Download H_-_Nutrition

B1: Humans as Organisms
Nutrition (H)
Nutrition
The digestive system digests (breaks down) food and absorbs the
products of digestion into the blood stream.
Digestion is the breakdown of large, complex, insoluble, non-diffusible
food substances into small, simple, soluble, diffusible food substances so
that they can be absorbed.
In mechanical digestion the food is broken down by the chewing action of
the teeth (mastication).
In chemical digestion the food is broken down by the actions of the enzymes.
Nutrition
Absorption is the transfer of the products of digestion into
the bloodstream (or lymphatic system).
digestion
absorption
Lymph
Fats
Fatty Acids
and Glycerol
digestion
absorption
Glucose molecules
Protein
digestion
absorption
Amino acids
Blood plasma
Starch
Nutrition
Below is a partly labelled diagram of the human digestive system present in the
abdominal cavity.
The digestive system includes the gullet (oesophagus), the stomach, the liver, the
pancreas, the small intestine and the large intestine.
Add these structures to the diagram using the empty labels shown. (Click to check your
answers).
Diaphragm
Liver
Gall bladder
Small intestine
Appendix
Gullet
Stomach
Pancreas
Large intestine
Rectum
Anus
Nutrition
The digestion of starch, proteins and lipids (fats and oils) is speeded up by
the actions of enzymes. These are present in the digestive juices.
Enzyme
Where
produced
Amylases
(Enzymes
which digest
carbohydrates).
Salivary glands,
pancreas and small
intestine.
Proteases
(Enzymes which
digest proteins).
Lipases
(Enzymes which
digest fats/oils).
Stomach,
pancreas and
small intestine.
Pancreas and
small intestine.
Substrate
(What it acts
on)
Starch and
other complex
carbohydrates
such as
glycogen.
Proteins.
Fats and
oils.
Where it acts
Products of
digestion
Saliva acts in the
mouth cavity.
Pancreatic and
intestinal juices
act in the small
intestine.
Simple sugars,
for example,
glucose.
Gastric juice
containing
proteases acts in
the stomach.
Pancreatic and
intestinal juices act
in the small
intestine.
Pancreatic and
intestinal juices act
in the small
intestine.
Amino acids.
Fatty acids and
glycerol.
Nutrition
The stomach:
produces hydrochloric acid which:
kills most bacteria taken in with food;
provides the best (optimum)
conditions for the stomach
enzymes to work.
The oesophagus carries food to the stomach from the mouth cavity, where it
has been chewed into smaller pieces by teeth (mastication) and mixed with
saliva to start chemical digestion of starch.
The muscular wall of the oesophagus (and other parts of the gut) contract in
a wave-like motion (peristalsis) to move the food along.
Bacteria also reach the stomach in swallowed mucus, wafted up the wind
pipe from the lungs, by the action of cilia lining the respiratory tract.
Nutrition
The liver
produces bile which is stored in the gall bladder. It is
released into the small intestine when food enters
after digestion in the stomach.
Bile has the following functions.
• Neutralises the acid from the stomach.
• Provides alkaline conditions which are
optimum for the pancreatic and intestinal
enzymes to work efficiently.
• Emulsifies fats (breaks the large fat droplets down into
smaller fat droplets). This enables faster breakdown by
lipase enzymes.
Can you think why emulsification of fats allows faster lipase action?
Smaller droplets of fat have a larger surface area relative to volume than
large droplets of fat. A larger surface area means there is a greater area
upon which lipases can act, thus, faster digestion.
Nutrition
The gall bladder collects and stores bile secreted by the liver. When the
stomach empties its contents into the small intestine, the gall bladder contracts
and empties the bile into the small intestine.
Bile contains:
• water which acts as a solvent for digested foods and digestive juices, and
• bile salts, for example, sodium hydrogen carbonate.
Sodium hydrogen carbonate neutralises the acidity from the stomach so that
the small intestine contents are alkaline. This provides optimum conditions for the
pancreatic and intestinal enzymes to operate well.
The bile salts also lower the surface tension of fats. This emulsifies fats. This
means that large fat droplets break into many minute fat droplets. This increases
the surface area of the fat relative to its volume and so lipase enzymes can act
faster. This means that fat can be digested and absorbed more readily.
Nutrition
The contents of the small intestine remain there for about 36 hours while being
churned by muscular action and subjected to enzyme digestion.
What do you think will be in these intestinal contents?
Simple sugars, amino acids, fatty acids and glycerol. These will be mixed up
with undigested carbohydrate, protein and fat.
Absorption of most of the simple sugars, amino acids, water, salts and vitamins
occurs through the small intestine wall into the blood stream.
Fatty acids and glycerol are absorbed into the lymph.
Indigestible material, for example, fibre, and undigested starch, protein and fat
remain in the large intestine, and form faeces. These are eventually pushed
into the rectum and released to the outside via the anus. This is called
“defaecation”.
