Syllabus Edition

First teaching 2023

First exams 2025

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Enzymes & Metabolism (HL IB Biology)

Exam Questions

5 hours68 questions
1a
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5 marks

Distinguish between anabolic and catabolic reactions. 

Include one example of each reaction.

1b
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2 marks

State the main mode of action of enzymes.

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2a2 marks

The protein Rubisco is an enzyme. 

What is the function of the enzyme Rubisco in living organisms? 

2b1 mark

Enzymes have a specific three-dimensional conformation that enables them to carry out their roles in living organisms. 

Which part of the amino acid determines the conformation of the protein?

2c2 marks

In certain conditions, such as high temperatures, the 3D conformation of proteins can be lost. 

(i)
What is the scientific name given to when a protein loses its 3D conformation? 

[1]

(ii)
State one condition, other than temperature, that can cause the 3D conformation of a protein to be lost. 

[1]

2d2 marks

Sketch a graph to show how the rate of reaction of Rubisco changes over a range of temperatures. 

Use the axes provided below.

e-2d

[2]

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3a1 mark

State the reason why enzymes are referred to as biological catalysts. 

3b3 marks

The image below shows a representation of an enzyme-controlled reaction.

enzyme-substrate-complex

Describe the events taking place in the image.

3c2 marks

State what is meant by the term 'enzyme specificity'?

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4a2 marks

A student wanted to investigate the effect of substrate concentration on the activity of an enzyme called catalase. Catalase is an enzyme that commonly occurs inside living cells where it breaks down toxic hydrogen peroxide into oxygen and water. The image below shows the experimental set up done by the student.

catalase-and-hydrogen-peroxide-investigation-sq

List two control variables that the student would need to be aware of in the experiment shown in the image.

4b
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1 mark

The student decided to make up solutions at five different hydrogen peroxide concentrations. Their measurements for these solutions are shown in the table below.

Concentration of hydrogen peroxide solution (%) Volume of hydrogen peroxide required (cm3) Volume of distilled water required (cm3)
10 10 90
8 B C
6 6 94
A 4 96
2 2 98

Give the measurements needed to fill in gaps A-C in the table. 

4c1 mark

After measuring out the range of hydrogen peroxide concentrations shown in part (b), the student carried out the experiment using the equipment set up in part (a). They recorded the volume of oxygen (the product) produced after one minute, and repeated this measurement three times at each concentration. Their results are shown in the table below.

results-table-for-catalase-experiment

Use the data in the table to calculate the value missing from the square marked X. 

4d2 marks

State the purpose of repeating the experiment three times at each concentration of hydrogen peroxide. 

4e4 marks

Using the data in part (c), draw a graph of hydrogen peroxide concentration against the mean volume of oxygen. 

4f2 marks

Deduce the conclusions that can be drawn from your graph from part (e). 

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5a
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2 marks

A researcher investigated the effect of pH on the activity of stomach enzyme pepsin. 

Their results are shown in the image below. 

pepsin-rate-of-reaction-at-different-ph-sq

The rate of reaction can be calculated by using the following formula:

reaction space rate space equals space fraction numerator Amount space of space product space produced space left parenthesis straight g space dm to the power of negative 3 end exponent right parenthesis over denominator Time space left parenthesis straight s right parenthesis end fraction

Calculate the rate of reaction at pH 4. Give your answer with the correct units.

5b2 marks

Describe the differences between the curves at pH 2 and pH 4.

5c1 mark

State why product production at pH 2 does not continue indefinitely but reaches a plateau at around 14.75 g.

5d3 marks
(i)

Predict the outcome if the pH were increased to pH 10.

[1]

(ii)

Explain your answer at part i).

[2]

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6a4 marks

Describe the processes that occur during an enzyme-catalysed reaction. 

6b4 marks

Outline the events that occur when enzymes are exposed to high temperatures. 

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7a1 mark

The graph below shows how enzymes affect biological reactions.

energy-level-diagram-with-and-without-enzyme-sq

Use the graph and your own knowledge of enzyme function to explain how enzymes function as biological catalysts.

7b2 marks

The graph shows how the addition of a molecule named here as molecule X affects the rate of an enzyme-controlled reaction. 

rate-of-reaction-with-the-addition-of-a-non-competitive-inhibitor-sq

Describe how the addition of molecule X affects the rate of reaction in the graph.

7c2 marks

The image below shows how molecule X interacts with the enzyme.

non-competitive-inhibitor-binding-to-enzyme-sq

Use the image to explain the results shown in the graph in part (b). 

