Topic 4 Digestive System Flashcards
The digestive system is an organ system where
several organs work together to digest and absorb food.
Physical digestion:
mouth (chewing) and stomach (churning) - breaks food into smaller pieces to increase the surface area for chemical digestion
Chemical digestion by enzymes which:
Are biological catalysts that speed up chemical reactions in living organisms
Are large proteins
Catalyse a specific reaction due to the shape of the active site being complementary to the shape of one specific substrate
Are denatured by high temperature and extremes of pH due to changes in the shape of the active site
Have an optimum temperature
Have an optimum pH.
The ‘lock and key theory’ is a simplified model of:
In reality:
enzyme action.
the active site changes shape a bit as the substrate binds to it. This enables a tighter fit, and is called the induced fit model
Digestive enzymes convert large food molecules into
small soluble molecules that can be absorbed into the bloodstream.
Carbohydrases break down carbohydrates to
simple sugars.
Amylase is a carbohydrase which
breaks down starch into glucose
Proteases break down
proteins to amino acids.
Lipases break down
lipids (fats) to glycerol and fatty acids.
carbohydrase sites of production
pancreas, salivary glands and small intestine
carbohydrase site of action
mouth and small intestine
protease sites of production
stomach pancreas and small intestine
protease action sites
stomach and small intestine
amylase site of production
salivary glands and pancreas
amylase site of action
mouth and small intestine
lipase site of production
pancreas stomach and small intestine
lipase site of action
small intestine
Bile is made in the
and stored in the
Its properties and why?
liver
gall bladder
-It is alkaline to neutralise hydrochloric acid from the stomach.
-It also emulsifies fat to form small droplets which increases the surface area.
-The alkaline conditions and large surface area increase the rate of fat digestion by lipase.
Explain how the small intestine is adapted for its role in absorption:
Very long, villi, microvilli: provide a large surface area
One cell thick lining: short distance for absorption by diffusion / active transport
Good blood supply: maintains a steep concentration gradient
The products of digestion are used to
new carbohydrates, lipids and proteins.
Effect of pH on enzyme action
identify variables
Independent variable: pH of solution
Dependent variable
Time taken to digest all the starch
Control variables
Volume and concentration of starch suspension
Volume and concentration of amylase solution
Temperature
Describe the main sources of error
Not judging the end point (when all starch was digested) accurately (dependent variable)
Not setting up the pH of the buffer solutions accurately (independent variable)
Suggest an uncontrolled variable
Evaporation of water from the tubes could cause the concentration of the amylase solution to change
Describe how to improve the accuracy of the experiment
Repeat the experiment and calculate a mean
Repeat the experiment at smaller intervals of pH
Take samples every 10s rather than every 30x
Describe how to improve the validity of the experiment
Repeat and calculate a mean
Use bungs to prevent evaporation of water from the tubes
Write a conclusion
the optimum pH for amylase is pH 7. At pHs higher or lower than 7 the amylase takes longer to digest the starch / the rate of reaction is lower.
This is because at pHs higher or lower than 7 amylase is denatured.
How do enzmyes relate to metabolism
The metabolic reactions which occur in cells to synthesise new molecules or break them down are often controlled by specialised proteins called enzymes
