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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
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
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
slide4

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)
carbohydrates5
Carbohydrates
  • polysaccharides (NOT sugar)
  • for energy storage
    • starch (store in plants)glycogen (store in animals)
  • Hydrolysis:Polysaccharide +H2O Disaccharides +H2O  Monosaccharides
slide6

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

slide7

Investigation 5.1

Test for Reducing Sugars (Benedict’s Test)

slide8

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.

slide9

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.

slide10

Investigation 5.2

Test for Starch (Iodine Test)

slide11

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.

slide12

iodine solution

distilled water

starch solution

B

A

What is the purpose of setting up tube B ?

Ans: To act as a control.

proteins
Proteins
  • elements: C, H, O, N, sometimes S, P
  • components : amino acidsforms dipeptides & polypeptides
  • Condensation:

Amino acids–H2O Dipeptides

–H2O  Polypeptide

proteins14
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
an amino acid molecules
An amino acid molecules

R

C

COOH

carboxyl group

H2N

amino group

H

the condensation and hydrolysis of a polypeptide
The condensation and hydrolysis of a polypeptide

4

1

2

5

3

condensation

hydrolysis

1

2

3

4

5

condensation of two amino acid to form a dipeptide
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

slide18

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

functions of proteins
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
slide21

Investigation 5.3

Test for Proteins (Biuret Test)

test for proteins biuret test
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

slide23

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.

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
slide25

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)
slide26

Investigation 5.4

Spot Test for Fat

slide27

Which substance, oil or water, leaves a permanent translucent spot on the filter paper ?

Ans: Oil.

slide28

Investigation 5.5

Emulsion Test for Fat

slide29

2 drops of cooking oil

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.

slide30

2 drops of cooking oil

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.

vitamins
Vitamins
  • 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
slide32

Vitamin 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)
slide33

Vitamin C

  • Destroyed after prolonged cooking
  • Necessary for wounds-healing

Vitamin D

  • Formed in Skin from Ultraviolet Light
  • Help to regulate Ca & P metabolism
slide34

Investigation 5.6

Detection of Vitamin C in Lemon Juice by using DCPIP

slide35

syringe

lemon juice

DCPIP solution

What colour change has occurred ?

Ans: The blue DCPIP decolourizes.

slide36

syringe

lemon juice

DCPIP solution

What conclusion can you draw ?

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

slide37

Vitamin

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

food tests

Substances

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
slide39

Mineral 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
slide40

Mineral(s)

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

slide41

Dietary Fibre

  • 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
balanced diet
Balanced 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
energy contents in food
Energy Contents in Food
  • 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)
factors affecting energy requirement
Factors affecting energy requirement
  • Sex
  • Age
  • Occupation
  • Physical Activities
  • Stage of individual(pregnancy, breast-feeding)
slide45

Investigation 5.8

Measure the Energy Value of Food

slide46

boiling tube

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.

slide47

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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