2010 PSLE Science

[ApronMama]

the kiasu student:

One of the questions from today's paper was like this:


A 200cm metal rod was heated for 20mins and expanded to a length of 210cm. John took another 200cm metal rod, made of the same type of metal, but thicker. He heated it for 20mins. Will the length of the thicker rod be shorter or longer than 210cm or be the same? Explain.

My answer: Longer. The amount of matter in the thicker rod was more than the amount of matter in the first rod, hence the thicker rod would expand to more than 210cm. :? :? :? :? :? :? :? :? :? :? :?

my ans:shorter. there is more matter in the thicker rod than in the first rod ,thus it requires more heat to expand the thicker rod to the same lenght hence ,with the same amount of heat , the thicker rod would ex pand to a lenght shorter than 210cm.

[beauty queen]

Polar bear:

Thanks.

One of my suggestions for the decomposition question was to put the jar in a dark room and my reason was that it would allow more decomposers to come into the jar, thus speeding up decomposition.

Can someone tell me if this is acceptable

No i do not think so. As the rotten log habitat or the leaf litter habitat is dark i am not sure darkness is a factor for the growth of decomposers

just my 2 cents

[anonymus]

beauty queen:

Polar bear:

Thanks.

One of my suggestions for the decomposition question was to put the jar in a dark room and my reason was that it would allow more decomposers to come into the jar, thus speeding up decomposition.

Can someone tell me if this is acceptable

No i do not think so. As the rotten log habitat or the leaf litter habitat is dark i am not sure darkness is a factor for the growth of decomposers

just my 2 cents

One of the factors for Rotting log habitat is dampness n darkness. So, i think polar bear ans is correct

[MOE Hater]

ApronMama:

Polar bear:

anybody know the answer to the insect X question. I put 28 days but many of my friends say that it is 24 days and what is the reason for insect X staying in water for the egg larva and pupa stages

I feel that it is 24 because the question said \"after the egg hatched\" ,so it should not include the time insect x stayedin the egg stage. :lol: :lol: :lol:

Thot 28 was excluding the egg stage!!!! I put 28! :shock:

[triplediao]

mrswongtuition:

Little Mermaid:

For the elephant question, I put :

The big ears help to trap air which is a poor conductor of heat.Thus,keeping the elephant cool. Wonder if it is correct!!! :?: :!:

Big ears do help to keep the elephant cool.
However, it is not due to the trapped air but the large surface area for them to lose the heat.

I didn't mention large exposed surface area. I mentioned about the large number of blood vessels found in the ear of the elephant A helping it to conduct heat away from its body. O.o Oops

[thensingsmysoul]

anonymus:

beauty queen:

[quote=\"Polar bear\"]Thanks.

One of my suggestions for the decomposition question was to put the jar in a dark room and my reason was that it would allow more decomposers to come into the jar, thus speeding up decomposition.

Can someone tell me if this is acceptable

No i do not think so. As the rotten log habitat or the leaf litter habitat is dark i am not sure darkness is a factor for the growth of decomposers

just my 2 cents

One of the factors for Rotting log habitat is dampness n darkness. So, i think polar bear ans is correct[/quote]Based on my mini 'research', darkness is not a factor that contributes to speeding up decomposition.

The answer is dependent on how the question is asked, but basically, the rate of decomposition is dependent upon:
* Temperature (the warmer the better);
* The availability of oxygen;
* Access by scavengers;
* Humidity, or wetness;
* Rainfall/Dampness;
etc...

[MOE Hater]

But must make sure temp not too high, or else bacteria all die and decomposition slowed down

[mum-in-action]

MOE Hater:

ApronMama:

[quote=\"Polar bear\"]anybody know the answer to the insect X question. I put 28 days but many of my friends say that it is 24 days and what is the reason for insect X staying in water for the egg larva and pupa stages

I feel that it is 24 because the question said \"after the egg hatched\" ,so it should not include the time insect x stayedin the egg stage. :lol: :lol: :lol:

Thot 28 was excluding the egg stage!!!! I put 28! :shock:[/quote]Hi, can someone share the answer for this insect X question,part b? The question is insect X has wings,which stage of insect X lives in the water/

[beauty queen]

thensingsmysoul:

anonymus:

[quote=\"beauty queen\"]
No i do not think so. As the rotten log habitat or the leaf litter habitat is dark i am not sure darkness is a factor for the growth of decomposers

just my 2 cents

One of the factors for Rotting log habitat is dampness n darkness. So, i think polar bear ans is correct

Based on my mini 'research', darkness is not a factor that contributes to speeding up decomposition.

The answer is dependent on how the question is asked, but basically, the rate of decomposition is dependent upon:
* Temperature (the warmer the better);
* The availability of oxygen;
* Access by scavengers;
* Humidity, or wetness;
* Rainfall/Dampness;
etc...

:)[/quote]
phew! I put put the bin in a warm habitat

[the kiasu student]

Polar bear:

Thanks.

One of my suggestions for the decomposition question was to put the jar in a dark room and my reason was that it would allow more decomposers to come into the jar, thus speeding up decomposition.

Can someone tell me if this is acceptable

You are half right and half wrong. I also said that should put it in a dark place, but not to attract decomposers nor allowing more of them go into the jar. This will reduce the rate of evaporation of the moisture from the moist leaves, hence more moisture is kept, as decomposers need water to decompose dead organisms, this would speed up decomposition.