cell
membranes, myelin sheaths, and certain hormones. Fatty acids
also help the body absorb fat-soluble vitamins. When a person
eats more food than is needed, the body stores the extra energy
as fat. Deposits of fat protect body organs and insulate the body.
SUPPORT FOR ENGLISH LANGUAGE LEARNERS
Vocabulary: Science Glossary
Beginning Write the following Vocabulary
terms on the board: carbohydrate, fat, protein,
vitamin, and mineral. Underline the syllables as
you model the pronunciation of the terms.
Write a short definition of each term on the
board. Provide appropriate pictures from newspapers or magazines to add a visual
component to the definitions (for example, a
picture of bread to be placed with the definition of carbohydrate).
972
Chapter 38
Intermediate Have the students complete the
science glossary activity described for beginning students. Then, with an English-proficient
student, each student should write sentences
using his or her choice of three of the Vocabulary
terms. A volunteer from each pair should read
the sentences out loud. Post these terms on a
word wall with other Vocabulary terms from
the chapter.
0970_0989_bi_c06_te
3/9/06
1:46 PM
Page 973
Make Connections
Mathematics Point out that no
more than 30 percent of the Calories
in the diet should come from fat. Ask:
If you eat 2000 Calories a day,
what is the maximum number of
Calories that should come from
fat? (600 Calories) Urge students to
read nutrition labels to find the total
fat content of foods they might eat in
a typical day.
Figure 38–4
Fats and
proteins are two of the six
nutrients the body needs. The
foods on the left contain essential
fatty acids. The foods below are
good sources of proteins.
Build Science Skills
Based on the structure of their fatty acid chains, fats
are classified as saturated or unsaturated. When there are
only single bonds between the carbon atoms in the fatty
acids, each carbon atom has the maximum number of
hydrogen atoms and the fat is said to be saturated. Most
saturated fats are solids at room temperature—including
butter and other animal fats.
Unsaturated fats have at least one double bond in a fatty
acid chain. Unsaturated fats are usually liquids at room temperature. Because many vegetable oils contain more than one
double bond, they are called polyunsaturated. Figure 38–4
shows foods containing both saturated and unsaturated fats.
People often consume more fat than they actually need. The
American Heart Association recommends a diet with a maximum of 30 percent of Calories from fat, of which only 10 percent
should be from saturated fats. The health consequences of a diet
high in fat are serious. They include an increased risk of high
blood pressure, heart disease, obesity, and diabetes.
Proteins Proteins have a wide variety of roles in the
body. Proteins supply raw materials for growth and
repair of structures such as skin and muscle. Proteins
have regulatory and transport functions. For example,
the hormone insulin is a protein that regulates the level
of sugar in the blood. Hemoglobin, a protein found in
red blood cells, helps the blood transport oxygen.
Proteins are polymers of amino acids. The body is
able to synthesize only 12 of the 20 amino acids used
to make proteins. The other 8, which are listed in
Figure 38–5, are called essential amino acids. Essential amino acids must be obtained from the foods that
you eat. Meat, fish, eggs, and milk generally contain
all 8 essential amino acids. Foods derived from plants,
such as grains and beans, do not. People who don’t eat
animal products must eat a combination of plant
foods, such as beans and rice, to obtain all of the
essential amino acids.
!
Figure 38–5 When plant foods
are eaten in the right combination,
they provide all of the essential
amino acids. Interpreting
Graphics Which amino acids are
found in both grains and legumes?
Corn and
Other Grains
Methionine
Tryptophan
Phenylalanine
Leucine
Threonine
Valine
Beans and
Isoleucine
Other Legumes
Lysine
Applying Concepts Explain the
concept of complementary proteins,
that is, proteins that individually lack
one or more essential amino acids
but together contain all eight. Point
out that the amino acids in grains,
such as corn, rice, and wheat, complement the amino acids in legumes,
such as beans, peas, and peanuts.
Challenge students to apply the concept of complementary proteins by
planning a meatless meal that contains all eight essential amino acids.
(Possible meals might include beans
with rice or peanut butter with bread.)
Use Visuals
Figure 38–5 Check that students
understand how to interpret the figure. Point out that it is actually a Venn
diagram. Ask: How can you find out
which amino acids are found in
particular foods? (Students might
think, incorrectly, that the information
is included on nutrition facts labels.)
Tell them that the amino acid content
of foods can be found on several
Internet Web sites, including the U.S.
Food and Drug Administration Web
site.
