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Cambridge IGCSE0610

Biotechnology and genetic modification

Biology 0610 Chapter Notes

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In this chapter

  1. 1Why bacteria are useful
  2. 2Rapid reproduction rate
  3. 3Ability to make complex molecules
  4. 4Few ethical concerns
  5. 5The presence of plasmids
  6. 6Yeast and ethanol for biofuels
  7. 7Yeast in bread-making
  8. 8Pectinase in fruit juice
  9. 9Biological washing powders
  10. 10Lactase and lactose-free milk
  11. 11Fermenters and large-scale production
  12. 12Conditions in a fermenter
  13. 13What genetic modification is
  14. 14Examples of genetic modification
  15. 15Cutting out and joining the gene
  16. 16Making the human protein in bacteria
  17. 17Advantages of genetically modified crops
  18. 18Disadvantages of genetically modified crops

1. Why bacteria are useful

Bacteria are useful in biotechnology and genetic modification because of their rapid reproduction rate and their ability to make complex molecules.

The question asks for features, not uses. Foods, drinks and medicines are products. They are not reasons.

Examiner insight

“Candidates sometimes misread this question and wrote about the ways in which bacteria are used in biotechnology; for example, to produce different foods, drinks or medicines.” “Better answers described the features of bacteria that make them useful in biotechnology, such as their fast reproduction rate and their ability to make complex molecules.”

Worked example 11 mark

Bacteria are used for many genetic modification and biotechnology purposes. Which factors make bacteria useful for genetic modification and biotechnology?

1 Bacteria can make complex molecules. 2 Bacteria do not mutate. 3 Bacteria are living organisms. 4 Bacteria reproduce rapidly.

A 1 and 3 · B 1 and 4 · C 2 and 3 · D 2 and 4

  1. 1

    B: statements 1 and 4. Bacteria make complex molecules and reproduce rapidly. [1]

2. Rapid reproduction rate

Bacteria have a rapid reproduction rate. An answer that says bacteria reproduce rapidly also earns the mark.

Name the feature with the term. Write fast reproduction rate, not a loose phrase such as ‘they grow fast’.

Examiner insight

“Describing bacteria as having a fast reproduction rate is a more accurate response than ‘they grow fast’.” “Bacteria are useful because they reproduce rapidly and have the ability to produce complex molecules.”

Worked example 11 mark

State one reason why bacteria are useful in genetic modification. Do not give a structural feature.

  1. 1

    fast reproduction rate (‘they grow fast’ is too vague) [1]

3. Ability to make complex molecules

Bacteria have the ability to make complex molecules. This is the reason. The useful products, such as insulin, are the result.

When a question asks why bacteria are useful, give the ability to make complex molecules and leave the product as an example at most.

Keep to bacteria. Yeast is not a bacterium.

Examiner insight

“It was common to see examples of the products that bacteria and fungi produce rather than reasons why they are useful.” “A common error was to refer to yeast as a bacterium, or to describe vaccine production using dead bacteria.”

Worked example 12 marks

A student writes: ‘Bacteria are useful because they make insulin.’ Explain why this is not a reason, and state the feature of bacteria it points to.

  1. 1

    insulin is a product (a use of bacteria), not a reason [1]

  2. 2

    the feature is the ability to make complex molecules [1]

4. Few ethical concerns

There are few ethical concerns over the manipulation and growth of bacteria. This is one of the two reasons to discuss at Extended level.

Give the reason in the syllabus's words. Say what the concerns are about: the manipulation of bacteria and their growth.

This reason is not a structural feature. When a question says not to give structural features, the presence of plasmids is ignored, but this reason still counts.

Examiner insight

“The lack of ethical concerns about using bacteria was also well-known.” “This proved to be a challenging question, with only some appreciating the reason why insulin from bacteria is regarded as a better ethical choice.”

Worked example 11 mark

Give one reason why bacteria are useful in genetic modification and biotechnology. Do not give a structural feature, their reproduction rate or the molecules they make.

