Chapter 10 Food and Diet
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Think about it
How do humans obtain food?
What are primary food substances?
What are protective food substances?
How can we test for the presence of some food substances?
Why is a balanced diet important to us?
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Joe is answering a questionnaire about diet and
fitness.
Do you think that Joe is fit?
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Joe is answering a questionnaire about diet and
fitness.
What makes him become fat?
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Joe is answering a questionnaire about diet and
fitness.
What health problems may he have?
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Joe is answering a questionnaire about diet and
We
need
to
eat
to
obtain
energy
fitness.
for our body activities.
However, if we take in energy
more than we need, like Joe, we
will become overweight and may
What
problems
may he have?
havehealth
health
problems.
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How do humans obtain food?
Humans have to obtain food from other organisms
 this mode of nutrition is called heterotrophic
nutrition (異養營養)
we are called heterotrophs (異養生物)
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How do humans obtain food?
Food has 3 main uses for us:
• provides energy and keeps us warm
• provides raw materials for growth and repair
• maintains health and regulates metabolism
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The food requirements of humans
We require 7 types of food substances to stay healthy.
Food substances
protective food substances
(保護性食物本質)
(to stay healthy)
primary food substances
(基本食物本質)
(essential to life)
vitamins
(維生素)
carbohydrates
fats
proteins
(碳水化合物)
(脂肪)
(蛋白質)
dietary
fibre
(食用纖維)
minerals
(礦物質)
water
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What are primary food substances?
Carbohydrates
• made up of carbon (C), hydrogen (H) &
oxygen (O) atoms
• H:O ratio is 2:1
 e.g. glucose C6H12O6
2:1
• can be classified into 3 types:
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What are primary food substances?
Carbohydrates
monosaccharides
disaccharides
polysaccharides
• simplest type of carbohydrates
• examples: glucose, fructose (果糖) &
galactose (半乳糖)
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What are primary food substances?
Carbohydrates
monosaccharides
disaccharides
polysaccharides
• formed by joining 2 monosaccharide molecules
through condensation, in the presence of enzyme
• during condensation, 1 water molecule is released
monosaccharide
+
condensation
(縮合)
disaccharides
+ H2O
monosaccharide
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What are primary food substances?
Carbohydrates
monosaccharides
disaccharides
polysaccharides
• disaccharides can be broken down into single
monosaccharide molecules through hydrolysis
monosaccharide
+
monosaccharide
condensation
(縮合)
disaccharides
hydrolysis
(水解)
+ H2O
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What are primary food substances?
Carbohydrates
monosaccharides
disaccharides
polysaccharides
• examples: sucrose (蔗糖) , lactose (乳糖) and
maltose (麥芽糖)
glucose + fructose
 sucrose + H2O
glucose + galactose
 lactose + H2O
glucose + glucose
 maltose + H2O
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What are primary food substances?
Carbohydrates
monosaccharides
disaccharides
polysaccharides
• long chains of monosaccharides joined together
• examples: starch, glycogen (糖原) and
cellulose (纖維素)
glucose
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What are primary food substances?
Carbohydrates
Sugars
• All water-soluble carbohydrates are called sugars.
• Some sugars can react with oxygen-containing
substances and remove oxygen from them.
 reducing sugars
• examples: glucose, fructose, galactose,
maltose and lactose
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What are primary food substances?
Carbohydrates
Sugars
• reducing sugars can form a brick-red
precipitate in Benedict’s test
(本立德試驗)
!
Sucrose does not have
this property!!
 non-reducing sugars
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What are primary food substances?
Carbohydrates
Functions:
• as a main source of energy
1 g of carbohydrates  17.1 kJ of energy
• If in excess  converted to glycogen or
fat for storage
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What are the sources of carbohydrates?
Sources:
Carbohydrates
• cereals (e.g. rice, wheat and oat)
• root crops (e.g. potatoes and taros)
• cereals food products (e.g. noodles, bread, biscuits cakes
and oatmeal)
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• Carbohydrates also present in the
form of sugars
• Fructose
a simple sugar
found in most fruits
• Sucrose
a double sugar
present in large quantities in
sugar cane and beet root
often sold as table sugar and
rock sugar
• Lactose
a double sugar
present in milk
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Fate of carbohydrates?
