IGCSE Biology Nutrition Revision

1. Nutrition
iGCSE Biology

2. Learning Outcome 1
• Explain in simple terms why food is
required by animals.

3. You are what you eat!!
• In this lesson you will
– Look at what is a balanced diet
– Carry out food tests on
• Starch
• Glucose
• Protein
• Fat
– Discuss what happens if you don’t eat
a balanced diet

4. Balanced Diet

5. What is a balanced diet?
• Your diet must include five groups of
food substances
– Carbohydrates, fats, proteins, minerals
and vitamins
• It must also include water and fibre.
• A balanced diet is a diet that
provides enough of these
substances in the correct
proportions to keep you healthy.

6. Carbohydrates
• Carbohydrates give us
energy.
• Chemical elements – C, H
and O.
• Starch is made from simple
sugars.

7. Testing for glucose
1. Pour some glucose solution into a
test tube
2. Add a few drops of benedict's
solution
3. Heat in a water bath

8. Testing For Starch
• Put a few drops of
starch solution on a
spotting tile.
• Add a few drops of
iodine.

9. Proteins
• Proteins are needed for
growth and repair.
• Proteins are made from
amino acids
• Chemical elements – C, H,
O, N (and S)

10. Testing for Proteins
1. Put 2 ml of protein
solution in a test tube
2. Add 2ml of Biurets
reagent

11. Fats
• Fats are an energy store,
protecting vital organs and
providing insulation.
• Fats contain C, H and O
• Fats are made from a
glycerol molecule and three
fatty acids.

12. Testing for fat (the emulsion
test)
• Add a few drops of cooking oil into
a test tube
• Add 2cm3 ethanol and shake
• Add 2cm3 water and shake again.

13. Nutrients

14. Learning Outcomes
• list the chemical elements that make up:
– carbohydrates
– fats
– Proteins
• Describe the synthesis of large molecules
from smaller basic units
• list the principal sources of, and describe
the importance of carbohydrates, fats,
proteins,.

15. Quick Revision
• A balanced diet must contain all the
essential nutrients in the correct amounts
and proportions.
• The nutrients needed are
–
–
–
–
–
–
–
Carbohydrate
Fat
Protein
Vitamins
Minerals
Fibre
Water.

16. Main Nutrients
Nutrient
Elements
present
Use in body
Good food
sources
Carbohydrate
Carbon,
hydrogen,
oxygen
Source of
energy
Rice, potato,
bread
Fats and oils
Carbon,
hydrogen,
oxygen
Source of
energy
Insulation
Butter, milk,
cheese, egg
yolk
Protein
Carbon,
hydrogen,
oxygen,
nitrogen
Growth and Meat, fish, eggs,
tissue repair soya, milk

17. What you really need to
remember!!
• Carbohydrates, fats and proteins
are all made up of the elements
carbon, hydrogen and oxygen
• Proteins always contain nitrogen
and sometimes sulphur
• One way to remember this is
– Carb O Hydrate

18. Carbohydrates
• Large carbohydrates molecules
such as starch and glycogen are
made up of long chains of smaller
units, e.g. monosaccharides
(glucose), which are held together
by chemical bonds

19. Fats
• Fats are made up of three fatty
acids and a glycerol

20. Proteins
• Proteins are made up of long chains
of amino acids

21. Food Tests
• What is the test for starch?
• What is the test for glucose?
• What is the test for protein?
• What is the test for fats?
• What does a positive result look like?

22. Learning Outcomes
• list the principal sources of, and describe
the importance of:
–
–
–
–
vitamins (C and D only)
mineral salts (calcium and iron only)
fibre (roughage)
water
• describe the deficiency symptoms for:
– vitamins (C and D only)
– mineral salts (calcium and iron only)

23. Vitamin C
• Function
– Maintain healthy skin and gums
• Good Food Source
– Citrus fruits, black currants, cabbage,
tomato, guava, mango
• Effect of deficiency
– Scurvy
• Bleeding under skin
• Bleeding gums

