Foods & Human (EE)

7/30/2019 Foods & Human (EE)

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III. Organisms and Environment

Essential life processes in animals (Part1A)

Foods and human

5.1 Different modes of heterotrophic nutrition

Plants can make their own food byphotosynthesis.

But, most organisms cannot make food themselves.

They have to take in organic matter from their surroundings.

They depend on other organisms for food supply.

The mode of nutrition is called heterotrophic nutrition.

Organisms that carry out heterotrophic nutrition = heterotrophs

Humans are heterotrophs and are totally dependent on other organisms for their food.

Heterotrophic nutrition is divided into 3 main groups:

I. Holozoic nutrition Animals like humans & cows carry out this mode of nutrition. They take in organic matter by feeding on other organisms.

E.g. (1) Humans obtain food by growing crops, rearing livestock,

fishing or hunting.

(2) Sheep feeds on grass.

II. Saprophytic nutrition Most bacteria & fungi carry out this type of nutrition.

They feed ondeadorganisms /non-living organic matter.

They cause decay, e.g. mushrooms.

III.Parasitic nutrition Parasites like tapeworms carry out this mode of nutrition. They live on / inside the body of other organisms (hosts) &

obtain organic food from them.

E.g. Tapeworm lives inside the intestine of humans to obtain food.

5.2 The food requirements of human

A The importance of food to us

1. Supply energy

Food is oxidized to release energy for supporting metabolism [doing activities] and

maintaining body temperature [keeping us warm].


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2. Support growth and repair

Food provides raw materials to support body growth and repair ofworn-out tissues

of our body.

3. Maintain health

Food contains substances that are important for maintaining health

[regulate metabolic activities and protect the body against diseases]

B The components of food substances

There are 7 types of food substances listed below:

Carbohydrates, lipids and proteins are organic compounds, which are called

biomolecules.

They contain carbon atoms.

1 Carbohydrates (Gk., Carbo carbon ; hydra water)

Carbohydrates are organic substances made up of carbon (C), hydrogen (H) and oxygen

(O) atoms.

They have a general chemical formula ofCx(H2O)yin which the H:O ratio is 2:1.

The basic unit of carbohydrates is simple sugar (saccharide).

*All water-soluble carbohydrates are called sugars.

According to the no. of sugar molecules, it can be divided into 3 main groups.

i) Monosaccharides (simple sugars) (Gk., mono, one) (CH2O)x

Monosaccharides are thesimplest forms of carbohydrates.

They cannot be hydrolyzedinto any simpler carbohydrates.

Examples:

Food substances

Primary food substances

{essential to life}

Carbohydrates Lipids Proteins Water

Protective food substances

{to stay healthy}

Vitamins MineralsDietary

fibre

Release energy growth+repair transport maintain health stimulate

gut activites


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a. 3-carbon sugars / trioses / (CH2O)3 / C3H6O3

- Important intermediates in respiration and photosynthesis

b. 5-carbon sugars / pentoses / (CH2O)5 / C5H10O5

c. 6-carbon sugars / hexoses / (CH2O)6 / C6H12O6

- Glucose, fructose, galactose

(i) Taste sweet

(ii) Soluble in water

(iii) Have reducing power (donate hydrogen/electron to other chemicals and

oxidized in the process)reducing sugars

- Glucose can be directly broken down to release energy.

- It is an immediate energy source for body activities.

ii) Disaccharides (double sugars) (C12H22O11)1. Disaccharides are formed when 2 monosaccharides combine, in the presence of an

enzyme.

This process is called condensation.

During the reaction, 1 water molecule is removed.

2. Disaccharides can be broken down into monosaccharides when water + a different

enzyme are present.

This reaction is called hydrolysis.

Some common disaccharides are listed below:

Types Components Functions / Usage

1. Maltose (malt Glucose + glucose (i) The storage form in some germinating


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sugar) seeds

(ii) Extracted from barley for brewing and

food manufacturing

2. Sucrose

(cane sugar)

(non-reducing)

Glucose + fructose (i) Table sugar consists of sucrose, which is

usually extracted from sugar cane.

(ii) Abundant in the stems of sugar caneand the roots of sugar beet; source of

commercial sugar

3. Lactose

(milk sugar)

Glucose + galactose Present in milk

All are reducing sugars except sucrose.