Fate:
Carbohydrates
• Simple sugars (e.g. glucose) :
 absorbed by body as the size are relatively small
 broken down
release energy
 an immediate energy source
• Double sugars :
 broken into simple sugars as the size is too large
Some tonic drinks, such as
“Lucozade”, are claimed to supply
energy quickly. Why do the
manufacturers make such a claim?
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• In the human body, carbohydrates may not
be used immediately in respiration. They
can be:
– stored as glycogen in the liver and skeletal
muscles
– converted into fat and stored inside the body
The glucose level in your blood rises
after a meal. Do you know why?
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What are primary food substances?
Fats
• made up of carbon, hydrogen and oxygen atoms
• H:O ratio  much greater than 2:1
• insoluble in water but soluble in organic solvents,
e.g. ether (乙醚) and ethanol (乙醇)
• at room temperature :
semi-solid form  fats
liquid form
 oils
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What are primary food substances?
Fats
• a fat molecule is usually formed from the
condensation of 1 glycerol (甘油) molecule
& 3 fatty acid (脂肪酸) molecules
condensation
+
3 fatty acid
molecules
+ H2O
hydrolysis
1 glycerol
molecule
1 fat molecule
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What are primary food substances?
Functions:
Fats
a) as a food reserve and stored in adipose tissues
(脂肪組織)
b) subcutaneous fat (皮下脂肪) reduces heat loss
c) as a shock-absorber for protection
d) help transport fat-soluble vitamins
e) important in forming cell membranes
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What are primary food substances?
Sources:
Fats
• Dietary fats can be divided into two main groups:
–Saturated fats and Unsaturated fats
• Saturated fats found in :
 meats, cheese, butter, egg yolk, palm oil, etc.
• Unsaturated fats found in:
 corn oil, olive oil, vegetable oil, fishes,
margarine, etc.
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What are primary food substances?
Proteins
• made up of carbon, hydrogen, oxygen and
nitrogen atoms
 some also contain sulphur (硫)
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What are primary food substances?
Proteins
• basic units  amino acids (氨基酸)
side chain (R group)
central carbon atom
amino group (氨基)
carboxyl group
(羧基)
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What are primary food substances?
amino acid
Proteins
+
amino acid
+
amino acid
condensation
polypeptide
dipeptide
+
amino acid
..
.
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What are primary food substances?
polypeptide
Proteins
+
polypeptide
+
polypeptide
combine
protein
+
polypeptide
..
.
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What are primary food substances?
Proteins
There are 20 types of amino acids.
• we can make 12 of them
 non-essential amino acids (非必需氨基酸)
• the other 8 must be obtained from food
 essential amino acids (必需氨基酸)
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What are primary food substances?
Proteins
• Many proteins are soluble in water.
• denatured at
 high temperatures
 high/low pH values
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What are primary food substances?
Functions:
Proteins
• for growth and repair
• provide energy if carbohydrates and fats
stored are used up
• excess amino acids cannot be stored and will be
broken down through deamination (脫氨作用)
 the remaining parts will be converted into
carbohydrates or fats
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Fate of Protein?
Fate:
Proteins
• broken down by the gut into amino acids before
absorption
• carried by blood to the cells to form different
types of proteins
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• Excess amino acids in the body are broken down
in the liver by a process called deamination
– The carbon and hydrogen form carbohydrate (or
sometimes fat), which may be stored up in the body or
broken down to release energy
– The nitrogen-containing part of the amino acid forms
ammonia, and quickly converted to urea which leaves
the body through the urine
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What are primary food substances?
Sources:
Protein
• present in meat, fish, egg white, milk and beans
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What are primary food substances?
• inorganic food substance
• no energy value
Water
Functions:
a) acts as a solvent
b) acts as a medium for chemical reactions
c) helps transport substances in the body
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What are primary food substances?
