KS4 Biology
B9a / Side 1
Digestion
Digestion is the process in which food is broken down and processed in the body.
Large insoluble molecules are broken down into small soluble molecules that can pass
by diffusion into the bloodstream. These soluble molecules then diffuse into body
cells so that important reactions can take place.
Digestion takes place by two processes:
1. Mechanical (Physical)
The cutting and crushing action of the teeth as feeding takes place achieves physical
digestion as well as the rhythmical contractions of the gut and stomach.
2. Chemical
This is carried out by acid and biological chemicals called enzymes
Feeding – The type of human teeth
Activity
Using B9a side 2 and mirrors, examine your teeth and record the number of each
type of tooth that you possess.
Sha Tin College
Science Department - February 16
KS4 Biology
B9a / Side 2
The Position of Human Teeth
The following diagram shows half the lower and upper jaw of a human:
Using different coloured pencils for each tooth type colour the diagram.
Using the mirror, count the number of each type of tooth that you posses and record
your results in the following table.
Type of tooth
Number
Incisor
Canine
Pre-molar
Molar (including wisdom teeth)
Total number of adult human teeth:
Reasons that this number may not be actually present:
Sha Tin College
Science Department - February 16
KS4 Biology
B9b / Side 1
The Types of Human Teeth
Complete the following table:
Diagram
Appearance (shape)
Function
INCISOR
CANINE
PRE-MOLAR
MOLAR
Sha Tin College
Science Department - February 16
KS4 Biology
B9c / Side 1
Structure of a Human Tooth
Using the table provided, label the following diagram
Number
Structure
Function
Pulp Cavity
Central space containing nerves and blood supply
Fibres
Combine with cement to anchor root to jaw
Crown
Part of tooth above the gum
Nerve
Sensory endings that respond to join and hot and
cold
Enamel
Extremely hard material forming sharp points and
edges – dead material
Cement
Helps attach root to jaw and acts as a shock
absorber
Root
Part of tooth that lies below the gum
Blood vessels
Supply food and oxygen to the living cells of the
tooth
Gum
Soft tissue surrounding the bone
Jaw
Bone that provides the support for the root of the
tooth
Dentine
Hard, bone-like material containing living cells
Sha Tin College
Science Department - February 16
KS4 Biology
B9c / Side 2
Structure of a Human Tooth
Complete the following paragraph below using the words provided. Each word may be
used more than once or not at all.
Food
Points
32
Canines
Molars
Enamel
Non-living
Diet
Snipping
Swallowing
Hard
Bone
Oxygen
Nerve
Pulp
Fibres
Teeth are designed for breaking down _______________.
_______________ teeth.
Cells
Edges
Front
An adult human has
Teeth are covered in _______________ which is
extremely _______________ and _______________ - _______________.
It
forms sharp _______________ and _______________.
Beneath it lies the
dentine
and
which
is
_______________.
hard
and
These
_______________
are
supplied
-like
with
contains
living
_______________
_______________ by blood vessels in the _______________ cavity.
and
Incisor
teeth are found at the _______________ of the mouth and are used for cropping
and _______________ at food. The 3 other kinds of teeth found in mammals are
_______________, premolars and _______________.
Sha Tin College
Science Department - February 16
KS4 Biology
B9d / Side 1
Tooth Decay
Activity
Take a portion of tablet and let it dissolve in your mouth for a few minutes. Using
the mirrors provided, look at your teeth.
What has happened?
Reference: Nelson P.143
Applin P.201
What is tooth decay caused by?
What is the substance formed on the surface of teeth called?
How is this substance formed?
What would happen if you did not clean your teeth?
What type of foods are bad for your teeth and why?
Sha Tin College
Science Department - February 16
KS4 Biology
B9e / Side 1
The Digestive System
The human gut, sometimes called the Alimentary Canal is a long coiled tube, which is
7-9m long. At one end food enters through the mouth (ingested). At the other end
the undigested remains of a meal are removed through the anus (egested). Digestion
and absorption take place in between.
Reference:
Nelson P.136
Applin P.204
Label the following diagram of the Alimentary Canal
Sha Tin College
Science Department - February 16
KS4 Biology
B9e / Side 2
Digestion
Once food has been taken into the alimentary canal (ingestion) it needs to be broken
down into small soluble compounds that are able to be absorbed through the walls of
the intestines (mainly the small intestine) into the bloodstream where it can then be
used by the body.
The 3 main food groups that need to be digested are:



Starch (A large insoluble carbohydrate)
Proteins
Fats
Complete the following table:
Type of molecule
Broken down into
Glucose
Elements present
Food types
CHO
Margarine, oil,
butter
CHON
What molecules are absorbed into the bloodstream?
Sha Tin College
Science Department - February 16
KS4 Biology
B9f / Side 1
Peristalsis – Moving food through the gut
The gut wall is made up of muscle layers that contract and relax thus enabling food
to move through the gut. This muscular action is called Peristalsis.
How does fibre in the diet help peristalsis to happen?
Why can humans not digest fibre?
Sha Tin College
Science Department - February 16
KS4 Biology
B9f / Side 2
Digestive Enzymes
The chemical process of digestion involves many different enzymes found at
different sites in the human gut.
Enzymes:

Are biological catalysts

Speed up chemical reactions without being used up

Made of protein

Non-living

Substrate specific. They have a special shaped groove that allows them to
bind with one specific substrate molecule. This groove is called the active site
of the enzyme. (Lock and Key Hypothesis)

