Transcript chemically digested.

Key Stage 4
Digestion
© Boardworks Ltd 2003
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© Boardworks Ltd 2003
The 7 food groups represent large chemicals. These
chemicals are often chains of smaller, more useful
chemicals, joined together.
One example is Carbohydrates.
Carbohydrates are made of long chains of
identical small sugar molecules.
Carbohydrate
Sugar
molecule
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The small sugar molecules are very
useful. The body can use them to make…
ENERGY
So the body has to break these large
food molecules up into smaller pieces.
However!
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Problem One
It is not enough to cut these foods up into pieces using
a knife. This would not release the sugars.
i.e. cutting a loaf of bread (carbohydrate) into slices
does not produce sugar.
This is because we can’t release sugars from
carbohydrates by physically breaking them up.
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The chain of sugars is held together by…
Chemical bonds.
Chemical bonds require a chemical
technique if they are to be broken.
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Problem 2
The food we start with is often large in size.
Being large, the food tends to be unable to
dissolve. We say it is large and insoluble.
This is a real problem. The food needs to be
soluble so that it can dissolve in the blood and thus,
be transported around the body.
The smaller the food, the more likely they will
dissolve.
So the digestive system has to cope with both
these problems.
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Remember….
The digestive system, being an organ system, is
made of a group of organs all working together.
i.e.
Each organ has a particular function but together
they get the job done.
The only visible parts of the digestive system are
the entry and exit points
Mouth
Anus
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Food looks very different when it leaves, compared to
when it enters!
Therefore the body must be doing something to the
food during its journey.
It is digested.
This means it is broken down. However, breaking
something up happens in 2 ways.
As we know all food has a physical shape and is
made of chemicals. These chemicals are held
together by chemical bonds.
© Boardworks Ltd 2003
It must be broken down using physical and
chemical methods.
physical
This allows it to
pass through the
small diameter of
the digestive
system.
To be broken down
physically, the
shape of the food
must be changed.
chemical
This allows useful
chemicals to be released
and dissolve in the blood.
To be broken
down chemically,
the bonds must
be broken.
© Boardworks Ltd 2003
Our digestive system uses both these methods of
digestion.
 Chemical Digestion
 Physical Digestion
As we move through the digestive system, we will see
one or both of these methods in action at any one
time.
So, in summary so far…
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Digestion is the chemical and physical breakdown of
large insoluble molecules into small soluble molecules.
Let’s take a close look at how this happens…
Open wide!
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All food enters our digestive system through the
mouth and waste material leaves through the anus.
Mouth
If we stretch the
digestive system out,
we can see that it is
really one long tube
with an opening at
each end. However, it
is a 9m tube!
Anus
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But how does a 9m tube fit into a space,
which is less than a metre long?
It is extremely folded !
In addition, the tube passes through organs on
its route from the mouth to the anus.
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The Digestive system
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As food moves through the system, it passes
through these organs.
Each organ has a slightly different effect on
the food.
Let’s start in the mouth.
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The mouth is where digestion begins. It is therefore
where we first meet chemical and physical methods of
digestion.
We will consider physical digestion first.
If you look in the mirror and smile, you immediately
notice your teeth.
You will also realise that your teeth are
different shapes.
You have 4 basic types of teeth.
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Each is designed to do a different job.
Premolar
Molar
Canine
Central
Incisor
Incisor
Latent
Incisor
Canine
1st Premolar
2nd Premolar
1st Molar
2nd Molar
3rd Molar
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© Boardworks Ltd 2003
The shape and size of each tooth is related to the
function they have in digesting (breaking down) food.
If we look at the teeth of other living organisms they too
have these 4 types of teeth. However, the size and
shape maybe different.
This is because
other organisms
may have a
different diet.
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Canine
Sharp pointed teeth, which are used to bite and tear food.
Incisors
Small rectangular shaped teeth, which are found between the
canines. They are used for cutting food.
Premolars
Found behind the canines and are used to grind soft food.
Molars
Found behind the premolars and are used to grind hard food.