FACTS AND FIGURES
How sweet it is
Because milk does not taste sweet, some people
are surprised to learn that it contains sugar. In
fact, 8 oz of milk contains 11 g of sugar, or more
than half the sugar in the same amount of orange
juice. Most of the sugar in milk is in the form of
lactose, which is broken down into simpler sugars
in the digestive tract by the enzyme lactase. Most
human infants produce lactase and can digest lac-
tose. Many adult humans, on the other hand, no
longer produce lactase. Therefore, they cannot
digest lactose. When some of these people drink
milk, the lactose ferments in their intestines and
causes gas, cramps, and diarrhea. Fortunately,
there are special milk products available that
lactose-intolerant people can digest because the
products contain lactase-producing bacteria.
Answers to . . .
When sweat evaporates
from the body surface, it carries heat
away, which cools the body.
Figure 38–3 Simple carbohydrates
provide the body with quick energy.
Figure 38–5 Phenylalanine, leucine,
threonine, and valine
Digestive and Excretory Systems
973
0970_0989_bi_c06_te
3/9/06
1:46 PM
Page 974
Vitamins If you think of carbohydrates, fats, and proteins as
38–1 (continued)
the fuel of an automobile, then vitamins are the ignition.
Vitamins are organic molecules that help regulate body
processes, often working with enzymes. As you can see in
Figure 38– 6, most vitamins must be obtained from food.
However, the bacteria that live in the digestive tract are able to
synthesize vitamin K. The skin is able to synthesize vitamin D
when exposed to sunlight. A diet lacking certain vitamins can
have serious, even fatal, consequences.
There are two types of vitamins: fat-soluble and watersoluble. The fat-soluble vitamins A, D, E, and K can be stored in
the fatty tissues of the body. The body can build up small stores of
these vitamins for future use.
Build Science Skills
Inferring Review the basic roles in
the body that are played by carbohydrates, fats, and proteins. Ask: What
do you think would happen if you
did not eat enough carbohydrates?
(You might feel tired because you
would not have enough immediate
energy, and you would lose weight
because your body would need to use
stored reserves of energy. Your digestive
system might not function properly due
to lack of fiber.) What do you think
would happen if you did not eat
enough fat? (Your supply of fatsoluble vitamins might be depleted,
which would affect functions such as
blood clotting, vision, or bone growth.
Because fats are needed for myelin
sheaths, the function of the nervous
system could be impaired.) What do
you think would happen if you did
not eat enough proteins? (Almost
every body function could be affected
because enzymes [proteins] make biochemical reactions efficient. You might
feel tired because the body could not
produce the hemoglobin needed to
carry the oxygen that cells use for cellular respiration.)
Use Visuals
Figure 38–6 Point out the column
for sources of vitamins and ask:
Which types of food seem to be
rich in many different vitamins?
(Vegetables, whole grains, and dairy
products) Next, call students’ attention to the column for function
of vitamins and ask: Which body systems need vitamins to function
properly? (Virtually all body systems)
Have students compare the functions
of the B vitamins in particular. Then,
ask: What general function do all
the B vitamins have in common?
(Metabolism) Remind students that
metabolism refers to all the chemical
reactions that build up or break
down substances in the body.
!
Figure 38–6 This table lists
the food sources and functions of
14 essential vitamins. The fatsoluble vitamins are listed in the
blue rows, and the water-soluble
vitamins in the white rows. Using
Tables and Graphs What is the
function of vitamin K?