  1. 1

    few ethical concerns over their manipulation and growth [1]

5. The presence of plasmids

Bacterial cells have a loop of DNA. They also have additional DNA molecules called plasmids. Bacteria do not have nuclei. The presence of plasmids makes bacteria useful in genetic modification, because plasmids can be transferred between cells.

A plasmid is a loop of DNA. It is not a bacterial cell.

Examiner insight

“Many candidates did not mention that in addition to the loop of DNA, prokaryotes also have additional DNA molecules called plasmids.” “Although many candidates appreciated that the plasmid is a loop of DNA, some incorrectly believed that it is a bacterial cell.”

Worked example 12 marks

Bacterial cells contain a loop of DNA and additional DNA molecules. Name these additional DNA molecules and state why they make bacteria useful in genetic modification.

  1. 1

    plasmids [1]

  2. 2

    plasmids can be transferred between cells [1]

Recap

  • Bacteria are useful in biotechnology and genetic modification because of their rapid reproduction rate and their ability to make complex molecules.
  • Give features, not uses. A medicine is a product, not a reason.
  • Write ‘fast reproduction rate’, not ‘they grow fast’.
  • Extended: there are few ethical concerns over the manipulation and growth of bacteria.
  • Extended: bacteria contain plasmids, additional loops of DNA that can be transferred between cells.

6. Yeast and ethanol for biofuels

Yeast respires anaerobically, which means without oxygen. Its anaerobic respiration produces ethanol and carbon dioxide.

The ethanol is used as a biofuel.

glucose → ethanol + carbon dioxide

Examiner insight

“Many candidates understood that yeast respires anaerobically to produce carbon dioxide and ethanol (biofuel).” “Few candidates specified anaerobic respiration or fermentation in their answers.”

Worked example 13 marks

Yeast is used to produce ethanol for biofuels. Describe the role of yeast.

  1. 1

    yeast respires anaerobically, without oxygen [1]

  2. 2

    anaerobic respiration produces ethanol [1]

  3. 3

    the ethanol is used as a biofuel [1]

7. Yeast in bread-making

Yeast is mixed into bread dough. Its anaerobic respiration produces carbon dioxide.

The gas forms bubbles in the dough, which makes the bread rise. The useful product here is the gas, not the ethanol.

Examiner insight

“Few candidates appreciated that carbon dioxide is the useful product of anaerobic respiration in the manufacture of bread.” “Slightly fewer candidates knew that respiration was the process that creates the gas bubbles that cause bread to rise.”

Worked example 12 marks

Explain why yeast is added to bread dough.

  1. 1

    anaerobic respiration by the yeast produces carbon dioxide [1]

  2. 2

    the carbon dioxide forms bubbles that make the dough rise [1]

8. Pectinase in fruit juice

Pectinase is an enzyme. It breaks down pectin, a carbohydrate found in the cell walls of many types of fruit.

Pectinase is used in the production of fruit juice. It increases the yield of juice and makes the juice clearer.

Examiner insight

“Few knew that pectinase is used in the production of fruit juice, many assigned it a role in human digestion, probably recognising the –ase ending of the word as indicating that it is an enzyme.” “Many candidates named an enzyme used to extract juice from fruit, but some gave the substrate (e.g., pectin) rather than the enzyme.”

Worked example 12 marks

State two reasons why pectinase is used in the production of fruit juice.

  1. 1

    increase the yield of fruit juice [1]

  2. 2

    increase the clarity of the fruit juice [1]

9. Biological washing powders

A biological washing powder contains enzymes. Examples are protease and lipase. Lipase removes an oil stain.

To investigate, wash stained cloths in solutions of different powders. Judge the intensity of each stain by eye. Include a control, to compare the effect of the solutions on the cloth.

Examiner insight

“Most candidates knew that lipase in washing powder removes an oil stain.” “Simple statements such as ‘to compare results’ were insufficient, better responses went on to explain that a control is used to compare the effect of the solutions on the cloth.”

Worked example 11 mark

Which enzyme would be used in a biological washing powder?