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Together, these teeth deal with most
foods that we put into our mouths.
Although they break the food up, they do not effect the
chemical bonds. Therefore, they are physically
digesting the food.
Once the teeth have digested the food, it may be small
enough to be swallowed. However, some food can be
sharp and it would be uncomfortable to swallow. The
food also needs chemically breaking down.
Therefore, the mouth produces a substance that solves
both of these problems at the same time.
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These glands (a special
type of tissue) produce
saliva, a sticky liquid.
As mentioned, the saliva has two jobs.
Being a liquid, it softens the food and allows the digested
food to be rolled into a ball just before it is swallowed.
It also contains a chemical known as an enzyme.
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What is an enzyme?
Enzymes are chemicals, which act to speed up chemical
reactions. They are produced from glandular tissue,
which is found all over the body.
In order to understand how an enzyme works, you have
to think of it as having a particular shape.
We will use the shape below to represent on particular
enzyme.
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Somewhere on the
surface of the enzyme is
an important region
known as the active site.
Enzyme
In order for an enzyme to be able to speed up a
reaction, it must attach to the chemicals that are
reacting. It does so using its active site.
© Boardworks Ltd 2003
+
The red area on these two
reacting chemicals represents
the area where the active site
of the enzyme will attach. The
enzyme will attach to both at
the same time.
Enzymes are very specific
Enzymes can only speed up certain reactions. If the shape of
the reacting chemicals does not match the shape of the active
site, the enzyme will not be able to work.
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Therefore, enzymes are specific to certain reactions.
As well as being specific to certain reactions, enzymes are
very particular about the environment that they work in.
To understand this, think of how you do homework.
You probably have a certain place to work, or you work at a
certain time, you may like listening to music whilst you work or
else you can only work if it is completely silent.
Well, different enzymes work best in different conditions. If the
condition is wrong, their active site can change shape. One
particular enzyme works best in acidic conditions (pH less than
7). If the pH rises and the conditions become alkaline, the
enzyme changes shape and stops working. It can no longer fit
with the reacting particles of the chemical reaction.
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pH 10
Which enzymes are made by the digestive
system?
The bulk of the food that enters the digestive system is
from the three main food groups:
Proteins
Carbohydrates
Fats
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Therefore, it is not surprising that the digestive system
has glands that produce enzymes that digest these
three types of food. Remember that the shape of the
chemicals within the different food groups will be
different. Therefore the shape of the enzymes that
digest these chemicals will also be different.
This means that an enzyme that digests fats will not
be able to digest proteins.
Let us look at the chemical structure of Fats, proteins
and carbohydrates to see why they require different
enzymes for their digestion.
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Carbohydrates
As we mentioned previously, carbohydrates are chains of
identical sugar molecules. The enzyme that digests
carbohydrates must be able to break the chemical bonds
between the individual sugar molecules.
Sites of enzyme attack
Sugar
The product of the chemical breakdown of carbohydrates
is sugar. The sugar is known as Glucose.
An enzyme that digests carbohydrates is known as a
Carbohydrase.
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The digestion of carbohydrates can be represented
by the following equation.
Carbohydrase
Carbohydrates
Sugars
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Proteins
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.
© Boardworks Ltd 2003
Imagine a bead necklace made up
of over 20 different kinds of bead.
Amino Acids
Site of enzyme attack
The enzymes that digest proteins must be able to
break the chemical bonds between the different
amino acids.
An enzyme that digests protein is known as a
Protease.
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The digestion of proteins can be represented by the
following equation.
Protease
Protein
Amino Acids
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Fats
Fats are made up of a molecule of glycerol phosphate
attached to three fatty acid molecules.
The enzymes that digest fats must be able to break the
chemical bonds between the glycerol phosphates and
the fatty acids.
Fats are also known as Lipids.
Its structure can be represented using the following
diagram.
Fatty
Acids
Site of
enzyme
attack
Glycerol
Phosphate
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The enzymes that digest fats must be able to break
the chemical bonds between the glycerol phosphates
and the fatty acids.