All taste sweet. (sucrose is sweeter than glucose, fructose is 30-40% sweeter than

sucrose)

All are soluble in water.(sucrose is almost 3 times more soluble than glucose, fructose

is the most soluble sugar)

iii) Polysaccharides (multiple sugars) (C6H10O5)n

They are long chains of monosaccharides joined together by condensation of many

monosaccharides.

They are insoluble in water (e.g. starch, glycogen, cellulose)

They do not taste sweet (tasteless).

They are non-reducing.


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Types of polysaccharides:-

(a)Starch It is the storage form of carbohydrates in plants.

The large and insoluble nature makes starch an ideal storage form of carbohydrate.

(b)Glycogen It is the storage form of carbohydrate in animals and

fungi.

It is more soluble than starch and exists in the cytoplasm

as tiny granules.

It is particularly abundant in liver and muscles of

humans.

(c)Cellulose It is the main component ofplant cell walls.

It has a stable structure and strong mechanical strength that makes it an important


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structural material of the cell wall in plants.

Starch, glycogen and cellulose are all made up ofglucose molecules.

But, glucose molecules are joined in different ways.

Through hydrolysis, polysaccharides are converted into monosaccharides which can be

readily used for respiration. Rice, wheat, fruits, noodles, bread and potatoes are rich in starch.

Functions of carbohydrates:-

They are the main energy source for the body.

Each gram of carbohydrate provides about 17.1 kJ of energy.

Types Functions**

Glucose It is oxidized in cells to release energy for supporting metabolic activities.

It affects the water potential of cells and body fluid (e.g. blood).

It is important in theregulation of water balance of the body.

Glycogen It is the storage form of carbohydrates in liver for regulating the glucose

level in blood.

It is also stored in muscles as energy reserves to meet the energy need

during vigorous muscular activities.

Cellulose It is not digested in our body

It is an important source of dietary fibre that keeps us healthy, so as to

stimulate theperistalsis of gut.


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Excess of carbohydrates:-

If too many carbohydrates are consumed, the excess carbohydrates will be converted to

glycogen / lipids.

Glycogen is stored in the liver and muscles.

Lipids are stored under the skin / around the internal organs.

2 Lipids

Lipids are also organic substances composed of carbon(C), hydrogen(H) and oxygen(O)

atoms.

The H : O ratio is much greater than 2:1.

E.g. olive oilC57H104O6 ; beef fatC57H110O6

Lipid is formed by the condensation reaction of 3 fatty acids & 1 glycerol molecule.

The product is a triglyceride (Gk., tri three ; glycer glycerol) molecule and 3 H2O

molecules.

Types of fatty acids:-

As most naturally occurring lipids contain the same alcohol, namely glycerol, it is the

FATTY ACIDS, determining the characteristics of any particular lipid.

1. Carboxyl group ()

All fatty acids contain a carboxyl group (-COOH) which is partially ionized and can

form ionic bonds. The carboxyl group is therefore polar and hydrophilic (water-loving).

2. Hydrocarbon chain

The remainder of the molecule is a hydrocarbon chain [CH3(CH2)n] of varying

length.

This chain is non-polar, hydrophobic / water-repelling.

a. The chain may possess one or more double bonds and is said to be unsaturated.

These fatty acids have low melting point & are mainly liquid at room temperature.

They are OILS and occur mainly in plants.


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e.g. oleic acid ()C17H33COOH with melting pointat 16oC

b. However, the hydrocarbon chain possesses no double bonds, it is said to be saturated.

These fatty acids have higher melting points and are solid at room temperature.

They are FATS & occur mainly in animals.e.g. palmitic acid () CH3(CH2)14COOH

stearic acids () CH3(CH2)16COOH

Types of lipids:-

1. Fats and oils

(i) Most animal lipidsare saturated and are in form of FATS that are solids /

semi-solids (e.g. pork, beeflard , butter) at room temperature.

Taking in too much saturated fatty acids may lead to cardiovascular diseases.

(ii) Most plant lipidsare unsaturated and are in form of OILS that are liquids

(e.g. olive oil , maize oil, corn oil, peanut oil) at room temperature.

(iii) Plant oil can be hardened to margarine by adding hydrogen to the oil.

During the process, the structure of the fatty acid molecules in the oil changes.

These fatty acids with changed structure are called TRANS FATS.