A DNA ligase · B maltase · C pectinase · D protease

  1. 1

    D: protease. [1]

10. Lactase and lactose-free milk

Lactase is the enzyme used to make lactose-free milk. It breaks down lactose into a simple sugar, such as glucose.

Like any enzyme, lactase is denatured by heat. The shape of its active site is altered, so lactose is not broken down.

Examiner insight

“Most candidates stated that heat would denature the enzymes, but did not continue their answer to explain that lactose would therefore not be broken down.” “Few candidates stated that the shape of the active site would be altered.”

Worked example 14 marks

A dairy heats lactase to a very high temperature before adding it to milk. The milk still contains lactose. Explain why.

  1. 1

    the heat denatures the lactase [1]

  2. 2

    the shape of the active site is altered [1]

  3. 3

    the active site is no longer complementary to lactose [1]

  4. 4

    so lactose is not broken down [1]

11. Fermenters and large-scale production

Fermenters are used for the large-scale production of useful products by bacteria and fungi. The products include insulin, penicillin and mycoprotein.

Penicillin is made by a fungus, Penicillium. Bacteria are useful because they have a rapid reproduction rate and can make complex molecules.

Examiner insight

“Bacteria are useful because they reproduce rapidly and have the ability to produce complex molecules.” “It was common to see examples of the products that bacteria and fungi produce rather than reasons why they are useful.”

Worked example 12 marks

Pectinase enzymes are naturally produced by microorganisms, including bacteria.

State two reasons why bacteria are useful in biotechnology.

  1. 1

    rapid reproduction rate [1]

  2. 2

    ability to make complex molecules [1]

12. Conditions in a fermenter

A thermometer monitors the temperature. A water jacket controls it and keeps it even. The pH is controlled using a buffer.

Air supplies oxygen for respiration. Nutrients such as carbohydrates and amino acids are added for growth and energy. A stirrer keeps the mixture uniform, which optimises growth.

Carbon dioxide is a waste gas produced during fermentation. It leaves through a gas outflow pipe. This stops the pressure rising inside the fermenter, and carbon dioxide is toxic to the fungus.

Examiner insight

“Candidates should be reminded that thermometers can be used to monitor the temperature but do not control it.” “Almost all candidates suggested that the contents of the fermenter were stirred to form a uniform mixture, but fewer candidates extended their answers to explain the purpose of optimising the growth of the bacteria.”

Worked example 14 marks

Describe and explain how the temperature and the pH are controlled in a fermenter.

  1. 1

    a thermometer monitors the temperature [1]

  2. 2

    a water jacket controls the temperature, keeping it even [1]

  3. 3

    a high temperature would denature the enzymes [1]

  4. 4

    the pH is controlled using a buffer [1]

Recap

  • Yeast respires anaerobically to make ethanol and carbon dioxide.
  • Ethanol is the biofuel. Carbon dioxide makes bread dough rise.
  • Pectinase breaks down pectin: more juice, clearer juice.
  • Biological washing powders contain enzymes such as protease and lipase.
  • Extended: lactase breaks down lactose to make lactose-free milk.
  • Extended: fermenters let bacteria and fungi make insulin, penicillin and mycoprotein.
  • Extended: control temperature, pH, oxygen, nutrients and waste products in a fermenter.

13. What genetic modification is

Genetic modification is changing the genetic material of an organism by removing, changing or inserting individual genes.

A definition is not a list of uses. Selective breeding and natural selection are different processes.

Examiner insight

“Many candidates did not write a definition but instead gave examples of the uses of genetic engineering instead.” “Very few candidates could name the process of changing genes in plants. The commonest incorrect responses were selective breeding or artificial selection.”

Worked example 11 mark

Genes can be inserted into crop plants to make them resistant to herbicides. Which process is this an example of?

A antibiotic resistance · B genetic modification · C natural selection · D selective breeding

  1. 1

    B: genetic modification. [1]

14. Examples of genetic modification

Genes are inserted into an organism to give it a new feature. There are four examples to know.

