Internal assessment resource reference number Bio/3/2 – A exemplars
PAGE FOR TEACHER USE
2004
BIOLOGY
Level Three
Achievement Standard 3.2
Research a contemporary biological issue
Credits: 3
Internal assessment resource reference number: Bio/3/2 – A version 1
“Which side are you on?”
EXEMPLARS
These exemplars show how specific topics can be used with the Internal Assessment Resource Bio3_2A version 1.
Date version published: 30 December 2001
Ministry of Education For use in professional development
quality assurance status and trial activity in 2002 and 2003.
4
© Crown 2001
Internal assessment resource reference number Bio/3/2 – A Exemplars
PAGE FOR TEACHER USE
Exemplar A:Techniques Used to Provide
Desirable Qualities in Crop Plants
Genetic transfer occurs in nature when a plant is infected by a soil bacterium, called Agrobacterium tumefaciens, at a wound site. The Agrobacterium transfers a piece of it’s own DNA into the chromosomes of the plant cells at the wound site (MAF website).
The T-DNA (transferred DNA) has genes for two characteristics which switch on in the plant cell. The first makes the plant cell produce hormones which cause the cell to grow and divide out of control, similar to the way a cancer cell does. These cells produced are loosely packed and form a tumour. The other gene forces the plant to produce opines which are sugars linked to amino acids. When the cells divide the new cells also contain the genes to produce opines. Plants can’t use the opines but are forced to make them.
The Agrobacterium lives between the cells in the tumour. It survives by getting nitrogen and opines from the plant cells. This is an extremely clever form of parasitism because through natural genetic engineering the Agrobacterium causes the plant to provide a home and make food for it.
Genetic engineering is based upon these principles. Scientists worked out that the genes responsible for the transfer of the DNA weren’t part of the T-DNA. This means the naturally transferred genes on the T-DNA could be deleted and replaced with other genes. Consequently the Agrobacterium can be used to transfer desirable genes to plants.
Two genes are put on the modified T-DNA. The gene of interest eg. resistance to pests/ disease. The other gene is a marker which allows the engineered cells to be identified eg. a gene for Kanamycin resistance.
The modified T-DNA is put into the Agrobacterium that no longer contains the natural T-DNA. Plant tissue is then taken eg a leaf disc or segment and dipped it in to the Agrobacterium (Hanson, 1999). The plant tissue is the transferred onto a culture medium designed to allow the plant cells to divide. The recipe for the media changes for different plants.
After two days the plant tissue is transferred to the same medium containing two supplements. The first being an antibiotic to prevent the Agrobacterium from growing further. The second is used for selecting the engineered cells which are linked to the marker gene eg. Kanamycin, which normally kills plant cells. This means only the cells with the marker genes for Kanamycin resistance are capable of growing (MAF website).
After about one month little Kanamycin resistance cell colonies are removed from the leaves and transferred to a culture medium that will induce the growth of shoots. Once formed the shoots are transferred to another medium that will induce root formation. They can then be carefully transferred to a greenhouse. The DNA in the plants can be checked to see if the new genes are present. The plants can be analysed to see if the new characteristic gives the desired effect eg. improved quality.
Other techniques can also be used to insert desirable characteristics in crop plants. These include: conventional cross breeding, genetic engineering by using Protoplast Fusion, Gene Gun Method and by using Bacterial Plasmids.
Conventional plant breeding involves transferring pollen from one plant to another.
Protoplast Fusion is when the cell walls of plant cells are digested by enzymes. These cells are then treated with polyethylene glycol which causes the cells to fuse. The Gene Gun Method is when microscopic particles of tungsten or gold that have a DNA coating are shot through the cell wall by a burst of helium. DNA can also enter a cell when incorporated into a bacterial plasmid.
These technologies allow scientists to transfer any source of DNA into crop pants. DNA can come from the same plant, other plants, fungi, bacteria, viruses, animals or artificial genes that are made in the lab. Scientists think this offers great potential for creating many crops with resistance to pests and diseases or being able to cope with drought, salt, temperature extremes or soil toxicities (MAF website). Colour, shape and texture, longer shelf life and improved composition, eg adding nutrient and anti oxidants, can be altered in plants. Crop plants can also be used for making medicines and biodegradable plastic.
The first commercial genetically engineered crop plant was the ‘Flavour Saver Tomato’, which was modified so the genes responsible for the fruit softening were turned off. This means the fruit can be left on the plant to fully ripen rather than being picked early. Because of this the tomatoes develop all natural flavours while on the plant. It also means when picked they stay firmer longer.
Other products about to be commercialised include sugarbeet which has herbicide resistance and Canola which contains modified fatty acids to make it healthier. Papaya with virus resistance has been produced along with potatoes, cotton, corn and tomatoes which all have insect resistance.
One of the main concerns is that people fear the unknown. Fagan (1999) says that we are being used as “unknowing guinea pigs” by companies making genetically engineered food. We won’t know for sure what will happen until we try something. The public does not tend to believe scientists when they assure us that the food is safe. This may be because in the past the public gave been assured that scientifically based procedures were safe when in fact they weren’t. For example, DDT was used widely as an insecticide for many years before the long term accumulative effects were realised. Although this isn’t directly related to genetic engineering it illustrates that the public have a reason for mistrust of new scientific applications.