7d1 mark

The image below shows another molecule, molecule Y.

competitive-inhibitor-sq

Suggest how molecule Y might interact with the enzyme shown in part (c).

7e2 marks

Sketch a line on the graph from part (b) to show how molecule Y might affect the rate of reaction.

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8a2 marks

State, with a reason, the type of enzyme inhibition shown in the image below.q2a_8-1_metabolism_medium_ib_hl_biology_sq

8b3 marks

Explain what is meant by allosteric inhibition.

8c3 marks
The graph below shows the relationship between substrate concentration and rate of reaction for a normal enzyme and a competitive inhibitor.

q2c_8-1_metabolism_medium_ib_hl_biology_sq

Explain the effect competitive inhibition has on the rate of reaction.

8d2 marks

State an example of a competitive inhibitor and describe its basic function.

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9a3 marks
Metabolic pathways exist in all living organisms.
 


Explain what is meant by a metabolic pathway.

9b3 marks

Describe the differences between anabolism, catabolism and metabolism.

9c2 marks

Metabolic paths require enzymes. Hexose kinase is the initial enzyme needed during glycolysis, it catalyses the phosphorylation of glucose by ATP. This reaction would occur without the presence of hexose kinase.

Explain the role hexose kinase has in this reaction.

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10a7 marks

This question is about metabolic pathways.

(i) Describe the meaning of the term metabolic pathway.

[3]

(ii) Outline how end-product inhibition can act to limit a metabolic pathway.

[4]

10b4 marks

Compare and contrast the allosteric and active sites of an enzyme.

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1a3 marks

Distinguish between anabolic reactions and catabolic reactions.

1b2 marks

Complete the table with tick marks (✓) in the appropriate boxes.

Cellular reaction Anabolic Catabolic
Fats → fatty acids and glycerol    
Accumulation of starch from sugars in plants    
Anaerobic respiration in yeast cells    
Hydrolysis of polypeptides into amino acids    
1c2 marks

The diagram below shows part of a biochemical pathway that takes place commonly in cells.oTEfImL9_q3c-2-1-metabolism-water-medium-ib-hl-biology-sq

 Deduce whether the pathway is anabolic or catabolic and give evidence from the diagram for your answer.

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2a3 marks

Lipase is an enzyme that breaks down lipids. The diagram below shows an experiment set up by a teacher to investigate the effect of lipase concentration on the hydrolysis of lipids.

The pH of beaker B is measured for 3 minutes at the start of the experiment. Beaker A containing lipase solution is added to beaker B. The data logger recorded the change in pH over the next 5 minutes.

q1a-2-4-enzymes-medium-ib-hl-biology-sq

State, with a reason, the predicted change in pH after the lipase has been added. 

2b2 marks

State two variables that must be controlled to carry out the experiment in part (a) accurately and reliably.

2c3 marks

For the experiment in part (a), draw a results table that could be used to record the results of the investigation. Your table should include suggested enzyme concentrations, and units should be stated. 

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3a2 marks

A protease is an enzyme that digests protein. A research scientist isolated protease C from a particular species of bacteria. The researcher investigated the effect of temperature on the rate of hydrolysis of a protein by protease C.  The unprocessed results can be seen in the table below.

Temperature / °C Mass of protein hydrolysed after 4 minutes / mg

Rate of hydrolysis /

10 470  
15 990  
20 1180  
25 1310  
30 1030  
35 420  
40 110  

Calculate (with appropriate units) the missing details in the table above.   

 

3b4 marks

Draw a graph of the results seen in part (a). Your graph should include an accurate scale and correct axis labels. q2b-2-4-enzymes-medium-ib-hl-biology-sq

3c1 mark

Suggest how the research scientist controlled the pH throughout the experiment.

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4a2 marks

Explain the aspect of enzyme and substrate structure that enables successful catalysis of a biochemical reaction.

4b1 mark

The sketch graph below shows how the rate of an enzyme-catalysed reaction varies for two separate independent variables. For curve A the independent variable is the concentration of enzyme.

 q3b-2-4-enzymes-medium-ib-hl-biology-sq

Identify the independent variable for Curve B.

4c3 marks

The sketch graph below shows how the rate of an enzyme-catalysed reaction varies as temperature changes. q3c-2-4-enzymes-medium-ib-hl-biology-sq

Explain the rates of reaction at positions A, B, and C on the curve. 