They are also linked with cardiovascular diseases.

Cakes, bread and fried food (e.g. chips) produced by hydrogenated oil


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contain trans fats.

2. Phospholipids

Phospholipids are lipids in which one of the fatty acids groups is replaced by phosphate

group (PO43-

) (from phosphoric acid)

3. Steroids ()

a. Cholesterol

An important component of cell membrane & some hormones

Found in the blood

Limits the movement of phospholipids in the cell membrane

Excessive intake of cholesterol in diet will lead to deposition on arterial wall

(inner walls of the blood vessels), thickening the wall (which become less elastic),and leading to a blockage.

High risk ofheart attacks and stroke will be experienced.

b. Steroid is important in the synthesis of steroid hormones such as female sex

hormones and vitamin A & D.

Fatty meats, nuts and dairy products are rich in lipids. (e.g. maize, pork, peanuts).

Lipids are insoluble in water but dissolve in organic solvents (e.g. ethanol, ether, etc).

Functions / excess of lipids:-

a. Lipids are also a source of energy.

Each g of lipid provides about 38.9 kJ of energy, which is more than twice that of

carbohydrates.

They provide 25-30% of daily energy requirement of the body.

b. Excess lipids will be stored in adipose tissues in the body.

These tissues are found under the skin as subcutaneous fat / around the internal organs.


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(1)They act as food reserve.

(2)They act as an insulator to reduce heat loss.

(3)Lipids stored around the heart and kidneys act as

shock-absorber to protect the internal organs.

c. Lipids are a major component ofcell membranes.

(phospholipids, cholesterol)

d. Lipids are involved in transporting and storing

fat-soluble vitamins (e.g. vitamins A & D) in the body.

3 Proteins Proteins are organic substances made up of carbon(C), hydrogen(H), oxygen(O) and

nitrogen(N).

Some also contain sulphur(S), phosphorous(P).

Proteins are big molecules which consist of large no. ofamino acids.

The basic building blocks of proteins are amino acids.

1. Each amino acid molecule contains a carbon atom in the center which carries a

carboxyl group (

COOH), an amino group(

NH2), a side chain(

R group) and ahydrogen atom.

2. Each amino acid has its own specific side chain.

3. 20 different amino acids are needed to make up all the different proteins in the body.

When the amino group of an amino acid & the carboxyl group of another are joined by

condensation (peptide bond), a dipeptide is formed.

subcutaneous fat


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Further combination of the dipeptide with other amino acids forms a polypeptide.

A protein consists of one / more polypeptide chains.

It can be hydrolyzed to amino acids in the presence ofH2O and a suitable enzyme.

E.g.

Insulin is made up of 51 amino acids (C254H317O75N65S6).

Occurrence of amino acids:-

Although there are >100naturally occurring amino acids, only 20 are used in the synthesis

of proteins.

1. 8 are essential amino acids because they cannot be made by the human body & have to

be taken in diet. (isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine)

2. The remaining 12 are non-essential amino acids; they can be made by human body, not

essential in human diet. (alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine,

proline, serine, tyrosine)

The 20 different amino acids can be joined together in thousands of different

combinations to create different polypeptides or proteins.

coiling and folding


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Types of proteins:-1. Fibrous proteins

a. They are composed of long & parallel polypeptide chains with regular and

repetitive sequence of amino acids.

b. These chains are cross-linked to from a fairly stable and insoluble structure so that

they form the important building materials of many structures (e.g. nails, hairs).

2. Globular proteins

a. They are composed of polypeptides with regular sequence of amino acids.

b. These chains are folded into spherical shape.

c. They are relatively unstable because their shape is maintained by different types of

bonding which are easily denatured by change of environmental conditions.

d. Most of them have metabolic functions. (e.g. enzymes, insulin, haemoglobin,

antibodies)

Properties of proteins:-

1 Easily denatured by high temperature & extreme pH

2 Slightly soluble in water to form colloidal suspension ()


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Functions of proteins:-

a. Proteins are important for the growth and repair of body tissues.

Almost all body structures, e.g. muscles & brain tissue, consist of proteins.

b. Enzymes, antibodies and some hormones are proteins. [metabolic regulators]

1. Enzymes speed up all the bio-chemical reactions in organisms, e.g. amylase.

2. Antibodies produced by white blood cells defend the body against germs.

3. Hormone regulates physiological processes, e.g. insulin controls the blood glucose

level.

