IGCSE Biology Essay

Plant breeders wanted to produce a better variety of tomato by selective breeding. Two plants, of the varieties Tangelo and Piranha, were crossed. (a) Some flowers of each variety were covered with cellophane bags. The diagram shows a covered flower and a brush. (I) Explain why some flowers were covered with cellophane bags during the selective breeding. . Suggest why a brush was needed. (b) Information about each variety of tomato is shown in the table.

Which features of Piranha would the plant breeders wish to see in the new breed f tomato? (Total 5 marks) 2. The diagrams show stages in the transfer and copying of the gene for growth hormone. (a) (I) Name the donor and recipient organisms for this gene transfer. Donor (it) During which stages is a restriction enzyme used? (iii) During which stage is aliases used? (iv)During which stages is the gene for growth hormone copied? (b) The boll weevil is an insect pest of cotton plants. A genetically modified virus which kills the boll weevil is being developed in the USA.

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Viruses reproduce rapidly, eave a high rate to mutation and can spread great distances. (I) Explain an economic advantage of using this genetically modified virus, rather than insecticide, to kill the boll weevil. Suggest why some people consider the use of the genetically modified virus to be hazard. (Total 9 marks) 3. Read the passage about oil palm trees. The oil palm is a plant which is grown to produce oil for cooking and for making soap. When properly cultivated, the oil palm can give higher yields of oil per hectare than any other oil-producing crop.

The trees can be grown from seeds, but there is a lot of variation in the new plants. After 10 years’ research, scientists managed to grow clones from pieces of oil palm. Extraterrestrial crops declared ‘safe’ for the environment Results of long term trials suggest that genetically modified crops are not likely to cause environmental damage. The worry is that genes from crops which had been genetically altered will ‘escape’ and spread to other species of plants, including weeds. However, scientists could find no evidence that this had happened.

Trials were done over ten years at four secret sites spread throughout the UK. (a) (I) Explain what is meant by the term clones. Suggest one advantage and one disadvantage of growing large areas of cloned oil palms. Advantage disadvantage (b) Some oil palms are still grown from seed. Suggest an advantage of growing oil palms from seed. (Total 4 marks) 4. The table describes the stages of a selective breeding programmer to produce cows which give more milk. The stages are in the wrong order. Circumscription male calves are mated then checked to find out which ones give most milk. Cattle to be parents are selected from herds with high milk yields. Calves are born. The selected cattle are mated. The best young females are then used to breed more cows. Write one letter in each box to show the correct order. The first one has been done for you. 1st2nd3rd4th5thB 5. The diagram shows stages in the production of genetically identical (cloned) sheep. (a) Name and describe the process by which the zygote becomes an embryo of two cells.

Name -? Description ) Sheep can be genetically modified to produce setup human proteins in their milk The required human gene is inserted into the DNA of a sheep zygote, using enzymes. The zygote is then cloned many times. (I) Describe one way in which enzymes are used to insert a human gene into sheep (it) State three potential benefits and two potential problems posed by the genetic modification of animals. Benefits Problems 6. Read the following article. (a) Give one possible benefit of growing genetically modified crops. (b) Explain why the scientists did the trials: (I) over ten years;

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