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5a7 marks

The sketch graph below shows the effects of varying the level of the independent variable, X, on the rate of an enzyme-controlled reaction. Lines A, B, and C represent three different independent variables which could be X.q5a-2-4-enzymes-medium-ib-hl-biology-sq 

(i)
Identify the independent variables that would cause lines A, B, and C.

 

(ii)
Use your knowledge of enzyme activity to explain the changes in reaction rate shown by lines A, B and C.
5b4 marks

An experiment was set up to investigate the effect of temperature on an enzyme-catalysed reaction in which the reaction mixture changes from clear-colourless to clear-dark blue as the reaction progresses.

Describe:

(i)
How the independent variable in the experiment could be controlled.

(ii)
How a colorimeter could be used to measure colour change.

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6a2 marks

Folate is a chemical used by cancer cells to make DNA during cell division. Folate is produced through the conversion of folic acid catalysed by the enzyme dihydrofolate reductase.

Methotrexate is a medicinal drug given to people with cancer, and other autoimmune diseases, as it acts as an inhibitor for the enzyme dihydrofolate reductase. 

The image below shows the chemical structure for the enzyme's normal substrate, folic acid, as well as the structure of its inhibitor, methotrexate. 

folic-acid-and-methotrexate-example-of-an-inhibitor-sqfolic-acid-and-methotrexate-example-of-an-inhibitor-sq

Using the images, suggest the method of inhibition used by methotrexate. Explain your answer.

6b3 marks

Folate is not just used by cancer cells during replication, but by any cells of the human body that replicate quickly.

Methotrexate is commonly used as part of chemotherapy treatment for cancer sufferers. 

Using this information, suggest why people that undergo chemotherapy lose their hair. 

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7a
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2 marks

Trypsin is an enzyme produced by the pancreas that hydrolyses proteins in the small intestine. 

The activity of trypsin was investigated by placing a small amount of the enzyme with a known concentration of protein.

The graph below shows the progress of this reaction when it is carried out at 25 °C.

3-2-fig-3-1

Calculate the initial rate of the reaction in the graph. Show your working.

7b2 marks

The procedure was repeated at the same temperature in the presence of a competitive inhibitor of trypsin.

Predict the results that will be obtained using the competitive inhibitor.

7c2 marks

Describe how your prediction for part b) would be different if a non-competitive inhibitor was used rather than a competitive inhibitor.

7d2 marks

The investigation was extended to compare the initial reaction rates of trypsin obtained from different species of animal. 

Suggest two advantages of calculating the initial reaction rates of enzyme catalysed reactions here rather than the reaction rates at another point during the experiment.

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8a1 mark

Threonine deaminase catalyses the conversion of threonine into an intermediate substrate, before producing the end product of isoleucine.

q3a_8-1_metabolism_medium_ib_hl_biology_sq

State which graph represents the relationship between threonine concentration and threonine deaminase concentration.

8b3 marks

Explain the effect a build up of isoleucine concentration would have on the activity of threonine deaminase.

8c3 marks

Explain how feedback inhibition is an example of negative feedback.

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9a2 marks

Plasmodium falciparum is a protozoan parasite of humans that causes malaria. Scientists have sequenced the proteome of this parasite and have determined a number of enzymes involved in its metabolic pathways. One such enzyme is hexokinase which is involved in the phosphorylation of glucose within the parasite.

The scientists tested two potential enzyme inhibitors, Inhibitor A and Inhibitor B, on the activity of hexokinase. The results are shown in the graphs below.q4a_8-1_metabolism_medium_ib_hl_biology_sq


Compare and contrast  the effect of the two inhibitors on the percentage inhibition.

9b2 marks

Deduce, with reasons, whether the inhibitors act as competitive or non-competitive inhibitors.

9c2 marks

The Plasmodium falciparum parasite depends on glycolysis for its survival, particularly the uptake of glucose from its host cells which is mediated by hexokinase.

The scientists investigated the action of hexokinase within Plasmodium falciparum.  They tagged hexokinase with two different potential drugs that inhibit its action. Their results are shown in the graph below.

q4c_8-1_metabolism_medium_ib_hl_biology_sq


Describe how to calculate the rate of reaction from the graph.

9d3 marks

The scientists concluded that drug 1 was less effective than drug 2.

Evaluate this conclusion.

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10a8 marks

Explain the effect of inhibitors on the activity of enzymes.

