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.
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 / NumberIncisor
Canine
Pre-molar
Molar (including wisdom teeth)
Total number of adult human teeth:
Reasons that this number may not be actually present:
KS4 Biology /B9b / Side 1
The Types of Human Teeth
Complete the following table:
Diagram / Appearance (shape) / FunctionINCISOR
CANINE
PRE-MOLAR
MOLAR
KS4 Biology /
B9c / Side 1
Structure of a Human Tooth
Using the table provided, label the following diagram
Number / Structure / FunctionPulp 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
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 / Molars / Snipping / Oxygen / CellsPoints / Enamel / Swallowing / Nerve / Edges
32 / Non-living / Hard / Pulp / Front
Canines / Diet / Bone / Fibres
Teeth are designed for breaking down ______. An adult human has ______teeth. Teeth are covered in ______which is extremely ______and ______- ______. It forms sharp ______and ______. Beneath it lies the dentine which is hard and ______-like and contains living ______. These are supplied with ______and ______by blood vessels in the ______cavity. 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 ______.
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?
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
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 / Elements present / Food typesGlucose / C H O
Margarine, oil, butter
C H O N
What molecules are absorbed into the bloodstream?
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?
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.
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 / Starch test / Sugar test1 / Starch
2 / Glucose
3 / Starch + Amylase
4 / Amylase
What does the water surrounding the visking tubing represent?
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?
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 actionAmylase
Protease
Lipase
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?
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.
KS4 Biology /B9h / Side 1
Activity: The Effect of Temperature on the Enzyme Amylase
AmylaseStarch / ------à / 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.
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?
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 / ReasonApproximately 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
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?
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 gutDigestion
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 - August 05