2. 2
Functions of food
1. Energy source – 90% used to make
ATP
2. Materials Source - for growth, repair,
defence
3. Continuity – replacement of cells and
reproduction
4. Metabolism - maintaining cells at
high level of chemical efficiency
3. 3
• Metabolism - all reactions in living body
• Anabolism building up of substances – input
of energy required
• E.g. photosynthesis, DNA replication, RNA
formation, muscle building
• Catabolism – breaking down of complex
molecules – e.g. digestion
• Enzymes protein biological catalysts,
catalyse reactions [speed up – not used up in]
• Respiration – release of energy from food
4. 4
Protein
• Chemical elements C, H, O, N also P and
S
• Biomolecular sub-units – Amino Acids [20]
• Linked by peptide bonds
• One or more chains
• Differ in sequence and number of a.a.’s
• Made in ribosomes
• Sources meat, fish, eggs, milk, cheese,
pulses
8. Shapes
• Globular or Fibrous
• Amino acids join together at angles
• so as the protein forms it becomes folded
• It can form a long fibre
• Or it can become a ball
• The function of a protein (enzyme) depends on
its shape
• If we heat much above 60oC or shake it
become denatured i.e. It loses its function
8
9. 9
Carbohydrate
Chemical elements C, H, O [ H:O ratio 2:1 ]
Monosaccharides [1 sugar unit]
Glucose [C6H12O6], fructose, galactose
Disaccharides [2 sugar units]
Maltose, sucrose [C12H22O11], lactose
Polysaccharides [many sugar units]
Starch [plants], glycogen [animals]
10. 10
Types of carbohydrates
Sugar
• Found in honey, jam, sweets , fizzy drinks,
alcohol.
• [Most processed foods have sugar added]
• Provides energy [quickly]
11. 11
Carbohydrates continued
Starch
• Found in potatoes, flour, bread, pasta,
rice, cakes etc.
• Provides energy [ more slowly over a
longer period]
• Test for with iodine which goes from
brown to blue/black if starch is present.
12. 12
Carbohydrates continued
Fibre [cellulose]
• Found in whole-grain cereals [e.g.
Weetabix, Shredded Wheat etc.]
and vegetables.
• Function to retain water and prevent
constipation and also cancer of the
bowel.
13. 13
Carbohydrate Roles
Structural
• Cellulose – plant cell walls – glued together
to make rigid structure
• Chitin – cell walls of fungi, insect cuticles
Metabolic
• Energy source – respiration of glucose
• Energy store
– Starch in plants
– Glycogen in animals
14. 14
Lipids [fats]
• Chemical Elements C, H, O
• Glycerol + 3 fatty acids
• Fat solid at RTP
• Oil liquid at RTP
• Lipids rich in saturated fatty acids [found
mainly in animal fats] are associated with
heart disease
• Sources – meat, milk, butter, cheese,
olives, maize, sunflower seeds
16. 16
Roles
Structural
• Phospholipid forms plasmalemma
• Insulates organs e.g.kidney
• Cuticle of leaves
Metabolic
• Storage of excess carbohydrate
• Energy by respiration
• Hormones – some are lipids
• Stores fat soluble vitamins e.g. D
17. 17
Other
• Heat Energy store – twice energy of
carbohydrates per gram
• insulation – sub-cutaneous layer
• Protection – pads on feet and hands
• Waterproofing – sebum on hair and skin
• Storage – adipose tissue
18. 18
Vitamins
• Non-protein substance required in tiny
amounts for healthy metabolism
• Vitamin C [Ascorbic Acid]
• Water soluble
• Found in fresh fruit [citrus] and
vegetables
• Deficiency disease [caused by lack of] –
scurvy – bleeding gums and poor wound
healing
21. 21
• Vitamin D [caliciferol]
• Fat soluble
• Source – dairy products,
liver, fish oils etc.
• Made by skin in sunlight
• Deficiency disease
• – rickets in children – bowed legs
• - Osteomalacia in adults
• Needed to absorb Ca from gut and
also tooth and bone formation
22. 22
Minerals
• Soluble inorganic salts that contain
essential elements
• 6 macro major – need in large amounts
– C, H, O, N, P and S
• 5 micro small amounts needed
– Na, K, Ca, Mg and Cl
• Trace Elements only tiny amounts needed
(mg) – Fe, Cu and Zn
23. 23
Examples of required minerals
Plants
• Ca – make middle lamella
• Mg – make chlorophyll
Animals
• Ca – bones and teeth
• Fe – Haemoglobin to transport O2
24. 24
Roles
• Present in compounds that make hard
parts of bodies
• Present in compounds that form soft
tissues
• Maintain correct fluid concentration of
cell and body fluids
25. 25
Water
• Transport medium for blood cells etc.
