Organisation: Digestion (AQA GCSE Biology: Combined Science)

Salivary amylase is produced and secreted by salivary gland cells in the mouth.

Carbohydrate digestion begins in the mouth.

Starch, a polysaccharide, is hydrolysed into the disaccharide maltose by salivary amylase.

The effect of changing pH and temperature on the digestion of starch was investigated by a group of students. The results are shown in Table 1 and Table 2 below.

Table 1 - Effect of pH

Table 2 - Effect of temperature

A student reads the following statement on the internet:

‘The main site for carbohydrate digestion is the small intestine.’

One of the students states that salivary amylase must be responsible for digesting starch in the small intestine. The student is incorrect.

Use the results in Table 1 to explain why.

Explain how temperature affects digestion using the results shown in Table 2.

A second form of amylase, pancreatic amylase, is responsible for continued carbohydrate digestion in the small intestine.

Explain how the digestion of food by enzymes in the intestine is not inhibited by the acid produced in the stomach.

Figure 1 below shows the human digestive system.

Figure 1

Carbohydrates are digested into sugars.

Write word equations to illustrate two other enzyme-catalysed chemical reactions that occur in the digestive system.

The cells lining the stomach continually produce mucus; this mucus forms a protective layer. Gastric infections with the bacterium Helicobacter pylori can cause stomach ulcers, painful sores in the lining of the stomach.

All species have adaptations that allow them to survive in their environment.

Suggest one such adaptation for Helicobacter pylori.

A stomach ulcer can result from damage to the wall of the stomach due to exposure to acid.

Suggest how a stomach ulcer might develop in an individual with a Helicobacter pylori infection.

Crohn’s disease is a disorder of the digestive system. One of factors contributing to Crohn’s disease is an individual's immune system attacking the lining of the intestines, leading to inflammation. Symptoms depend upon the severity and location of inflammation.

Individuals with unmanaged Crohn’s tend to lose weight.

Suggest a reason why.

The liver has many roles in the body.

As well as detoxifying a number of substances, the liver also produces bile, a yellowish-brown fluid that is stored in the gallbladder.

One of the main components of bile is bilirubin.

The liver produces this yellow-brown pigment when it breaks down haemoglobin released from broken down red blood cells.

Explain how red blood cells transport oxygen from the alveoli to other parts of the body.

The liver is also responsible for producing much of the body’s cholesterol.

If levels of cholesterol in the body are too high, there is a risk that solid ‘gallstones’ may form in the liquid bile.

The gallbladder is connected to the small intestine by a narrow duct (tube) which can become blocked by these gallstones.

It is not uncommon for individuals with gallstones to form very pale faeces.

Suggest why.

One form of cholesterol found in the blood is LDL.

Suggest the consequences of an individual having too high a level of LDL cholesterol in their blood.

A group of students wanted to investigate the effect that temperature has on the activity of pepsin, a protease.

They used the following method:

1. Put 4 cm³ of 1% protein solution into a boiling tube.
2. Put 4 cm³ of pepsin solution into a second boiling tube.
3. Put both boiling tubes into a water bath at 20 °C.
4. After 4 minutes, add the pepsin solution to the protein solution together in one boiling tube, mixing together with a stirring rod.
5. After 20 seconds, add a drop of the mixture to a drop of Biuret solution in one well of a spotting tile.
6. Repeat step 5 until the Biuret solution no longer changes colour.
7. Repeat steps 1 – 6 at 10 °C (using an ice water bath), 30 °C, 40 °C and 50 °C.

Why did the student leave the protein and pepsin solutions in the water bath for 4 minutes in step 3?

The temperature of the human body is 37 °C.

Figure 2 below shows the incomplete results of the experiment.

Complete the diagram in Figure 2 to show the results you would expect at 30 °C and at 40 °C

You should write a tick or a cross in each well of the spotting tile.

Figure 2

There are other ways to investigate the breakdown of protein by pepsin.

The concentration of protein present in the solution every 20 seconds can be measured using a colorimeter.

What are the advantages of using this method rather than the method used by the students?

In a colorimeter, the amount of light that cannot pass through a solution is measured; giving the ‘absorbance’ of a solution.

The graph in Figure 3 below shows a calibration curve of concentration of protein versus absorbance.

Figure 3

An experiment was carried out to investigate the activity of a protease on a 1% protein solution.

The absorbance at 30 °C was 0.8 arbitrary units after 20 seconds.

Using the calibration curve, estimate the final concentration of protein in this solution after 20 seconds?

The concentration of protein in the solution at 10 °C after 1 minute is different from the concentration at 30 °C after 1 minute.

Explain why.

The student repeated the experiment but incubated the protease and 1% protein solution at 80 °C

The absorbance was measured at approximately 1.14 arbitary units.

Suggest a reason for this result.

A student drew the diagram showed in Figure 1 under a title which said "An organ"

Figure 1

Suggest whether the student is correct to label the diagram in this way, justify your answer.

Explain why an artery could be considered an organ but a capillary cannot.

Blood can be considered to be a tissue.

Explain why.

Mechanisms exist in the human body to ensure that the core body temperature remains constant at 37 °C.

Explain why this is important.

Describe the function of structure X shown in Figure 2.

Figure 2

A student noticed that chewing rice or potatoes for a long time resulted in a sweet taste developing in the mouth.

Explain why this is.

Explain why an enzyme only catalyses one reaction.

The small intestine is the main site of digestion and absorption of nutrients in the human body.

Describe how the small intestine is adapted for its function.

Describe the digestion of starch in the human body.

When calculating the rate of an enzyme-controlled reaction, which of the following would be the most suitable unit of measurement?

Figure 3 shows the activity of three different digestive enzymes across a range of pH's.

Figure 3

Using information from Figure 3, explain where in the human digestive tract enzymatic digestion of protein starts.

Explain the effects of pH on amylase, use Figure 3 to support your answer.

Describe a suitable method to investigate the effect of pH on the time taken for amylase to digest starch.

You don't need to include a risk assessment in your method.

A group of students investigated the effect that pH has on the activity of amylase.

Their results are shown in Figure 4.

Figure 4

Calculate the rate of reaction (amount of starch digested) at pH 7.0.

Use the equation:

                             

Figure 5 shows the organs of the human digestive system.

Figure 5

Some people may need to have organ Y removed, but can still lead a normal life. 

Suggest why people can still lead a normal life without organ Y.

In some cases, people who have organ Y removed (see Figure 5) may need to adjust their diet and avoid certain foods.

Suggest why.

A student would like to test a sample of food to show which biological molecules are present.

Describe how the student should prepare the food sample ready for testing.

The results are shown in Table 1 where '+' represents a positive result and '-' represents a negative result.

Table 1

The lab concluded that one of the samples was honey.

Using the results in Table 1, explain which sample was most likely to be honey.

One of the samples tested by the lab in part (b) was identified to be coconut milk.

Figure 6 shows a nutrition facts label from a packet of coconut milk which lists all the nutritional information.

Figure 6

Table 2 shows the visual observation and result for an iodine test of the sample of coconut milk.

Table 2

Complete Table 2 using the information from the nutrition facts label in Figure 6

Many people make claims on the health benefits of consuming coconut milk and say it should form a major component of your diet.

Explain why people should be careful of consuming too much coconut milk. Use the information in the nutrition facts label in Figure 6 to support your answer.