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Functions 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. Carbohydrates. elements : C, H, O ratio of H : O = 2 : 1 monosaccharides C 6 H 12 O 6

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Functions of food l.jpg
Functions 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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Carbohydrates

  • elements : C, H, O

    • ratio of H : O

      = 2 : 1

  • monosaccharides

    • C6H12O6

    • all are sweet & soluble in water

    • all are ReducingSugars

    • include Glucose, Fructose & Galactose


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surcose

Carbohydrates

  • disaccharides(from 2 monosaccharides)

    • C12H22O11

    • all are sweet & soluble in water

  • Maltose ( 2 glucose molecules )

  • Sucrose ( glucose + fructose)

  • (non-reducingsugar)

  • Lactose ( glucose + galactose)


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Carbohydrates

  • polysaccharides (NOT sugar)

  • for energy storage

    • starch (store in plants)glycogen (store in animals)

  • Hydrolysis:Polysaccharide +H2O Disaccharides +H2O  Monosaccharides


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Functions of Carbohydrates

  • 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


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Investigation 5.1

Test for Reducing Sugars (Benedict’s Test)


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A

B

glucose solution + Benedict’s solution

distilled water + Benedict’s solution

water bath

Is there any colour change in tubes A and B ?

Ans: Only the mixture in tube A has a colour change.


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A

B

glucose solution + Benedict’s solution

distilled water + Benedict’s solution

water bath

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.


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Investigation 5.2

Test for Starch (Iodine Test)


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iodine solution

distilled water

starch solution

B

A

What is the final colour in tube A ?

Ans: The solution in tube A changes from brown to blue black.


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iodine solution

distilled water

starch solution

B

A

What is the purpose of setting up tube B ?

Ans: To act as a control.


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Proteins

  • elements: C, H, O, N, sometimes S, P

  • components : amino acidsforms 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

R

C

COOH

carboxyl group

H2N

amino group

H


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The condensation and hydrolysis of a polypeptide

4

1

2

5

3

condensation

hydrolysis

1

2

3

4

5


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Condensation of two amino acid to form a dipeptide

O

R1

H

H

C

H2N

C

N

C

COOH

OH H

H

R2

H2O

R1

H

O

C

H2N

C---N

C

COOH

H

H

R2


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Proteins

  • 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


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Functions of Proteins

  • 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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Investigation 5.3

Test for Proteins (Biuret Test)


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Test for proteins / Biuret test

egg 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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copper sulphate solution

egg white + sodium hydroxide solution

water + sodium hydroxide solution

B

A

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.


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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 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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Investigation 5.4

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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Investigation 5.5 translucent spot on the filter paper ?

Emulsion Test for Fat


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2 drops of cooking oil translucent spot on the filter paper ?

2 cm3 of alcohol

2 cm3 of distilled water

A

after shaking to form a clear solution

shake and then allow to stand

emulsion

2 drops of cooking oil

2 cm3 of distilled water

2 cm3 of distilled water

B

oil

shaking

shake and then allow to stand

water

Which test tube has an emulsion formed ?

Ans: Test tube A.


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2 drops of cooking oil translucent spot on the filter paper ?

2 cm3 of alcohol

2 cm3 of distilled water

A

after shaking to form a clear solution

shake and then allow to stand

emulsion

2 drops of cooking oil

2 cm3 of distilled water

2 cm3 of distilled water

B

oil

shaking

shake and then allow to stand

water

What happens to the other tube ?

Ans: The mixture separates into two layers because fats do not dissolve in water.


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Vitamins translucent spot on the filter paper ?

  • 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 A translucent spot on the filter paper ?

  • 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 C translucent spot on the filter paper ?

  • Destroyed after prolonged cooking

  • Necessary for wounds-healing

Vitamin D

  • Formed in Skin from Ultraviolet Light

  • Help to regulate Ca & P metabolism


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Investigation 5.6 translucent spot on the filter paper ?

Detection of Vitamin C in Lemon Juice by using DCPIP


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syringe translucent spot on the filter paper ?

lemon juice

DCPIP solution

What colour change has occurred ?

Ans: The blue DCPIP decolourizes.


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syringe translucent spot on the filter paper ?

lemon juice

DCPIP solution

What conclusion can you draw ?

Ans: Lemon juice contains vitamin C which decolourizes blue DCPIP.


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Vitamin translucent spot on the filter paper ?

Sources

Deficiency Disease

A

Egg yolk, milk, cheese, carrot, green vegetables

Night blindness

C

Fresh fruits & green vegetables

Scurvy

D

Cod liver oil

& egg yolk

Rickets


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Substances translucent spot on the filter paper ?

Test

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

Clear

Milky emulsion

Vitamin C

DCPIP

Blue

Colourless (decolourize)

Food Tests


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Mineral Salts translucent spot on the filter paper ?

  • 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) translucent spot on the filter paper ?

Sources

Functions

Deficiency Disease

Calcium & Phosphorus

Cheese, milk, vegetables

Making bones & teeth

Important for blood clotting & muscle contraction

Rickets

Iron

Liver, eggs, beef, green leafy vegetables

Structural component of Haemoglobin

Anaemia


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Dietary Fibre translucent spot on the filter paper ?

  • mainly cellulose

  • indigestible material for human

  • give bulk to food & stimulate peristalsis  preventConstipation

  • lack of dietary fibre: Large Intestine Cancer

  • sources: wholemeal cereals, unpolished rice, fresh vegetables & fruits


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Balanced Diet translucent spot on the filter paper ?

  • 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 Food translucent spot on the filter paper ?

  • 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 requirement translucent spot on the filter paper ?

  • Sex

  • Age

  • Occupation

  • Physical Activities

  • Stage of individual(pregnancy, breast-feeding)


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Investigation 5.8 translucent spot on the filter paper ?

Measure the Energy Value of Food


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boiling tube translucent spot on the filter paper ?

thermometer

water

burning peanut

Explain why the energy value of the peanut is lower than those from standard tables.

Ans: Because there are a number of inaccuracies associated with this method due to incomplete combustion and heat loss.


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Basal Metabolic Rate (BMR) translucent spot on the filter paper ?

  • 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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~ translucent spot on the filter paper ?END ~