Thank you for your help.
What's your take on part(b)?

for question a, another variable that must be kept the same maybe one of these
- keep other food sources for the grasshopper constant. for example leafs
- make sure there are no other things that will eat the wheat
- also the soil will have other organisms like ants and worms because the grasshopper habitat has many things. so keep the other organisms the same
- maybe the water temperature added is different. this needs to stay the same
- we learn about decomposers to get rid of the dead grasshoppers. keep this the same too

Additional answers for part A include:
- The age / size of grasshoppers. The bigger the grasshopper the more food they consume.
- The size of the wheat plants.

With regards to part B, Mr Tan may have chosen to use Brand S as the pesticide has killed more grasshoppers. Perhaps this brand took longer to kill the grasshoppers so initially they ate more wheat plants but as time went by it killed more grasshoppers. The impact is that in the future, there would be less grasshoppers allowing more wheat plants to grow.

For question like partB, comparison is needed.


Although Brand S was selected even though it did not killed as many grasshopper as brand Q did, Brand S pesticide allowed Mr Tan's wheat to survive much more as compared to Brand Q.

2 component answers are needed for such questions as there are 2 results in the end.

Hi all,

Answer for part (a): The amount of pesticides used for each brand must be kept the same. (Note, this is not mentioned in the description. Pesticides against grasshoppers are sprayed on plants, hence amount sprayed must be kept the same for each brand)

Answer for part (b): Mr Tan decides to use Brand S because it kills many grasshoppers like Brand Q but it had little effect on wheat plant survival compared to the effect of Brand Q (Similar to Benjamin's answer).

Here is another answer to part (b): Mr Tan decides to use Brand S because if he wants to use the pesticide again to completely remove the grasshopper population, Brand S would eliminate all grasshoppers but still allow the wheat plant population to survive.

Here's how it would look like after the second round of using the pesticides
(Assuming all conditions are kept constant & assuming that the extent of death to wheat plants and grasshoppers are the same for each brand. E.g. if brand P killed 45 plants and 20 grasshoppers, we assumed it will kill to the same extent when used again):



Of course, the table did not take into consideration the reproduction of grasshoppers & wheat plants after the first time of using the pesticides. But this table helps to show clearly that Brand S would be an effective pesticide. Moreover, in real life, pesticides are sprayed over the same plot of crops periodically.

On a side note, some pesticides against locusts cripple the reproductive capabilities of the insects instead of killing them. In this way, the pesticides are effective by disrupting the life-cycles of the insects - no way to reproduce.

The table which was missing from the previous post: