Transcript Digestion Powerpoint - School

28/03/2017
Food and Digestion
W Richards
Worthing High School
Why do we need food?
We need to consume a balanced diet which contains
a variety of food in the proportions shown in the
diagram.
The body needs:
•
Carbohydrates which
provide energy.
•
Proteins for repair and
growth.
•
Vitamins and minerals to
keep the body healthy.
Food types
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Type
Found in
Uses
Carbohydrates
Bread, potatoes, cereal
Energy
Fats
Cream, butter, milk, oil
A store of energy
Proteins
Meat, fish, eggs
Building and repairing cells
Vitamins
Vegetables, cereal
Keep things “ticking over”
Minerals
Meat, milk, cereal
Strong teeth etc
Fibre
Fruit + veg, cereal
Keeps you regular!
Water
Water!
75% of the body is water
What do carbohydrates provide?
Starchy foods contain carbohydrates, which
are
made of long chains of identical small sugar
molecules.
1 Sugar
molecule
Carbohydrate
What do carbohydrates provide?
The body has to break these large food
molecules up into smaller pieces.
The small sugar molecules are very useful. The
body can use them to make…
ENERGY
This energy is used to make the body work.
What do proteins provide?
As with carbohydrates, proteins are made of chains
of chemicals. However, instead of the chain
containing identical molecules, in protein these
molecules are different.
Protein is made up of chains of amino acids. There
are over 20 different kinds of amino acid.
Protein is used to allow the body to grow and to
repair the body.
Food tests 1
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To investigate what happens in digestion we need to be able
to test for different foods. Here are two simple tests:
1) The test for starch:
Drop some iodine onto the food. If
the iodine turns BLUE/BLACK then
STARCH is present.
2) The test for simple sugars (e..g
glucose)
Boil the food with some Benedict’s
solution. If an orange
“precipitate” appears then the
food contains simple sugars
Iodine
Food tests 2
1) The test for protein:
Add 5cm3 of dilute sodium hydroxide
followed by 5cm3 of dilute copper
sulphate. If protein is present it
will produce a purple colour.
2) The test for fats:
Shake the food with about 10cm3 of
ethanol in a test tube. Pour some
of the solution into a tube
containing water. If fat is
present the water will turn
cloudy white.
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The digestive system
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The whole point of digestion is to break down our food so
that we can get the bits we need from it…
The main foods
affected are
CARBOHYDRATES –
these are broken down
into GLUCOSE
Mechanical
digestion
Food is firstly broken down (mechanical breakdown)
into smaller parts by the teeth in the mouth. It is
then mixed with saliva and swallowed.
The
stomach
Food enters the stomach, which is basically a
muscular bag, filled with hydrochloric acid (HCl).
Two things happen here:
• Chemical breakdown of the food.
• Microbes are destroyed.
cross section of stomach
food enters
from the
gullet
muscle tissue
digested food leaves
The small intestine
Food enters the small intestine from the stomach. It passes
along the small intestine where the soluble food is taken into
the blood through the walls.
The small intestine
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This is where the “small parts” are absorbed into our blood
stream…
Everything else
passes into the
large intestine
Glucose gets
absorbed into
the blood
The large intestine
The remains of the food are then passed on to large
intestine (colon).
All that is left is waste material and water. The body will
want to leave the waste material within the digestive
system but the water is valuable and so it is re-absorbed
here.
The waste material is passed to the rectum where it is
stored until it leaves the body through the anus.
Why breakdown large molecules into smaller
ones?
The body must go through mechanical and chemical digestion
to convert large insoluble molecules into smaller soluble ones.
Carbohydrate molecule
Protein molecule
(folded up)
Sugar
Fat molecule
This is because smaller molecules can
pass through the walls of the small
intestine and then dissolve into the
blood stream. Larger molecules cannot
do this.
Enzymes
Enzymes are chemicals which break the larger molecules
down into smaller molecules. There are three types of
enzymes that you need to know about.
Enzymes
The three types of enzymes
are:
• Carbohydrase chops carbohydrates into smaller sugar
molecules.
• Protease cuts proteins into the soluble amino acids.
• Lipase breaks fats down into the smaller fatty acids and
glycerol.
Proteins
digestion
Proteins are digested in the stomach by an enzyme called
Protease. This enzyme needs to work in an acidic
environment. Protease breaks proteins (chains of different
molecules) down into up to 20 different amino acids (four of
which are shown).
Protease
Amino acids
Folded up protein chain
Starch/
carbohydrates
Carbohydrates are chains of identical sugar molecules.
The enzyme called Carbohydrase breaks the chemical
bonds between the individual sugar molecules (called
glucose) as part of digestion.
Carbohydrase
Long
carbohydrate
Small
sugar
Fats
Fats are digested in two stages:
• Firstly bile (released by the gall bladder) allows the fat to
“mix” with water by breaking the fat up into smaller
droplets. This is called emulsification.
Bile
• Secondly, an enzyme called Lipase breaks the fats down into
the smaller fatty acid molecules and glycerol.
+
Lipase
Fatty
Fat
acid
Glycerol
Enzymes
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Enzymes are chemicals produced by the body to help
_______. When they react with food they break it down
into ______ pieces which can then pass into the ______:
Carbohydrase breaks _______ (a
carbohydrate) down into glucose:
Protease breaks _______ down
into amino acids:
Lipase breaks fats (_____) down
into fatty acids and glycerol:
Words – blood, lipids, proteins, digestion, starch, smaller