Fats are also known as Lipids.
An Enzyme that digests fat (lipid) is known as a
Lipase
The digestion of fats can be represented by the following
equation.
Lipase
Fat
Fatty Acids +Glycerol Phosphate
© Boardworks Ltd 2003
Of these three enzymes, the only one that is released
within the mouth is Carbohydrase. This is partly because
the conditions within the mouth are suitable for
Carbohydrase action. It works best within an alkaline
(pH > 7) environment.
Let’s represent the three food groups using colours.
Carbohydrates
Fats
Proteins
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The digestive action of the mouth can be
summarised in the following diagram.
Physical
Digestion
Chemical
Digestion
The food could now
pass down either
the Trachea
(windpipe) or the
Gullet/Oesophagus.
Sugars
Chemically
and physically
digested
Physically
digested
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Swallowing and Peristalsis
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Swallowing Notes
The semi-digested food has been formed into a ball by
the tongue and is now swallowed.
The ball firstly moves to the pharynx, the region at the
back of the mouth where there is a junction between
two pipes.
It needs to pass down through the Gullet. To ensure
that it does not fall into the trachea and thus block our
breathing, a small flap moves to cover the tube.
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Swallowing Notes
The flap is known as the Epiglottis. If ever food
accidentally got into the trachea, we would choke and try
to cough it back out.
How do we swallow?
Once the ball of food has passed through the top of the
gullet, it is forced downwards by muscle contraction.
© Boardworks Ltd 2003
The swallowing process finishes with a muscle known
as a sphincter relaxing and the food passes into the
stomach.
The sphincter muscle found at the entry and exits
points of the stomach
acts rather like a
drawstring on a bag.
It allows the stomach to shut off both entry and exit
points and hold food inside it.
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The Stomach
The stomach is basically a muscular bag, filled with
Hydrochloric Acid (HCl).
cross section of stomach
food enters
from the gullet
muscle tissue
glandular tissue makes:
Hydrochloric Acid, Mucus
and Protease enzyme
digested food leaves
liquids mix with the food
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When the food enters the stomach.
The sphincter contracts behind it.
The food is then subjected to
a coordinated attack.
Firstly the
the hydrochloric acid
…attacks any microbes
(bacteria) that may have
been swallowed
accidentally when the
food was eaten.
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Secondly, the hydrochloric acid provides the perfect
conditions for
Protease Enzyme
…to work in. These enzymes begin digesting the proteins in
the swallowed food.
These proteins are broken down to release the amino acids.
Protein
Protease
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Protease enzymes work best under acidic conditions
(pH < 7)
Amino Acids
Thirdly, the muscular tissue of the stomach has the ability to
contract and relax and in doing so, physically grinds the food
inside it.
The mucus is produced to protect the lining of the stomach
from the acid. If the mucus were not present, the hydrochloric
acid could actually digest the tissue that had made it.
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Presence
of HCl
Wall of
stomach is
protected
Muscle and
Glandular
tissue
Layer of
Mucus
The hydrochloric acid, mucus, food and enzyme solution is
given the name, Gastric Juice.
© Boardworks Ltd 2003
A summary of the digestive action of the stomach can be
represented in the diagram below.
Protein
Sugar
Fat
Carbohydrate
Physical
Digestion
Chemical
Digestion
Muscular tissue
of stomach
Protease enzyme
and Hydrochloric
Acid
Sugars
Carbohydrates
Fats
Amino
Acids
Proteins
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It is clear that the large insoluble foods are slowly being
digested to produce the small soluble foods.
Carbohydrates
Amino Acids
Proteins
It is also clear that the Fat has yet to be chemically
digested.
This happens in the next section of the digestive system.
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The Small Intestine
The name of this organ is deceiving. Although it is
called small, it can stretch up to 6 metres in length. In
order to fit into the body, it is heavily folded.
When the gastric juices
leave the stomach, they
pass into the small
intestine.
small intestine
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Problem!
The gastric juices are acidic! There could be a
danger of the lining of the small intestine being
digested.