24. Vitamin D
• Function
– Needed to maintain hard bones
– Helps absorb calcium from small
intestine
• Good Food Source
– Milk, cheese, egg yolk, fish liver oil
– Made in skin when exposed to sunlight
• Effect of deficiency
– rickets

25. Calcium
• Function
– Healthy teeth and bones
– Normal blood clotting
• Good Food Source
– Milk, cheese, fish
• Effect of deficiency
– Rickets
– Slow blood clotting

26. Iron
• Function
– Formation of haemoglobin in red blood cells
• Good Food Source
– Red meat, liver, kidney, eggs, green
vegetables (spinach), chocolate
• Effect of deficiency
– Anaemia
• Constant tiredness
• Lack of energy

27. Fibre
• Function
– This is cellulose which we can not digest
– It adds bulk to the undigested food in the
intestines, maintaining peristalsis
• Good Food Source
– Vegetables, fruit, wholemeal bread
• Effect of deficiency
– Constipation
– Long term deficiency may lead to bowel
cancer

28. Water
• Function
– Formation of blood, cytoplasm
– Solvent for transport of nutrients and
removal of waste
– Enzymes only work in solution
• Good Food Source
– Drinks, fruits, vegetables
• Effect of deficiency
– dehydration

29. Pupil activity
• Design a mind map to summarise
the information you have been
taught so far on Nutrients.

30. Main
Nutrients
fibre
vitamins
Nutrients
water
minerals

31. Learning Outcomes
• describe the use of microorganisms
in the food industry, with reference
to yoghurt, bread and single cell
protein
• describe the uses, benefits and
health hazards associated with food
additives, including colourings

32. Micro-organisms in the food
industry
• Micro-organisms are heterotrophic – they
take in ready made foods molecules from
their environment.
• Examples of Microbes useful in food
production
– Acetobacter – vinegar production
– Lactobacillus - yoghurt and cheese
production
– “ripening” bacteria in cheese production
– Fusarium and mycoprotein

33. Use of micro-organism
process
Use of microorganism
Baking
Yeast is mixed with flour, sugar and water to make dough. The
yeast respire the sugar and produce pockets of carbon dioxide
that makes the dough rise.
When the bread is baked the yeast is killed.
Brewing
Yeast respires sugar to form ethanol and carbon dioxide. The
ethanol makes the drink alcoholic and the carbon dioxide gives
the drink its fizz. The process is called fermentation.
Yoghurt
making
Bacteria are used to ferment milk at 46oC. As a result lactic acid is
produced which makes the milk lumpy (coagulate). The
temperature is then reduced to 5oC to prevent further bacterial
action. The whole process is carried out in sterile conditions
Single-cell
protein
This is a protein produced by microorgansism such as bacteria.
Fungi or unicellular algae in a fermentation vessel. While the
product contains 72% protein it does not taste very nice and is
expensive to produce. An alternative is quorn – this is a
mycoprotein made from a filamentous FUNGUS, which has 12.2%
protein, low fat content and 6% fibre.

34. Food Additives
• Food Additives are substances with
no nutritional value
• They are added to improve the
–
–
–
–
Appearance
Flavour
Texture
Storage properties of food

35. antioxidants
• Stop food reacting with oxygen,
which may spoil the taste of the
food or change it’s colour

36. Colourings
• Improve the appearance of food
• Some colourings can be hazardous
– Sunset yellow
• Hyperactivity
• Allergic reactions and asthma

37. Flavourings
• Enhance the taste of the food
– MSG – monosodium glutamate in
processed food
– Sugar
– Artificial sweetners e.g. aspartame

38. Preservatives
• Give processed foods a longer shelf
life by preventing the growth of
micro-organisms
• Disadvantages of preservatives
– Sulphur dioxide - destroys vitamin B1
– Sodium nitrite - carcinogen

39. Progress Question
• Learn the groups of food preservatives listed
below.
•
•
•
•
Antioxidants
Colourings
Flavourings
Preservatives
• For each group state:
– Its function in processed food
– One advantage of its use
– One disadvantage of its use
• Use page 46 and 47 in your textbooks to help
you

40. Learning Outcomes
• describe tests for:
–
–
–
–
starch (iodine solution)
reducing sugars (Benedict's solution)
protein (biuret test)
fats (ethanol)
• Applying knowledge on food tests
to identify unknown liquids

41. Activity
• Use your knowledge of food tests
from last week to identify the food
groups found in solutions A, B C and
D.