Vitamins
Vitamin
Sources
Yellow, orange, and dark green
vegetables; dairy products
Important for growth of skin cells;
important for night vision
D (calciferol)
Fish oils, eggs; made by skin when
exposed to sunlight; added to
dairy products
Promotes bone growth; increases calcium
and phosphorus absorption
E (tocopherol)
Green leafy vegetables, seeds,
vegetable oils
Antioxidant; prevents cellular damage
K
Green leafy vegetables; made by
bacteria that live in human intestine
Needed for normal blood clotting
B1 (thiamine)
Whole grains, pork, legumes, milk
Normal metabolism of carbohydrates
B2 (riboflavin)
Dairy products, meats, vegetables,
whole-grain cereal
Normal growth; part of electron transport
chain; energy metabolism
Niacin
Liver, milk, whole grains, nuts, meats,
legumes
Important in energy metabolism
B6 (pyridoxine)
Whole grains, meats, vegetables
Important for amino acid metabolism
Pantothenic acid
Meats, dairy products, whole grains
Needed for energy metabolism
Folic acid
Legumes, nuts, green leafy
vegetables, oranges, broccoli, peas,
fortified bread and cereal
Coenzyme involved in nucleic acid
metabolism; prevents neural-tube defects
in developing fetuses
B12 (cyanocobalamin)
Meats, eggs, dairy products, enriched
cereals
Coenzyme in nucleic acid metabolism;
maturation of red blood cells
C (ascorbic acid)
Citrus fruits, tomatoes, red or green
peppers, broccoli, cabbage,
strawberries
Maintenance of cartilage and bone;
antioxidant; improves iron absorption;
important for healthy gums, tissue repair,
and wound healing
Biotin
Legumes, vegetables, meat
Coenzyme in synthesis of fat; glycogen
formation; amino acid metabolism
Choline
Egg yolk, liver, grains, legumes
Required for phospholipids and
neurotransmitters
HISTORY OF SCIENCE
How vitamins were named
In the 1800s, sailors in the Japanese navy developed a nervous disorder named beriberi when
they were fed a mostly white-rice diet. The sailors
became extremely weak and suffered uncontrollable muscle spasms. Toward the end of the
1800s, a Dutch doctor noticed that prisoners who
were fed mostly white rice also developed
beriberi, whereas prisoners who were fed ordinary
brown rice did not. The doctor inferred that some
974
Chapter 38
Function
A (retinol)
factor in the hull of the rice, which was removed
when brown rice was converted to white, was
needed by the body to prevent beriberi. A short
time later, a Polish chemist isolated the factor and
named it “vital amine,” because it was so important to life and because he thought its chemical
structure was that of an amine compound. He
was incorrect with regard to the latter, but the
name stuck and gave birth to the term vitamin.
0970_0989_bi_c06_te
3/9/06
1:46 PM
Page 975
Address Misconceptions
Ask students: Can taking a daily
vitamin pill make up for a lack of
vegetables, whole grains, dairy
products, or other vitamin-rich
foods in the diet? (Some students
might say “Yes.”) Explain that foods
such as these are rich not only in
vitamins but in other nutrients as
well. Ask: What other nutrients do
whole grains, vegetables, and dairy
products provide? (Vegetables and
whole grains provide carbohydrates,
vitamins, and minerals. Dairy products
provide proteins, fats, and
minerals.)
Important Minerals
Mineral
Sources
Function
Calcium
Dairy products, salmon, sardines,
kale, tofu, collard greens, legumes
Bone and tooth formation; blood
clotting; nerve and muscle function
Phosphorus
Dairy products, meats, poultry, grains
Bone and tooth formation; acid-base balance
Potassium
Acid-base balance; body water balance; nerve
function; muscle function
Meats, dairy products, many
fruits and vegetables, grains
Chlorine
Table salt, processed foods
Acid-base balance; formation of gastric juice
Sodium
Table salt, processed foods
Acid-base balance; body water balance; nerve
function; muscle function
Magnesium
Whole grains, green leafy vegetables
Activation of enzymes in protein synthesis
Iron
Meats, eggs, legumes, whole grains,
green leafy vegetables, dried fruit
Component of hemoglobin and of electron
carriers used in energy metabolism
Fluorine
Fluoridated drinking water, tea,
seafood
Maintenance of tooth structure; maintenance
of bone structure
Iodine
Seafood, dairy products, iodized salt
Component of thyroid hormones
Zinc
Meats, seafood, grains
Use Visuals
Figure 38–7 Guide students in
analyzing the information presented
in the table by asking: Which minerals are needed for healthy bones
and teeth? (Calcium, phosphorus, and
fluorine) Which mineral is needed
for normal blood clotting?
(Calcium) Which minerals are found
in meats? (Phosphorus, potassium,
iron, and zinc) Which minerals are
found in grains? (Phosphorus, potassium, magnesium, iron, and zinc)
What one type of food could you
eat to increase the amount of fluorine, iodine, and zinc in your diet?
(Seafood)
Component of certain digestive enzymes
The water-soluble vitamins, which include vitamin C and the
B vitamins, dissolve in water and cannot be stored in the body.
Therefore, they should be included in the foods you eat each day.
Eating a diet containing a variety of foods will supply the daily
vitamin needs of nearly everyone.
Food stores and pharmacies sell vitamin supplements.
Taking extra-large doses of vitamin supplements does not benefit
the body; and, in some cases, it may cause real harm. Excessive
amounts of vitamins A, D, E, and K can be toxic.
! Figure 38–7 Minerals are
sometimes called trace elements
because they are needed by the
body in such small amounts.
