3.3 Digestion & Absorption

Figure 1 shows a cell commonly found in the small intestine.

Figure 1 

Identify organelle C and suggest why there are large numbers of organelle C in these cells.

The structures labelled A can be damaged when people suffer from coeliac disease which is a disease of the human digestive system. They tend to have lower concentrations of amino acids in their blood. 

Explain why they have low concentrations of amino acids in their blood.

Figure 2 shows one of the ways in which amino acids are absorbed from the small intestine into the blood.

Figure 2

Cyanide is an inhibitor of mitochondria. In the presence of cyanide, the concentration of  sodium ions in the cell rises and amino acid absorption stops. 

Explain why sodium ions and amino acids will not be absorbed from the lumen of the small intestine in the presence of cyanide. 

What is the mechanism of movement represented by Q? Explain your answer.

Scientists investigated if there was a difference in lactase activity in adult mice who were fed different types of carbohydrate diets as newborn mice. The mice were divided into four groups all of which were fed a standard diet only differing in the carbohydrate content. Table 1 shows their results. 

Table 1

The data is presented with standard deviations for each group. Suggest why the standard deviations differ. 

A group of scientists concluded that increasing glycogen in the diet in adults was the most effective way to increase lactase activity. Evaluate this conclusion.

Lactose is often found in milk with many adults unable to digest lactose and suffering from intestinal problems if they drink milk. Figure 1 shows an industrial reactor used to produce lactose-reduced milk.

Figure 1

Suggest one benefit of immobilising lactase in this reactor. 

Using Figure 1, explain three reasons why the milk must be passed through the reactor several times.

Figure 1 shows some of the events that occur when lipids are digested and absorbed in the small intestine. 

Figure 1

Use Figure 1 to describe how the large lipid droplet is absorbed into the blood stream. 

A group of scientists wanted to investigate the effect of lipase and a 11% bile salts solution on the digestion of triglycerides. Figure 2 shows their results.

Describe and explain the results shown in Figure 2.

The investigation was repeated at a temperature that was 10 C° lower. Sketch on Figure 3 below the graph you would expect to see at this lower temperature for lipase solution with 11% bile salts.

Figure 3

When chylomicrons leave the epithelial cell, they enter small lymphatic capillaries called lacteals. Suggest how chylomicrons leave the epithelial cell and explain your answer. 

Bacteria are often used in industries when scientists need large amounts of enzymes.Describe how bacteria divide and suggest why they are used in industry to provide enzymes.  

Some bacteria are able to secrete proteases outside of their cells. Suggest and explain an advantage of this. 

Mammals can produce extracellular proteases as well as membrane-bound enzymes such as dipeptidases. Explain why dipeptidases are important in protein digestion. 

Endopeptidases are enzymes that hydrolyse the internal peptide bonds found in long polypeptide chains whereas exopeptidases hydrolyze terminal peptide bonds. Soybean and other legumes contain chemicals that inhibit endopeptidases such as trypsin. Explain the effects of these chemicals on protein digestion and absorption. 

Figure 1 below outlines the mechanism of lipid digestion and absorption.

Figure 1

What type of cell is cell A?

Figure 1 shows the formation of lipid droplet and micelles. Explain the advantages of these structures.

Triglycerides are hydrolyzed by the enzyme lipase.

A student wanted to investigate the breakdown of triglycerides in cow milk by human lipase at 20 °C.

They recorded the pH of a sample of cow’s milk before and after adding human lipase. They used a pH meter to measure the pH. Their results are shown in figure 2.

Figure 2

Describe and explain the changes in pH after human lipase is added.

The student carried out his experiment at a controlled temperature of 20 °C. They repeated the experiment at 25 °C.

Draw a line on the graph (Figure 2) to show the results you would expect at 25 °C.

Figure 1 below shows the digestion pathway of proteins. 

Figure 1  

Name the missing molecule X and missing enzyme Y.

Describe the different actions of endopeptidases and exopeptidases.

Pancreatitis is a medical condition that can lead to the pancreatic duct becoming blocked. It can also cause protein-digesting enzymes to be released into the bloodstream. Suggest one reason why this might be harmful.

Figure 2 below illustrates the co-transport mechanism for the absorption of amino acids into the blood by a cell lining in the small intestine.

Figure 2

Use Figure 2 and your knowledge of the co-transport mechanism, to explain why epithelial cells in the small intestine contain a large number of mitochondria.

Describe the role that enzymes play in the digestion and complete breakdown of starch.

A lab technician set up the experiment shown in Figure 1 below.

Figure 1

After 20 minutes, the samples were taken from the liquid in the beaker, and from the liquid inside the Visking tubing. Biochemical tests were carried out on these samples.
Complete Table 1 by placing an X in each box that you predict will have shown a positive result.

Table 1

Justify your answers for part (b).

Describe the colour change that takes place for a positive result with Benedict’s solution.

State where bile is produced and stored in the human body.

Bile salts bind to fat droplets and break them down into smaller fat droplets. Explain how this process makes lipid digestion more efficient.

The products of protein and carbohydrate digestion require a co-transporter system for absorption into the epithelial cells of the small intestine. The products of lipid digestion can enter by simple diffusion. 

Explain why this is possible.

Lactose intolerance is a common occurrence in the adult population. An individual who is lactose intolerant no longer produces the enzyme lactase in their ileum. Two students were tested for lactose intolerance. They both fasted for 12 hours before drinking a liquid containing 60 g of lactose. The glucose concentration in their blood was measured for the next 125 mins. The results are shown in Figure 1 below.

Figure 1

Suggest which individual is lactose intolerant. Justify your answer.