• inorganic food substance
• no energy value
Water
Functions:
d) helps regulate the body temperature
e) acts as a reactant in hydrolysis
f) dilutes waste and toxins
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How do we obtain and lose water?
Water
• Obtain water through intake of foods and drinks.
Water is also produced during respiration
• Lose water through breathing, sweating, urination
and egesting
• 6-8 glasses of water are needed per day
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Brief Revision
amino
1 The basic units of proteins are ______
acids .
_____
2 Under Benedict’s test, reducing sugars will
brick-red precipitate.
give a _________
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Brief Revision
non-reducing
3 Sucrose is an example of ____________
sugars.
4 Those amino acids that must be obtained
amino acids .
from food are called essential
_________________
5 Excess amino acids can / cannot be
stored in our body.
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What are protective food substances?
Vitamins
• organic food substances
• needed in small amounts
• no energy value
• help control various metabolic
reactions
• vitamin deficiency diseases will be
resulted if we do not take in enough
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What are protective food substances?
solubility
A
Vitamins
C
D
fat-soluble
water-soluble
fat-soluble
• the synthesis and • the uptake of
• forming a visual
repair of
calcium and
pigment for vision
connective tissues
phosphate ions from
in dim light
blood into the cells
essential condition
for
• healing wounds
• the formation of
and
keeping
gums
• protecting the
bones and teeth
(齒齦),
teeth
and
cornea (角膜)
skin healthy
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What are protective food substances?
solubility
A
Vitamins
C
D
fat-soluble
water-soluble
fat-soluble
• keeping the linings • building up
resistance to
of the alimentary
canal, the breathing infection
essential system and the skin • preventing
for
healthy
common cold
• helping iron
absorption by our
body
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What are protective food substances?
A
• night blindness
(夜盲)
• drying up and
deficiency thickening of
the cornea
diseases
Vitamins
C
• scurvy (壞血病)
with the following
symptoms:
D
• soft teeth and
bones
• rickets (佝僂病)
 the connective
tissue breaks down • bone fractures
slowly
• easy infection of  teeth become loose
the lining of the
and gums bleed
lungs and
easily
trachea (氣管)
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What are protective food substances?
A
sources
Vitamins
C
D
• fish-liver oil
• green vegetables
• fish-liver oil
• butter
• citrus fruits like
oranges, lemons
and grapefruits
• milk, cheese and
egg yolk
• eggs yolk and
green
vegetables
• carrots (contain
carotene 胡蘿
蔔素 which can
be converted
into vitamin A
in the liver)
• certain amount of
vitamin D can be
produced by the
skin in sunlight
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Excess vitamins A will be stored in the liver
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What are protective food substances?
Minerals
• inorganic food substances
• needed in small amounts
• no energy value
• important in regulating metabolism
and building body tissues, e.g. bones
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What are protective food substances?
Minerals
Calcium
• essential for
 formation of bones and teeth
 blood clotting (凝血)
 muscle contraction (肌肉收縮)
and transmission of nerve signal
• deficiency disease:
rickets and slow clotting
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What are protective food substances?
Minerals
Calcium
• Children and pregnant woman
requires in large amount of it
Sources:
• Milk, cheese, yogurt and
green leafy vegetable
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What are protective food substances?
Minerals
Iron
• essential to make haemoglobin
(血紅蛋白)
• deficiency disease: anaemia (貧血)
• women need more iron than men
because of mensuration (月經)
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What are protective food substances?
Minerals
Iron
Sources:
• Liver, beef, eggs and some
vegetables
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What are protective food substances?
Dietary fibre
• known as roughage (粗糙食物)
• an organic substance from the cell
walls of vegetables and fruits
• cannot be digested in humans since
we have no such enzyme
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What are protective food substances?
Dietary fibre
• it can stimulate peristalsis (蠕動)
 prevents constipation (便秘)
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Brief Revision
1 Deficiency in vitamin A will result in
night blindness .
_____________
2 Deficiency in vitamin C will result in
scurvy .
______
3 Deficiency in vitamin D will result in
rickets .
