Q&A - PSLE Science

[Verysuperkiasu]

Question:

Cutting down of trees will cause the phenomenon ‘global warming’. Which of the following are involved in global warming?
A: burning of trees causes the carbon in the tree to combine with oxygen in the air to form carbon dioxide.
B: Carbon dioxide in the atmosphere acts as a blanket to trap heat in the Earth.
Without trees, Sun heats up te Earth’s surface directly.
Soil erosion will destroy aquatic life forms, which in turn will enhance global warming subsequently.

(1) A and B only
(2) A, B and C only
(3) A, B and D only
(4) A, B, C and D

Answer is (4). My son doesn’t think C and D are involved in global warming. Is he correct or is he wrong. His answer is (1).

[atutor2001]

Intermezzo:

hi atutor2001 ~ thanks for all your invaluable input into this forum.
i don't quite understand this question though..
seems to me that in such a case of metamorphosis, practically all physical parts of the insect has changed. even the legs (although they are true legs) are different after changing into a butterfly.

is it accepted in such a case to give the answer as \"No parts of the insect remained unchanged\" ?

Hi Intermezzo
In science, I forced myself to remember that \"change\" would mean becoming a new \"substance or form\" (for e.g. simple eye becomes compound eye).

Changes in terms of shape and size are not considered as \"change\". That kind of change (if I am not wrong) should be called \"grow\". So although the shape and size of the \"True Legs\" did change, their overall structures \"did not change\".

Hope that my concept is correct.

Cheers

[Guitar]

ss501:

hi,

The answer given is 4, pls help to explain, thanks.
http://i51.tinypic.com/2ufaib7.jpg\">

Water evaporates at different temperatures.So, 4 is the correct ans.

[bcs-dad]

Hi All,


For the question below (for question part a), the answer key is \"Oxygen\". Can some body please explain this?

My DS answer is Carbon dioxide.

http://i51.tinypic.com/x1wwat.png\">

Thanks in advance..

[Newkiasu2011]

Does CFC cause global warming?


CFC causes ozone layer depletion. Ozone is a green house gas and causes global warming. If CFC reduces ozone, then does it mean that CFC does not affect global warming.

I read that CFC itself is a greenhouse gas. In that case, it should cause global warming.

[Nebbermind]

Newkiasu2011:

Does CFC cause global warming?


CFC causes ozone layer depletion. Ozone is a green house gas and causes global warming. If CFC reduces ozone, then does it mean that CFC does not affect global warming.

Think CFC is the greenhouse gas and not ozone. It depletes the ozone layer which in turn allow more of the sun's energy to reach the earth.

[Newkiasu2011]

thanx


http://en.wikipedia.org/wiki/Greenhouse_gas
The above link mentions ozone as one of the gh gas. Hence confusing. I agree that ozone layer reduces the sun's heat and UV rays from reaching earth.

[Nebbermind]

atutor2001:

But option (4) specifically stated \"....but not in flask A\".

For science, this is a very strong statement and it would mean that not a tiny bit of milkiness is allowed in A.\"

I go for (1)

CO2 is a trace gas. While there may be precipitation (is that the right word?), I believe it's not enough to turn the water milky. I'll got for (4)

[ms_lim]

Please help on this question :


http://i53.tinypic.com/o54xh2.jpg\">

Ans key : (1), dd's ans : (3)

[ms_lim]

Please help on part (b) :

http://i52.tinypic.com/9kvwug.jpg\">