These weeds are growing in a farmer's field. The weeds compete with the soybean plants the farmer grows, so he needs to get rid
of them. For a few years, the former relies on manually removing the woods, but that is labor intensive and limits how much crop he can grow. The farmer decided to change his crop to genetically modified soybeans that are herbicide resistant. This allows the farmer to use chemicals to remove the weeds. With this GM soybean, the chemical kills the woods but does not harm the crop. For many years this works, and allows the farmer to expand his farm and grow more soybeans. But then, one of the farmer's fields has a large weed plant remaining after the field has been sprayed with herbicide 1. Which of the following is the likely reason the weed has remained?
a. The weed needed to be resistant in order to survive, so it became resistant
b. A mutation appeared in one weed plant that made that weed not susceptible to the herbicide
2. Which of the following is likely to happen if that weed stays in place?
a. The trait will spread to nearby weeds
b. The weed will survive long enough to reproduce
c. In time, the herbicide will no longer be effective on that field.
Parasite: Parasites are different from predators because parasites only take resources from one host, whereas predators eat many prey. A good example of this is the trematode parasite Schistosoma mansoni. An adult schistosome parasite lives inside of just one human host