10b3 marks

Distinguish between an enzyme catalysed reaction and a non enzymatic reaction.

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1a
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2 marks

Washing powders often contain different types of enzymes that break down substances in stains. An investigation was carried out into washing powder that contained enzymes and washing powder that did not contain enzymes. The graph below shows the results of this investigation.

6-1-hard-q1a

Some of the substances that cause food stains are large insoluble proteins. 

Explain how washing powder containing enzymes would be able to remove these stains.

1b
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3 marks

The manufacturers of the washing powder containing enzymes claimed that their washing powder was more effective at removing tough stains compared to the washing powder without enzymes.

Based on the results of the investigation in part a), evaluate the claim of the manufacturers.

1c
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1 mark

The investigation at part a) was carried out at 40 °C.

Suggest a reason for this.

1d
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3 marks

The investigation was repeated at a temperature of 85 °C.

Predict, with a reason, the expected results from this investigation.

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2a1 mark

Certain plants that reproduce sexually contain an enzyme called pyrophosphatase. This enzyme plays a role in ensuring self-incompatibility, which is a mechanism that prevents a plant from fertilising itself. The selective advantage of self-incompatibility is that more cross-breeding can occur within a species, which has long term benefits for evolution and for maintaining a large pool of alleles.

Known volumes of pyrophosphatase and substrate can be mixed in a cuvette with a dye that starts as colourless and develops into a blue colour over time. The rate of colour development can be measured in a colorimeter by measuring the absorbance of light at a wavelength of 620 nm (red light). 

The graph shows the mean rate of reaction of pyrophosphatase measured over five repeats at 20°C.

mean-rate-of-reaction-of-pyrophosphatase-graph-sq

State why the wavelength of 620 nm was selected for this experimental measurement.

2b
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3 marks

Use the graph from part (a) to calculate the rate of the reaction at 100 seconds. Give your answer in suitable units. 

2c2 marks
(i)

Predict the effect that a higher enzyme concentration at the start of the experiment would have on the results calculated in part (b).

[1]

(ii)

Explain your answer in part (i).

[1]

2d3 marks

As the temperature increases, the rate at which pyrophosphatase works also increases up to a point, before decreasing. 

Explain why these changes in the reaction rate take place.  

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3a4 marks

In humans, the enzyme sucrase hydrolyses sucrose. This reaction occurs in the small intestine at 37°C.

(i)

Explain why sucrase can only hydrolyse sucrose.

[2]

(ii)

Describe how sucrase enables this reaction to take place at normal body temperature.

[2]

3b3 marks

A solution containing sucrose and sucrase was divided equally between two test tubes. One test tube (A) was heated to a temperature of 85°C, and the other (B) was kept at 37°C, as shown in the diagram below. Both test tubes were monitored for 30 minutes.

h-2b

 

(i)

Identify which test tube(s) would contain monosaccharides.

[1]

(ii)

Explain your answer in part (i).

[2]

3c2 marks

Suggest two sources of error that could arise from an experiment to measure the effect of temperature on the rate of an enzyme-controlled reaction.

Assume that in this experiment, the dependent variable is measured as the volume of a gas produced.  

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4a3 marks

Outline how changes in substrate concentration affects the rate of enzyme action. 

4b5 marks

Sometimes the active site of enzymes can be blocked or "inhibited" by substances that aren't the specific substrate for that enzyme. 

Suggest how this would affect the rate of reaction of an enzyme-catalysed reaction as well as some possible uses of enzyme inhibitors in medicine. 

4c7 marks

Plan an investigation to determine how changing the temperature of amylase affects the rate of reaction of the digestion of starch to maltose. 

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5a3 marks

Many products of multi-step cellular reactions act as inhibitors of the enzymes that catalyse the preceding steps in a metabolic pathway.

For example, ATP acts as a non-competitive inhibitor of the enzyme pyruvate kinase, which catalyses the final step of glycolysis.

pyruvate-kinase-sq

Suggest how the inhibition of pyruvate kinase by ATP allows cells to prevent overproduction and wasting of cellular energy.

5b4 marks

The graphs below shows the effects of increasing substrate concentration on enzyme activity in the presence and absence of a competitive and a non-competitive inhibitor.  

effects-of-increasing-substrate-conc-on-enzyme-activity-with-inhibitors-sq

Sketch a line on both graphs to indicate the effect of increasing inhibitor concentration in each case. Explain the position and shape of each line.  

5c4 marks

Compare and contrast the features of a substrate and a competitive inhibitor.  

