University of Bristol
Wellcome Trust
Recommended by:
Society of Biology
PEEP for Physics & Ethics at GCSE

Genetically Modified Crops

Are GM crops safe for the environment?
GM crops, herbicides and pesticides. 

One of the claims for GM crops are that they could allow farmers to use fewer pesticides (herbicides and insecticides). Pesticides are expensive and have many health risks for farm workers.

GM crops have been developed that: 

  • can withstand being sprayed with specific herbicides (weedkiller) 
  • manufacture insecticide chemicals within their own cells.
  • Such plants need to be sprayed less often than conventional crop plants. 

See the Biodiversity section for more on pesticides.

Gene flow & evolutionary opportunity:
Could GM crops lead to super weeds & super bugs?

GM Opponents have argued that GM crops will cross breed with wild relatives nearby, allowing the herbicide resistance gene to move into other species. They fear this could lead to herbicide resistant "Super Weeds". 

If a crop plant makes its own insecticide in its cells, insects (who would normally only be exposed to such chemicals in infrequent lethal doses) will experience them as a normal part of their environment. This could  create the conditions for insects who eat them to evolve a resistance to such toxins, potentially leading to insecticide resistant "Super Bugs". 

GM opponents fear that that the long term effects may be that farmers could actualy end up having to use larger quantities of stronger herbicides and persicides to combat such resistant pests.

But GM supporters point out that:-

  • Any risk from gene flow is to do with the properties of the particular gene transferred, not the means by which it got into the original plant.
  • Gene flow can occur just as easily with conventionally cross bred plants.
  • To create a Super Weed, any gene transferred will have to give the recieving plant a distinct advantage over its surrounding competitor plants that enables it to breed more successfully than them.

Question:  If this is a genuine risk, is it fair to blame it specifically on GM crops alone?


Finding evidence for gene flow between GM crops and other plants is not the same as finding evidence for Super Weeds. Read the following article:  GM crops created superweed, say scientists

1. Does one case of finding of a plant with herbicide resistance make it legitimate to claim that Super Weeds have arrived?

2. What circumstances would it take for that plant to count as a "Super Weed"? And does this occurrence fulfil these criteria?

TASK: Go to the News Archive and use the search box there to search for "superweed". (N.B. don't put in the plural form superweeds). What do you find?


 GM crops and biodiversity


What's your opinion?

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NOT RATED schmoo 05-08-10 13:17
i was looking for evidence, like a survey or something with real numbers!!! this is just fact and opinion!
NOT RATED David 06-08-10 10:51
Ok, here you go -
"GM plants 'established in the wild'"

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Organic farmers

One way organic farmers combat insects is to spray their crops with a solution of the bacterium Bacillus thuringiensis, which produces the Bt toxin that is lethal to insects but harmless to humans.

Insect resistant GM crops are often engineered to produce the same Bt toxin in their cells. If these GM crops cause insects to become resistant to the toxin (see left), it will not only affect conventional farmers, but also make the Bt technique unavailable to organic farmers too.