Inferring Why do you think some
cities and towns add fluoride to their
water supplies?
Why is it important not to take more than the
recommended amount of certain vitamins?
Minerals Inorganic nutrients that the body needs, usually
in small amounts, are called minerals. Some examples of
minerals are calcium, iron, and magnesium. Calcium is a major
component of bones and teeth; and iron is needed to make
hemoglobin, the oxygen-carrying protein in red blood cells.
Calcium, sodium, and potassium are required for normal functioning of nerves. Figure 38–7 lists some of the minerals needed
by the body.
Although the body does not metabolize the minerals it takes
in, it does lose many of them in sweat, urine, and other waste
products. How are these important chemicals replaced? Many
of these elements are found in the living tissues of plants and
other animals. By eating a variety of foods, you can meet your
daily requirement of minerals.
N STA
Download a worksheet on nutrition
for students to complete, and find
additional teacher support from
NSTA SciLinks.
N S TA
For: Links on nutrition
Visit: www.SciLinks.org
Web Code: cbn-0381
BIOLOGY UPDATE
Please pass the selenium
Scientists continue to discover new substances in
food that play important roles in the body. For
example, in 1996 researchers at the Arizona
Cancer Center found that patients who received
200 !g per day of the trace mineral selenium had
a 50 to 60 percent lower risk of dying from lung,
prostate, or colorectal cancer. Scientists still do
not understand why selenium seems to protect
against cancer, and not all scientists are convinced
of its cancer-fighting abilities. Nonetheless, the
results of the Arizona study have sparked further
research to test selenium for its effect on specific
cancers. Selenium is found in foods such as grain,
meat, and fish, and most people in the United
States eat enough of these foods to receive the
recommended dietary allowance of 55 to 70 !g
per day. However, this may not be enough
selenium for an anticancer effect.
Answers to . . .
They can be stored in
the fatty tissues of the body and may
reach toxic levels.
Figure 38–6 Vitamin K is needed for
normal blood clotting.
Figure 38–7 To prevent cavities in
children’s teeth
Digestive and Excretory Systems
975
0970_0989_bi_c06_te
3/9/06
1:46 PM
Page 976
38–1 (continued)
Nutrition and a Balanced Diet
Nutrition and a
Balanced Diet
It’s no easy task to figure out the best balance of nutrients for
the human diet, but nutritionists have tried to do exactly that.
The result is MyPyramid shown in Figure 38–8.
The new food pyramid—MyPyramid—classifies foods into
six categories: grains; vegetables; fruits; milk; meat and beans;
and fats, sugars, and salts. Each color in the pyramid represents
a different food category. The narrow yellow bar represents fats,
sugars, and salt; those should be used sparingly. The large
orange bar represents the grains, especially whole grains, which
should make up the largest part of your diet. The figure climbing up the side of the pyramid represents exercise. You should
try and get at least 30 minutes of exercise each day. A personalized eating plan, based on your age, gender, and activity level
can be found at www.mypyramid.gov.
Food labels can also be used to choose healthful foods. A food
label provides some general information about nutrition, listing
the Daily Values and the Calories per gram for protein, carbohydrates, and fats. The daily value shows you how the particular food
fits into the overall daily diet. Daily values are based on a 2000Calorie diet, and nutrient needs are affected by age, gender, and
lifestyle. Rapidly growing adolescents and other groups of people
need more nutrients than the daily values indicate.
When choosing foods, you should use the information on food
labels to compare similar foods on the basis of their proportion of
nutrients to Calories. When you choose a food, it should be high in
nutrition and low in Calories.
Use Visuals
Figure 38–8 Arrange to give students access to the Internet so that
they can develop a personal eating
plan based on MyPyramid. Challenge
students to plan one day of meals
and snacks that altogether contain
the correct number of servings from
each food group. Call on a few students to share their meal plans with
the class. Note that individual eating
plans will vary based on the student’s
age, gender, and activity level.
For: Food Pyramid activity
Visit: PHSchool.com
Web Code: cbp-0381
Make Connections
Environmental Science Point out
that if you follow the food pyramid,
most of the food you eat will come
from the grains, vegetables, and
fruits groups. Ask: Where are grains
and plants always found in a food
chain, and what role do they fill?
(They are always found on the bottom,
and they fill the role of producer.)
Explain that only 10 percent of the
energy at one level of a food chain is
passed on to the next level. Conclude
by saying that people can get far
more energy from plants by eating
plants directly than by eating animals
that eat plants.