• Excellent solvent – good medium for
chemical processes
• Strong cohesion [ sticking to itself] and
adhesion [sticking to other substances]
– transpiration stream
• Temperature stable – needs a lot of
heat to change temperature
26. 26
• Participant in metabolic reactions
– Anabolism – removes water
– Catabolism – adds water
– Photosynthesis – uses
– Respiration – produces
• Participant in movement into and out of
cells – medium for movement
• Control of cell shape – osmosis causes
turgor pressure – guard cell opening
• Component of cytoplasm
27. 27
Hormones as regulators of
metabolic activity
• Are signal that activate specific
metabolic programs in their target
cells by
a) Influencing transport of materials
across membranes
b) Activating or inhibiting enzymes
c) Activating or inhibiting genes and
thus influence protein synthesis
28. 28
Metabolism influenced by
hormones
Insulin
• Uses
1.Uptake of amino acids and
glucose by living cells
2.Protein synthesis
3.Lipid formation
29. 29
Balanced Diet
• One that contains the correct amounts of
carbohydrates, proteins, fats, vitamins,
minerals and water.
• Depends on age, the sex of the individual
and the activities being undertaken by the
individual.
• Teenagers should intake 12000 kJ for
boys and 9600 kJ for girls per day
32. 32
Dieting
• Most people who go on a diet do so
because they are overweight.
• It usually means that the intake and
variety of food is reduced drastically.
• This is bad because it does not give a
balanced diet and the weight lost is
usually put back on very quickly.
• To lose weight you must reduce the
amount of fatty foods and eat more fruit
and vegetables.
33. • Undernourished
• Not enough food
• At its worst starvation
• Over 1/3 of the worlds population is
undernourished
• Malnourished
• The wrong proportions of the various food types
• Too much fat leads to obesity, coronary heart
disease
• Too much sugar can lead to diabetes
33
34. 34
How to loose weight
• Reduce fat intake
• Reduce alcohol intake
• Increase vegetable, fruit and cereal
intake
• Increase exercise
36. 36
Fats
Brown Paper Test
• Rub some fat [butter] on brown paper
• Rub water on another piece
• Dry paper
• If a translucent spot stays its a fat.
• [translucent means lets light through
but you can’t see through it]
37. 37
Starch
Iodine Test
• Add some iodine solution
[brown] to the suspected starch
e.g. bread and potato.
• If it goes from brown to
blue/black then starch is present
38. 38
Proteins
• Place sample in test tube [albumen]
• Add sodium hydroxide solution and mix
• [caution sodium hydroxide solution is
caustic - burns skin]
• add a few drops of copper sulphate
solution.
• If it turn from blue to purple/violet then
protein is present
39. 39
Reducing Sugars
• Place some glucose in a test tube
• Dissolve in water
• Add Benedict’s Solution [or Fehling’s
solution A +B and mix] which is blue
• Place in a hot water bath at <100oC
for 3 minutes
• If it turns red/orange then glucose [ a
Reducing Sugar] present
40. 1. Give 4 functions of food
2. Test for starch
3. Elements present in proteins
4. Test for protein
5. Two elements with ratio 2:1 in carbohydrates
6. Test for reducing sugars
7. Name a water [fat] soluble vitamin, its source
and a disease caused by a lack of it.
8. What are these types of diseases called?
40
41. 9. Test for fats
10.Give the uses of roughage.
11.What is a balanced diet?
12.What does malnourished mean?
13.What is a fat composed of?
14.Fat / oil
15.Saturated – source and difference
16.Macro, micro and trace elements.
17.What is a trace element?
18. two examples of minerals needed by (a)
plants and (b) animals and what each does
41
42. Answers
1. Give 4 functions of food [4] energy / material
source / continuity / metabolism
2. Test for starch [4] add iodine / starch present
brown / to blue-black / absent stays brown
3. Elements present in proteins [6] C, H, O, N, S,
P
4. Test for protein [3] add biuret reagent / blue to
lilac if present
5. Elements in carbohydrates with ratio [4] C,H,O
/ 2H : 1O 42
43. 6. Test for reducing sugars [4] Benedict’s / heat
gently / blue / to red pptte
7. Name a water [fat] soluble vitamin, its source
and a disease caused by a lack of it. [3] C,
citrus fruits, scurvy
8. What are these types of diseases called? [1]
deficiency
43
44. 9. Test for fats [3] brown paper / permanent /
translucent spot
10.Give the uses of roughage [3] prevent
constipation / eases digestive transit / absorbs
water / prevents cancer
11.What is a balanced diet? [2] All nutrients / in
correct amounts
12.What does malnourished mean? [3] Too much
or too little / of one or more / food types
13.What is a fat composed of? [3] Glycerol / 3 /
fatty acids
44
45. 14.Difference between fat and oil [3] fat solid /
oil liquid / room conditions
15.Saturated – source and difference [2] animals
/ forms cholesterol
16.List [7] (a) Macro, C H O N S P (b) micro Na K
Ca Mg and Cl (c) trace elements Fe, Cu, Zn.
17.What is a trace element? [2] Only needed / in
tiny amounts
18. Two examples of minerals needed by [8] (a)
plants Mg, Chlorophyll Ca Pectate and (b)
animals Fe Haemoglobin Ca Bones and teeth45
