B3.5-B3.7 (How The Digestive System Works (The digestive system is a long,…
How The Digestive System Works
Food contains large, insoluble molecules such as starch (a carbohydrate), protein, and lipid. Tha large molecules must be digested into smaller, soluble molecules that can be absorbed into the blood.
are produced by specialised cells in glands and the lining of the small intestine.
pass out of the glands into the cavity of the digestive system - they work
the cells, unlike most enzymes.
come into contact with the food so it is digested.
The digestive system is a long, hollow, muscular tube. The digestive system:
breaks the food into smaller pieces to increase the surface area for enzymes to work on.
mixes the food with digestive juices that contain enzymes.
has muscles to move the food along.
has areas with different levels of pH, for example, the mouth and small intestine are alkaline whilst the stomach is acidic.
absorbs the small, soluble food molecules into the blood in the small intestine.
Each type of food is digested by a specific enzyme.
) is produced by the salivary glands, the pancreas, and the small intestine. Amylase catalyses the digestion of starch into sugars in the mouth and small intestine.
are produced by the stomach, the pancreas, and the small intestine. Proteases catalyse the breakdown of proteins into
in the stomach and small intestine.
is produced by the pancreas and the small intestine. Lipase catalyses the breakdown of lipids (fats and oils) to
Making Digestion Efficient
Human digestive enzymes work best at body temperature, 37°C, so the temperature in the digestive system is optimum. Different enzymes have different optimum pH levels.
Protease enzymes in the stomach work best in acid conditions. Glands in the stomach wall produce hydrochloric acid to create very acidic conditions.
Other proteases, amylase, and lipase work best in the small intestine where the conditions are slightly alkaline.
Food leaving the stomach is very acidic so its pH must be changed. To do this the liver produces
that is stored in the gall bladder and released into the small intestine when food enters.
neutralises the stomach acid
makes the conditions in the small intestine slightly alkaline.
emulsifies fats (breaks large drops of fats into smaller droplets) to increase the surface area of the fats for lipase enzymes to act upon.
Factors Affecting Enzyme Action
The effect of temperature on enzyme action
Reactions take place faster when it is warmer. At higher temperatures the molecules move around more quickly and so collide with each other more often, and with more energy.
Enzyme-catalyzed reactions are similar to other reactions - when the temperature is increased the rate of an enzyme-catalyzed reaction increases. However, after increasing the temperature beyond a certain point the rate no longer increases.
If the temperature gets too high the enzyme stops working because the active site changes shape. The enzyme becomes
The effect of pH on enzyme action
Each enzyme works best at a particular pH. Some enzymes work best in acid conditions, such as those found in the stomach, while others need neutral or alkaline conditions.
The folded shape of the protein molecule that forms an enzyme is held together by forces. A change in pH affects these forces, which in turn changes the shape of the active site.
At the optimum pH the active site has the best shape so that the enzyme works most efficiently.
When the pH is too acidic or too alkaline, the enzyme becomes denatured as the shape of the active site changes.