4. Haemoglobin in red blood cells increases the oxygen-carrying capacity to transport

oxygen to the tissues.

c. If carbohydrates and lipids stored in the body are used up [under extreme starvation],proteins may be broken down to provide energy for the body.

Each gram of protein provides about 18.2 kJ of energy.

Meat, eggs, fish, bean & dairy products are rich in protein.

Excess of proteins:-

Excess amino acids in the body cannot be stored.

They are broken down by the liver.

The amino group is removed from the amino acid and changed to urea.

This process is called deamination.

The urea is passed out in urine.

The remaining parts of the amino acids are converted into carbohydrates / lipids.

Deficiency of proteins:-

A lack of protein in diets may lead to a deficiency disease called kwashiorkor.

This condition is common in children in developing countries where meat, eggs and

milk are limited.

Children with kwashiorkor grow poorly.

They have a swollen belly because of the accumulation of tissue fluid.

4 Water (H2O)

Water has no energy value, but it is essential for life.

Water is essential to maintain many life processes in organisms.

Water makes up the largest percentage by weight of most organisms.

70% of our body weight is water.


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Functions of water:-

1. As a solvent

It dissolves various substances and provides the medium for chemical reactions to take

place in cells.

2. As a medium for chemical reactions to take place

3. As a transport medium.

For example, in form of blood, it transports nutrients, respiratory gases, and

metabolic wastes around the body.

4. As a reactant in some metabolic reactions

Breaking down certain complex food substances during the digestion of food.i.e. to hydrolyze (digest)food (complex organic substances) into simpler forms.

5. As a cooling agent

Water removes heat when it evaporates from the body of an organism.

It acts as a cooling agent to help regulate body temperature.

E.g. Sweating (perspiration) in humans

Many food and drinks are rich in water.

Excess of water:-

Humans lose water continuously through sweating, urination, breathing and egestion.

Most excess water is passed out from the body as urine.

Therefore, we should drink about 6-8 glasses of water every day to replace for the loss.

5 Vitamins

Vitamins are organic food substances (organic compounds) needed in small amounts.

They have no energy value, but they help regulate many metabolic reactions. [act as

co-enzymes]

Some of them can be made by our body while the rest have to be obtained from the diet.

* Plants can produce all their vitamins.

(i) Vit. B & C are water-soluble, are more easily destroyed by oxygen in air / heat.

(ii) Vit. A & D are lipid-soluble, are more heat-resistant. [usually stored in animal fats /

plant oils]


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(1) Vitamin A (fat-soluble/lipid-soluble) (C20H30O)

Daily needs: 750g

Functions: Help form a visual pigment in the retina of our eyes (necessary for vision in dim

light)

Keeps the cornea of eyes, skin, lining of alimentary canal & the breathing system

healthy

Food sources: Fish-liver oil

Milk

Green vegetable (broccoli)

Carrot {contain an orange pigmentcarotene , converted to vitamin A in liver}

Deficiency

disease:

a. Poor vision in dim light /night blindness

b. Drying up of cornea & skin

c. Easy infection of the lining of the lungs & trachea

(2) Vitamin C (ascorbic acid C6H8O6) (water-soluble, easily destroyed by oxygen in

air / high temperatures)

Daily needs: 30g

Functions: Needed for the growth & repair ofconnective tissues (help keep body structures

in place)

Help heal wounds

Important to healthy gums & skin

Food sources: Vegetables (e.g. green pepper, broccoli)

Fruits (espec. citrus fruitsorange, lemon, kiwifruits ; guavas)

Deficiency

disease:

SCURVY

a. Weak & bleeding gums, resulting in loose teeth

b. The body bleeds easily, causing bruises under skin (bruised skin)

c. Slow recovery of wounds

Sailors on long voyages without getting fresh fruits / vegetables will have scurvy

(3) Vitamin D (fat-soluble/lipid-soluble) (C28H44O)

Daily needs: 2.5gFunctions: Promote the uptake of calcium (Ca

2+) & phosphate (PO4

3) ions from gut

Calcium, phosphate ions are essential for keeping bones and teeth strong.

Vitamin D is particularly important to actively growing children.