5d2 marks
When studying plant species in areas of high biodiversity, or any extreme environment, it is often useful to look at the metabolic pathways linked to the adaptations of the plants.
To investigate the metabolic pathways scientists can determine the proteome of the plant, or just focus on the proteome of specific specialised cells. 
Suggest why just studying the proteome alone might not be enough to fully understand the metabolic pathways in the plant.

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6a2 marks

Copper (II) ions act as non-competitive inhibitors of the enzyme catalase.

Describe how copper (II) ions work to inhibit the activity of catalase.

6b4 marks

Catalase is found in all living things that are exposed to oxygen. It protects cells from damage by breaking down the toxic chemical hydrogen peroxide into water and oxygen.

Numbers of fish living in copper contaminated water have shown a decline in numbers. Scientists can study the action of catalase in fish in order to understand the full impact of copper contamination on the fish.

A group of students carried out an experiment to explore the effects of copper sulfate on the action of catalase. They measured the activity of catalase exposed to different concentrations of copper sulfate.

The results of their experiment are shown in the table below.

Concentration of copper sulfate (moles dm-3) Volume of oxygen gas produced (cm3)
0.00 15.70
0.05 11.32
0.10 8.12
0.15 6.25
0.20 4.98

In the space provided below, draw a graph of the results in the table.

HPNaaK_S_axes-for-graph-of-copper-pollution-and-catalase-activity-sq

6c2 marks

What can the students conclude from their results?

6d3 marks

Three rivers in the Scottish Highlands were polluted with copper, which affected the aquatic wildlife. Scientists were provided with one dead brown trout, Salmo trutta, from each of the rivers.

Scientists were unable to take a direct measurement of the copper ion concentration in the river.

Using the information provided in part (b), suggest the dependent, independent and control variables of an experiment using the fish tissue to compare the copper ion pollution in the three rivers.

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7a3 marks

Antifreeze is a chemical often used in vehicles, such as cars, to act as an engine coolant.

A small number of people have accidentally consumed antifreeze and become poisoned as a result. Once a person consumes antifreeze it is important that they receive treatment straight away, otherwise, there is a risk of death. This is because if the methanol goes to the liver it can be broken down by the enzyme alcohol dehydrogenase into toxic products such as methanoic acid and formaldehyde. If the methanol can't bind to the enzyme it will just be excreted via the kidneys and the person can be saved. 

One method of treating methanol poisoning, in the rare instances where no other treatment is available, is to use large quantities of the alcohol ethanol. 

Suggest how ethanol might be able to save someone from methanol poisoning. 

7b1 mark

Although it may be an effective antidote, suggest why it is not recommended that people with methanol poisoning consume ethanol other than in extreme circumstances where no other treatment is available. 

7c2 marks

One medicinal chemical that can be used to treat antifreeze poisoning is called fomepizole, which is a competitive inhibitor of the enzyme alcohol dehydrogenase.

Fomepizole is 160,000 times more likely to bind to alcohol dehydrogenase than methanol. 

Using your knowledge of enzyme structure, suggest how this might be possible. 

7d3 marks

Scientists were trying to investigate the rate of reaction of alcohol dehydrogenase by measuring the quantity of product, methanoic acid, produced over time, with a fixed quantity of methanol added at the start. 

The graph below shows their results. 

rate-of-reaction-calculation-graph

Use the graph below to calculate the rate of reaction of alcohol dehydrogenase after 3 minutes. 

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8a3 marks

Phosphofructokinase (PFK) is an enzyme that catalyses an important step in the glycolysis process of respiration. PFK is inhibited by ATP. 

PFK is known as the "pacemaker" enzyme for respiration. 

Suggest what is meant by the term "pacemaker" in this context. 

8b5 marks

Describe and explain the similarities and differences between competitive and non-competitive enzyme inhibition.  

8c7 marks

The image below shows the pathway the human body uses to metabolise lactose. 

qlyp3ce-graphic-for-metabolic-pathways-sq

There is a genetic condition that exists called galactosemia, which causes large quantities of galactose to build up in the body, particularly in the liver tissues. 

If left untreated, it can be very harmful to sufferers, in the worst cases, it can lead to death. 

Galactosemia is rare and only occurs in around 1 per 60,000 births for people of European ancestry, often skipping a generation before re-emerging.

Using the information from the question and your own knowledge, suggest the cause of galactosemia, some symptoms, a type of treatment for the condition. 

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