______
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Brief Revision
4 Calcium is good for the growth of bone
teeth .
and _____
5 Lack of dietary fibre in diets will result in
constipation .
____________
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How can we test for the presence of
some food substances?
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Detection of food substances by food tests
A Test for glucose using Clinistix paper
Procedure:
1 Transfer a drop of
glucose solution to
the well of a spot
plate.
Clinistix
paper
glucose
solution
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Detection of food substances by food tests
A Test for glucose using Clinistix paper
Procedure:
2 Dip the test end of a
Clinistix paper into
the sample and
observe any colour
change. A purple
colour indicates the
presence of glucose.
Clinistix
paper
glucose
solution
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Detection of food substances by food tests
B Test for reducing sugars using Benedict’s test
Procedure:
1 Mix equal volumes
(e.g. 1 cm3) of
glucose solution and
Benedict’s solution
in a test tube.
Benedict’s
solution
glucose
solution
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Detection of food substances by food tests
B Test for reducing sugars using Benedict’s test
Procedure:
2 Boil the mixture in a water bath for 5 minutes.
water bath
boiling water
glucose solution
+
Benedict’s solution
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Detection of food substances by food tests
B Test for reducing sugars using Benedict’s test
Procedure:
3 Stand the test tube in a test tube rack for 15 minutes and
observe any change in the mixture again. A brick-red
precipitate indicates the presence of reducing sugars.
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Detection of food substances by food tests
C Test for starch using iodine test
Procedure:
1 Transfer a drop of
starch solution to the
well of a spot plate.
iodine
solution
starch
solution
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Detection of food substances by food tests
C Test for starch using iodine test
Procedure:
2 Add a drop of iodine
solution to the
sample and observe
any colour change. A
blue-black colour
indicates the
presence of starch.
iodine
solution
starch
solution
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Detection of food substances by food tests
D Test for fats using grease spot test
Procedure:
1 Transfer a drop of cooking
oil to a filter paper and let it
dry in the air for 5 minutes.
cooking oil
filter paper
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Detection of food substances by food tests
D Test for fats using grease spot test
Procedure:
2 Hold up the filter paper to
the light and observe any
translucent (半透明的) spot.
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Detection of food substances by food tests
D Test for fats using grease spot test
Procedure:
3 Immerse the filter paper into an organic solvent.
Take it out and let it dry.
4 Examine the filter paper against light again. Note
any change in the filter paper. The disappearance
of the spot indicates the presence of fats.
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Detection of food substances by food tests
E Test for proteins using Albustix paper
Procedure:
1 Transfer a drop of egg
white solution to the
well of a spot plate.
Albustix
paper
egg white
solution
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Detection of food substances by food tests
E Test for proteins using Albustix paper
Procedure:
2 Dip the test end of an
Albustix paper into
the sample and
observe any colour
change. A blue-green
colour indicates the
presence of proteins.
Albustix
paper
egg white
solution
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Detection of food substances by food tests
F Test for vitamin C using DCPIP solution
Procedure:
1 Put 1 cm3 of DCPIP
solution in a test tube.
DCPIP solution
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Detection of food substances by food tests
F Test for vitamin C using DCPIP solution
Procedure:
2 Add in vitamin C solution
drop by drop. Stop when
there is any persistent colour
change. A colourless colour
indicates the presence of
vitamin C.
vitamin C
solution
DCPIP solution
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Detection of food substances by food tests
F Test for vitamin C using DCPIP solution
Procedure:
3 Boil a test tube of 5 cm3 of vitamin C solution in a boiling
water bath for 5 minutes. Allow the test tube to cool in a
beaker of cold water. Heat destroys the reducing property of
vitamic C and so there is no colour change in the solution.
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Investigation of the food substances present in
common foods
A Test for food substances in liquid food sample
Procedure:
1 Put about 1cm3 of the liquid food sample into 6 test tubes.
2 Perform the food tests as in previous Practical. Use
distilled water as a control.
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Investigation of the food substances present in
common foods
B Test for glucose, reducing sugars, starch, proteins and
vitamin C in solid food sample
Procedure:
1 Grind the small pieces of
food with a small
quantity of cool distilled
water.
small
pieces of
food
+
cool
distilled
water
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Investigation of the food substances present in
common foods
B Test for glucose, reducing sugars, starch, proteins and
vitamin C in solid food sample
Procedure:
2 Squeeze the ground
materials through several
layers of muslin or a
filter paper. Put the
extract into 5 test tubes.
pre-moistened
fine muslin
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Investigation of the food substances present in
common foods
B Test for glucose, reducing sugars, starch, proteins and
vitamin C in solid food sample
Procedure:
3 Perform the food tests as in previous Practical. Use
distilled water as a control.
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Investigation of the food substances present in
common foods
C Test for fats in solid food sample
Procedure:
1 Grind the small pieces of food with a small quantity of
distilled water.
2 Transfer the ground materials to a boiling tube containing
some distilled water.
3 Boil the suspension in a boiling water bath. Any fats or
oil in the food will escape as oil droplets.
4 Test for fats as in previous Practical. Use distilled water
as a control.
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Design an investigation to compare the vitamin C
content in different fruits and vegetables
In the past, scurvy was common among sailors whose diets were
limited to biscuits and salted meat. It was not known until 1753
that lemons and oranges, which were rich in vitamin C, could
help prevent the disease.
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Design an investigation to compare the vitamin C
content in different fruits and vegetables
Are lemons and oranges the best sources of vitamin C?
Design and perform an experiment to compare the vitamin C
content in different fruits and vegetables.
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What is a balanced diet?
Diet (膳食) refers to all the food we eat.
A balanced diet
A balanced diet (均衡膳食) consists of all of the
seven types of food substances in the right amounts.
carbohydrates
proteins
fats
minerals
vitamins
water
dietary fibre
In addition, we should take in 6 to 8 glasses of fluid
every day.
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Why is a balanced diet important
to us?
Different people need different balances in their diets.
For example:
• a child needs more proteins
than an older person
because …
1) a child is growing actively
2) a child needs more energy
per unit of weight to maintain
the body temperature
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Why is a balanced diet important
to us?
• a person whose workload is
heavy needs more energy
than one whose workload is
lighter
because …
the former needs more energy for
muscular activities
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Why is a balanced diet important
to us?
• a male usually needs more
energy than a female
because …
1) he has more muscles to respire
2) thinner subcutaneous fat
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Why is a balanced diet important
to us?
• a pregnant woman needs
more carbohydrates,
proteins, minerals and
vitamins
because …
her foetus (胎兒) needs energy
and raw materials
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Why is a balanced diet important
to us?
• a pregnant woman also
needs more calcium,
vitamin D and iron
because …
The formation of bones and
blood in the embryo need these
food substances
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Why is a balanced diet important
to us?
• a Breast-feeding woman
also needs more
carbohydrates (e.g.
lactose), proteins, vitamins
(e.g. vitamin A) and
minerals (e.g. calcium)
because …
For the production of milk
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10.9 Balanced Diet (p. 85)
Critical Thinking 10.1
Average daily energy requirements of different
groups of people
A (kg) B (kJ)
This table shows the
average body weights (A)
and average daily energy
requirements (B) of
different groups of people.
Analysis
1. Referring to the data
in the table, construct
a bar chart showing
the average daily
energy requirements
per unit body weight of
different groups of
people.
Newborn baby
3
1 800
Age 2
7
5 000
Age 5
20
7 500
Age 10
30
9 500
Age 15
Age 25 (F)
- office worker
Age 25 (M)
- office worker
- road worker
Pregnant woman
Breast-feeding
woman
45
12 000
55
9 000
65
65
55
12 000
15 000
10 000
55
11 500
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10.9 Balanced Diet (p. 86)
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10.9 Balanced Diet (p. 86)
Analysis
2. Make a comparison between different people, as
listed below. Find out which one shows a higher
energy requirement per unit body weight, and
suggest reasons for the difference.
