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Digestion
Textbook B Chp 11
Topics
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•
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Overview of Digestion
Parts & Functions of Alimentary Canal
Enzymes
Food Tests
Overview
• Big Idea: what happens when (& after) we eat
food?
• Why do we need to eat food in the first place?
– For Energy
– For growth
– For maintenance (to remain healthy)
Processes of Eating
1.
2.
3.
4.
5.
Ingestion
Digestion
Absorption
Assimilation
Egestion
ALIMENTARY CANAL
Parts of the Digestive System
1.
2.
3.
4.
5.
6.
7.
Mouth
Oesophagus
Stomach
Small Intestine
Large Intestine
Liver, Pancreas, Gall Bladder
Rectum, Anus
Alimentary Canal
Video
• Once Upon a Time…Life (Part 1)
• https://www.youtube.com/watch?v=M1PuS2NVOw
• Once Upon a Time…Life (Part 2)
• https://www.youtube.com/watch?v=M4e6qf8r
8Tk
• Once Upon a Time…Life (Part 3)
• https://www.youtube.com/watch?v=QY5q4GJ
OOgg
Mouth
• Chewing breaks up food into
smaller pieces
– Increase surface area for
digestion
• Saliva softens & moistens food
(aid digestion)
• Saliva contains the enzyme
amylase
– Amylase converts starch to
maltose
Oesophagus
• Carry food from
mouth to stomach
through the
process peristalsis
Stomach
• Many layers of muscle
surround the stomach walls
– mixes food by contraction and
relaxation of muscles
• Contains hydrochloric acid (pH
1-2)
– kills bacteria
– provides an acidic environment
for enzymes (proteases) to work
• Proteases convert protein to
amino acids
Small Intestines
• The small intestines are made up of three
parts: duodenum, jejunum and ileum
• Duodenum
– contains several types of enzymes to digest food
– amylase convert starch to maltose
– lipase convert fat to fatty acid & glycerol
– protease convert protein into amino acids
Small Intestines
• While food is in the duodenum, different
substances from other organs are also
released into the duodenum to aid digestion
– Bile
• Produced from Liver, stored in Gall Bladder, and
released to duodenum through the Bile duct
• Bile emulsifies fat, making fat globules smaller and
increasing surface area
– Pancreatic juice released from Pancreas
• Amylase, protease and lipase
Small Intestines
• The small intestines are
very long so that there is
large surface area to
absorb digested food
• The surface area is
increased further by the
presence of villi, fingerlike structures
• Greater surface area allow
for faster absorption of
digested food
Other Parts
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•
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Large Intestine (colon) absorbs water and mineral salts
Rectum stores undigested remains of food (faeces)
Anus, where faeces is expelled from the body
Did you know: colonoscopy
Physical vs Chemical Processes
• Throughout digestion, there is a combination
of physical and chemical processes
• Physical processes involve breaking food down
into smaller parts, but does not change the
nature of the food (e.g. chewing, churning,
emulsification)
• Chemical processes involve breaking food
down into different chemical components
(e.g. work by enzymes)
ENZYMES
Enzymes
• Recall: what is a chemical reaction?
• An enzyme is a catalyst, something which
speeds up chemical reactions (but is not “used
up” in the process; remains unchanged)
• The “raw material” which an enzyme works on
is called the substrate, the “end product” is
called the product
• Enzymes are made of proteins
• Enzyme activity is affected by temperature as
well as pH (acidity)
Enzymes & Temperature
• Recall in particulate model, we studied that at
higher temperatures, molecules move faster
• Enzymes and substrates collide with each
other more frequently when temperature is
raised, increasing rate of reaction
• However, if the temperature becomes too
high, the enzyme becomes denatured (i.e.
changed in shape, become useless)
• Optimum temperature around 40 °C
Enzymes & pH
• pH is a measure of acidity
• Neutral is pH7, less than 7 is acidic, more than 7
is alkali (or basic)
• Stomach has around pH 1-2 (very acidic) due to
the presence of hydrochloric acid produced by
gastric juices
• Enzymes have an optimum pH, depends on type
of enzyme (stomach protease pH 2, salivary
amalyse at pH 8, pancreatic lipase at pH 11)
Enzyme Summary
Enzyme
Location
Substrate
Product
Amalyse
Mouth (from
Starch
Salivary Glands) &
Duodenum (from
Pancreas)
Maltose
Protease
Stomach,
Duodenum (from
Pancreas)
Protein
Amino Acids
Lipase
Duodenum (from
Pancreas)
Fat
Fatty Acid +
Glycerol
FOOD TESTS
Food Tests
• There are 4 food tests you need to perform for
your lab. These tests check if there are certain
nutrients present in the sample.
1. Benedict’s test (for reducing sugars)
2. Iodine Test (for starch)
3. Emulsion Test (for fat/oil)
4. Biuret Test (for protein)
Food Test Summary
Nutrient
Test Name
Starch
Iodine Test
Glucose/Malto Benedict’s Test
se
Protein
Biuret Test
Fat/Oil
Ethanol
Emulsion
Nutrient
Present
Blue-Black
Nutrient
Absent
Remains
Brown
Remains Blue
Red-Orange
Precipitate
Violet Solution Remains Blue
White
Remains
Emulsion
Colourless
Summary
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Overview of Digestion
Parts of Alimentary Canal
Enzymes
Food Test