Q&A - PSLE Science

[xznat]

The anomalous expansion of water as it freezes. Ice has a crystalline structure which leaves relatively (as compared to water) large spaces in between H20 molecules. Thus when the molecules rearrange themselves they take up more space (ie occupy a larger volume), hence creating an outward force on the glass.

[carebear]

concerned9999:

hi, i need help on this question on how to explain it. I know why but i dont know how to explain it...


When a glass of water is put into a freezer and is taken out from the freezer after a few hours, the glass is observed to be cracked. why does the glass crack?

Water contracts when it is cooled, like most solids.
However when it reaches 4deg C it start to expand rather than contract. It will expand further as it reaches its freezing point.
Glass however contracts as it is cooled.
So if the ice expands and the glass contract, the ice will break the glass.

[concerned9999]

thanks xznat and carebear for the explanation now i know how to explain in exams

[concerned9999]

thanks xznat and carebear for the explanation now i know how to explain in exams

[starlight1968sg]

I doubt the special property of water (ie expand at 4 deg C) is tested in p6 ?!

[TanMeiMei]

I beg to differ from xznat. How one earth can this take place. Was it stated anywhere that the container was filled to the brim and tightly sealed with no room for expansion to take place?

[raghupavithra]

any body know the psle online study guide for students

[hashroop]

Hi, need help with this MCQ question:

Tubes grow from the pollen grains towards the ovary to pass_____.
option 1) the pollen grains to the ovules
Option 2) the male reproductive cells to the ovules
Correct answer?

I’ve eliminated the other two irrelevant option but I’m scratching my head with the above two options. Thank you in advance.

[tianzhu]

hashroop:

Hi, need help with this MCQ question:

Tubes grow from the pollen grains towards the ovary to pass_____.
option 1) the pollen grains to the ovules
Option 2) the male reproductive cells to the ovules
Correct answer?

I've eliminated the other two irrelevant option but I'm scratching my head with the above two options. Thank you in advance.

Hi

I am more inclined to pick (2).

We need to see the difference between pollination and fertilisation.

Pollination occurs when pollen grains are transferred from the anther of one flower to the stigma of the same flower or another flower of the same kind.

Fertilisation is the process in which a male cell fuses with the female cell.

You may find more information from PSLE Science Guide (MC).

Best wishes

[hashroop]

Thank you for the clarafication. Have a great day ahead.