Q&A - PSLE Science

[Tinkerbelle]

Verysuperkiasu:

ms_lim:

Please help to explain Qn #25 from Pei Chun 2011 Prelim, Ans key is 2 :


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This was also my question.....the below article might help?

http://factoidz.com/boil-water-in-a-paper-cup/

Just scroll down a little

Interesting. Thanks for sharing, verysuperkiasu.

[Tang]

atutor2001:

P5G:

Please help.


http://i54.tinypic.com/r8573s.gif\">


TIA.

To me both (1) and (3) are possible options but I will pick (1) because of the words \"after a day\".

For some seeds, it will take a long time to germinate unless we soak the seek in water first (e.g. rice grain). So I am assuming that the time needed for a seed to germinate is primarily determined by the time needed for the seed to absorb sufficient water. Therefore, in the above experiment, during the period where there is no air, it allows time for the seed to get thoroughly soaked. Once air is introduced, the seed can carry out cell respiration immediately to release energy for germination to begin.

Hi,

Since the seeds germinate after a day, the changed variable must be something that is not necessary for germination to take place. So answer should be (2) or (4). But since this is a Science question, I will just have to pick (2) as my final answer.

[Verysuperkiasu]

Tinkerbelle:

Interesting. Thanks for sharing, verysuperkiasu.

You're welcome

[Verysuperkiasu]

peichun prelim 2011 section b q39b


Mr Leong wanted to use a metal barbecue grill P or Q, that would result in the food being less burnt.

Picture of P shows some thinner metal strips with bigger gaps between the strips.
Picture of Q shows some thicker metal strips with narrower gaps between them.

Based on the diagram, which grill should he use. Give a reason.

Answer key is Q. thicker strips = large surface area in contact = conduct heat away faster to the air so food won't get burnt. My question ; but won't the bigger surface area of the strips also conduct heat faster to the food as well which will burn the food?

If choose P, also not right coz the bigger gaps means fire in direct contact with the food which will get burnt.

Pls enlighten me....

[atutor2001]

Tang:

atutor2001:

[quote=\"P5G\"]Please help.


http://i56.tinypic.com/16jj4mg.gif\">


TIA.

I will pick (2) because its twisted look appears to be more suitable for clinging to tree trunks.

Hi,

I have done an online search for pictures of woodpecker, the photophoto shows that the correct answer should be (4).[/quote]Hi Tang
The key word in the question is \"opposable claws\" which I take to mean that one claw can be moved to touch one or more of the remaining claws. Therefore, (2) appears to match the description.

[atutor2001]

Verysuperkiasu:

peichun prelim 2011 section b q39b


Mr Leong wanted to use a metal barbecue grill P or Q, that would result in the food being less burnt.

Picture of P shows some thinner metal strips with bigger gaps between the strips.
Picture of Q shows some thicker metal strips with narrower gaps between them.

Based on the diagram, which grill should he use. Give a reason.

Answer key is Q. thicker strips = large surface area in contact = conduct heat away faster to the air so food won't get burnt. My question ; but won't the bigger surface area of the strips also conduct heat faster to the food as well which will burn the food?

If choose P, also not right coz the bigger gaps means fire in direct contact with the food which will get burnt.

Pls enlighten me....

I will pick the thicker strips because large surface area in contact = faster cooking AND also more even distribution of heat = prevent localised burning of food.

[chrisu]

Well I'm totally clueless about such questions from Preparing for PSLE Science by EPH. Anyone can explain why the answer?


Q6 : Book answer is (3)
http://img.photobucket.com/albums/v160/guppiesonli/Misc/Q6.jpg\">

7 : Book answer is (4)
http://img.photobucket.com/albums/v160/guppiesonli/Misc/Q7.jpg\">

Thank you.

[atutor2001]

I think the first thing to do is to find the relationship between A&B; A&vegetation and B&Vegetation.


From graph of A & B, it is quite ok to see that A eats B because when A goes up, B comes down and vice versa.

From the graph of B and vegetation, the relationship was quite ok at first, showing that when vegetation increases, B also increases (and vice versa). Therefore, B eats the vegetation. This trend changes when A increase rapidly which causes B to decrease which then leads to the vegetation increasing as there are now less B eating them.

The graph of A and vegetation does not show any relationship.

With that we can confirm the food chain to be
\"Vegetation -> B -> A\"

The graph shows a sudden increase in A due to unknown reason (maybe migration from other places). Therefore, to prevent extinction of B (i.e. need to increase B), technically, we can either reduce A or increase vegetation. However, the graph also shows that vegetation is already increasing which means the death rate of B (killed by A) is way much faster than birth rate and the option of increase vegetation is not feasible.

For Q7, in the wild life reserve, the food chain is usually
plant -> herbivore (e.g. deer) -> carnivore (lion)

Hope my method is ok

[chrisu]

Thank you atutor2001 for the time and effort, really appreciate it.


Just a little more explanation on this;
Regarding the graph of B and vegetation. If vegetation increases, B aslo increases (and vice versa) - why B eats vegetation then? If B eats vegetation, then shoudn't be B increases, vegetatin decreses and vice versa? Thanks.

atutor2001:

From the graph of B and vegetation, the relationship was quite ok at first, showing that when vegetation increases, B also increases (and vice versa). Therefore, B eats the vegetation.

[atutor2001]

Sorry forgot to explain this part.

Under normal situation, the increase in population size of an organism is usually triggered by increase in food supply and vice versa. Therefore, the graph of the food source should always change direction BEFORE the graph of the consumer. i.e. there must be more food first which will lead to more B being produced as it takes time to reproduce and vice versa. Increase in vegetation can be due weather.

If both the vegetation and B are increasing at the same rate or vegetation is increasing at a faster rate than B, then both organisms will keep increasing.

However, if the increase in B is faster than increase in vegetation, it will reach a point where vegetation will start to decrease (graph of food source will change direction first) and then B will also start to decrease (graph of consumer will change direction later)

chrisu:

Thank you atutor2001 for the time and effort, really appreciate it.

Just a little more explanation on this;
Regarding the graph of B and vegetation. If vegetation increases, B aslo increases (and vice versa) - why B eats vegetation then? If B eats vegetation, then shoudn't be B increases, vegetatin decreses and vice versa? Thanks.

atutor2001:

From the graph of B and vegetation, the relationship was quite ok at first, showing that when vegetation increases, B also increases (and vice versa). Therefore, B eats the vegetation.