Luckily two substances
are produced to stop
this happening. The
first is mucus and we
have seen how this
works. The second is
Bile.
Bile is made in the Liver. It is a yellow/green
liquid that is naturally alkaline (pH > 7).
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This means that when Bile and the Gastric
Juices meet,
…the result is neutralisation of the acid.
pH >7 +
pH <7
Neutralisation
This is essential for the lipase (the enzyme that
digests fat) to function properly.
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Part of the Small Intestine
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Let’s consider the process of fat digestion.
This section of the digestive system exemplifies the
true idea of an organ system as a group of organs
working together for a common function.
The influential organs in the digestion of fat are the:
Liver
Gall bladder,
Pancreas
Small intestine.
Each organ plays its part in turning Fat into fatty acids
and glycerol phosphates
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Liver produces
Bile
Fat within the
gastric juice
It is released from the Gall
bladder and passes down
through the bile duct
The Bile and the fat meet within the small intestine.
The Bile emulsifies the fat. This basically means the
fat is physically broken into smaller pieces.
Emulsification
Notice that the fat has not been chemically digested, only
physically. The result is a greater surface area over which the
enzyme, lipase, can attack the fat.
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small
intestine
The pancreas and
the small intestine
now release
enzymes. Both
organs produce all
three enzymes,
Carbohydrase,
protease and lipase.
pancreas
If we just consider fat, the
lipase begins to break its
chemical bonds.
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Lipase
Glycerol
Phosphate
Fat
Fatty
Acids
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In summary the digestive action of the small intestine and associated
organs can be represented in the following diagram.
Fat
Sugar
Carbohydrates
Amino Acids
Physical Digestion
Bile emulsifies the
fat. Muscular action
of the small intestine
Protein
Chemical Digestion
Lipase enzyme
Protease enzyme
Carbohydrase enzyme
Sugar
Amino Acids
Fatty Acids
Glycerol
Phosphate
© Boardworks Ltd 2003
We have now digested all the large insoluble foods into
small soluble foods.
The three processes of chemical digestion can be
summarised as follows.
Large insoluble
food
Enzyme
Small soluble food.
Carbohydrates
carbohydrase
Sugars
Proteins
protease
Amino acids
Fats
lipase
Glycerol phosphates
and fatty acids.
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There is a further advantage for the small intestine in
being a narrow tube.
With the enzymes being produced in the lining of the tube,
it is essential that the food be forced to mix with them to
ensure that there is efficient digestion before the food
passes through the organ.
If the tube is tight, the food is forced against the sides of
the tube and thus, mixes directly with the enzymes.
Enzymes come into
contact with food.
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Now that the large insoluble molecules have been
digested down into the small soluble molecules, the
body must separate them from the waste food that has
not been digested.
No food is 100% useful and so there will always be
some waste that needs excreting.
In order to understand how the body carry’s out this
selection procedure, we need to take a closer look at
the lining of the small intestine.
At first glance, it appears to have a flat surface.
However, if we consider what it has to do, we will
understand why this idea cannot be correct.
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The small intestine is the site of absorption of useful
molecules of digested food.
These molecules must pass across the lining of the small
intestine and enter the blood stream.
Their destinations are
the cells of the body.
The cells constantly
need these chemicals
and therefore the
absorption process
must be very efficient
to keep up with
demand.
Energy
Therefore…..
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If the absorption process had to occur across a normal
lining, it would not be able to satisfy the demand of the
body for these soluble food molecules.
i.e. not enough molecules would pass across the lining
in the desired time.
The only way to improve this situation would be to create
a larger surface area over which absorption could occur.
That is exactly what is present in the small intestine
What looks like a normal lining, is in fact a highly folded
lining, which creates an enormous surface area in a
small space.
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The result of this folding means that
the surface area of the lining of the
small intestine is enormous!
This increases the number of places
where small soluble food molecules
can pass across and move into the
blood.
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Where is the blood?
The blood is found in minute small vessels known as
capillaries. The capillaries are found protruding into the villi.