Human genes are inserted into bacteria to produce human proteins, such as insulin.

Genes are inserted into crop plants to give resistance to herbicides, resistance to insect pests, or improved nutritional qualities.

Examiner insight

“The point that herbicide resistance would enable weeds to be killed without harming the crop was missed by some candidates.” “A common error was to describe this as an immunity rather than a resistance.”

Worked example 12 marks

Crops can be genetically modified to be resistant to herbicides and insecticides.

(i) State one reason why farmers use herbicides.

(ii) State one reason why farmers use insecticides.

  1. 1

    (i) to kill weeds, or reduce competition with weeds, or to increase yield [1]

  2. 2

    (ii) to kill insects that feed on crops, or so crops will not be eaten by insects, or to increase yield [1]

15. Cutting out and joining the gene

The DNA making up a human gene is isolated using restriction enzymes. They cut the whole gene out of the human DNA, forming sticky ends.

The bacterial plasmid is cut with the same restriction enzymes. This forms complementary sticky ends: their base sequences are complementary because the same enzyme made both cuts.

DNA ligase inserts the human DNA into the plasmid. The result is a recombinant plasmid.

Examiner insight

“The best answers made it clear that the same restriction enzyme must be used to open the plasmid as was used to cut the TPA gene from human DNA.” “Common errors were to mix up the two enzymes, or to describe cutting the gene into pieces, rather than cutting the whole gene from a piece of DNA.”

Worked example 11 mark

What is the function of an enzyme used in genetic modification?

A DNA ligase: isolates the DNA of a human gene · B DNA ligase: inserts human DNA into bacterial plasmid DNA · C restriction enzyme: inserts recombinant plasmid DNA into bacteria · D restriction enzyme: isolates the recombinant plasmid DNA

  1. 1

    B: DNA ligase inserts human DNA into bacterial plasmid DNA. [1]

16. Making the human protein in bacteria

The recombinant plasmids are inserted into bacteria. Specific details are not required.

The bacteria containing recombinant plasmids multiply. Bacteria are useful because of their rapid reproduction rate, and because they can produce complex molecules.

The human gene is expressed in the bacteria, which make the human protein. This is the end of the process, not the start.

Examiner insight

“Most candidates answered this correctly, but a significant number thought that the expression of the human insulin gene in bacteria was a starting point rather than the desired outcome.” “Describing bacteria as having a fast reproduction rate is a more accurate response than ‘they grow fast’.”

Worked example 12 marks

Genes can be inserted into bacteria to produce human proteins, such as insulin. State two reasons why bacteria are useful for this process.

  1. 1

    rapid reproduction rate [1]

  2. 2

    can produce complex molecules [1]

17. Advantages of genetically modified crops

Genetically modified crops include soya, maize and rice. Their new genes give resistance to herbicides, resistance to insect pests or improved nutritional qualities.

A herbicide kills weeds but not the modified crop, so there is less competition from weeds. Insect-resistant crops will not be eaten by insects. Both help to increase yield.

Examiner insight

“Increasing yield was the most common advantage of GM crops that was given. Many candidates also knew other examples such as improving the nutritional value or conferring resistance to factors other than insects.”

Worked example 12 marks

A farmer grows soya that has been genetically modified to be resistant to a herbicide. Explain one advantage to the farmer of growing this soya.

  1. 1

    The herbicide kills the weeds but does not harm the soya. [1]

  2. 2

    There is less competition from weeds, so the yield increases. [1]

18. Disadvantages of genetically modified crops

Genetically modified seeds are expensive, and a farmer may have to buy them every year.

There is a risk of cross-breeding with wild plants, such as wild rice. Other disadvantages are a reduction in biodiversity and ethical concerns.

Examiner insight

“The best responses described the issues with having to purchase seeds every year and the associated expense of this as well as the risk of cross-breeding with wild rice.” “Several candidates gave reference to reduced vitamins or taste which did not gain credit.”

