Download Module 4: Genetics

Module 6:
Human Health and Physiology
6.1 Digestion
6.1.1 Explain why digestion of large
food molecules is essential.
1. Molecular size: food molecules are too large to be transported
across the membranes of the intestines and the membranes of
a capillary.
1. Molecules found in the plants and animals that we eat are not
useful to us. We must digest these foods so they can reassemble into useful forms
6.1.2 Explain the need for enzymes in
digestion
 Enzymes are biological
catalysts that speed up
reactions without being
consumed.
 They lower the activation
energy of reactions so
less energy is needed for
the reaction to occur
 Allow higher reaction
rates at lower
temperatures
6.1.3 State the source, substrate, products
and optimum pH conditions for one
amylase, one protease and one lipase.
6.1.4 Draw and label a diagram of the
digestive system.
 Alimentary canal: mouth,
esophagus, stomach,
small intestine, large
intestine (colon), rectum
 Accessory organs: gall
bladder, liver, and
pancreas
What does the markscheme say?
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esophagus — attached to both mouth and stomach;
stomach — j-shaped sac attached to esophagus and u-shaped portion of
small intestine;
large intestine — wider diameter than small intestine, attached to small
intestine;
pancreas —eaf-shaped, in u-shaped region of small intestine with small duct
connected to small intestine;
liver — large, triangular, to left of stomach;
gall bladder — small sac drawn on top of liver with tube connected to small
intestine at same region as duct from pancreas;
anus —at end of large intestine but narrower in diameter;
6.1.5 Outline the function of the stomach,
small intestine and large intestine.
 Stomach: has a muscular wall that churns food with
gastric juice:
Pepsin: protease
HCl: creates acidic environment needed for pepsin to be
active; helps break down food
Mucus: lines stomach wall to prevent damage from HCl
6.1.5 Outline the function of the stomach,
small intestine and large intestine.
 Small Intestines: most nutrients are absorbed here
Accessory organs secrete bile (from liver/gall bladder),
trypsin, lipase, amylase, and bicarbonate (from pancreas)
Wall is lined with villi and microvilli which increase SA for
adsorption of digestion molecules
6.1.5 Outline the function of the stomach,
small intestine and large intestine.
 Large Intestines: primary function is water
absorption
The water kept in the undigested food helps move the food
along the alimentary tract before it becomes waste
Home to mutualistic bacteria (i.e. they synthesise vitamin K)
6.1.6 Distinguish between absorption and
assimilation.
1. Absorption: digested food molecules are first
transported across the epithelial cells of the small
intestine and this is followed by transport into the
blood
2. Assimilation: digested food molecules are
incorporated into body tissues
6.1.7 Explain how the structure of the villus is
related to its role in absorption and transport of
the products of digestion.
 Undigested food cannot pass
through villus epithelium
 Digested nutrients pass through
epithelium and enter the capillary
bed or lacteal
 Increases surface area for
absorption