PSLE 2012 - Science

[creamyhorror]

concerned_of_PSLE 10:

I thought should be anther because the stigma may be pollinated beforehand without pollen grain fertilisation cannot happen

If pollination has already occurred, then how will removing the anther help? It doesn't make sense to ask the question if the flower is already pollinated and will produce seeds soon.

vaidyanathan padmini:

How about friction question from McQ.....
My dd's answer is only C as friction opposes motion...
Only the box in c is moving so it should have friction

What was the question? I haven't seen it, but friction can act on objects to stop them from moving, even if the objects aren't moving at all. That's called static friction.

[thesjarox]

vaidyanathan padmini:

How about friction question from McQ.....

My dd's answer is only C as friction opposes motion...
Only the box in c is moving so it should have friction

Confirmed with teacher-A,B and C.
Friction also acts on stationary objects. That's why forces have to overcome the friction before being able to move the object. Also, if there were no friction acting on an object,the object would glide across the surface, like ice, and would never stop.
Thus, A is also correct.

[fantasy1]

HI


How abt section (B) qn
Something abt the type of colour used for photosynthesis. For Part when they removed the water plants, what observation will the person see to ensure result at part (B) is correct?

[celeste13love]

Clairifina:

Is my answer correct for the mist question?


The mist system gives out water droplets. As water is not a conductor of heat, it will not conduct heat to the surroundings and thus it will help to cool the surrounding air.

I say that \"when the most touches our skin, it will evaporate. When evaporating, it also takes heat away from our body, hence making us cooler\"

[celeste13love]

I found the paper pretty ok... It wasn't that tough although Booklet B was a little tricky. ok, so I just wanted to confirm a question with you guys... Um you know there was a question about a control set-up in Booklet A? The one about the substance to remove oxygen and beans? Well, I put my answer as the set-up with water... Because I remember my science teacher telling me before that a control set-up is made to ensure that it is the variable changed that affects the results... And the question had absolutely nothing to do with carbon dioxide and carbon dioxide does not affect the results... And you might be thinking \"But the question has got nothing to do with water too!!\" But idk I think that's the most suitable answer OMG I wrote so much ^^

[atutor2001]

wsywin2012:

atutor2001:

[quote=\"wsywin2012\"]
stigma i think... already mentioned on

I thought it should be ovules. If there is no elaboration on \"how the part is removed\", I would think that the ovules can be removed through genetic manipulation - isn't that how they produced seedless fruits such as grapes and papaya. However, if it is ovules, then \"remove\" is a bad choice of word.

umm there wasnt an option for ovules[/quote]Thanks for clarifying. Mistaken it to be open ended question. I will also pick stigma as the answer.

[fantasy1]

may I know what is yr answer?

[atutor2001]

creamyhorror:

atutor2001:

[quote=\"James Ang\"]
The use of fans creates wind which is moving air and the presence of wind increases the rate of evaporation and produces a greater cooling effect.

Fan is used to disperse the mist to reach different parts of the room so that the room will cool down at a faster rate. It is also to prevent the tiny water droplets from combining into large droplets (precipitation like rain cloud) that would fall to the floor and wet the room.

I think all 3 points are correct. Higher air movement inherently results in an increased evaporation rate.
[/quote]In normal cases of evaporation, the water is a \"huge\" body that does not move. So wind helps to remove the \"hotter\" and more humid air surrounding this water body, replacing it with cooler air and less humid air. As a result, the rate of evaporation will increase.

For this question, the mist are tiny water droplets that follows the wind. So the water droplets will move with the wind to different parts of the room, gaining heat from that part of the room where it has reached and evaporates.

[fantasy1]

What is the answer for the water setup qn :?

[777]

Anybody know the answer for the ballon question in booklet A? (the question is something like why the ballon become smaller in the refrigerator?)


My answer is 2