Core Ch5
Food and Humans
5.1 Modes of nutrition
1. Autotrophic nutrition
---photosynthetic (obtain food from inorganic substances)
2. Heterotrophic nutrition
---saprophytic (feed on dead organisms/non-living organic matter)
---parasitic (obtain organic food from living host)
---holozoic (feed on other organisms)
5.2.1 Carbohydrates
-reducing sugars
-taste sweet, soluble in water, form brick-red precipitate in Benedict’s test
-e.g. glucose, fructose, galactose
-non-reducing sugars
-do not taste sweet, insoluble in water
-e.g. polysaccharides like starch, glycogen, cellulose, disaccharide like sucrose
-monosaccharides join together to form disaccharides/polysaccharides by
condensation
-polysaccharides/disaccharides break down by hydrolysis
-food source: cereals, potatoes, fruits and vegetables
-Functions:
1. main energy source of body activities (1g of carbohydrate provides 17.1kJ of
energy)
---glucose is directly broken down to release energy in respiration
---disaccharides and polysaccharides are broken down into
monosaccharidesrelease energy in respiration
2. energy reserves
---excess carbohydratesglycogen stored in liver/muscles
3. a source of dietary fibre (cellulose)
5.2.2 Lipids
-Lipids dissolve in organic solvents but insoluble in water
-formed from the condensation of 3 fatty acid molecules and 1 glycerol molecule
-food source: fatty meat, seeds, nuts, milk and dairy products
-Functions:
1. energy reserves (1g of lipid provides 38.9kJ of energy)
2. stored as subcutaneous fat under the skin to reduce heat loss(act as an
insulator)
3. shock absorber to protect the internal organs
4. form cell membranes (phospholipids) & hormones (some hormones are lipid
in nature)
5. involved in transporting and storing lipid-soluble vitamins (A & D)
5.2.3 Proteins
-amino acid contains:
-a carbon atom at the centre
-an amino group
-a carboxyl group
-a hydrogen atom
-a side chain
-amino acid join to form dipeptide/polypeptide by condensation,
polypeptide/dipeptide break down by hydrolysis
-polypeptide coils and folds in specific ways due to the formation of chemical
bonds between amino acids on the polypeptide3D shape of proteins (a protein
may consist of one or more polypeptides)
-Food source: meat, fish, eggs, beans, milk and dairy products
-Functions:
1. amino acids are broken down to release energy if carbohydrates and lipids are
used up (1g of protein provides 18.2kJ of energy)
2. prevent kwashiorkor---a deficiency disease
(weak muscles, swollen abdomen due to the accumulation of tissue fluid)
3. Structural proteins: for growth and repair of body tissues (e.g. muscles)
4. Functional proteins: form enzymes, hormones, antibodies
5.2.4 Minerals
(i) Calcium
-Food source: milk and dairy products, green vegetables, tofu, canned sardines
-Deficiency disease: rickets in children (soft bones, legs bend under the weight of
the body, cannot grow to normal height)
-Functions:
1. for the formation of bones and teeth
2. involved in blood clotting, muscle contraction, sending messages in the
nervous system
(ii) Iron
-Food source: beef, liver, cabbage, spinach, raisins
-Deficiency disease: anaemia (not enough haemoglobin to carry oxygen to the
brainfaint easily)
-Functions:
1. a component of the haemoglobin (a pigment in RBC that carries oxygen around
the body)
5.2.5 Vitamins
(i) Vitamin A (lipid-soluble)
-Food source: fish liver oils, liver, dairy products, vegetables and fruits containing
carotene (liver converts carotene into vitamin A)
-Deficiency disease: night blindness, drying up of cornea and skin, easy infection
of the lungs and trachea
-Functions:
1. form a pigment(which is responsible for dim light)in the retina
2. keep the skin, cornea, lining of the alimentary canal and breathing system
healthy
(ii) Vitamin C (water-soluble) (destroyed when exposed to O2 and high temp)
-Food source: fresh vegetables and fruits
-Deficiency disease: scurvy
-weak and bleeding gums
-poor healing of wounds
-small red spots on the skin
-joint pain
-Functions:
1. help the growth and repair of connective tissues
2. promote the absorption of iron
3. help the immune system work properly
(iii) Vitamin D(lipid-soluble)
-Food source: fatty fish, fish liver oils, liver, egg yolks (produced by the skin under
sunlight)
-Deficiency disease: rickets
-Functions:
1. promote the absorption of calcium and phosphate ionskeep bones and teeth
strong
5.2.6 Dietary fibre
-Food source: vegetables, fruits, wholemeal products
-Deficiency disease: constipation, colorectal cancer
-Functions:
1. add bulk to foodstimulate peristalsis
2. holds a lot of waterallow the faeces to remain softallow the faeces to pass
out easily
5.3 Food test
1. Clinistix paper test (test for the presence of glucose)
---paper turns from pink to purple if glucose is present
2. Benedict’s test (test for the presence of reducing sugar)
---brick-red ppt forms if reducing sugar (e.g. glucose, maltose..) is present
3. Iodine test (test for the presence of starch)
---iodine solution turns from brown to blue-black if starch is present
4. Grease spot test (test for the presence of lipids)
---if lipids is present: a translucent spot is observed at first, but it disappears
after immersing it in an organic solvent
5. Albustix paper test (test for the presence of proteins)
---paper turns from yellow to green if protein is present
6. DCPIP test (test for the presence of vitamin C)
---DCPIP is decolourized (from blue to colourless) if vitamin C is present
5.4.1 Food pyramid
-Definition of balanced diet: consists of all the food substances in the right
amounts and proportions
-foods are classified into six groups in the pyramid
5.4.2 Factors affecting our dietary requirements
(i) Age
---Children require a large amount of proteins, calcium and iron for building body
tissues, such as muscles, bones and teeth
---Children require the greatest amount of energy per unit body mass among all
the age groups, as they have the highest growth rate and the highest metabolic
rate
---Children’s surface area to volume ratio is the highesthighest rate of heat
losshigher metabolic rate to compensate for the heat loss
(ii) Sex
---Males require a larger amount of energy, as they have higher metabolic rate
(larger body size + more muscles)
---Males have less fat under the skinhigher rate of heat losshigher metabolic
rate to compensate for the heat loss
---Males need more proteins for the growth and repair of muscles
---Females need more iron to replace the loss of iron during menstruation
(iii) Level of activity
---physically active workers need more carbohydrate-rich food
(iv) Body status
---pregnant women need more energy and proteins for the growth of foetus
---pregnant women need more iron for the formation of foetal RBC
---Breast-feeding mothers need more nutrients intake for milk production
---Breast-feeding mothers need less iron than ordinary women as their
menstruation stops
Question bank:
1. Starch and oil are storage products commonly found in plants. Explain the
advantages of using these materials for storage.