For: Food Pyramid
activity
Visit: PHSchool.com
Web Code: cbe-0381
Students learn about the food
groups and how they can be
combined to form a healthy diet.
!
Figure 38–8 MyPyramid
illustrates the main characteristics of
a balanced diet. Interpreting
Graphics Why do you think
nutritionists recommend that you limit
your intake of fats, oils, and sweets?
FACTS AND FIGURES
Eating bugs
Although eating bugs sounds disgusting to most
Americans, in many other cultures bugs are considered to be an excellent food source. For
example, in Mexico worms are served on tortillas,
and in Colombia ground-up ants are spread on
bread. Hundreds of other examples could be
given. Why are bugs so appealing? Most insects
are not only cheap sources of complete protein,
but they are far cleaner and much lower in fat
976
Chapter 38
than other sources. Insects can also be very tasty.
Deep-fried larvae and grubs, for example, are said
to be delicious. Although most Americans do not
deliberately eat bugs, they still get a lot of bugs in
their diet—in fact, a whopping pound or two per
person a year. Microscopic pieces of insects are
found in many processed foods, including jam,
peanut butter, tomato sauce, and frozen vegetables. In some foods, the addition of insects can
actually increase the nutritional content.
0970_0989_bi_c06_te
3/9/06
1:46 PM
Page 977
Make sure students understand that
the daily values on the nutrition label
depend on the total Calories in the
diet. Active teens may need 2500 or
more Calories a day instead of the
2000 Calories that are used for calculating the percent daily values.
Answers
1. 4 g of fat and 6 g of protein
2. A gram of fat has 9 Calories.
Protein and carbohydrate each have
4 Calories per gram.
3. Total fat: less than 65 g; sodium:
less than 2400 mg; fiber: 25 g
4. Yes; it supplies 45% of the daily
value of iron.
5. Students should recommend foods
that are low in sodium.
Evaluating Food Labels
Federal regulations require that labels on packaged
foods display the nutrients each food contains and the
percentage of daily value each nutrient represents for
a person, as well as serving size, number of servings
per container, and Calories per serving. Carefully
examine the nutritional information on the cereal
label shown. Based on the information on the label,
answer the questions that follow.
1. Calculating If you ate 2 cups of this product,
how many grams of fat would you eat? How many
grams of protein?
2. Interpreting Graphics How many Calories are
in a gram of fat? Of protein? Of carbohydrate?
3. Interpreting Graphics On a 2000-Calorie diet,
what is the Daily Value for total fat? For sodium?
For fiber?
4. Evaluating Advertising claims for this product
say that it is a good source of iron. Is this promotional claim true?
5. Going Further People with hypertension, or
high blood pressure, often are advised to restrict
their intake of sodium. Visit a local food store and
look at the labels on 5 types of packaged foods.
From this information, recommend which of the
foods would be healthful for people who have
hypertension.
3 ASSESS
Evaluate Understanding
Call on students to name the six
types of nutrients and to describe
their roles in the body.
Reteach
Have students review the food pyramid. Then, have them name the
nutrients that foods in each group
are rich in. (For example, the vegetable
food group is rich in carbohydrates,
vitamins, and minerals.)
38–1 Section Assessment
1.
Key Concept List the six
nutrients needed by the body.
2.
Key Concept What is the
importance of water in the body?
3. Why is fiber an important part of
your diet?
5. Critical Thinking Using
Tables and Graphs Which
vitamins and minerals promote
healthy bones? (Hint: See
Figure 38–6 and Figure 38–7.)
Designing a Brochure
Design and create a brochure
that explains how the body
uses the six nutrients
necessary for normal function.
Use images from magazines
or from the Internet to
illustrate your brochure.
Brochures should demonstrate an
understanding of the most important functions of each of the six
types of nutrients.
4. How are vitamins and minerals
similar? How are they different?
If your class subscribes to the iText,
use it to review the Key Concepts in
Section 38–1.
38–1 Section Assessment
1. Water, carbohydrates, fats, proteins, vitamins, and minerals
2. Some body tissues, such as blood, are
mostly water, and water is needed for many
vital body processes, including chemical
reactions, elimination of wastes, and keeping the body cool through evaporation.
3. Fiber adds bulk to the material moving
through the digestive system, helping it to
process food more effectively.
4. Both vitamins and minerals are nutrients
that are needed in small amounts for good
health, but vitamins are organic molecules,
whereas minerals are inorganic.
5. Vitamins C and D, calcium, phosphorus,
and fluorine
Digestive and Excretory Systems
977