Worked example 12 marks

A country grows genetically modified rice. State two disadvantages of genetically modifying crops.

  1. 1

    The seeds are expensive and may have to be bought every year. [1]

  2. 2

    There is a risk of cross-breeding with wild rice. [1]

Recap

  • Genetic modification = changing the genetic material of an organism by removing, changing or inserting individual genes.
  • Human genes go into bacteria to make human proteins, such as insulin.
  • Genes go into crop plants for resistance to herbicides, resistance to insect pests or improved nutritional qualities.
  • Extended: a restriction enzyme cuts out the human gene, leaving sticky ends.
  • Extended: the same restriction enzyme cuts the plasmid. DNA ligase joins the gene in, making a recombinant plasmid.
  • Extended: recombinant plasmids go into bacteria. The bacteria multiply and the gene is expressed to make the human protein.
  • Extended: GM crops can raise yield. Disadvantages are expensive seeds, cross-breeding with wild plants, less biodiversity and ethical concerns.

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. State two features of bacteria that make them useful in biotechnology and genetic modification.2 marks
  2. A student writes: ‘Bacteria are useful because they grow fast.’ Rewrite the point using the correct term.1 mark
  3. State whether each of these is a feature of bacteria or a use of bacteria: (a) the ability to make complex molecules, (b) producing insulin, (c) a rapid reproduction rate.3 marks
  4. A student says bacteria are useful because they are living organisms. Explain why this does not earn credit.2 marks
  5. A question asks: ‘State two reasons why bacteria are useful in biotechnology.’ Four students each give one answer: P ‘They are used to make foods and drinks.’ Q ‘They have a rapid reproduction rate.’ R ‘They do not mutate.’ S ‘They can make complex molecules.’ State which two answers earn the marks, and say why each of the other two does not.3 marks
  6. A question asks why bacteria are useful in biotechnology. A student answers: ‘Yeast is a bacterium that is useful because it makes bread.’ State two things wrong with this answer, and give one reason that would earn the mark.3 marks
  7. Besides a rapid reproduction rate and the ability to make complex molecules, state two other reasons why bacteria are useful in biotechnology and genetic modification.2 marks
  8. A question says: ‘Give two reasons why bacteria are useful in genetic modification. Do not give structural features.’ A student answers: ‘They contain plasmids’ and ‘They have a fast reproduction rate.’ Say which answer is not credited and suggest a replacement from the Extended syllabus.2 marks
  9. A company uses bacteria to make a complex molecule for use as a medicine. Its leaflet says: ‘Our bacteria are ideal for genetic modification because the DNA in the nucleus of one cell can be transferred to another cell.’ (a) State what is wrong with the words ‘in the nucleus’. (b) Name the two kinds of DNA molecule found in a bacterial cell. (c) State which of these two the leaflet should name, and why it makes bacteria useful in genetic modification.5 marks
  10. A trainee at a company that grows genetically modified bacteria is asked why bacteria were chosen. (a) The trainee writes: ‘Bacteria are useful because they make medicines and they grow fast.’ Explain why ‘they make medicines’ is not a reason, and rewrite the sentence so that it gives two reasons in the correct terms. (b) The trainee is then asked to discuss two further reasons, and writes: ‘Bacteria are plasmids, and it is ethical.’ Write an answer that earns full marks.6 marks
  11. Name the organism whose anaerobic respiration produces ethanol for biofuels.1 mark
  12. A student says that bread dough rises because yeast makes alcohol. Explain what really makes the dough rise.2 marks
  13. A student says that pectinase is a digestive enzyme in the human stomach. State what pectinase is really used for and give two reasons for using it.3 marks
  14. A shirt has an oil stain. It is washed in a biological washing powder. (a) State what a biological washing powder contains. (b) Name the enzyme that removes the oil stain.2 marks
  15. Name the useful product of anaerobic respiration in yeast for (a) biofuels and (b) bread-making.2 marks
