AQA GCSE Biology: Combined Science

Topic Questions

2.1 Organisation: Digestion

1a2 marks

Figure 1 shows four different levels of organisation and a number of descriptions.

Figure 1

organisation-level-2

Draw one line from each organisation level to the correct description.

1b1 mark

Below are some statements about tissues.

Identify the incorrect statement.

  • A tissue is a group of similar cells.

  • Tissues are often organised together to perform a specific function.

  • Epithelial and muscle are both types of tissue.

  • Tissues only contain one type of cell.

1c3 marks

Table 1 lists some organ systems found in the human body.

Complete the table by listing two organs for each organ system.

Table 1

Organ System Organ
Musculoskeletal system  
Circulatory system  
Respiratory system  
1d1 mark

Complete the sentence.

Choose the answer from the box.

Unspecialised cells          Organs          Organ systems          Epithelial tissue

Large multicellular organisms are made up of _____________________.

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2a2 marks

Figure 2 shows three different tissue types present in the human stomach and a number of functions.

Figure 2

tissue-type

Draw one line from each tissue type to the correct function.

2b1 mark

In which organ of the human body is most of the glucose absorbed into the bloodstream?

  • Small intestine

  • Large intestine

  • Stomach

  • Pancreas

2c1 mark

Figure 3 shows the organs of the human digestive system.

Figure 3

human-organs

What is the internal pH of organ X?

  • pH 0

  • pH 1.5 - 2.0

  • pH 7.0 - 7.5

  • pH 11.5 - 12.0

2d3 marks

Explain how the internal pH of the stomach is beneficial.

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3a2 marks

The pancreas produces a range of enzymes involved in the digestion of food.

Define the term enzyme.

3b1 mark

One of the enzymes that the pancreas produces is amylase.

Which other organs produce amylase?

  • Salivary glands.

  • Stomach.

  • Small intestine.

  • Salivary glands and small intestine.

3c2 marks

Figure 4 shows an enzyme and an associated molecule labelled X that can bind with the enzyme at location Y.

Figure 4

enzyme

What are molecule X and location Y known as?

3d3 marks

The 'lock and key hypothesis' is often used as a model to describe the action of enzymes.

Using this model and Figure 4 for help, explain how enzymes work.

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4a2 marks

Figure 5 shows the effect of temperature on the rate of an enzyme-catalysed reaction. 

Figure 5

qhDN~XCN_1-1

Explain why the rate of an enzyme-catalysed reaction decreases after point B

4b
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2 marks

A scientist investigated how the digestive enzyme amylase breaks down starch into the sugar maltose.

He added the enzyme to a solution of starch and measured the concentration of starch every 10 minutes.

The results are shown in Table 2.

Table 2

Time (min) Concentration of starch ( mg cm -3 )
0 17.2
10 11.1
20 7.2
30 5.3
40 4.2

Rate of reaction can be calculated using the following equation:

Rate space of space reaction space equals space fraction numerator mass space of space starch space broken space down over denominator time space taken end fraction

Calculate the average rate of the reaction between 0 and 20 minutes.

4c1 mark

Bile is a secretion that helps with digestion.

Which of the following statements about bile are correct?

  1. Emulsifies fats.
  2. Enzymes in bile help digest food.
  3. Helps to provide the optimum pH.
  4. Is acidic. 

  • 1 & 2

  • 1 & 3

  • 1 & 4

  • 2 & 3

4d1 mark

Figure 6 shows the organs of the human digestive system.

Figure 6

7OGGvL6F_1

Bile is produced by organ X

Name organ X.

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5a1 mark

Which reaction does the enzyme protease catalyse?

  • Lipids to fatty acids.

  • Starch to maltose.

  • Proteins to amino acids.

  • Lipids to glycerol.

5b2 marks

During the digestive process, digestive enzymes break down larger molecules into smaller molecules such as amino acids, fatty acids and simple sugars like glucose.

Suggest what the body does with the products of digestion.

5c2 marks

A student used the following method to identify what type of food molecule was present in a sample of food.

  1. Prepare food sample by breaking food up with a pestle and mortar.
  2. Add some distilled water and stir the mixture.
  3. Add a few drops of iodine solution and gently shake.
  4. Observe for any colour change. 

Which food substance were they testing for?

5d3 marks

Table 3 shows a list of positive and negative results for some tests that can be used to detect the presence of food substances.

Table 3

Test reagent Substance being tested Result if positive Result if negative
    Purple Blue
    Blue/black Orange/brown
    Green/orange/red Blue

Complete the empty cells in Table 3 listing the test reagent and substance being tested. 

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1a2 marks

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

Figure 1

human-organs-2

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

1b2 marks

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

1c2 marks

Blood can be considered to be a tissue.

Explain why.

1d4 marks

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

Explain why this is important.

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2a4 marks

Describe the function of structure shown in Figure 2.

Figure 2

human-organs-3

2b3 marks

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.

2c4 marks

Explain why an enzyme only catalyses one reaction.

2d6 marks

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.

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3a4 marks

Describe the digestion of starch in the human body.

3b1 mark

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

  • g cm-3 mmol-1

  • sec-1

  • mg cm-3 min-1

  • mol/L

3c4 marks

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

Figure 3

enzyme-activity

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

3d6 marks

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

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4a6 marks

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.

4b
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3 marks

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

Their results are shown in Figure 4.

Figure 4

starch

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

Use the equation:

                             R a t e space equals space fraction numerator 100 over denominator t i m e end fraction
 

      

4c3 marks

Figure 5 shows the organs of the human digestive system.

Figure 5

organs-2

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.

4d2 marks

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

Suggest why.

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5a3 marks

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.

5b3 marks
A food testing lab was sent four samples of food to test, they carried out some simple tests using chemical reagents.

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

Table 1

Sample Benedict Biuret Sudan III Iodine
1 +  –   –
2 + +
3 + + +
4 _ +

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.

5c3 marks

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

nutrition-facts

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

Table 2

Reagent used Visual observation positive or negative
Iodine Orange
Benedict's    
Biuret    
Sudan III    

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

5d4 marks

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.

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1a3 marks

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

pH Time taken to digest starch in minutes
3.0 38
4.0 26
5.0 17
6.0 13
7.0 7
8.0 8

   

Table 2 - Effect of temperature

Temperature in C Time taken to digest starch in minutes
10 20
20 14
30 11
40 6
50 12
60 23

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.

1b3 marks

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

1c2 marks

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.

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2a2 marks

Figure 1 below shows the human digestive system.

Figure 1

digestive-tract

Carbohydrates are digested into sugars.

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

2b1 mark

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.

2c2 marks

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.

2d2 marks

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.

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3a4 marks

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.

3b2 marks

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.

3c3 marks

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.

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4a1 mark

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?

4b2 marks

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

pepsin-experiment

4c2 marks

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?

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5a1 mark

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

protein-digestion-graph

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?

5b2 marks

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.

5c2 marks

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.

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