2. Nutrition (Humans)
Learning objectives:
Be able to identify the sources and describe the functions of carbohydrate,
protein, lipid (fats and oils), vitamins A, C and D, the mineral ions calcium
and iron, water and dietary fibre as components of the diet.
Be able to describe the structure and function of the human alimentary
canal.
Be able to understand the role of digestive enzymes.
Be able to investigate the energy content in a food sample.
Starter:
1. Write the word equation for photosynthesis?
2. Describe the role of the Palisade mesophyll
layer?
3. Explain the relationship between light
intensity and the rate of photosynthesis?
3. From the specification
(e) Nutrition
Humans
2.24 understand that a balanced diet should include appropriate proportions of carbohydrate,
protein, lipid, vitamins, minerals, water and dietary fibre
2.25 identify the sources and describe the functions of carbohydrate, protein, lipid (fats and oils),
vitamins A, C and D, the mineral ions calcium and iron, water and dietary fibre as components of
the diet
2.26 understand how energy requirements vary with activity levels, age and pregnancy
2.27 describe the structure and function of the human alimentary canal, including the mouth,
oesophagus, stomach, small intestine (duodenum and ileum), large intestine (colon and rectum)
and pancreas
2.28 understand how food is moved through the gut by peristalsis
2.29 understand the role of digestive enzymes, including the digestion of starch to glucose by
amylase and maltase, the digestion of proteins to amino acids by proteases and the digestion of
lipids to fatty acids and glycerol by lipases
2.30 understand that bile is produced by the liver and stored in the gall bladder
2.31 understand the role of bile in neutralising stomach acid and emulsifying lipids
2.32 understand how the small intestine is adapted for absorption, including the structure of a
villus
2.33B practical: investigate the energy content in a food sample
5. Food group Source Function
Carbohydrates Rice, pasta, potato Release of energy through respiration
Proteins Meat, fish, nuts, beans Growth and repair
Lipids Butter, milk, eggs, olive oil or
sunflower oil
Are a store of energy
Vitamin A Carrots, liver, butter Vision, healthy skin and strong
immunity against infection
Vitamin C Citrus fruits, broccoli Heal wounds and maintain healthy
connective tissue
Vitamin D Eggs, oil fish, humans can make
vitamin D when our skin is exposed to
sunlight.
Maintain healthy bones and teeth
Calcium Milk, egg, cheese Maintain healthy bones and teeth, for
normal blood clotting and to control
muscle contractions
Iron Red meat, beans, nuts, liver To produce haemoglobin, found in red
blood cells
Water Food and drink Regulate body temperature, transport
Fibre Fruit, vegetable, cereals Provides bulk, which helps the walls of
the intestine move food and faeces
along the gut
6. Energy requirements
Age, activity levels and pregnancy are factors that effect
the amount of energy we need.
As you grow older the
energy you need increases
as you reach adulthood.
7. Energy requirements
A pregnant women needs more
energy as she is carrying more
mass. The more mass a person is
carrying the higher the energy
content.
8. Energy requirements
Sedentary people
need less energy than
those people who are
active.
For example, an adult
office worker might
need 10,000 kJ per day,
but a manual worker
might need 15,000 kJ
per day.
9. Digestive system
Digestion is the chemical and
mechanical breakdown of food.
It converts large insoluble
molecules into small soluble
molecules, which can be
absorbed into the blood.
The alimentary canal (or gut)
is the digestive tract that runs
from the mouth to the anus.
Mouth Oesophagus
Stomach
Small
intestine
Duodenum
ileum
Large
intestine
Rectum
Colon
Pancreas
10. Mouth
Is where food enters
the alimentary canal, it is
involved in the mechanical
digestion of food. It is here
where saliva containing
amylase is added, that begins
the digestion of carbohydrates.
11. Oesophagus
Is a muscular tube
which moves food to
the stomach.
Movement along the
alimentary canal
happens via muscular
contractions called
peristalsis.
17. Stomach
Is a muscular organ, which
churns food breaking it
down. The stomach contains
hydrochloric acid and
enzymes (pepsin) that
aid the breakdown of food.
18. Bile
Bile is an alkaline
substance produced by
the liver and stored in the
gall bladder.
Food leaving the stomach
is acidic after being in the
stomach. However, the
enzymes in the small
intestine work better in
alkaline conditions. Bile
neutralises stomach acid
and emulsifies fat.
19. Emulsification
Bile turns large fat droplets into smaller droplets which
creates a larger surface area for lipases to work on.
Bile contains sodium hydrogencarbonate, which is an alkali.
21. Small intestine
At the duodenum (the first section of the small
intestine) more enzymes breakdown carbohydrates,
proteins and fats into smaller molecules.
At the ileum, which is the final section of the intestine,
any food still not absorbed, is absorbed into the blood.
The small intestine is made up of the finger-like
structures called villi.
Villi are very good at absorption because they have a
large surface area, very thin walls and a strong network
of capillaries surrounding them.
Microvilli
22. Large intestine
• In the colon, water is
absorbed back into the
body.
• The remaining undigested
food is called faeces;
this passes towards
the rectum where it is
stored before being
released via the anus.
23. Digestive enzyme
Enzyme Organ/gland where
the enzyme is
produced
Substrate End- products
Protease Stomach, pancreas Protein Amino acids
lipase Pancreas Lipids Fatty acids and glycerol
Maltase Small intestine Maltose Glucose
Salivary amylase Salivary glands Starch Maltose
Pancreatic amylase pancreas Starch Maltose
24. Calorimetry
Method:
1) Pour 20 cm3 cold water into a
boiling tube.
2) Set up your apparatus, as
shown in the diagram.
3) Record the start temperature.
4) Record the mass of your food
sample.
5) Heat the food until it catches
fire.
6) Heat the water using the flame
from the burning food.
7) Record the final temperature.
Investigate the energy content
in a food sample
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25. Model results
Food sample Mass of food
(g)
Start
temperature
End
temperature
Energy
transferred (J)
Energy
content of
food (J/g)
Pasta 0.20 22 37 1260 6300
Wotsits 0.48 22 45 5628 11725
Bread 0.21 22 35 1092 5200
Energy transferred (J) = mass of water (g) × 4.2 (J/g°C) × temperature
increase (°C)
Energy in food per gram (J/g) = mass of water (g) × 4.2 (J/g°C) × temperature
increase (°C)
Mass of food (g)
1 cm3= 1g
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Corepractical6
26. Worked example
Food: Wotsits
Mass of food= 0.48 (g)
Mass of water= 20 (g)
Start temperature =22 OC
End temperature =45OC
To work out the energy transferred use the equation:
Energy transferred (J) = mass of water (g) × 4.2 (J/g°C) × temperature increase (°C)
Energy transferred (J) = 20 (g) × 4.2 (J/g°C) × (44-22°C)
=5628 J
To work out the Energy in food per gram use the equation:
Energy in food per gram (J/g) = mass of water (g) × 4.2 (J/g°C) × (44-22°C)
Mass of food (g)
Energy in food per gram (J/g) = 20 (g) × 4.2 (J/g°C) × (44-22°C)
0.48 (g)
= 11725 J/g
Corepractical6
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29. Exam-style question
Describe one role of bile in digestion? (2 marks)
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30. Exam-style question
Describe one role of bile in digestion? (2 marks)
-emulsifies fats
-to give a large surface area for enzyme action
Or
-neutralises (stomach) acid
-to give optimum / alkaline conditions for lipase/enzymes to work (effectively)