(a)
a 5-year-old child and an adult;
Ans: The energy required by a child is higher than
that of an adult, because (1) he needs energy for
growth, (2) he tends to be more active physically, (3)
a relatively greater surface area of the body means
that more energy is required to maintain body
temperature
(b)
an office worker and a road worker;
Ans: A road worker needs more energy for
maintaining greater muscular activity than an office
worker
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10.9 Balanced Diet (p. 86)
Analysis
2. Make a comparison between different people, as
listed below. Find out which one shows a higher
energy requirement per unit body weight, and
suggest reasons for the difference.
(c)
A pregnant woman and a woman who is not
pregnant and not breast-feeding.
Ans: A pregnant woman requires more energy
because extra energy is used in maintaining the
growth of the developing embryo
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What happens to the body of a starving
person?
• When the daily energy requirement of a
person is not being met,
– glycogen stored in the liver and skeletal
muscles,
– fat stored under the skin or around internal
organs,
will be used to release energy, leading to
weight loss
• If the fat stored in the body becomes
depleted, some body proteins (e.g.
skeletal muscles) will be used. This
will adversely affect the person’s
health
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Diets of people in different countries
 People in different countries
have different diets. Try to find
out the differences in diets,
and how these are related to
the people’s social, cultural
and economic backgrounds.
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Health problems resulting from an
improper diet
1) Obesity (癡肥)
if we take in more energy than our body needs
and the body weight exceeds normal
 overweight
 in serious cases: obesity
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Health problems resulting from an
improper diet
2) Anorexia nervosa (神經性厭食)
when the energy intake < normal requirement
 the person may become thin and unhealthy
 serious cases: anorexia nervosa
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Health problems resulting from an
improper diet
 Discuss with your classmates
how eating disorders such as
anorexia nervosa can affect
health.
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Summary concept diagram
Food
consists of
food substances
when in the right types
and amounts
balanced diet
if not in the right types
and amounts
improper diet
leads to
detected
by
health problems
examples are
food tests
obesity
anorexia nervosa
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Summary concept diagram
food substances
can be
primary food substances
protective food substances
include
vitamins
minerals
dietary fibre
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concept diagram
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Summary concept diagram
primary food substances
include
fats
carbohydrates
proteins
water
made up of
made up
of
polypeptides
made up of
amino acids
fatty acids
glycerol
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concept diagram
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Summary concept diagram
carbohydrates
classified into
monosaccharides
disaccharides
polysaccharides
some are
reducing sugars
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concept diagram
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Chapter 10 (p. 91)
The following statements contain some wrong concepts commonly
held by students. Point them out and give correct statements.
1. Animals cannot use cellulose for food.
Ans: Other than human, cellulose contributes to the diet of
many animals, especially herbivores, such as sheep, cattle
and rabbit
2. Excess amino acids are useless and they are removed
from the body as urea.
Ans: Excess amino acids are broken down by the liver, the
resulted carbon and hydrogen form carbohydrates that may
be stored up in the body or broken down to release energy
through respiration. The remaining nitrogen-containing part
forms ammonia and quickly converted to urea for excretion
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Chapter 10 (p. 91)
The following statements contain some wrong concepts commonly
held by students. Point them out and give correct statements.
3. Essential amino acids are more important than the nonessential amino acids.
Ans: Both essential and non-essential amino acids are
important to the body. Where non-essential amino acids are
the ones the body is able to synthesize, while essential
amino acids are the ones must be obtained from food
4. The human body cannot synthesize vitamins.
Ans: Vitamins are mostly come from food, but vitamin D can
also be produced in human skin when exposed to sunlight
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Chapter 10 (p. 91)
5. A vegetarian diet would not make a person become
overweight.
Ans: Although a vegetarian diet includes mainly plant
products, the consumption of large amount of
carbohydrates-rich plant products, such as rice and potato,
can still make a person become overweight
6. To avoid being overweight, we can take in more
carbohydrates but less fats.