42. Learning Outcomes
• understand the concept of a
balanced diet
• describe:
– a balanced diet related to age, sex
and activity of an individual
– the effects of malnutrition in relation to
starvation, coronary heart disease,
constipation and obesity

43. What happens if you don’t
eat a balanced diet.
What is this cartoon
trying to demonstrate?
Can you think of any
examples of health
problems that arise
from not eating a
balanced diet?
Give three examples and
explain the effects on
health.

44. Dietary requirements
• Adequate diet
– Provides sufficient energy for the
performance of metabolic work
• Balance diet
– Provides all the dietary requirements in
the correct proportions
• 1/7 fat
• 1/7 protein
• 5/7 carbohydrate

45. Dietary requirements
• Energy is provided by fat and carbohydrate
intake
• Dietary requirements depend on
– Age
• Energy demand increases until we stop growing
– Sex
• Males use up more energy than females
– Activity
• Physical work will use up more energy than office work.

46. An Unbalanced diet
Malnutrition
• An unbalanced diet could lead to
– Obesity
• Risks include coronary heart disease and diabetes
– Too much animal fat can lead to high
cholesterol
• Risks include coronary heart disease and angina
– Lack of protein in diet can lead to kwashiorkor
– Lack of fibre can lead to constipation and
bowel cancer
– Vitamin and mineral deficiencies

48. Pupil Activity
• Calculating BMI
• Follow the instructions on the sheet
to calculate your own BMI
• Answer the questions

49. Learning Outcomes
• Describe the effects of alcohol and
the dangers of its misuse

50. Effects of alcohol
• Alcohol is a drug
– It affects the nervous system
– Depressant
– Affects judgement and reaction time

51. Effects of Alcohol
• In small amounts
– Feeling of relaxation
• In larger amounts
–
–
–
–
–
Affects balance
Dizziness
Slurred speech
Problems with vision
unconsciousness

52. Alcohol
• Long term effects
–
–
–
–
–
Addiction – alcoholism
Cirrhosis of the liver
Stomach ulcers
Cancers of the digestive system
Heart disease
• Drinking during pregnancy
– Can affects the fetus
– Increasing risk of miscarriage
– Decreasing the average birth weight

53. Pupil Activity - BINGE
• Read through the information provided
• Should pubs stop cutting prices
– Write a paragraph on what you think
– Write a paragraph from the point of view from
one of the six characters.
• Remember whether or not you are for the
scheme or against it you must give
reasons.

54. Learning outcomes
• discuss:
– the problems of world food supplies
– the problems which contribute to
famine

55. Famine
• A severe shortage of food can lead to
famine.
• Malnutrition
– Suffer from deficiency disease
– weakened immune system
• Results in
– Adults too ill to work
– Children become ill, adults care for them
– People die and society lacks experience and
knowledge

56. Problems that lead to famine
• unequal distribution of food
– Some areas produce more food
• environment is more suitable
• More advanced agriculture
– Food surpluses can not always be moved to
areas where food is limited
• Drought
– Water is essential for plant growth and for
healthy animals
– Low rainfall reduces crop yield.

57. Problems that lead to famine
• Flooding
– Unpredictable flooding can reduce crop yield
– Plants are damaged
– Fertile soil can be washed away
• increasing population
– Need for food increases
– More buildings reduces land available
– More domestic animals reduces land
available for food production

58. Prep - Questions on Energy
• For Wednesday
– Question 1
• For Friday
– Questions 2, 3 and 4

59. Digestion

60. Learning Outcomes
• identify the gross structure of the
alimentary canal and associated
organs (mouth, oesophagus,
stomach, small intestine: duodenum
and ileum, large intestine: colon and
rectum, anus, pancreas, liver)
• define ingestion, digestion,
absorption, assimilation and
egestion

61. What happens to the food
we eat?

62. The gut as a production line

63. What happens to the food we
eat?
• Ingestion
– Intake of food into the mouth
• Digestion
– Breaking down large, insoluble food
molecules into smaller soluble ones
using enzymes

64. • Absorption
– Digested food molecules pass across
the wall of the small intestine into the
blood or the lymph
• Assimilation
– Uptake of food molecules by cells

65. • Egestion
– Passing out of undigested food, in the
form of faeces, from the anus
• Deamination
– Removal of nitrogen containing part of
an amino acid as urea.

66. Pupil Activity
• Label the diagram of the digestive
system.
– Use the textbook supplied to help if
needed
– Design a table to link the structure and
function of different parts of the
digestive system.

67. mouth
tongue
Salivary glands
oesophagus
trachea
liver
stomach
Gall bladder
Small
Duodenum
intestine ileum
appendix
pancreas
Large
colon
rectum intestine
anus

68. Learning Outcomes
• define ingestion, digestion,
absorption, assimilation and
egestion
• describe the functions of the
alimentary canal's various parts in
relation to ingestion, digestion,
absorption, assimilation and
egestion of food

69. Learning Outcomes
• identify the types of human teeth
and describe their functions
• state the causes of dental decay
and describe the proper care of
teeth

70. Digestion
• Digestion is the breakdown
of large, insoluble food
molecules into small,
soluble food molecules so
that they can be absorbed
into the blood stream.

71. Feeding in mammals
• Mechanical digestion
– teeth are used to bite pieces of food
and to chew it into smaller pieces
• The shapes of teeth are suited to
their function.
– Incisors and canines are used for biting
– Premolars and molars are used for
chewing and crushing food.

72. Human Jaw

73. teeth
• There are different types of teeth, each
specially shaped to perform a particular
job.
– Incisor
• A broad flat sharp tooth found at the front of the
mouth. Designed for biting and cutting food.
– Canine
• A sharp pointed tooth for piercing flesh and tearing.
– Pre-molar & molar
• A broad flat tooth with many cusps. Its rough
surface is used for crushing, grinding and chewing
food

74. Structure of a tooth
• Colour in your
diagram of the
tooth,
• Colour in the
positions of the
different types of
teeth in the
human jaw

75. Structure of a tooth
enamel
crown
root
dentine
gum
Pulp cavity
cement

76. Causes of dental decay
• Bacteria and food deposits form plaque
• Bacteria feed on sugars and produce
acid
• Acid dissolves the enamel forming a hole
• Dentine dissolves more rapidly
• If hole reaches pulp cavity can lead to
bacterial infection, toothache and
abscess

77. Proper care of teeth
• Avoid sugary foods
• Use dental floss or a tooth pick
• Use a fluoride toothpaste
• Visit dentist regularly

78. Fluoride
• Growing children absorb fluoride
from their diet
• It becomes part of enamel of
developing teeth
• Enamel becomes more resistant to
tooth decay

79. Adding fluoride to public
water supplies
• Advantages
– Tooth decay in
children
decreases
– No need to
buy fluoridated
toothpaste
• Disadvantages
– Form of mass medication
– Fluoride can cause
mottling (white patches)
of teeth
– Only benefits growing
children
– Unnecessary if proper
care of teeth is taken
– Side effects (bone
cancer?)

80. Learning Outcome
• describe the processes of chewing
and peristalsis

81. Digestion of Food
• The digestion of food can either be
mechanical or chemical.
• Mechanical digestion includes
– Chewing
– Action of muscles in oesophagus, stomach and
small intestine
• In chemical digestion enzymes catalyse the
breakdown of larger food molecules into
smaller food molecules.

