A field of Bt cotton has 5000 young bollworm larvae on it…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A field of Bt cotton has young bollworm larvae on it. In a model, of the living larvae die each day after they start to feed, and none are added.
- How many larvae live after the first day?
- How many live after the second day?
- On which day does the number fall below for the first time?
Need a reminder? The key ideaShow
The soil bacterium Bacillus thuringiensis makes crystals of an inactive protoxin. In the alkaline gut of an insect, the crystals dissolve and the protoxin becomes the active toxin. It binds to the midgut cells, makes pores, and the cells swell and burst. The toxin gene is called cry. The genes cryIAc and cryIIAb control the cotton bollworms, and cryIAb controls the corn borer. Most Bt toxins act on one group of insects only.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Start: larvae. Each day of the living larvae die, so live.
Plan. Multiply by for each day.
Step 1. Day 1. larvae.
Step 2. Day 2. larvae.
Step 3. Later days. Day 3: . Day 4: . Day 5: , which is below .
Answer: ; ; day .
Check. The number after day is . For this is , and for it is .
Watch out. The mortality is a made up value. The real figure depends on the toxin, the pest and the plant.
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