PSLE 2009 - Science

[justsay]

caroline3sg:

There was a question in the PSLE Science thread in this forum which ask which brand of pesticide P, Q, R, S is effective. All options are decrease, the ans is to choose the option which crop decrease the least & pests decrease the most.


So based on this, my girl's ans to the PSLE question is decrease/decrease. Of course, the reason supporting this ans is not as logical as kohjl jr, but \"spraying a lot of pesticides\" will sure do some damage to the veg and if fruit trees are sharing the same plot of land, the soil would also have pesticides.

The Question:
The farmer found that alot of caterpillars were eating his crops. The farmer sprayed alot of pesticides onto them. Which of the following is correct?

My answer:
Crops-increased
Fruits-increased

Reason: Even if the pesticides kill some of the plants, pesticides will kill most of the caterpillars. Since there are no more caterpillars feeding on the leaves, the number of crops will increase and therefore, the number of fruits will increase.

From: kohjl Jr



Hi caroline3sg,
Are you talking about the same question or another question ?

[kohjl]

atutor2001:

Hi Kohjl (Mummy)


I have not seen better answers than those from your son. His concept is clear and his answer is precise. Your are so blessed.

Hi atutor2001

Thank you for your kind comments.

My son loves Science, and he enjoys having discussions with his brother (Year 4, RI) so I guess that's how he picks up many Science concepts. He also enjoys reading National Geographic mags and the like, and his favourite TV channel is Discovery channel. He just loves Mythbusters!

Just a clarification in case anyone is wondering: the scientific reasoning he writes about in each of his forum postings is entirely his own; I don't even edit it. I only add to the part under \"The Question\" to make it clearer to readers cos I have the benefit of having my son draw the diagram for me, while readers don't. It is to help parents better understand the question. Other than that, all answers are his own.

Thanks again for your encouragement. And yes, I feel very blessed - not only because of this son, but by my whole family!

[tutormum]

Hi Kohjl,

Which school is your son in? Does he want to go to RI? My son shares the same interests as yours and his best friend is also very good in Science (he top his prelim). How I wish both our sons are friends cos I'm sure my son has a lot to learn from him. My son's problem is being stubborn in his thinking and unless you can convince him, he'll refuse to listen. :x He believe in Mythbusters more than what I say. :lol: I'm hoping he'll get into RI but I'll be stressed if he does.

[chk707]

justsay:

caroline3sg:

There was a question in the PSLE Science thread in this forum which ask which brand of pesticide P, Q, R, S is effective. All options are decrease, the ans is to choose the option which crop decrease the least & pests decrease the most.


So based on this, my girl's ans to the PSLE question is decrease/decrease. Of course, the reason supporting this ans is not as logical as kohjl jr, but \"spraying a lot of pesticides\" will sure do some damage to the veg and if fruit trees are sharing the same plot of land, the soil would also have pesticides.

The Question:
The farmer found that alot of caterpillars were eating his crops. The farmer sprayed alot of pesticides onto them. Which of the following is correct?

My answer:
Crops-increased
Fruits-increased

Reason: Even if the pesticides kill some of the plants, pesticides will kill most of the caterpillars. Since there are no more caterpillars feeding on the leaves, the number of crops will increase and therefore, the number of fruits will increase.

From: kohjl Jr



Hi caroline3sg,
Are you talking about the same question or another question ?

Thats true. I was also confused when my son asked me this question, but i found out that catapillars grow into butterflies and helps to pollinate the flowers. Without pollination, the flowers of the plants will not get fertilised and could not transform into a fruit. So i think the answer is Vegetable increase, Fruits decrease.

[PlasmaStorm]

atutor2001:

Hi Kohjl (Mummy)


I have not seen better answers than those from your son. His concept is clear and his answer is precise. Your are so blessed.

Thank you!

(Formerly kohjl Jr )

From: PlasmaStorm

[caroline3sg]

justsay

yes, I am referring to the same question. I am just stating the reason why my girl put veg decrease, fruit trees decrease.

[acelancer]

justsay:

I cant upload the picture. Keep giving me timeout error.


Goto http://www.pslescience.blogspot.com

If the question on adding a bulb parallel to one of the bulbs in series was drawn this way, I would agree that the answer should be (2) would be brighter.

the pic of the adding a bulb parallel to one of the bulbs in series question was not like tht. it was another way... but similar.(a small difference may make a great differrence)

[Augmum]

My gal also mentioned the diagram looks different. according to her, the added parallel bulb is in the middle and the connection of the wire is extended and connected to the right side (something like that).


any pupil here remembers the exact diagram drawn.

[tutormum]

Can anybody provide the question on anther and stigma thingy? Thanks

[PlasmaStorm]

There was an MCQ question about a farmer who had discovered caterpillars on his plants, and he thus sprayed “a lot” of pesticides on the plants. The question then asked whether the number of plants had increased/decreased, and whether the fruit yields had increased/decreased.


This topic can generate a few hours of discussion and cannot be answered so simplistically. The answer would depend greatly on the context of the situation that the examiner has in mind. A Primary 6 child answering this question would not only need to understand the concepts but also has to read the mind of the examiner as to what is the context of the question. Please let me explain:

SIZE OF THE LAND: Historically, a farmer that uses DDT on his crops and fruit trees would ensure that his plants are not eaten by insects such as caterpillar (and hence his number of plants would increase), and he would also have an increase in the yield of fruits. In our Asian context, the farm would generally be a small holding of not more than one kilometre square. Thus, even if all the insects were killed, including those required for pollination, insects from the surrounding areas would still provide sufficient coverage for pollination to occur. (Note: Bees are known to fly as far as 5km for food.)

However if the farm is very large, then the pesticide could reduce pollination to such an extent that the yield of fruits would decrease. This would be the case in America where large farms are the norm and which may be tens to hundreds of kilometres in size.

TYPE OF INSECTICIDE: Most insecticides that are used in our modern context are those that target a specific species or only the caterpillar stage of the butterfly. These are called “narrow-spectrum” pesticides. More importantly, they are developed so as not to harm bees as the bees are the most important form of pollinators for farmers. So even if the farmer uses a lot of insecticide, he would not harm the bees. Neither would narrow-spectrum pesticides kill the plants/crops or affect the yield adversely since this is, after all, why farmers use pesticides in the first place – to have healthy plants and boost yield.

TIMING OF THE INSECTICIDE SPRAYING: If the insecticide was sprayed after pollination, then the yield of fruit would increase. If the insecticide was applied just before pollination began and the farm was very large (and assuming that broad-spectrum insecticide was used and all bees were killed), then the yield of fruit would decrease. If the fruits were ripening on the tree, then the yield of fruit would increase. If the tree was not flowering yet or had just produced a batch of fruits, then killing all the bugs and caterpillars would not make much of a difference as they would just return the next season. Then the answer would be plants increased and fruits, no difference. There are so many permutations because there are just so many parameters that are not given in the question. How would the student know which assumption to make?

If the answer is expected to be plants decreased, fruit decreased, then we are assuming that the farmer is so stupid or ignorant of farming technology that he sprays so much broad-spectrum insecticide until he poisons the plants leading to a decrease in the number of plants and hence fruit yield.

So what exactly are the parameters and context of the question? How big was the farm – small Asian farms or large American farms? What kind of insecticides were used – narrow-spectrum or broad-spectrum type that killed all insects? When was the insecticide applied? How would the children know if all these parameters are not clearly stated in the question?

The assumptions underlying this question and debate thereof could be the subject of a long JC-level General Paper discussion. It certainly cannot be a multiple-choice question for P6 students at PSLE level.

This question should not have been set in the first place without clear information on the context and parameters provided.

It is therefore little wonder that there is so much dissent and debate on this Question in this forum.

Regards.
Father of PlasmaStorm
(Formerly known as kohjl Jr )