The shape of the enzyme will change with a change of temperature or pH. If
the change in pH is extreme or the temperature rises above the optimum
working temperature for that enzyme the enzyme will become denatured
(change shape so much that it can not fit with the substrate) and its activity
will be destroyed.
Activity
This experiment demonstrates that digestion is required to break down molecules so
that they are small enough to pass through into the bloodstream.
Amylase is an enzyme, which breaks down starch into smaller glucose molecules.
Where is amylase found in the body?
Set up the following experiment using Visking Tubing. This mimics the gut by allowing
small soluble molecules to pass through by diffusion.
Sha Tin College
Science Department - February 16
KS4 Biology
B9f / Side 3
1. Set up the Visking Tubing bags as shown in the above diagram. Your teacher
will demonstrate this.
2. Fill the labelled bags with the following solutions and put in a 37C water bath
for 15 minutes.
3. Using a pipette, take 2 samples from the water in each boiling tube. Test one
sample for starch and the other for sugar.
Record your results in this table:
Test-tube No
Solution
1
Starch
2
Glucose
3
Starch + Amylase
4
Amylase
Starch test
Sugar test
What does the water surrounding the visking tubing represent?
Sha Tin College
Science Department - February 16
KS4 Biology
B9f / Side 4
What is the purpose of test-tube 4?
Why does the body need to digest starch?
Why was warm water used to cover the pieces of visking tubing?
Why is it best to use only enough water to just cover the pieces of visking tubing?
Sha Tin College
Science Department - February 16
KS4 Biology
B9g / Side 1
Digestive Enzymes
These can be classified under three broad headings:
Reference: Nelson P.138
Applin P.203
Complete the following table:
Enzyme
Reaction speeded up
Site of production
Site of action
Amylase
Protease
Lipase
Sha Tin College
Science Department - February 16
KS4 Biology
B9g / Side 2
Factors Which Affect Enzyme-Controlled Reactions
The rate of an enzyme-controlled reaction is determined by some important factors.

Temperature

pH
This is the reason that enzymes are found working at different locations in the body.
Temperature
Explain what is happening in Part A of the graph?
Sha Tin College
Science Department - February 16
KS4 Biology
B9g / Side 3
What is the optimum temperature for this enzyme? What does this mean?
What happens to the rate of the reaction as temperature continues to increase after
the optimum temperature?
pH
Most enzymes have an optimum pH of around 7, which is the pH found within most
cells. However, there are exceptions.
Where in the body would you expect to find an enzyme, which has a pH optimum of
1-2? Explain why.
Give an example of this type of enzyme.
What would happen if the pH of a cell suddenly changed?
Try to think of an example, which would cause the pH of the cell to change.
Sha Tin College
Science Department - February 16
KS4 Biology
B9h / Side 1
Activity: The Effect of Temperature on the Enzyme Amylase
Amylase
Starch ---------------------------
Maltose
1. Water baths are set up at the following temperatures




37C
55C
75C
Room temperature – desktop
2. For each temperature, label 2 test tubes, starch and enzyme. Measure 2ml of
each solution and place into the correct tubes.
3. Place the labelled tubes into the appropriate water bath.
4. Leave for 5 minutes.
5. Pour enzyme solution into the starch test tube and stir. Start a stopwatch.
6. Every minute from then on put on one-drop of the mixture on to a dropping tile
using a clean glass rod. Test with iodine.
7. Repeat for each temperature.
Results
Produce a table of results and plot a graph. Then answer the following questions.
Sha Tin College
Science Department - February 16
KS4 Biology
B9h / Side 2
Why is the temperature so important?
Why is it important to keep the solutions separate at first?
At what temperature is there the faster breakdown of the starch solution?
Is this what you would expect?
What has happened to the enzyme when the temperature is too hot?
What would happen if you changed the pH of the solutions?
Sha Tin College
Science Department - February 16
KS4 Biology
B9i / Side 1
Absorption of Food – Small Intestine
Food has to be absorbed into the bloodstream so that the body can make use of it.
This takes place in the small intestine. The small intestine possesses many features
that ensure that this process is efficient. Reference: Nelson P.139, Applin P.206.
Complete the table below:
Feature
Reason
Approximately 5m long
Very narrow
Inner surface is folded into villi
projections
Each villi is covered with microvilli
The cell lining is only 1 cell thick
Well supplied with blood vessels
Lacteal present
Sha Tin College
Science Department - February 16
KS4 Biology
B9i / Side 2
Answer the following questions.
1. Which blood vessel does the absorbed food pass into?
2. Where does this vessel take the blood to in the body?
3. What is the process called that allows the passage of food through the wall of
the intestine?
4. How would you describe the food at this stage of digestion?
5. What is the purpose of the Lacteal?
6. Why is the Lacteal important?
7. The lining of the gut is selectively permeable. What does this mean and why is
this important for absorption?
8. Why do vitamins and minerals not need to be digested before they are absorbed?
Sha Tin College
Science Department - February 16
KS4 Biology
B9i / Side 3
Egestion
By the time food reaches the rectum most of the food substance have been
absorbed into the blood. All that remains is undigestable food (fibre), bacteria and
some dead cells from the lining of the alimentary canal wall. This mixture forms the
faeces, which are egested through the anus.
Complete the following table.
(Remember that some of the process occur in more that one place along the gut.)
Process
Where does it happen in the gut
Digestion
Absorption of digested food molecules
Absorption of water
Egestion
What is the difference between excretion and egestion?
Give 3 examples of excretion
Sha Tin College
Science Department - February 16