Q&A - PSLE Science

[atutor2001]

Verysuperkiasu:

atutor2001:

(a) The rate of photosynthesis of water plants without the presence of light (in darkness) is faster at higher temperature.
OR
The rate of photosynthesis of water plants without the presence of light (in darkness) is slower at higher temperature.
....

(b) All the water plants will die because there is no light for it to carry out photosynthesis to make food.

Sorry to ask - but the inner surface of the box is aluminium foil although outer is glass, so by right, there shouldn't be any photosynthesis that takes place since light can't penetrate? Pls correct me if I'm wrong.... thanks.

Yes you are right that photosynthesis cannot take place with the aluminium covering the box.

However, this question is testing the concept of \"hypothesis\" and not on photosynthesis. Hypothesis is a \"prediction\" on what we think is likely to happen for a certain situation. The information in our hypothesis needs not be factually correct. The purpose of creating an hypothesis is to help us in designing the experiment. We must then carry out an experiment to verify if our hypothesis/prediction is correct.

This question is actually reversing the order of activity. That is, we a given experiment set up and is asked to guess what is the likely hypothesis that the person is trying to verify/confirm.

From the experiment set up given, he has carried out the experiment in darkness. He has tried to collect air bubbles. He has changed the temperature (the variable that is changed).

From the above information, we can then guess that he is trying to find out how the rates of photosynthesis will be affected by temperature - which is how I come out with the hypothesis.

In other words, as long as the experiment set up can be used to verify the hypothesis that we have created our hypothesis should be accepted.


An example of a hypothesis that is not acceptable in this question is :

\"The lesser the amount of water is, the slower will be the rate of photosynthesis.\" (in the 2 set ups, the amount of water are the same and this experiment set up cannot be used to confirm the hypothesis)

[atutor2001]

P5G:

Should the answer for (c) be:

Plot D. It has the least number of plants per plot so there is less competition for nutrients, water and space.


TIA.

Answer is plot A. Plot A has the most number of plants per plot which will cause overcrowding. Plants grow taller to compete for sunlight when there is overcrowding.

[atutor2001]

P5G:

Please help for 33 (b)



TIA.

Seed A because it is first dispersed by explosive action and is then dispersed by wind as it has wing-like structure.

[atutor2001]

P5G:

Please help.


Will I be marked wrong if my answer for (c) is

Both plants can carry out respiration.


TIA.

Under very strict marking scheme you might not get any mark because the living things are grouped into plants, fungi and animals. So it is assumed that the processes requested by the question should also be classified accordingly.

Therefore, it usually safer to assume so and put the answer as \"photosynthesis\" because it is a process that is confined to plants only.

[atutor2001]

deleted as info is wrong

[andante]

andante:

Hi all,

I would like to find out whether the following is structural or behavioural adaptation.
- an earthworm releases mucus to help it slide through the soil quickly when it is threatened.

My DD thought that it is structural adaptation. Pls advise.

Hi,
Can someone help me on the above question ? why ?

Thank you.

[andante]

Hi,

For the question below, can someone help to explain why there will be burn mark on the leaf ? thx
http://i55.tinypic.com/20adxub.jpg\">

[Nebbermind]

atutor2001:

Herbie:

hi atutor,

The answer on the answer sheet is 3.

If the nail is being magetised, it shld also be able to attract the paper clip and attract the magnet too right??

I have to disagree with the answer given in the answer sheet.

The key word in the question is \"can be sure\". That means the option chosen must be 100% correct with no allowance for other possibility.

It is true that if the nail is being magnetised, it should be able to attract the paper clip and the magnet.

However,

Possibility 1
It is also true that if the nail is NOT magnetised, it would still be attracted to the magnet.

Possibility 2
It is also true that if the nail is NOT magnetised but if the paper clip is magnetised, the nail will be attracted to the paper clip. (unless it is stated clearly in the question that the paper clip is not magnetised)

Therefore, it is a norm that to confirm whether if an object is a magnet, we need to use repulsion.

I recently came across a similar qn for P3 like asking how to determine if a magnetic material has been magnetized. My answer to my P3 was to use the compass.

I donch think a magnetized nail will be strong enough to repel a permanent magnet.

Also, if it attracts another magnetic material, we can't be sure which is the magnetized one or both are.

So the only way to tell is to bring it towards a compass but there's no 'D only' answer.

Juz my 2c

[Herbie]

Nebbermind:

atutor2001:

[quote=\"Herbie\"]hi atutor,

The answer on the answer sheet is 3.

If the nail is being magetised, it shld also be able to attract the paper clip and attract the magnet too right??

I have to disagree with the answer given in the answer sheet.

The key word in the question is \"can be sure\". That means the option chosen must be 100% correct with no allowance for other possibility.

It is true that if the nail is being magnetised, it should be able to attract the paper clip and the magnet.



However,

Possibility 1
It is also true that if the nail is NOT magnetised, it would still be attracted to the magnet.

Possibility 2
It is also true that if the nail is NOT magnetised but if the paper clip is magnetised, the nail will be attracted to the paper clip. (unless it is stated clearly in the question that the paper clip is not magnetised)

Therefore, it is a norm that to confirm whether if an object is a magnet, we need to use repulsion.

I recently came across a similar qn for P3 like asking how to determine if a magnetic material has been magnetized. My answer to my P3 was to use the compass.

I donch think a magnetized nail will be strong enough to repel a permanent magnet.

Also, if it attracts another magnetic material, we can't be sure which is the magnetized one or both are.

So the only way to tell is to bring it towards a compass but there's no 'D only' answer.

Juz my 2c [/quote]Hi Nebberminded

Yr explanation sounds logical too. Sci is so complex. I have to get my dd to ask her sci teacher liao.

Cheers

[Herbie]

Nebbermind:

atutor2001:

[quote=\"Herbie\"]hi atutor,

The answer on the answer sheet is 3.

If the nail is being magetised, it shld also be able to attract the paper clip and attract the magnet too right??

I have to disagree with the answer given in the answer sheet.

The key word in the question is \"can be sure\". That means the option chosen must be 100% correct with no allowance for other possibility.

It is true that if the nail is being magnetised, it should be able to attract the paper clip and the magnet.



However,

Possibility 1
It is also true that if the nail is NOT magnetised, it would still be attracted to the magnet.

Possibility 2
It is also true that if the nail is NOT magnetised but if the paper clip is magnetised, the nail will be attracted to the paper clip. (unless it is stated clearly in the question that the paper clip is not magnetised)

Therefore, it is a norm that to confirm whether if an object is a magnet, we need to use repulsion.

I recently came across a similar qn for P3 like asking how to determine if a magnetic material has been magnetized. My answer to my P3 was to use the compass.

I donch think a magnetized nail will be strong enough to repel a permanent magnet.

Also, if it attracts another magnetic material, we can't be sure which is the magnetized one or both are.

So the only way to tell is to bring it towards a compass but there's no 'D only' answer.

Juz my 2c [/quote]Hi Nebberminded

Yr explanation sounds logical too. Sci is so complex. I have to get my dd to ask her sci teacher liao.

Cheers