Q&A - PSLE Science

[starlight1968sg]

Hi,

I need some help.
We know many living things reproduce sexually ie a male and a female are needed for fertilisation. What are the animals reproduce asexually?
Thanks.

[atutor2001]

[quote]..... in psle you are meant to utilise your prior knowledge and answer .....[/quote]
Above statement is true only if there are no such clauses in the questions :

\"based/referring on the diagram given\"
\"based/referring on the picture\"
\"based/referring on the experimental setup\"
\"based/referring on the observation\"

In Q34, those 2 \"magic words\" are not in the question. Therefore, we can use our prior knowledge.

So all dear students, we need to analyse the question very carefully, lookout for \"keywords\" - e.g. base/refer; all the; only; ....

[Tang]

atutor2001:

[quote]..... in psle you are meant to utilise your prior knowledge and answer .....

Above statement is true only if there are no such clauses in the questions :

\"based/referring on the diagram given\"
\"based/referring on the picture\"
\"based/referring on the experimental setup\"
\"based/referring on the observation\"

In Q34, those 2 \"magic words\" are not in the question. Therefore, we can use our prior knowledge.

So all dear students, we need to analyse the question very carefully, lookout for \"keywords\" - e.g. base/refer; all the; only; ....[/quote]
Hi Auntie atutor2001,


This question may not have the 2 'magic words', but it has 4 'magic words'.


Q34c) From the experiment above, what can you conclude


So I believe no prior knowledge should be used.


Although Flask A is supposed to remove carbon dioxide based on our knowledge, the experiment does not show us that carbon dioxide indeed exists.
[But since Flask A is to remove carbon dioxide found in the surrounding air, it may infer that the surounding air contains carbon dioxide rather than based on prior knowledge.]

In the TOPIC 'Air', we learned that air contains hydrogen, oxygen, carbon dioxide and other gases.


In the TOPIC 'Respiratory systems', we learned that air inhaled is poor in carbon dioxide (0.03%) and air exhaled is rich in carbon dioxide (4%).


So can the experiment actually shows the second TOPIC rather than the first TOPIC.


By stating that 'air breathed out contains more carbon dioxide than the surrounding air' based on the second TOPIC is actually correct. It also does not contradict the experiment as Flask D shows that there was carbon dioxide in the air breathed out and the statement also does not imply that carbon dioxide exists in the surrounding air because

the experiment shows
carbon dioxide in air breathed in = 0, carbon dioxide in air breathed out > 0.


By extrapolation, if carbon dioxide in air breathed in = 0.03%, carbon dioxide in air breathed out > 0.03%.


So both answers should be accepted.


For further discussion please.

[CoffeeCat]

Mr tang your extrapolation reasoning is interesting but …

I would just like to point out that what we learned about experimental setup is that more often than not our conclusion is tied to the hypothesis, which determined the experimental setup and design.
if the examiners truly wants a comparison statement, this experimental setup should include a setup where the surrounding air is passed into limewater(a control ) and an observation saying that which limewater turns chalkier.
An actual comparison is needed, not reasoning by extrapolation even though it makes sense with prior knowledge that the process in respiration does not cause any decrease in carbon dioxide (that it is assumed or provided that there is no side effect in the process of respiration that causes usage of carbon dioxide).
In other words the experimental design of an existence hypothesis differs from a comparison hypothesis. This explains why some of us do not support the p5g answer.
So in this case what p5g have pointed out coupled with your reasoning forms the basis for a new hypothesis to be tested out by an experiment.

Mr tang has done well in pointing out that the existence of carbon dioxide in surrounding air is being hinted by the question.

It is possible that p5g answer is acceptable under the marking scheme as it is possible that the psle examiners are not so particular about experimental setup.

[atutor2001]

[quote]From the experiment above[/quote]

Hi Tang,

Nice to see you back. Have you been solving math questions with all your shortcuts? I love them.

Back to the magic words. Those 4 magic words are different from mind because they do not restrict the question to the picture. \"Experiment\" is not the same as \"experimental setup\". The word \"Experiment\" will include steps and procedure taken but are not depicted in the picture. So can use prior knowledge for this question lah.