Nutrition
The small intestine is adapted to achieve maximum absorption of water, salts, vitamins and
digested foods.
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•
•
•
It has a folded inner surface to increase its surface area for absorption.
It has its surface developed into millions of small finger-shaped projections called villi.
It has many blood capillaries to absorb food into. The absorbed food is then carried in
the blood directly to the liver.
fat droplets and partly digested fat is absorbed into special ducts called lacteals. These
carry lymph (a type of tissue fluid) which is eventually returned to the blood.
List,
(1) digested foods absorbed into A,
(2) non-digested substances absorbed
Columnar epithelium
into A and
Dense capillary network (A)
(3) substances absorbed into B.
.
Lacteal (B)
(1). Simple sugars, amino acids, fatty
acids and glycerol.
Vertical section of a villus
(2). Water, salts, vitamins.
Artery from heart
Vein to liver
(3). Fat droplets and partly
digested fat.
Nutrition
Test questions on the digestive system
1. Try to complete the following table:
Substance
Action
Where found
Amylase
Digests starch to simple sugars
Protease
Digests proteins to amino acids
Stomach, pancreas, small
intestine
Hydrochloric acid
Kills bacteria, provides an acid
medium for enzymes to work
Stomach
Lipase
Digests fats to fatty acids and
glycerol
Pancreas and small intestine
Saliva, pancreas, small intestine
2. Think of three functions of bile in the small intestine.
Neutralises stomach acid, provides an alkaline medium for the enzymes to work,
emulsifies fats.
3. What substances in the human diet do not require digesting?
Water, mineral salts, vitamins.
Nutrition
•
•
•
•
•
The chemical reactions inside cells are controlled by enzymes.
An enzyme is a biochemical catalyst which can increase the rate of a
biochemical reaction.
An enzyme works faster as the temperature rises, up to a maximum called the
optimum temperature. Above this temperature, because they are made of
protein, they are broken apart (denatured) and no longer work.
Enzyme action is also affected by the surrounding pH. They work best at their
optimum pH..
Enzymes are also found outside cells, although they will have been made in
cells and then secreted. Thus digestive enzymes are found in the digestive
juices in the digestive system.
Nutrition
The graph shows the effect of temperature on the rate of enzyme action.
Mean body temperature (37oC)
In view of this graph why is it important to maintain
body temperature close to its mean value?
Rate of
enzyme
action
Because the enzymes in the body work best at the
mean body/optimum temperature. Any deviation
from the mean reduces the efficiency of enzyme
action.
Temperature
Nutrition
Under suitable conditions, a protease enzyme will digest the gelatine of
exposed developed film so that the black deposits of silver salts will fall off
the film and form a deposit at the bottom of the test tube.
This can be used as a tool to investigate the effects of temperature, or pH, or
enzyme concentration, on the action of protease enzymes.
A developed film was cut into 1 cm squares and each piece was immersed in 5cm3 of a
pH 4.0 buffer solution.
The test tubes were placed in ice and waterbaths at 10oC, 20oC, 30oC, 35oC, 40oC and
50oC to acclimatise.
5cm3 of temperature acclimatised 1% protease solution was then added to each tube
and the contents mixed.
Controls were also set up and temperature acclimatised. 5cm3 of distilled water was
added to the controls instead of protease solution.
The tubes were left to incubate for 10 minutes and then observed for black deposits of
silver salts.
Try to complete the table of results on the next slide.
Nutrition
Temperature oC
Clarity of film/amount of
deposit
Explanation
0
Film black, no deposit.
Temperature too low to enable
enzyme activity.
10
Film black, trace of deposit.
20
Film showing a few clear
areas, small deposit.
30
Film showing mostly clear,
large deposit.
As temperature is increased
the rate of enzyme action
increases and so progressively
more deposit is formed and the
film becomes clearer.
35
Film completely clear, biggest
deposit.
Enzyme action tends to be
greatest near the optimum
temperature.
40
Film showing some clear
areas, medium deposit.
At temperatures above the
optimum the rate of enzyme
action decreases.
50
Film black, no deposit.
Enzyme activity has ceased
due to enzyme denaturation.
All controls
Film black, no deposit.
No digestion because no
enzyme is present.
Nutrition
Food Tests:
Iodine test for starch – starch turns iodine blue/black.
Add some drops of brown
iodine solution to the food.
If it contains starch the iodine
will turn blue/black.
Nutrition
Food Tests:
Biuret test for protein – turns purple.
Add some sodium
hydroxide (NaOH)
solution and shake
with care.
Then add some dilute
copper sulphate
solution.
If the pale blue colour turns
purple there is protein
present.
Nutrition
Food Tests
Benedict’s test for simple sugars – an orange precipitate.
Add blue Benedict’s solution to food in test tube.
Orange precipitate indicates
food contains simple sugars.
Put into a water bath
HEAT
Do not heat directly!