Ans: Since carbohydrates are important food substances to
provide energy, the intake of large amount of
carbohydrates can make a person overweight
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Chapter 10 (p. 91)
To test your knowledge about nutrition, visit:
• http://web.ukonline.co.uk/webwise/spinneret/
nutrition/humnut.htm
• http://web.ukonline.co.uk/webwise/spinneret/
nutrition/diet.htm
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10.9 Balanced Diet (p. 89)
A study of anorexia nervosa
Based on the information given, discuss
the following with your classmates:
• your idea about body build
• the proper ways to reduce body
weight if necessary
~ End of Activity 10.1 ~
Back to main text
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10.9 Balanced Diet (p. 90)
Vegetarian diet
Questions for Discussion
1. Why can a vegetarian diet reduce the risk of having
heart diseases?
Ans: Vegetarians are people who eat only plant products.
Their diets contain low levels of saturated fats. Thus, the
vegetarian diets tend to reduce the risk of having heart
diseases
2. Why is it possible to obtain maltose from starch?
Ans: Apart from low level of fat, the plant foods in the
vegetarian diet are rich in dietary fibre, which tends to
make a person feels full. This can help to prevent a person
from over-eating
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10.9 Balanced Diet (p. 90)
3. How can a vegetarian ensure that the diet provides
sufficient proteins?
Ans: Vegetarians should consume more beans and nuts to
obtain sufficient proteins
4. Why farmlands can support a larger human population
with a vegetarian diet?
Ans: A piece of farmland can only support a small amount of
livestock and produce a limited amount of animal products.
Therefore, the same piece of farmland can support a larger
human population with a vegetarian diet
5. What kinds of nutrients are usually deficient in a
vegetarian diet? How can this problem be overcome?
Ans: A vegetarian diet is usually deficient in certain
vitamins and minerals. These can be overcome by taking
yeast extract or other food supplements with the diet
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End of Chapter 10
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While Stephanie is eating, she wonders what will
happen to the food in her body.
Dear food, can you tell
me what happens to you
after I have eaten you?
What happens to the food in our body so that
107
we can obtain nutrients?
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While Stephanie is eating, she wonders what will
happen to the food in her body.
Dear food, can you tell
me what happens to you
after I have eaten you?
What are the structures inside our body for
this process?
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While Stephanie is eating, she wonders what will
Foodtoisthe
processed
the digestive
happen
food in herby
body.
system (消化系統) in our
body before
Dear food, can you tell
what happens to you
the nutrients are readyme
for
use.
after I have eaten you?
This system consists of many
structures specially adapted for
human nutrition.
What are the structures inside our body for
this process?
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How is food ingested?
solid food is broken down into small pieces in
the mouth cavity
 by the actions of the teeth and tongue
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The structure of a tooth
crown (齒冠)
neck (齒頸)
root (齒根)
the region above the gum
the region surrounded by the gum
the region embedded inside the jawbone
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The structure of a tooth
1) Enamel (琺瑯質)
• the outermost, non-living,
hard layer
• mainly made of calcium
phosphate and a small amount
of organic matter
• protects the tooth
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The structure of a tooth
2) Dentine (牙本質)
• the middle layer
• hard and bone-like, but softer
than enamel
• has strands (縷) of living
cytoplasm running through it
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The structure of a tooth
3) Pulp cavity (髓腔)
• the innermost part
• contains living cells, blood
vessels and nerves
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The structure of a tooth
4) Cement (牙骨質)
5) Periodontal
membrane (牙周膜)
6) Jawbone
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The structure of a tooth
1) Incisors (門齒)
• chisel-shaped (鑿形的)
• sharp
• has 1 root
• for biting and cutting off food
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The structure of a tooth
2) Canine (犬齒)
• pointed and curved
• well-developed in carnivores,
e.g. lion
• has 1 root
• For piercing and tearing
flesh
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The structure of a tooth
3) Premolars (前臼齒)
• broad top with cusps (尖突) in
humans, or ridges in sheep,
with sharp edges in dogs for
cutting
• has 2 roots
• for chewing, crushing and
grinding food
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The structure of a tooth
4) Molars (臼齒)
• similar to premolars but larger
• has 3 roots