The blood
approaches
the villus,
picks up the
absorbed
food
molecules
and then
leaves.
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Remember that the small intestine lining is made up of
thousands of villi.
Here is a summary of the process of absorption.
A
B
Sugars
S
O
R
Amino Acids
P
T
Fatty Acids
and Glycerol
Phosphates
B
L
O
O
D
I
O
N
Any indigestible food will leave the small intestine without having been
absorbed
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Let us now move on to the next organ in the system, the large
intestine (colon).
As the food enters this organ, 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.
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This water will need to be retained by the body in order to
prevent dehydration.
Remember that all the liquids you drink provide the largest
source of water for the body. All this fluid passes through
the digestive system.
Again, this is the job of the blood.
The blood reabsorbs the excess water that is mixed with
the waste food.
Again, if something is going to be absorbed, it
must have somewhere to go.
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Again, this is the job of the blood.
The blood reabsorbs the excess water that is mixed with
the waste food.
LARGE
B
L
O
O
D
INTESTINE
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Once the excess water has been reabsorbed, the waste
material then passes into a storage organ called the
rectum. This waste material mainly consists of
indigestible food. It makes up the bulk of the faeces
(solid excrement) that will be excreted.
rectum
It is stored here until the body is ready to excrete.
In order for this to happen, another sphincter muscle
must relax. This opens the anus and the faeces can pass
out of the system.
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We have now finished our journey through the digestive
system. We have seen the chemical and physical
digestion of large insoluble into small soluble food.
It is important to remember that the digestive system
relies heavily on the presence of two important types of
body tissue.
1. Glandular
Tissue
This is responsible for the
production of the digestive
enzymes.
2. Muscular Tissue
Through constant contraction
and relaxation, the food is kept
moving through the system,
from the mouth to the anus.
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Digestion
Activity one
Chew it all over
Copy and complete the following statements which summarise the topic
of digestion. In each case, choose which of the two words is correct.
Digestion is the process of breaking LARGE / SMALL
molecules of food into LARGE / SMALL molecules of food.
The LARGE / SMALL molecules we start with are
INSOLUBLE / SOLUBLE which means they CAN / CAN’T
dissolve in water.
The LARGE / SMALL molecules produced by digestion are
INSOLUBLE / SOLUBLE which means they CAN / CAN’T
dissolve in water. These molecules need to be SMALL /
LARGE and INSOLUBLE / SOLUBLE so that they can pass
through the lining of the LARGE / SMALL intestine and into
the WATER / BLOOD.
© Boardworks Ltd 2003
Activity two
Fill in the gaps in the text below.
two
“Digestion involves ___________
types of process. These
mechanical digestion and secondly _________
chemical
are firstly ____________
carried
digestion. Chemical digestion is __________
out by
enzymes which are chemical produced from
___________
glandular tissue. Specific enzymes break down
___________
specific types of food. For example ____________
carbohydrase
__________
enzyme breaks down carbohydrates
___________ . Mechanical digestion
muscle
involves teeth and the tongue but mostly ____________
contraction e.g. the squeezing of the muscular lining of the
stomach
__________.”
enzymes
muscle
carbohydrates
chemical
mechanical
glandular
specific
two
carried
stomach
carbohydrase
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Activity three
Help! Use the words below to create 3 equations to
show what happens when we digest:
1. Carbohydrates
2. Fats
3. Protein.
Carbohydrates
Fats
Amino acids
Double Sugar
Lipase
Single Sugar
Glycerol Phosphate
Glucose
3 Fatty Acids
Maltose
Protein
Protease
Carbohydrase
© Boardworks Ltd 2003
Activity four
True or False?
Work your way along the route, answering each statement
with simply ‘true’ or ‘false’. There are 15 questions.
Saliva contain
enzymes?