(\"Experimental Setup\" refers to just the apparatus)

[P5G]

Please help.



http://www.orlesson.org/orp/09Sc/2009-Sc-SA1-MGS.pdf


Q26) When a child suffers from high fever, there is a practice to place a wet towel around the child's head and neck. What do you think is the possible reason for doing that?

(1) The wet towel provides coldness to the body.
(2) The wet towel is a poor conductor of heat to prevent heat from entering the body.
(3) The wet towel is a good conductor of heat to conduct heat away from the body.
(4) The wet towel allows evaporation to happen around the body.

Worksheet answer is 4).

My answer is (1.

Which is correct?


Q29) Please refer to the picture.

Worksheet answer is (2).

My answer is (4).

Which is correct?



Q33c) Please refer to the question and picture attached.

My answer is sunlight and water.

Will it be acceptable?

TIA.

[tianzhu]

Hi P5G


It’s a usual practice to wet a towel using water in a scenario as described in the question.For Q26, I am inclined to go for option (4).

Option (1) ----- The wet towel provides coldness to the body. If you interpret provides coldness as supplies coldness to the body, as heat travels from a hotter region to a lower region, the wet towel cannot supply coldness to a warmer body.
Option (2) is offside for obvious reason.
Option (3) is out as water is a poor conductor of heat.
Option (4) is logical as evaporation is a cooling process.

For Q29, I’d go for option (2).Remember that light travel in a straight line.
Note -----I think angles of incidence and reflection are not covered in primary science.I am not sure whether teachers would be very particular about this or not.As the diagram may not reflect the original one due to duplication, option(4) is also a possible answer.

For Q33, a diagram is provided and you are required to answer based on the context in the question.

This question concerns germination of seeds. In primary science, students learnt about the three conditions for germination, water, air and warmth.
There is no information given in the question to suggest that are jars are placed under sunlight.

The conditions for a plant to grow well are air, water, sunlight/light and nutrients(minerals)

Based on this question, I’d go for water and air.

Best wishes

[atutor2001]

P5G:

Please help.



http://www.orlesson.org/orp/09Sc/2009-Sc-SA1-MGS.pdf


Q26) When a child suffers from high fever, there is a practice to place a wet towel around the child's head and neck. What do you think is the possible reason for doing that?

(1) The wet towel provides coldness to the body.
(2) The wet towel is a poor conductor of heat to prevent heat from entering the body.
(3) The wet towel is a good conductor of heat to conduct heat away from the body.
(4) The wet towel allows evaporation to happen around the body.

Worksheet answer is 4).

My answer is (1.

Which is correct?

Hi P5G

In science, the terms \"hotness\" and \"coldness\" means \"temperature\".

For example, the \"coldness\" of the water is just right for bathing, means that the temperature of the water is ok.

Therefore, we cannot \"provide coldness\" (i.e. provide temperature) to a body\". The correct way to say it is \"We remove heat (energy) from the body to make it colder (i.e. of lower temperature). So the wrong science term is used in Ans 1 and is not acceptable.

[Sun_2010]

P5G:

Please help.



http://www.orlesson.org/orp/09Sc/2009-Sc-SA1-MGS.pdf


Q26) When a child suffers from high fever, there is a practice to place a wet towel around the child's head and neck. What do you think is the possible reason for doing that?
Q33c) Please refer to the question and picture attached.

My answer is sunlight and water.

Will it be acceptable?

TIA.

Hi P5G,
For 26, the option 1 - is incorrect, you can only remove heat energy from an object , cant add coldness to it.
Moreover, a wet towel will be at room temperature , so the amount of heat a transfered from the warm body to the towel is not substantial if it were not for the evapoaration of the water which needs more heat.
So ans is definetely 4.

As for the germination question 33c, seeds do NOT need exposure to sunlight for germination. Air , water and warmth ( i think temp abt 25 deg C + is ideal)

[Tang]

P5G:

Please help.



http://www.orlesson.org/orp/09Sc/2009-Sc-SA1-MGS.pdf

Q33c) Please refer to the question and picture attached.

My answer is sunlight and water.

Will it be acceptable?

TIA.

Your answer is acceptable since it refers to the young seedlings after 1 week.

The young seedlings need sunlight, air (carbon dioxide) and water to make food (photosynthesis) and oxygen for respiration.