1. 1
   A student examined a thin section of small intestine lining under a microscope and observed many small, finger-like projections covering the surface. Each projection contained a network of blood capillaries and a central lacteal, and its surface cells had many tiny membrane projections.

   (a)

   Which structure covering the lining of the small intestine increases the internal surface area for absorption?

   [1 mark]

   • AVilli
   • BAlveoli
   • CNephrons
   • DStomata

   (b)

   What is the main function of the lacteal found at the centre of each villus?

   [1 mark]

   • ATransport of absorbed glucose and amino acids
   • BTransport of absorbed fatty acids and glycerol
   • CSecretion of amylase into the small intestine
   • DProduction of bile to emulsify fats

   (c)

   Explain how the tiny membrane projections on the surface cells of the villus (microvilli) and the blood capillaries inside the villus contribute to efficient absorption.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A doctor measured the water content of material passing through different regions of a patient's gut. Most water was found to have already left the gut contents by the end of the small intestine, with a further small amount absorbed afterwards, leaving semi-solid faeces.

   (a)

   In which region is this further small amount of water absorbed?

   [1 mark]

   • AStomach
   • BOesophagus
   • CColon
   • DRectum

   (b)

   Which two substances, in addition to water, are absorbed from the small intestine into the blood?

   [1 mark]

   • ABile and mucus
   • BStarch and protein
   • CCellulose and urea
   • DGlucose and amino acids

   (c)

   Explain why most nutrient absorption occurs in the small intestine rather than the colon.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A patient with a damaged small intestine has villi that are flattened and reduced in number, as shown by biopsy. Doctors are concerned about the effect on the patient's ability to absorb nutrients from digested food.

   (a)

   Explain three effects this would have on the absorption of nutrients.

   [3 marks]

   (b)

   Suggest and explain four ways in which the structure of the small intestine wall is adapted for efficient absorption, and state why this efficiency is important for the body.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A group of students investigated absorption in the small intestine by comparing the surface area of a smooth tube with that of a tube lined with villi and microvilli of the same overall length. They found the villus-lined tube had a much greater absorptive surface area.

   (a)

   Describe how villi and microvilli increase the surface area available for absorption, and explain, using ideas about diffusion and active transport, how this increased surface area speeds up the movement of nutrients into the blood.

   [6 marks]

   (b)

   Explain why a person whose small intestine has been surgically shortened is likely to suffer from poor absorption of nutrients, and discuss how the body's structures for absorption help to compensate as much as possible.

   [6 marks]

   Total for question 4: 12 marks

End of questions