• for chewing, crushing and
grinding food
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Milk teeth and permanent teeth of humans
2 sets
milk teeth (乳齒)
• smaller and whiter than
permanent teeth
• delicate (易受損的) and will
gradually fall out
permanent teeth (恆齒)
• replace milk teeth
• will not be replaced by
new teeth if lost
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Dentition (齒系)
 a term used to describe the types and
arrangement of teeth in a mammal
 represented by a dental formula (齒式)
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Dentition (齒系)
Upper jaw
Front
Rear
Lower jaw
incisors
canines
premolars
molars
upper jaw
2
1
2
3
lower jaw
2
1
2
3
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Dentition (齒系)
Upper jaw
The dental formula is:
2123
2123
Front
Rear
Lower jaw
incisors
canines
premolars
molars
upper jaw
2
1
2
3
lower jaw
2
1
2
3
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Dental diseases
Tooth decay (蛀牙)
• known as dental caries
• oral bacteria, food debris and saliva
(唾液) form a plaque (牙菌膜) on
tooth surface
• oral bacteria break down the sugar in
food debris to form acid
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Dental diseases
Tooth decay (蛀牙)
• acid dissolve the enamel and makes
small holes
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Dental diseases
Tooth decay (蛀牙)
• bacteria reach the holes and digest
the dentine
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Dental diseases
Tooth decay (蛀牙)
• bacteria reach the holes and digest
the dentine and infect the tissue
in pulp cavity
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Dental diseases
Tooth decay (蛀牙)
• the acid will irritate the nerves and
cause toothache
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Dental diseases
Tooth decay (蛀牙)
• for serious cases, abscess (膿腫) is
formed and the tooth will lose
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Dental diseases
Tooth decay (蛀牙)
• if not too serious, the decayed area can
be drilled out and replaced with a filling
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Dental diseases
• sugary food
 enhance acid production
 pH of plaque
pH of
plaque
time
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Dental diseases
• if pH of plaque < critical pH (臨界pH值)
 decay can occur
pH of
plaque
critical pH
time
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Dental diseases
• pH will return to normal after about
30 minutes
pH of
plaque
critical pH
time
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11.2 Teeth (p. 107)
Critical Thinking 11.1
The changes in pH in the mouth of a person before
and after eating candy
This graph shows the
changes in pH in the
mouth of a person before
and after eating a candy.
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11.2 Teeth (p. 107)
Questions
1. Describe the changes in pH inside the mouth after
eating a candy.
Ans: The pH is
maintained at
about 6.6 before
eating the candy,
and continues to
drop below 5.2
after eating it.
The level
gradually returns
to normal after
about 10 minutes
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11.2 Teeth (p. 107)
Questions
2. From the results, what can you tell about the
relation between eating candies and tooth decay?
Ans: The pH is
dropped below the
level that is
reported to cause
tooth decay after
eating the candy. In
other words, eating
candies is more
likely to cause tooth
decay
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Dental diseases
Periodontal disease (gum disease)
• bacteria trap plaque under the gum and
release toxins (毒素)
 destroy the periodontal membrane
 periodontal pockets (牙周袋)
formed around the tooth
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Dental diseases
Periodontal disease
• calculus (牙石) formed from
plaque
calcium secretions
in the saliva
• difficult to remove
• its rough surface lets plaque
accumulate further
The processes of tooth
decay and the formation
of periodontal disease
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Dental diseases
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Dental diseases
The symptoms of periodontal disease are:
1. bleeding gum after brushing the teeth
2. red or swollen gums
3. the teeth looking longer than before
4. bad breath
5. aching or itching gums
6. loosening teeth
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Dental diseases
Prevention of dental diseases
1 Brush your teeth regularly.
Brush your teeth properly.
2
3 Use toothpaste that contains fluoride (氰化物).
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Dental diseases
Prevention of dental diseases
4 Use dental floss (牙線) to remove plaque.
Improve your brushing style with
the help of dental disclosing
agents (牙菌膜顯示劑).
5
6 Do not eat too much sugary food.
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Dental diseases
Prevention of dental diseases
7 Have a balanced diet with adequate nutrients.
Do not bite very hard materials.
8
9 Have a dental check-up at least twice a year.
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