-both starch and lipid are insoluble in water (1), therefore osmotically
inactive (1)
-oil has high energy value (1)/can provide a large amount of energy
-starch molecules are closely packed can be easily stored without taking up
much space (1)
2. In terms of water relations, explain why animal cells store glycogen instead of
simple sugars.
-glycogen is osmotically inactive/insoluble in water (1)
-accumulation of glycogen does not affect the water potential (1)
-cell will not burst due to the net influx of water by osmosis (1)
-if a cell stores too high conc of simple sugars which are osmotically
active/soluble in water (1),
-water potential of the cell will be affected (become low) (1)
-cell will burst due to the net influx of water by osmosis (1)
3. Why is vitamin D deficiency more damaging to children than to adults?
-children need more calcium and phosphate ions than adults as children
continue to grow (1) whereas adults stop growth (vitamin D promote the
absorption of calcium and phosphate ions)
-insufficient vitamin D will lead to poor bone formation/bone
deformity/rickets/soft bones/poor teeth development (1)
4. Marathon runners are usually advised by their coaches to take a
high-carbohydrate meal one day before the race. In terms of carbohydrate
metabolism, explain why this practice can be an advantage of marathon
runners.
-digestion/breakdown of high-carbohydrate meal produces a lot of simple
sugars/glucose (1)
-a lot of glycogen will be formed from the excess simple sugar/glucose (1)
-glycogen is stored in liver/muscles as energy reserve for use at the race (1)
5. Explain why a breakfast rich in cereals is preferable to a breakfast rich in
meat for a person who is going to jog for a long distance after a few hours.
-cereals contain complex carbohydrates (starch) (1), this provides an
immediate supply of simple sugars/glucose (1) for respiration to release
energy for muscular activities (1)
-meat, however, contains mainly protein and fat (1), the digested products of
which require further metabolism before they are available as respiratory
fuel to release energy for muscular activities (1)
6. Describe a food test to show fat is present in ham.
-rub a piece of ham on a filter paper (1)
-a translucent spot will remain after drying (1)
-immerse the paper in an organic solvent and the spot will disappear (1)
7. Explain how method 2 (inserting a silicone balloon into her stomach through
her mouth and filling it up with water) can help the woman lose weight.
-as the space inside the stomach is reduced,/as it is easier for the woman to
have a sense of fullness, (1)
-less food would be eaten (1)
-if the energy input is less than the energy used/energy expenditure (1)
-food/fat reserve will be metabolized to produce energylose weight (1)
8. Suggest two reasons why a diet with more vegetables may help people to
reduce the chance of becoming obese.
-the diet has high content of dietary fibre (1)
-which is indigestible/add bulk to food to give the sense of fullness (1)
-it also has low fat content (1)
-hence the overall energy intake through this diet will be lowered (1)
thus, the chance of becoming obese is reduced.
9. State and explain two considerations regarding the nutritional content of food
when you plan a healthy diet to reduce body weight.
-the overall energy intake should be less than the overall energy expenditure
(1)
-so that food reserve will be metabolized and used (1)
-the diet should also contain sufficient amount and type of nutrients (1)
-for proper functioning of body (1)
Food & Nutrition (★★★+)
Food requirements
(a) The concept of balance diet {CE 06-5, CE 07-9(b)}
-total energy intake＞＞total energy output ->> obesity/gain weight
-total energy intake＜＜total energy output ->> lose weight
(b) Energy value of different types of food/Carbohydrates as an immediate
source of energy {AL 02 PIIA-3(a)(I), AL 10 PIIB-5(c)}
(c) General functions of different types of food {DSE 14 P1-11}
(d) Long term health problem brought about by excessive intake of fat, sugar
or sodium in food {AL 99 PIIC-9}
(e) Food test {Benedict’s test, DCPIP test, Ph test for the presence of fatty
acids}
(f) Calorimeter