MAKING SENSE OF
DIGESTION AND ENZYMES
IGCSE Biology
2.2 Food and Digestion
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• Can you label a diagram of the digestive system and explain
the functions of the mouth, oesophagus, stomach, small
intestine, large intestine and pancreas?
• Can you explain what the following terms mean: ingestion,
digestion, absorption, assimilation and egestion?
• What is peristalsis?
• Can you explain how digestive enzymes are used to break
down starch, protein and fat?
• Where is bile produced and stored? What are its roles?
• How do villi aid absorption in the small intestine?
• 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.
mouth
salivary gland
oesophagus
liver
stomach
gall Bladder
Small
intestine
pancreas
duodenum
ileum
colon
rectum
appendix
anus
Large
intestine
• Chemical digestion occurs when the enzyme
in the saliva breaks down starch into
.
• Mechanical digestion occurs as the teeth
break the food down into smaller chunks. This
gives a larger surface area for the enzymes to
work.
• The chewed lump of food passes from the
mouth into the stomach via a tube called the
oesophagus or gullet.
• The food is now referred to as CHYME
Oesophagus
• The food is held in the stomach for several hours.
• Mechanical digestion occurs as the muscular stomach wall
churns up the food.
• The stomach wall secretes
which kills
bacteria to protect us from food poisoning.
• A protease enzyme called
breaks down protein in the
stomach into amino acids.
• A sphincter holds the food in the stomach until it is ready to
be released into the first part of the small intestine called the
duodenum.
• Several enzymes are added into the duodenum by the
pancreas in the form of a liquid called pancreatic juice.
• These include:
,
and
.
• Also added at this stage is
.
• Bile is made in the liver and stored in the
.
• Bile is not an enzyme. It’s function is to
large
lipids.
• This means they become small fat droplets which
increases the surface area for the enzyme lipase to work.
• Bile and pancreatic juice are both alkali in order to
neutralise the food covered in stomach acid.
• Food moves along the gut by a process called
.
• The gut has two layers of muscle, one is
and
the other is
.
• They work together to push the food along like a
squeezing wave.
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• By this stage the food has been broken down
fully into small enough molecules to be
absorbed into the blood.
• The ileum is adapted for this process.
• It has a very large surface area due to
and
.
Villi: contains adaptations to increase the rate of absorption
(diffusion)
2.
3.
Has a ___________ ___________ ___________ to increase rate of
diffusion into blood
___________ ___________ of ___________ that increases the rate
of diffusion
Contains a ___________ that absorbs ___________ & ___________
4. Has a network of ___________ ___________ that allow for faster
diffusion of digested food into the ___________
The food molecules get transported in the blood to the tissues
where they get ___________ into cells.
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1.
VILLI adaptations
• The first part of the large intestine absorbs water.
• This is called the
.
• All that is left is indigestible fibre which is called
faeces.
• This is stored in the rectum and expelled through the
anus. This is called
.
Term
Definition
Ingestion
Food is taken into the mouth.
Digestion
Food is broken down from large insoluble molecules to small soluble
molecules. This can be done mechanically and chemically.
Absorption
Molecules diffuse into the blood.
Assimilation
Molecules are used by the body for various processes such as building
or repairing cells.
Egestion
Undigested food leaves via the anus.
Enzyme
Location
Breaks down
Into
Amylase
Saliva/Small
Intestine
Starch
Maltose
Pepsin
Stomach
Protein
Amino Acids
Trypsin
Pancreatic
Juice
Protein
Amino Acids
Maltase
Small Intestine
Maltose
Glucose
Lipase
Pancreatic
Juice
Lipids
Glycerol and
Fatty Acids