Leaving Certificate
Biology Plus
Chapter 28
Human nutrition
Heterotrophic nutrition involves:
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Ingestion (taking in food)
Digestion (breaking down food)
Absorption (food entering the body)
Egestion (removing waste).
The human digestive system
In the mouth:
• The four types of teeth are incisors, canines, premolars
and molars
• The enzyme amylase digests starch to maltose.
The oesophagus:
• Is a muscular pipe
• Moves food by peristalsis.
Peristalsis is a wave of muscular action that forces food
through the intestines.
Fibre stimulates peristalsis.
Peristalsis
The stomach:
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Stores and digests food
Is a muscular bag
Churns food to make chyme
The stomach lining makes:
(i) Mucus
(ii) Pepsinogen (becomes pepsin in acid; pepsin digests
protein to peptides)
(iii) Hydrochloric acid (pH 1–2), which kills bacteria and
softens food.
The pancreas makes:
• Sodium hydrogen carbonate (neutralises acid from the
stomach)
• The enzymes (i) Amylase (starch to maltose) and (ii) Lipase
(lipid to fatty acid and glycerol).
The digestive roles of the liver:
• Makes bile, which emulsifies fat
• Makes sodium hydrogen carbonate to neutralise acid
• Stores many nutrients.
The duodenum is the main location for digestion. It makes a
range of digestive enzymes.
The relationship between the alimentary canal
and the liver and pancreas
In the ileum:
• Food is absorbed
• There is a lining of numerous
villi to increase surface area
• Glucose and amino acids are
absorbed into the bloodstream
and taken to the liver
• Fatty acids and glycerol enter
the lacteals and are
transported in lymph and
returned to the bloodstream
for distribution around the
body.
The relationship between the ileum and the liver
The appendix and caecum are vestigial
(i.e. have lost their former use).
The colon reabsorbs water from the waste, forming faeces.
The junction of the small and large intestines
Symbiotic bacteria in the colon:
(i) Make vitamins and digest
cellulose
(ii) Break down cellulose
(iii) Prevent the growth of diseasecausing organisms.
The rectum stores faeces.
TS of the colon
There are seven components of a balanced diet:
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Carbohydrate
Lipid
Protein
Minerals
Vitamins
Fibre
Water.
The amount of food a person requires depends on age,
activity, gender and health.
The four food groups and their average number of servings
per day are:
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Cereals, bread and potatoes (6+)
Fruit and vegetables (4+)
Milk, cheese and yoghurt (4)
Meat, fish and poultry (2).
The food pyramid