(!!! Vitamin D isnot the component of bones)

Food sources: Fish-liver oil

Dairy products (milk, butter, egg, fish)

Deficiency

disease:

a. Rickets in children

The children have weak legs, may bend under the weight of their body)

b. Easy bone fractures in adults (with brittle bones) (or even osteoporosis)


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Absorption 1. Vitamin D can be produced by the skin under sunlight. [ultra-violet light]

2. Calcium-rich food & weight-bearing exercises are useful to slow down calcium loss

from bones in adults.

(1 mg = 10-3

g ; 1g = 10-6

g)

6 Minerals

Minerals are inorganic food substances needed in small amounts.

They have no energy value, but are important in regulating many metabolic reactions

(e.g. blood clotting) & building body tissues (e.g. bones).

We need various minerals, e.g. calcium, iron, iodine, potassium, phosphorus.

Minerals Daily needs Functions

Calcium

(Ca2+

)

500 mg (1)Essential for the formation of bones & teeth

Children need a lot of calcium to harden their bones & develop

teeth as they grow up.

(2)Blood clotting

(3)Muscle contraction

Deficiency diseases

(1)Rickets in children

(2)Osteoporosis in adults(3)Bleeding / haemorrhage

Food sources

Green vegetables (e.g. broccoli)

dairy products (e.g. cheese, milk, yoghurt, etc)

Iron

(Fe2+

)

(Fe3+

)

10 mg Functions

It is a component ofhaemoglobin in red blood cells, a pigment in red

blood cells that carries oxygen around the body.

Deficiency diseasesAnaemiawith pale face, tired easily and faint because ofinsufficient

haemoglobin to carry oxygen

Food sources

Beef , meat

Liver, kidney

Vegetables

Yeast, egg

(1 mg = 10

-3

g)


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7 Dietary fibre

Dietary fibre (roughage) is an organic food substance, mainly consists ofcellulose from

plant cell walls.

Dietary fibre does not give us energy since we do not have the enzyme to digest it.

Function of dietary fibre:-

It is essential to our health because it holds a lot of water to enable faeces to remain soft.

It also adds bulk to food to stimulate its movement along the alimentary canal (=

peristalsis). [facilitate peristalsis of the gutto move foodalong it]

In this way, faeces can be passed out of the body more easily.

Plant foods (e.g. vegetables, fruits & cereals) contain dietary fibre.

Deficiency of dietary fibre:-

Lack of dietary fibre cannot properly stimulate the colon, food moves along the gut very

slowly.

It causes excessive absorption of water from food.

As a result, the faeces become so dry & hard, making egestion very difficult (=

constipation).

In extreme case, it may lead to intestinal cancer.

5.3 Food tests

Based on the chemical properties of food substances, scientists have developed various

tests to test for their presence in food.

To ensure the +ve result observed is due to the food substance but not other factors, a

control using distilled water instead of the sample should be included in the food test.

A Detection of food substances by food tests

[I] Test for glucose using Clinistix paper (Clinistix paper test)

Clinistix paper can be used to detect the presence of glucose in food.

It is commonly used to detect glucose in urine.

A positive result shows that the person may suffer from diabetes.

Dip the pink test end of Clinistix paper into the sample and observe any colour change.

A purple colour indicates the presence of glucose.

Negative resultno colour change Positive resultpurple


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[II] Test for reducing sugars using Benedicts test

To test for reducing sugars, e.g. glucose, maltose, fructose.

*Use water bath instead of Bunsen flame Water bath has a better control over the temperature & and

can preventbumping of the mixture.

A brick-red precipitate indicates the presence of reducing sugars.

The concentration of reducing sugars can affect the result:

Blue (with no glucose present) < green < yellow < orange < red, and then brick red /

brown (with high r. sugar present)

A colour change would signify the presence of glucose.

Summary of reaction:

[III]Test for starch using iodine test

Iodine solution detects for the presence of starch by changing its original brown colour

to blue-black.

Negative resultno colour change Positive resultblue-black colour

(water bath)


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[IV]Test for lipids using grease spot test

1. Add a drop of cooking oil / egg white solution (control proteins) / distilled water

(control) to a filter paper and let it dry in air for 5 mins.

2. Hold up the filter paper to the light & observe any translucent spot.

3. Put the filter paper into an organic solvent (e.g. ether, acetone). Take it out and let it dry.

4. Examine the filter paper against light again.

The disappearance of the spot indicates the presence of lipids.