  16. A student washes one stained cloth in a biological washing powder solution and one in water only. Explain why she uses the cloth in water only and state one way she judges the results.3 marks
  17. Lactase is used to make lactose-free milk. (a) State what lactase does to lactose. (b) A dairy adds lactase to milk that is too hot. The milk still contains lactose. Explain why.4 marks
  18. A student is asked why bacteria are useful in biotechnology. She writes: ‘Bacteria make insulin and penicillin.’ (a) State the mistake she has made about penicillin. (b) State two reasons why bacteria are useful in biotechnology.3 marks
  19. To make lactose-free milk, a dairy heats milk to 72 °C to kill pathogens, cools it, then adds lactase. A new worker adds the lactase before the heating instead. The table gives the lactose in each milk. (a) Calculate the percentage decrease in lactose, from untreated milk, for the usual method. (b) Explain why the worker's milk still contains most of its lactose. (c) Suggest why the worker's milk contains slightly less lactose than untreated milk. | milk | lactose / g per 100 cm³ | | --- | --- | | untreated | 4.8 | | usual method | 0.1 | | worker's method | 4.6 |6 marks
  20. A fungus makes penicillin in a fermenter. The table gives the temperature inside. The gas outflow pipe is also blocked. A technician says: ‘The thermometer will lower the temperature.’ (a) Calculate the mean rate of temperature rise from 3 hours to 6 hours. (b) State what is wrong with the technician's statement and name the part that has failed. (c) Explain how the rise in temperature could stop penicillin being made. (d) Explain two problems caused by the blocked gas outflow pipe. (e) The technician suggests switching off the air supply. Explain why this is a mistake. | time / hours | 0 | 1 | 2 | 3 | 4 | 5 | 6 | | --- | --- | --- | --- | --- | --- | --- | --- | | temperature / °C | 24 | 24 | 24 | 24 | 28 | 32 | 36 |9 marks
  21. Name the type of organism that receives human genes so that it makes human proteins.1 mark
  22. State three examples of genetic modification in crop plants.3 marks
  23. A maize plant is modified so that insects that feed on it die. Name this feature of the maize and state one benefit to the farmer.2 marks
  24. A farmer says: ‘My sheep are genetically modified, because I only breed from the ones with the thickest wool.’ Explain why he is wrong.2 marks
  25. Name the enzyme that cuts the human gene from human DNA. Name the enzyme that joins the gene into the bacterial plasmid.2 marks
  26. These steps are in the wrong order. A the bacteria multiply; B the human protein is made; C DNA ligase joins the gene into the plasmid; D the same restriction enzyme then cuts the plasmid; E the recombinant plasmid is inserted into bacteria; F a restriction enzyme isolates the human gene. Write the letters in the correct order.3 marks
  27. Explain why the same restriction enzyme is used to cut the human gene and the plasmid.2 marks
  28. A student labels a plasmid that has had a human gene inserted as ‘a genetically modified organism’. Give the correct name for this plasmid. Name the organism that is genetically modified in this process.2 marks
  29. A farmer grows rice. Wild rice grows at the edges of her fields. A company offers her seed for rice that is genetically modified to be resistant to insect pests. She must buy new seed from the company every year. A student gives her this advice: ‘The rice will be immune to insects, so the yield will go up. But the plants are expensive, and growing one crop over a large area is a disadvantage of genetic modification.’ (a) The advice contains three errors. Identify and correct each one. (b) State the risk from the wild rice that the advice leaves out. (c) State two other disadvantages of genetically modifying crops that are not about cost.6 marks
  30. A laboratory wants bacteria to make TPA, a human protein. A technician writes this method. 1 A restriction enzyme cuts the TPA gene into pieces. 2 A different restriction enzyme cuts the bacterial plasmid. 3 The cut ends of the gene and the plasmid are called active sites. 4 A restriction enzyme joins the gene into the plasmid, forming a genetically modified organism. 5 The gene is expressed to make TPA. Then the plasmids are inserted into bacteria, which multiply. Steps 1, 2, 3 and 5 each contain one error and step 4 contains two. Correct all six errors.6 marks

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