Q&A - PSLE Science

[starlight1968sg]

Vanilla Cake:

(b) Why did the \"cloud\" move higher and higher? (2 marls)


Answer given: The air above the spout got warmer and so condensation would like place higher where it was cooler.

Is the answer given correct? Could you pls help to answer part (b) of this question? TIA for your time and effort. Much appreciated.

Didnt expect this ans but think of it, quite true as the hot air right from the spout pushes the \"cloud\" higher.

[tianzhu]

Hi VC


The answer from the WS is a logical one.

Best wishes

[tianzhu]

Watermist Gun


The gun works by spraying the water out into a fine mist instead of spurting a jet of water as a conventional hose does.

http://www.youtube.com/watch?v=24PdBM-phVQ

How are water mists more effective than conventional water jets in fighting fire?

Give it some thoughts using concepts within PSLE Science syllabus.

Best wishes

[Vanilla Cake]

starlight1968sg:

Vanilla Cake:

(b) Why did the \"cloud\" move higher and higher? (2 marls)


Answer given: The air above the spout got warmer and so condensation would like place higher where it was cooler.

Is the answer given correct? Could you pls help to answer part (b) of this question? TIA for your time and effort. Much appreciated.

Didnt expect this ans but think of it, quite true as the hot air right from the spout pushes the \"cloud\" higher.

tianzhu:

Hi VC

The answer from the WS is a logical one.

Best wishes

Hi Uncle tianzhu/starlight1968sg,

Thks for your response to my question. Pls pardon my ignorance as I still cannot come up with the right answer after watching the video clip and reading the answer given. Could you pls enlighten and share how the correct answer is to be written?

Also back to MCQ Q30 - Option (3) of the same paper. I don't understand option 3 that \"Carbon dioxide is not returned to leaves\" is correct in concept. Pls kindly guide and explain on this.

Sorry to bother you and thks in advance for your help.

[starlight1968sg]

Vanilla Cake:

starlight1968sg:

[quote=\"Vanilla Cake\"] (b) Why did the \"cloud\" move higher and higher? (2 marls)


Answer given: The air above the spout got warmer and so condensation would like place higher where it was cooler.

Is the answer given correct? Could you pls help to answer part (b) of this question? TIA for your time and effort. Much appreciated.

Didnt expect this ans but think of it, quite true as the hot air right from the spout pushes the \"cloud\" higher.

tianzhu:

Hi VC

The answer from the WS is a logical one.

Best wishes

Hi Uncle tianzhu/starlight1968sg,

Thks for your response to my question. Pls pardon my ignorance as I still cannot come up with the right answer after watching the video clip and reading the answer given. Could you pls enlighten and share how the correct answer is to be written?

Also back to MCQ Q30 - Option (3) of the same paper. I don't understand option 3 that \"Carbon dioxide is not returned to leaves\" is correct in concept. Pls kindly guide and explain on this.

Sorry to bother you and thks in advance for your help.[/quote]Sorry I can't answer your question properly.
I am thinking of the actual cloud formation. As water vapour in the air rises, it cools, condensation occurs and thus a (real) cloud is formed.
Similarly, the hot air from the spout rises = pushing the \"cloud\" higher. Thus pushing the location of condensation (to occur) to higher.... :roll:

[ParentingChildren]

Vanilla Cake:

(b) Why did the \"cloud\" move higher and higher? (2 marls)


Answer given: The air above the spout got warmer and so condensation would like place higher where it was cooler.

Is the answer given correct? Could you pls help to answer part (b) of this question? TIA for your time and effort. Much appreciated.

Condensation needs to happen on a cool environment (water vapour needs to lose heat). The air near the spout, like stated in your answer, would get too warm for condensation to occur. Since hot air rises, the hot water vapour rises until it is cool enough for condensation to occur.

Hope that explains why the \"cloud\" move higher and higher.

[tianzhu]

[quote]MCQ Q30 - Option (3) of the same paper. I don't understand option 3 that \"Carbon dioxide is not returned to leaves\" is correct in concept.[/quote]
Hi VC

The question asks a student to identify which of them is wrong.

Focus on the respiratory system in plants; you may refer to PSLE Science Guide (MC)

Plants respire all the time, day and night. Carbon dioxide is released and oxygen is taken in during respiration.This explains why \"Carbon dioxide is not returned to leaves\" is correct in concept.

Do not get it mixed up with photosynthesis.

Best wishes

[tianzhu]

Hi VC


Steam is hot water vapour at boiling point(100 degree Centigrade).
It condenses when it meet a cooler/colder surface.

I think students are more familiar with experiment involving holding a glass plate or copper sheet near a kettle spout.

In the beginning, one can see many water droplets on the surface of the glass plate or copper sheet as the hot steam condenses to form water droplets when it touches the cooler surface of the glass plate or copper sheet.

After some time, condensation cannot take place as the glass plate or copper sheet has become hotter.

Applying the same concept, in the beginning steam condenses to form white clouds as it touches the cooler surrounding air near the kettle spout.

After some time, the surrounding air near the spout gets hotter, so no condensation takes place. For condensation to take place again, the steam has to move further away to come into contact with the cooler surrounding air which is further away from the spout. This explains why the cloud moves higher and higher.

Best wishes

[Tang]

Vanilla Cake:

Compare the following differences between the respiratory and circulatory system in plants and in human beings. Which of them is wrong?


Option 1
Plant: Exchange of gases takes place in the leaves
Human: Exchange of gases takes place in the lungs

Option 2
Plant: Oxygen is pumped to all parts of the plant
Human: Oxygen is pumped to all parts of the body

Option 3
Plant: Carbon dioxide is not returned to leaves
Human: Carbon dioxide is returned to the lungs.

Option 4
Plant: There is no blood to carry food around the plant
Human: Blood carries food around the body

Answer given is option (2).
Is this correct?
Option (1) and option (4) are obviously correct.
Pls help to explain why option (2) is chosen instead of option (3) for this question.
TIA for your time and effort.

Hi,

I personally think option (3) is the correct answer.


Respiration is the conversion of food to energy. For this process to take place, oxygen is used up and carbon dioxide is produced.


Exchange of gases takes place at the leaves through stomata. So oxygen needs to be pump from the leaves to all parts of the plant and carbon dioxide to the leaves to be removed. The former shows that option (2) is correct while the latter shows that option (3) is wrong, hence the correct answer - option (3).

[janet88]

Hi Parents,

I happened to see this 'Science PSLE Revision & Examination Papers (2E)…is it worth while getting ? TIA

This thread is really interesting and explainations are clear. Thanks.
I’ve been reading up P5 Science to get a feel and don’t quite understand…now I do.