Sample

Presence of translucent spot after drying

Before immersing into

organic solvent

After immersing into

organic solvent

Cooking oil

Egg white solution Distilled water ---

Note:-

a. The translucent spot caused by lipids is permanent.

b. On the contrary, the translucent spot caused by water disappears as water evaporates.

c. Lipids but not proteins are soluble in organic solvents.

d. Therefore, the translucent spot caused by lipids disappears whereas the one caused by

proteins remains on the filter paper.

[V] Test for proteins using Albustix paper

Albustix paper can be used to detect the presence of proteins in food.

It is commonly used to detect proteins in urine.

A +ve result shows that the person may suffer from kidney disease.

Dip the yellow test end of Albustix paper into the sample & observe any colour change.

A green colour indicates the presence of proteins.

Negative resultno colour change Positive resultgreen


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[VI]Test for vitamin C using DCPIP solution

The DCPIP (dichlorophenol indophenol) solution in oxidized state is blue.

Vitamin C can reduce DCPIP solution and change its colour to become colourless.

We should not shake the tube too vigorously; otherwise, oxygen in the air bubbles

produced by shaking will lower the reducing power of vitamin C.

Dip the vitamin C solution to the DCPIP until the solution becomes colourless.

1. Boil a test tube of 5 cm3 of vitamin C solution in a water bath for 5 mins.

2. Allow the test tube to cool.

3. Do the test again with theboiled vitamin C solution.

- Heat destroys the reducing property of vitamin C, there is no colour change inthe solution.

- Therefore, we should not boil / overheat fruits or vegetables to prevent the loss of

vitamin C.

DCPIP is not suitable for detecting the presence of vitamin C in a sample containing

glucose.

Glucose is reducing & will also decolourize DCPIP, no matter vitamin C is present

in the sample or not.

B Food tests with different sample in different physical states

(1) For solid examples, we have to grind them up with water.

(2) Extracts are then obtained by filtering the ground materials.

So that we can use the examples to do food tests involving Clinistix paper, Albustix

paper, DCPIP solution, etc.

(3) Lipids may not come out from some solid examples.

(4) We need to grind up the samples and boil them before doing the grease spot test.

(5) The food tests can be also used to detect the presence of biomolecules

(carbohydrates, lipids and proteins) in living tissues.


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Summary

Food Test Procedure Positive result

Reducing sugar Benedicts Test Add Benedicts solution (blue) and

heat

Brick-Red precipitate

Glucose Clinistix Paper Test Dip coloured end (pink) to glucose

solution

Pink purple

Starch Iodine test Add brown iodine solution to starch Brown blue-black

Lipid Grease spot test 1. Add on filter paper.

2. Then dip the paper in organic

solvent (ether).

A translucent spot which

disappears after dipping in

organic solvent.

Protein Albustix paper test Dip the coloured end (yellow) to

protein solution

Yellow green

Vitamin C DCPIP solution Dip the vitamin C into blue DCPIP Blue colourless


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5.4 Foodstuffs

Different foods contain different food substances in different amounts.

Their energy values are also different because of different amounts of carbohydrates,

lipids and proteins they contain.

1. The energy values of carbohydrates and proteins are approximately the same.

2. Lipids contain more than twice the energy of carbohydrates / proteins.

Food substance Energy value (kJ / g)

Carbohydrates 17.1

Lipids 38.9

Proteins 18.2

The table below shows the compositions of some common foods.

It tells us the amount of major food substances & energy values in 100g of each food.


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5.5 Balanced diet

A Defining balanced diet

Diet refers to all the food we eat.

To maintain health and meet the energy needs of our body, we must have a balanced

diet.

A BALANCED DIET consists of all the food substances in the right amounts and

proportions.

To design a balanced diet, dieticians apply 2 concepts:

1. 6 basic food groups

2. Food pyramid

The food pyramid is a general guide to having a balanced diet.

The amounts of the 6 food groups in a balanced diet are represented by their relative

size in the food pyramid.

Principles of healthy eating:-

a. Eat cereals as the largest portion of food in every meal.

b. Eat a lot ofvegetables & fruit.

c. Eat moderate amount ofmeat, dairy products & beans.

d. Reduce eating food with high salt, fats & sugar content.

e. A daily fluid intake of 6-8 glasses (1 glass = 250ml)

2+3 everyday:-

To keep healthy, it is recommended to have at least 2 servings of fruits + 3 servings of

vegetables every day.