Blood transports the nutrients to
the needy parts of the body
Digestion turns large insoluble
molecules into small soluble
molecules
All food is digested
by the body
Nutrients are absorbed
by blood in the pharynx
Blood flows along the
digestive system picking up
nutrients
The food we eat can pass through
the digestive system in 1hr
© Boardworks Ltd 2003
The small and large intestine
basically perform the same function,
just at different speeds
Solid food must be turned to liquid
before it can be absorbed
Food is broken down by
chemical process only?
Water is mainly reabsorbed in
the small intestine.
The small intestine is
shorter than the large
intestine
Starch and sugar are
examples of
carbohydrates
The presence of villi
increases the surface
area of the small
intestine
Lipase enzyme
works best in acidic
conditions
© Boardworks Ltd 2003
Activity five
Down the Hatch!
Questions
*
*
• What type of acid is found in the stomach? (12)
• The ___________ (10) links the stomach to the
pharynx.
• The __________ (7) juices are found within the
stomach.
• What happens to the water in the large intestine?
(10)
• Where does the process of digestion actually begin?
(5)
• This organ stores waste material before it is
discharged from the body? (6)
• The _________ (6) moves the food around in the
mouth, preparing it for its journey.
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*
*
*
*
• ___________ (5) transports the dissolved nutrients
around the body.
• The first section of the digestive system is known as
the l________. (5)
• The chemicals that help to break down food are
collectively called __________. (7)
• We eat or ________ food. (6)
• This is the name for the soft fleshy part of the throat
that stops food going down the trachea.
E___________. (10)
• At the rear of the mouth, this region receives the
bolus of food from the tongue. (7)
• The main part of the small intestine is known as the
D____________. (8)
© Boardworks Ltd 2003
*
*
*
• These provide the mechanical breakdown of food in
the mouth? (5)
• This organ can be SMALL or LARGE? (9)
• The collective name for the useful chemicals that are
absorbed across the lining of the small intestine? (9)
• The product of the previous question? (5)
• The name for the muscular bag that contains acid?
(7)
• Food is __________ (7) down in the digestive
system using both chemical and mechanical
methods.
Now for the bonus 5 points
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Activity six
You will notice that 9 of the questions have a small green
asterisk beside them.
Take the first letter of each of the answers to these
questions. Put these letters in the box below.
Now rearrange them to
find the mystery word!
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Word Search
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© Boardworks Ltd 2003
Multiple choice questions
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1. Which type of tissue helps to move food
along the digestive system?
A liver tissue
B muscle tissue
C glandular tissue
D brain tissue
© Boardworks Ltd 2003
2. Which type of tissue makes digestive
enzymes?
A liver tissue
B muscle tissue
C glandular tissue
D brain tissue
© Boardworks Ltd 2003
3. Which of the following are examples of
carbohydrates?
A amino acids, glycerol
B starch, fatty acids
C sugar, amino acids
D starch, sugar
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4. What is/are the breakdown product/s of
starch?
A fatty acids
B amino acids
C glycerol
D sugars
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5. What is/are the breakdown product/s of
proteins?
A fatty acids
B amino acids
C glycerol
D sugars
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6. What is/are the breakdown product/s of fat?
A fatty acids and glycerol
B amino acids
C glycerol
D sugars
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7. Which of the following are examples of large,
insoluble molecules?
A protein, amino acids, starch, glycerol
B starch, fats, proteins
C fatty acids, glycerol, glucose, amino acids
D fats, amino acids, starch, glycerol
© Boardworks Ltd 2003
8. Which of the following are examples of small
soluble molecules?
A protein, amino acids, starch, glycerol
B starch, fats, proteins
C fatty acids, glycerol, glucose, amino acids
D fats, amino acids, starch, glycerol
© Boardworks Ltd 2003
9. Which of the following are examples of
molecules that can be absorbed across the lining
of the small intestine and into the blood?
A fatty acids, glycerol, glucose, amino acids
B starch, fats, carbohydrates, proteins
C protein, amino acids, starch, glycerol
D fats, amino acids, starch, glycerol
© Boardworks Ltd 2003
10. Water is absorbed across the wall of this
structure.
A liver
B large intestine
C oesophagus
D pancreas
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11. What is digestion?