Some people are concerned about genetically modified food because they believe these new genes will make compounds that cause allergies (IBAC, 2000) of toxic responses. However scientists maintain that because they know a great deal of information about the genes and that such possibilities can be predicted ahead of commercial release. Scientists also say that such events are even more likely from traditional breeding methods that have been used for about the last 50 years because not much is known about the genes being transferred by these methods or the results once in the new plant. Other genes may also be passed on from the wild plant. These can go undetected (Lean, Angres & Jury, 2000).
I think it is very important that people understand the science behind the processes used. Without this knowledge people are basing there views on emotions and hearsay. The basic ideas are relatively easy to grasp. After knowing how specific the techniques are, people should be more informed to make decisions about whether to eat genetically modified food. Recently legislation has been passed to make genetically modified food labelled. How strict these regulations will be, is yet to be decided, but it is considered that labelling will help inform the public and allow them choice.
Referenced list
Conner, A.J. (1997) Genetically Engineered Crops Environmental and Food Safety Issues. The Royal Society of New Zealand.
Fagan, J.B. (1999) The Health Risks of Genetically Engineered Foods. Published in Canterbury’s Digest, Autumn 1999. Christchurch: ASG.
Hanson, M. (1999) University Bursary Biology. Auckland: ESA Publications (NZ) ltd.
IBAC, (2000). Biotechnology in NZ Consultation Report. Wellington: Independent Biotechnology Advisory Council.
Leon, G., Angres, V., and Jury, L. (2000). GM genes can spread to people and animals. Independent. 28 May, 2000.
MAF website http://www.maf.govt.nz/MAFnet/schools/activities/gmfbio.htm Methods of gene transfer. Accessed 29/8/2001.
Exemplar B:
Biological Control
Students portfolio contained researched material covering biological information and opinions relating to the issue
Possums, known as Trichosurus vulpecula, are pests that were introduced into New Zealand in the late 1830’s. People thought that they would be very good supply of furs and skins. Only a few were introduced into the South Island but when things went well they were introduced into the North Island and now they are found in 90 % on New Zealand. It is estimated that there are currently 60-70million possums in NZ (MAF web site 2001). There are no natural predators in NZ so the population is increasing.
I believe the current issue linked to the possum population is the possibility of TB (tuberculosis) being transferred to cows and people. If TB transferred it would have a huge impact on the export meat industry and also New Zealanders could not eat the meat. Dairy cows would be killed if there were tested positive for TB but some other animals like deer are placed on movement control.
Most people think that possums are a pest because they damage the trees in the forests. They eat the young foliage and flowers of the pohutakawa trees so much that the trees die. Because of NZ geological history these native tress were not used to having an animal like possums browse them. They also eat native birds eggs, decreasing their populations. Some people work as possum trappers and sell the possum meat, skins and fur. The meat is used to make cat and dog food. This means that possums are useful because providing jobs for the unemployed people.
People used to trap to kill possums but there were problems with cats and other animals getting caught. The Regional Council uses cyanide baits to control possum numbers in our area. This is very expensive and people are concerned at other animals will eat the bait.
There are many ways for controlling possum numbers; biological, chemical and mechanical. Everyone wants to get rid of the possum but generally people do not like the idea of these (cute and fluffy) creatures to be hunted or to die a slow death.
Lots of biological control methods are being trialled. If the scientists are going to use these methods they have to also find ways to deliver the biocontrol method to lots of possums. They are trying baits, sprays, use of a natural vector such as possum viruses and use of transgenic plants.
Possums breed very quickly and have two breeding seasons per year – this is one of the main problems. There are potential methods of biological control and I will outline a paper written by a scientist named Phil Cowen in 2000, which he presented to the biotechnology conference.
He sates that possums have few parasites and so it is not easy to get a parasite to infect and kill possums. They do though have a worm which lives in their gut and kills them – perhaps this could be used. The best way believes Phil Cowen is to use viruses – there is a new virus called wobbly possum virus. This has been in NZ since the time of the possum release. If this virus was altered it may be able to kill possums in larger numbers. Mr Cowen is a consultant and has no direct benefit in using the virus so I take his opinion at face value and do not believe it is bias.
In immunocontraception and immunosterilisation the possum is immunised against some of the proteins used in reproduction. They then made antibodies against these proteins which stops them from reproducing. The contraceptive carrots were first trailed on a south Auckland farm in late 2000. Results have been positive according to the Auckland DOC office. Computer modelling suggests that more than 60% of the females would need to be made infertile for this to have an impact ( landcare web site)
Weighing up the positive and negatives of each of the control methods is an important task for the Department of Conservation. Important factors to look at are the effect on endemic and introduced species, the health risk to people, whether or not the soil biota will be affected, the sustainability and the economic viability need to be weighed. For this reason there is always a group of people to discuss the issue. This group is comprised of scientists, local Iwi, farmers, and members of Parliament. I will now outline what various groups’ views are.
The local community of Waitangi would like individuals to go on possums hunting trips. As the possum are nocturnal the workers would need to stay in the bush overnight waiting to shoot. Workers would be paid per possum killed and could also take the carcasses home to get the fur off them. Although this method does have The advantage is that in this tourist town with a large leakage of chemicals into streams (if toxins were used as baits) and no other animals are killed – except for the odd rabbit who gets in the firing path of the worker!