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(a)1 serving (80g) of fruits is about 2 pieces of small-sized fruits (e.g. plum) / 1 piece of

medium-sized fruit (e.g. orange) + 1/2 piece of large-sized fruit (e.g. banana)

(b)1 serving of vegetables is about 1/2 bowl of cooked vegetables.

B Factors affecting our dietary requirement

The balanced diet differs from person to person, depending on a number of factors.

(i) Age

Children need more energy relative to their body size than adults.

They have a largersurface area to volume ratio than adults, therefore a great

heat loss. As they grow actively, they need more proteins, calcium & iron for building new

tissues.

i) Teenagers need more calcium & vitamin D than adults for growth because

they are at the stage ofactive bone growth.

ii) Teenagers are at the stage ofactive growth that need more iron to produce

more red blood cells.

(ii) SexIn general, males need more energy than female.

This is because males usually have a larger body size,more muscles (need more

energy to contract) & a more active lifestyle than females.

Also, there is less subcutaneous fat in males, so they lose heat more rapidly than

females.

At the same time, female need more iron than males, since they have to produce

more red blood cellsto replace for themonthly blood lossduring menstruation.

(iii) Level of activity

People doing more muscular activities require more energy.

A construction worker requires more energy than an office worker.

The former needs a diet which is rich in:

a. carbohydrates to supply enough energy, and

b. proteins for muscle development.


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(iv) Body status

(i) Pregnant women have higher daily energy need than a normal woman

because extra energy is used to support the development of thefoetus. [foetal

development]

They need more carbohydrates, proteins, minerals & vitamins because

their foetuses need energy & raw materials for making new tissues.

(ii) Breast-feeding mothers need an extra supply of nutrients in the diet for milk

production.

Both need more calcium & vitamin D to support the rapid bone growth of the

foetus / baby.

Both need more iron for the foetus / baby to produce their red blood cells.

The daily energy requirements & the recommended intake of food substances fordifferent groups of people are tabulated below.

If the energy uptake is insufficient, the body will oxidize the stored glycogen & lipids to

meet the needs.

This will cause drop in body mass.


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C Health problems resulting from an improper diet

Eating both too much / too little food is unhealthy & can lead to different health

problems.

1. Over-nutrition (over-eating)

If we eat too much (= the energy intake is greater than the energy needs /

consumption / energy consumed), the excess energy will be stored as fats in the

body.

This will cause a gain in weight.

When our body weight exceeds a normal level, we are said to be overweight.

The condition of seriously overweight = obesity.

Overweight people have a higher risk of developing high blood pressure,

heart disease, gall stone, diabetes, etc.

Theirjoints may easily become damaged because of their weight.

2. Under-nutrition (under-eating)

If we eat too little (= the energy intake is less than the needs of our body), the

glycogen & lipids will be used.

In extreme starvation, the proteins in our body will also be consumed.

We will have a loss in weight and become thin.

Malnutrition/ various deficiency diseases will result.

Malnutrition is the condition resulting from the lack of one or more of the food

substances that are required in the diet to maintain health.

(a)Kwashiorkor (protein deficiency disease)

Due to the lack of food (especially proteins)

Will suffer from stomach distension, muscle wastage, anaemia, retarded growth

(b)Eating disorders

Some people are improperly on diet without proper medical guidance.

So, they are under-weight (too thin) and will seriously affect their health.

Their blood glucose level may be below normal & will faint easily.

(c)Anorexia nervosa

It is another disease of under-eating. It is a kind ofmental illness.

The patients consider themselves fat even though they are very slim.

They fear of putting on weight & refuse to eat (lose appetite).

Without proper treatment, they will become dangerously weak.

This disease can be fatal.


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D* STSE Food labels

To help consumers make healthy food choices, the HKSAR government has required

manufacturers to provide food labels on pre-packaged food since 2007.

A food label helps us understand the composition & the energy content of that food.

It also provides us with other information like food additives.

They are added to prevent food from going bad / give it colour or flavour.

Nutrition label must include the information on energy & 7 nutrients specified for labelling

(1+7), namely, protein, carbohydrates, total lipids, saturated fatty acids, trans fatty acids,

sodium & sugars.

Foods & Human (EE)

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