Cambridge IGCSE®
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Cambridge IGCSE® Biology, Chemistry and Physics
* Biology - Mary Jones and Geoff Jones * Chemistry - Richard Harwood and Ian Lodge * Physics - David Sang
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Our Cambridge IGCSE Science Coursebooks with CD-ROM give comprehensive and accessible coverage. Visit our website for syllabus information when available. Suggestions for practical activities are included, designed to help develop the required experimental skills. Exam-style questions at the end of each chapter and a host of revision and practice material on the CD-ROM are designed to help students maximise their chances in their examinations. Answers to the exam-style questions in the Coursebook are provided on the CD-ROM. 978-1-107-61479-6
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Physics Coursebook with CD-ROM
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22
22.1 What is biotechnology?
Biotechnology involves using living organisms to carry out processes that make substances that we want. Usually, the term is only used when microorganisms are involved, or when plants or animals are used to produce something other than food. We have been using microorganisms to make various products for us for thousands of years. Yeast has been used to make bread and alcohol. Bacteria have been used to make yoghurt and cheese. Of course, people did not know that these microorganisms were involved in the processes they used. Today, we still use microorganisms to make these foods, but we now also use them to make many other substances, such as enzymes. And, in the 1970s, a new branch of biotechnology began, when scientists first found out how to take a gene from one organism and put it into a different one. This is called genetic engineering, and it has opened up entirely new possibilities for using microorganisms and other organisms.
Biotechnology
In this chapter, you will learn about: why bacteria are used in biotechnology and genetic engineering how yeast is used to make ethanol and bread the uses of pectinase and other enzymes in industry and the home how penicillin is made genetic engineering, and some of the ways it is useful to us
S
Enzymes to treat disease Gaucher disease is a rare inherited illness caused by a recessive allele of a gene that affects how the body deals with fat molecules. The normal allele causes the production of an enzyme that helps in fat metabolism. This is missing in people with Gaucher disease. As a result, a fatty substance called glucocerebroside builds up in several body organs, including the spleen and liver (Figure 22.1). There are several types of the disease, but all of them can cause severe damage to various organs. Researchers thought that if they could replace the missing enzyme, they might be able to improve the health of at least some of the people who have this disease. In the 1970s, a method was found to extract this enzyme from human placentas. The results were encouraging, but with only very small supplies of the enzyme it was never going to be possible to treat many people. In the 1980s, scientists found a way to make the enzyme using genetic engineering. Now larger quantities of it were available, and it was much cheaper. The enzyme could also be made in a slightly modified form, which made it work better. Today, some patients with Gaucher disease are given regular doses of the enzyme. This does not cure the disease, but in some people it does help to reduce their symptoms, and improves the quality and length of their lives.
Clear, informative diagrams and photos
22.2 Using yeast
cytoplasm
ribosome oil droplet mitochondrion Figure 22.2
vacuole
A yeast cell.
Using microorganisms
spleen liver
Figure 22.1 This diagram shows the position of the liver and the spleen, which become enlarged in people with Gaucher disease.
Biotechnology and genetic engineering often make use of microorganisms, such as bacteria and microscopic fungi. There are several reasons for this. Bacteria and fungi are very small, and are easy to grow in a laboratory. They do not take up a lot of space. They reproduce very quickly. They are able to make a huge range of different chemical substances. S No one minds what is done to bacteria and fungi. There are no ethical issues like those that might arise if we used animals. Although bacterial cells are very different from animal and plant cells, in fact we all share the same kind of genetic material – DNA. The genetic code is the same for bacteria as it is for humans and all other organisms. So we can take a gene from a human cell and place it into a bacterial cell, and it will work to produce the human protein. As well as their ‘main’ DNA – their ‘chromosome’ – bacteria also have little loops of DNA called plasmids. These are quite easy to transfer from one cell to another. We can use plasmids for moving genes from one organism’s cells to another.
Figure 22.3 Yeast cells seen with a scanning electron microscope. You can see little buds growing from some of the cells – this is the way that yeast reproduces.
glucose
ethanol + carbon dioxide
This process is also called fermentation.
Making biofuels We have seen (page 288) that we need to reduce our use of fossil fuels. One alternative is to use plants to provide sugars, which yeast can then break down to form ethanol. The ethanol – sometimes called bioethanol – can then be used as a fuel. Maize is one of the crops that is used in this process. It is first treated with amylase enzymes, which break
Chapter 22:
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Supplementary material is clearly marked
Yeast is able to respire anaerobically. When it does so, it produces ethanol and carbon dioxide.
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Study tips and worked examples are contained cell wall within the Coursebook cell membrane along with nucleus key definitions
Yeast is a single-celled fungus. Figures 22.2 and 22.3 show yeast cells.
Biotechnology
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