05 food requirements_in_human
TRANSCRIPT
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Functions of FoodFunctions of Food
• to maintain life• to supply energy & give warmth
– carbohydrates– fats– proteins
• for growth and repair– Proteins
• keep healthy & help to fight against disease
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• elements : C, H, O– ratio of H : O = 2 : 1
• monosaccharides– C6H12O6
– all are sweet & soluble in water– all are Reducing Sugars– include Glucose, Fructose & Galactose
CarbohydratesCarbohydrates
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disaccharides (from 2 monosaccharides)
– C12H22O11
– all are sweet & soluble in water– Maltose ( 2 glucose molecules )– Sucrose ( glucose + fructose) (non-reducing sugar)– Lactose ( glucose + galactose)
CarbohydratesCarbohydrates
surcosesurcose
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CarbohydratesCarbohydrates
• polysaccharides (NOT sugar) • for energy storage
– starch (store in plants)glycogen (store in animals)
• Hydrolysis: Polysaccharide +H2O
Disaccharides +H2O Monosaccharides
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main source of energy cellulose: - fibrous material of Plant Cell Wall - dietary fibre: stimulates Peristalsis excess carbohydrates - stored as glycogen in liver & muscle - stored as fats under skin
Functions of Functions of CarbohydratesCarbohydrates
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Test for Reducing Sugars (Benedict’s
Test)
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Is there any colour change in tubes A and B ?Ans: Only the mixture in t
ube A has a colour change.
A Bglucose solution
+ Benedict
’s solution
distilled water +
Benedict’s solution
water bath
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What is the sequence of change when there is a colour change ?
Ans: The blue solution changes first to green, then to a yellow coloration and eventually a brick-red precipitate is produced.
A Bglucose solution
+ Benedict
’s solution
distilled water +
Benedict’s solution
water bath
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Test for Starch (Iodine Test)
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What is the final colour in tube A ?
Ans: The solution in tube A changes from brown to blue black.
iodine solution
starch solutio
n
distilled water
A B
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What is the purpose of setting up tube B ?Ans: To act as a contro
l.
iodine solution
starch solutio
n
distilled water
A B
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ProteinsProteins• elements: C, H, O, N,
sometimes S, P• components : amino acids
forms dipeptides & polypeptides• Condensation: Amino acids –H2O Dipeptides –H2O Polypeptide
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Proteins
• are compounds of carbon, hydrogen, oxygen, nitrogen and sometimes sulphur, phosphorus
• amino acids: – unit of proteins
– about 20 different types
– essential and non-essential types
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An amino acid molecules
H2Namino group
COOHcarboxyl group
C
R
H
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The condensation and hydrolysis of a polypeptide
5
1 4
3
2
1 2 3 4 5
hydrolysiscondensation
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Condensation of two amino acid to form a dipeptide
H2N C
R1
H
C
O
OH HN
H
C
H
R2
COOH
H2N C
R1
H
O
H
C
H
R2
COOHC---N
H2O
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cannot be stored
- excess proteins are deaminated by liver
~ to Urea which will be excreted
away by Kidney
~ to Carbohydrates (Glycogen) which will be stored in Liver
ProteinsProteins
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Functions of Functions of ProteinsProteins
• for growth and repair of body cells
(as structural components (cell membrane and cytoplasm) of cells)
• to produce hormones and enzymes and antibodies
• to give energy• for making Haemoglobin in blood• for making Antibodies
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Deficiency disease of proteins
Kwashiorkor
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Test for Proteins (Biuret Test)
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Test for proteins / Biuret testegg white solution
1 cm3 NaOH solution
Put CuSO2 solution drop by drop, and shake the mixture after addition of each drop
Positive result: purple colour
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What colour changes in tubes A and B ?Ans: Mixture in tube A
changes from blue to purple while mixture in tube B remains blue without any change.
copper sulphate solution
egg white + sodium hydroxide solution
water + sodium
hydroxide
solution A B
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Lipids ( fats & oils )Lipids ( fats & oils )• elements : C, H, O• components of 1 lipid
molecule: 1 glycerol + 3 fatty acids• insoluble in water • soluble in organic solvent
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Functions of LipidsFunctions of Lipids give energy component of cell membrane form fatty tissues under skin
> to store energy
> acts as insulator to keep warm to transport fat-soluble vitamins (A, D, E, K)
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Spot Test for Fat
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Which substance, oil or water, leaves a permanent translucent spot on the filter paper ?