A The breakdown of large molecules into small
molecules.
B The building up of large molecules from small
molecules.
C The absorption of large molecules across the lining
of the small intestine.
D The removal of waste products from food.
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12. What is absorption?
A The movement of large molecules from the small
intestine into the circulatory system.
B The movement of small molecules from the large
intestine into the circulation.
C The movement of small molecules from the
circulation into the small intestine.
D The movement of small molecules from the small
intestine into the circulation.
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13. A carbohydrase is an enzyme that speeds
up the breakdown of
A vitamins.
B fats.
C carbohydrates.
D proteins.
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14. A lipase is an enzyme that speeds up the
breakdown of
A vitamins.
B fats.
C carbohydrates.
D proteins.
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15. A protease is an enzyme that speeds up the
breakdown of
A vitamins.
B fats.
C carbohydrates.
D proteins.
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16. Where are carbohydrases produced?
A stomach, pancreas and small intestine
B salivary glands, pancreas and small intestine
C pancreas and small intestine
D salivary glands and small intestine
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17. Where are lipases made?
A stomach, pancreas and small intestine
B salivary glands, pancreas and small intestine
C pancreas and small intestine
D salivary glands and small intestine
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18. Where are proteases made?
A stomach, pancreas and small intestine
B salivary glands, pancreas and small intestine
C pancreas and small intestine
D salivary glands and small intestine
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19. Which of the following conditions best
suits the action of the protease enzymes in
the stomach?
A alkaline
B neutral
C acidic
D doesn’t matter
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20. What is the name of the acid that is found in
the stomach?
A citric acid
B sulphuric acid
C nitric acid
D hydrochloric acid
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21. Which of these is a function of the acid
found in the stomach?
A speed up the reproduction of bacteria
B neutralise the food entering the stomach
C kill bacteria
D make the food entering the stomach more alkaline
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22. What is the name of the alkaline fluid that is
produced by the liver and stored within the gall
bladder? This liquid will then be released into
the small intestine.
A urea
B bile
C lipase
D hydrochloric acid
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23. What does the bile do to the acidity of the
food arriving from the stomach?
A breaks it down
B nothing
C neutralises it
D makes it alkaline
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24. Bile also causes the emulsification of fats.
What does this mean?
A This is the break-up of a large fat droplet into many
smaller fat droplets.
B This is the change in colour of food when it comes
into contact with bile.
C This is the joining together of fat droplets to make a
chain.
D This is the breakdown of fats into fatty acids and
glycerol.
© Boardworks Ltd 2003
25. Why is the emulsification of fats useful?
A It reduces the surface are of the fats so lipases work
more effectively.
B It increases the surface area of fats so that lipases
work less effectively.
C It increases the surface are of fats so that lipases
work more effectively.
D It reduces the surface area of fats so that lipases
work less effectively.
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26. Enzymes in the digestive system “speed up”
the digestion of food. The scientific word for
“speeding up” such chemical reactions is
A acceleration
B catalysis
C absorption
D neutralisation
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27. The scientific name for the material that
leaves the digestive system via the anus is…
A urine.
B fibre.
C faeces.
D solids.
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28. Which of the following foods are examples
of carbohydrates?
A meat, pulses, cereals and eggs
B milk, butter, margarine, eggs
C cereals, fruits and vegetables
D meat, fruits and milk
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29. Which of the following foods would be
useful if you wanted to make cell membranes?
A fish, eggs and pulses
B cheese, butter and margarine
C vegetables, cereals and cheese
D eggs, cereals and fruits
© Boardworks Ltd 2003
30. If a piece of food was passing through your
digestive system, which of these is the correct
order of organs that it would pass through?
A mouth, gullet, pancreas, small intestine, large
intestine, anus
B mouth, gullet, stomach, large intestine, small
intestine, anus
C mouth, gullet, stomach, pancreas, large intestine,
anus, rectum
D mouth, gullet, stomach, small intestine, large
intestine, rectum, anus
© Boardworks Ltd 2003