82. Digestion in the mouth and
oesophagus
• Chewed food is mixed with saliva in the
mouth
• Saliva contains
– Amylase is an enzyme which starts to digest
starch into sugars (maltose)
– Mucus helps soften the food making it easier
to swallow
• The bolus travels down the oesophagus
with the aid of peristalsis

83. Peristalsis in the gullet

84. Digestion of Starch
• Take 10ml of 1% starch solution
– Test for starch
– Test for sugars

85. Action of amylase on
starch
• Put a drop of iodine solution into all the
wells on a white spotting tile
• Add 10ml 1% starch solution and 10ml 1%
amylase solution to a test tube.
• Every minute, test the contents of the test
tube for starch.
• After 15 minutes – test the solution for the
presence of sugars
• Write a conclusion on your results

86. Learning Outcomes
• The significance of producing small,
soluble molecules
• describe:
– digestion in the alimentary canal
– the functions of a typical amylase,
protease and lipase, listing the
substrate and end-products

87. Digestion
• Digestion is the breakdown
of large, insoluble food
molecules into small,
soluble food molecules so
that they can be absorbed
into the blood stream.

88. Digestion in Alimentary Canal
• Physical Digestion
– Increases the surface area of food
• Chewing in the mouth
• Churning food in stomach and small
intestine
• Bile emulsifies fats – turns them into smaller
droplets with a larger surface area

89. Digestion in Alimentary Canal
• Chemical Digestion
– Breakdown of large insoluble molecules
into smaller soluble ones
– Enzymes act as biological catalysts –
they speed up the process
– They work efficiently at body
temperature (37OC) and at a suitable
pH

90. Digestive enzymes
• There are different types of digestive
enzyme
– Proteases break down proteins into amino acids
– Lipases break down fats into fatty acids and
glycerol
– Amylase breaks down starch into maltose
(sugar)
• Maltose is then broken down by maltase to form
glucose

91. Summary – digestive enzymes
Enzyme
Site of action substrate End products
Amylase Mouth,
duodenum
Starch
Maltose
Glucose
Protease Stomach,
duodenum
Protein
Amino acids
fat
Fatty acids
glycerol
lipase
duodenum

92. Chemical Digestion
• Hydrogen carbonate ions
– Secreted by pancreas
– Neutralises acid, enabling enzymes in small
intestine to work
• Bile
– Produced by liver, stored in gall bladder,
secreted into small intestine
– Emulsifies fats (Larger surface area for
enzymes to work on)

93. Prep
• Surface area and digestion
– Read the information
– Answer questions 1- 3
– Answer question Ho2
• A snake swallowed a mouse whole. Explain
why it took several days to digest it.

94. Learning Outcomes
• define the term catalyst
• define enzymes as proteins that
function as biological catalysts
• describe the effect of changes in
temperature and pH on enzyme
activity

95. Enzymes
• Are proteins
• Are produced by cells
• Change chemical substances into new
products
• Are “specific” to one substance
• Work best at their “optimum
temperature” (around 30 – 40oC)
• Work best at an optimum pH

96. Protein Digestion
• Protein digestion occurs in the stomach
and small intestine.
• Protease enzymes are produced by the
gastric pits in the stomach lining or by the
pancreas.
• In the stomach, hydrochloric acid is also
produced which provides the optimum
pH for trypsin to work

97. Protein Digestion
• Add 2ml of protein solution to three
test tubes.
• Number the test tubes 1, 2 and 3
1. Add 1ml HCl
2. Add 1ml Water
3. Add 1ml HCl
• Do not add the trypsin until last
1. Add 0.5ml water
2. Add 0.5ml trypsin
3. Add 0.5ml trypsin

98. Protein digestion
• Leave for 10 minutes
• Test each of the test tubes for the
presence of protein using Biurets
reagent.
• Explain your results.

99. Fat Digestion
• Milk does not dissolve in water, in the
digestive system, bile produce by the liver
(stored in the gall bladder) emulsifies fats
to give a larger surface area for enzymes
to work on.
• You are going to use phenolphthalein to
investigate the effect of bile on the
digestion of fat.