Ans: Oil.
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Emulsion Test for Fat
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Which test tube has an emulsion formed ?Ans: Test tube A.
2 drops of cooking oi
l
2 cm3 of alcohol
2 cm3 of distilled water
after shaking to form a clear
solution
shake and then allow to
stand
emulsion
oilwater
shake and then allow to
stand
shaking
2 drops of cooking oi
l
2 cm3 of distilled water
2 cm3 of distilled water
A
B
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What happens to the other tube ?Ans: The mixture separates into two layers beca
use fats do not dissolve in water.
2 drops of cooking oi
l
2 cm3 of alcohol
2 cm3 of distilled water
after shaking to form a clear
solution
shake and then allow to
stand
emulsion
oilwater
shake and then allow to
stand
shaking
2 drops of cooking oi
l
2 cm3 of distilled water
2 cm3 of distilled water
A
B
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VitaminsVitamins• no energy value• essential for small amount
to maintain good health• water soluble vitamins
( B, C )• fat soluble vitamins
( A, D, E, K )
excessive of some vitamins may be harmful
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Vitamin AVitamin A formed in the body from Carrotene
(a yellow pigment in carrots)
destroyed at high temperature
essential for forming visual purple (maintain dim light vision)
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Vitamin CVitamin C Destroyed after prolonged cooking
Necessary for wounds-healing
Vitamin DVitamin D Formed in Skin from Ultraviolet Light Help to regulate Ca & P metabolism
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Detection of Vitamin C in Lemon Juice by using
DCPIP
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What colour change has occurred ?
Ans: The blue DCPIP decolourizes.
syringe
lemon juice
DCPIP solution
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What conclusion can you draw ?Ans: Lemon juice contains
vitamin C which decolourizes blue DCPIP.
syringe
lemon juice
DCPIP solution
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Vitamin SourcesDeficiency
Disease
A
Egg yolk, milk, cheese, carrot, green vegetables
Night blindness
CFresh fruits &
green vegetables
Scurvy
DCod liver oil & egg yolk
Rickets
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Food TestsFood TestsSubstance
sTest
Original Colour
Positive Result
Reducing Sugar
Benedict’s Blue Orange ppt
Starch Iodine Brown Blue-black
Protein Biuret Blue Violet
Fats/Oils Spot --- Translucent
spot
Fats/Oils Emulsion ClearMilky
emulsion
Vitamin C DCPIP BlueColourless (decolourize)
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Mineral SaltsMineral Salts regulate body metabolism essential for healthy growth necessary for construction of
certain tissues needed in small amount include Ca, S, K, Na, Mg, Fe, I
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Mineral(s) Sources FunctionsDeficiency
Disease
Calcium & Phosphor
us
Cheese, milk, vegetables
Making bones & teethImportant for blood clotting & muscle contraction
Rickets
Iron
Liver, eggs, beef, green leafy vegetables
Structural component of Haemoglobin
Anaemia
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Dietary FibreDietary Fibre mainly cellulose indigestible material for human give bulk to food & stimulate peristalsi
s prevent Constipation lack of dietary fibre: Large Intestine Ca
ncer sources: wholemeal cereals, unpolishe
d rice, fresh vegetables & fruits
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Balanced DietBalanced Diet• have enough food to supply
enough– energy
•carbohydrates, fats, proteins– body building materials
•proteins– substances to maintain health
•vitamins, minerals, water & dietary fibres
• malnutrition : not having balanced diets for long time
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Energy Contents in Energy Contents in FoodFood
• Calorimeter is used to measure the amount of energy contained in a particular type of food
• Carbohydrate (17kJ/g)
• Protein (18kJ/g)
• Fat (39kJ/g)
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Factors affecting energy Factors affecting energy requirementrequirement
• Sex• Age• Occupation• Physical Activities• Stage of individual
(pregnancy, breast-feeding)
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Measure the Energy Value of
Food
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boiling tubewater
burning peanut
thermometer
Explain why the energy value of the peanut is lower than those from standard tables.Ans: Because there are a n
umber of inaccuracies associated with this method due to incomplete combustion and heat loss.
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Basal Metabolic Rate (BMR)Basal Metabolic Rate (BMR) minimum amount of energy
needed by an individual lying awake in bed to maintain breathing, body temperature & heartbeat
varies from one individual to another
daily energy requirement > basal metabolic rate
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