100. Fat Digestion
• Take 4 test tubes and number them
1, 2, 3 and 4.
• set up the test tubes as shown in the
table below.
Test tube
1
2
3
4
Milk
3 ml
3ml
3ml
3ml
Bile
0
0.5ml
1 ml
1ml
Water
1ml
0.5ml
0
0

101. Fat Digestion
• Add 5 drops of phenolphthalein to each
test tube
• Add sodium carbonate to each test tube
until the solution goes pink.
• Add 0.5ml of lipase to test tubes 1, 2 and
3.
• Add 0.5 ml water to test tubes 4.
• Observe your results. Try to explain what
you are observing.

102. Learning Outcomes
• define enzymes as proteins that
function as biological catalysts
• describe the effect of changes in
temperature and pH on enzyme
activity

103. Effect of temperature on
enzymes
• The optimum temperature for enzyme
controlled reactions is around 37oC
– Above optimum
• Slows reaction down
• Enzyme becomes denatured – enzyme loses it shape,
deforming the active site so that the substrate no
longer fits.
– Below optimum
• Slower reaction – lack of energy in molecules

104. Graph – effect of temperature
on the rate of enzyme activity

105. Effect of pH on enzymes
• pH of a solution is how acid or alkaline it is
• Most enzymes have optimum pH 7
• Exceptions
–
–
–
–
Pepsin
Salivary amylase
Catalase
Pancreatic amylase
pH2.0
pH 6.8
pH 7.6
pH 9.0
stomach
mouth
plants
duodenum

106. Effect of pH on enzymes
• An extreme pH can denature
enzymes – permanently altering the
active site

107. Graph - Effect of pH on
enzyme activity

108. Pupil Activity
• Question sheet on enzymes

109. Learning Outcomes
• identify the small intestine as the
region for the absorption of digested
food
• describe the significance of villi in
increasing the internal surface area
• describe the structure of a villus,
including the role of capillaries and
lacteals

110. What happens next?

111. Absorption in the ileum
• The small intestine is well designed
for absorption, it has
– Thin lining
– A good blood supply
– A very large surface area (about 9m2)

112. Villi
• Increase the surface area for absorption
• Each villus contains
– Blood capillaries that absorb glucose and
amino acids
– Lacteals which absorb fatty acids and
glycerol
• Absorption is by
– Diffusion – thin lining only 1 cell thick
– Active transport – cells contain mitochondria
to provide energy

113. Absorption in the Villi

114. The Model Gut
A model of absorption

115. “the model gut”

116. Making a model gut
• Wash a 12cm length of visking
tubing (A) in warm water.
• Tie a knot in one end
• Fill the tubing with 10cm3 of starch
and glucose solution(B).
• Wash the outside of the tubing.
• Put it into a boiling tube
containing DI water (C)
– holding it in place with a rubber
band
C
B
A

117. Model Gut Results
• In the next lesson
– Take a sample of the water in the
boiling tube
• Test the water for glucose
• Test the water for starch

118. Conclusions of the
experiment
• Draw conclusions from the
experiment, explaining what the
results were, and how the model gut
represents the real situation
• E.g. what does the water represent,
what does the Visking tubing
represent, etc.

119. Learning Outcomes
• indicate the role of the hepatic
portal vein in the transport of
absorbed food to the liver

120. Hepatic portal vein
• Transports absorbed food from the
small intestine to the liver
• After a meal, high concentrations of
glucose and amino acids are in the
blood
– The liver reduces the levels back to
normal

121. The liver
• Excess glucose arriving in the liver is
converted to glycogen for storage
• Excess amino acids can not be
stored in the body
– The liver removes these from the blood
and breaks them down to form an
energy source and urea.

122. Fat
• Fatty acids and glycerol are
absorbed into the lacteals
• Body cells take up the re-formed fat
molecules
– Used in respiration as a source of
energy
– Stored

123. Large intestine and the
elimination of waste.
• A watery mix of enzymes and
undigested food (mainly fibre)
moves into the colon.
• Water is absorbed back into the
blood stream.
• Faeces are compacted in the
rectum and egested through the
anus.

124. Pupil Activity - Diagrams
• Use your notes and your textbooks
to help you label the diagrams.
• Complete for prep.
• There are key words and phrases in
the boxes beside the diagrams to
help you.

125. The end
What do
they think
they are
looking at?