Q&A - P3 Science

[atutor2001]

ChiefKiasu:

..... If the material allows heat to be conducted through it before it expands, then the rate of expansion of the gas will negate any perceived effects of the expansion of the container. .........

Fully agreed with your analysis. However, all common materials do not behave this way. So all primary school answers for such questions (regardless it is heating or cooling) must state that the ink drop moves slightly in a certain direction before moving in the opposite direction.

[kitty2]

Please help with these questions,thanks


1) John had 2 similaar pieces of bread.he placed each of these pieces of bread in 2 identical jars,x and y.He added a few drops of water to the bread in jar x only.The jar x turned mouldy and jar y turned slightly mouldy.

a) Why did John make the jars airtight?
b) A 3rd piece of bread was heated in the oven.If this piece of bread was put in another airtight jar,what would John expect to see after 3 days?


2)Melissa wanted to find out the volume of the air in a container.She filled it to the brim with 250 cm cube of stones.

a) The most likely volume of the container is

1)less than 250 cm cube
2)is equal to 250 cm cube
3)more than 250 cm cube

[adhdadhd]

Try with best knowledge to answer,


1) John had 2 similar pieces of bread. He placed each of these pieces of bread in 2 identical jars, x and y. He added a few drops of water to the bread in jar x only. The jar x turned mouldy and jar y turned slightly mouldy.

a) Why did John make the jars airtight?
To make the experiment fair, all bread must be exposed to same amount of air.

b) A 3rd piece of bread was heated in the oven.If this piece of bread was put in another airtight jar,what would John expect to see after 3 days?
The bread in this jar will not turn mouldy.

[adhdadhd]

We have to put some common sense in this question,

it said "stones", and did not elaborate clearly… if you fill a container (with unknown shape given) with stones, these stones will not be able to fill the containter fully, so my best answer is 3.

2) Melissa wanted to find out the volume of the air in a container. She filled it to the brim with 250 cc of stones.

a) The most likely volume of the container is

1)less than 250 cc
2)is equal to 250 cc
3)more than 250 cc

[peggy]

My ans is also 3. There are air gaps in between the stones and air also takes up space. Hence, the vol shld be more than 250cc.

[tianzhu]

Hi


In primary science, students learnt that bread mould grows quicker in dark, wet and warm conditions.

In answering part (a), one needs to know the concept of a fair test. We conduct a fair test by making sure that we change one factor (variable) at a time while keeping all other variables the same. In this experiment, we want to find out how water affects the growth of mould in bread.

By keeping the jars airtight, one ensures that the moisture from the surrounding air does not reach the bread. Furthermore water from the bread in jar X is also not lost to the surrounding air.
Craft your answer around these pointers.

For part (b), the moisture in the bread is removed by heating in an oven and the high temperature of the oven will destroy most moulds. Therefore the bread will not be mouldy.

Do we stop here? For me, it’s a definite yes. I’ll take a walk in the park to enjoy the scenery.

However, some parents may go on and ask whether the bread is put in the jar in hot or cold conditions. The question does not give any indication. Through experiences, they may know that cookies made by lovely mothers and wives should not be kept directly from the oven into containers. As in any open ended question, there is always a tendency for multiple interpretations. I would wonder whether students would think of that under intense examination environment.

Well, it’s up to you to decide. If you want to make your life more interesting, one may argue that condensation occurs when the hot bread is placed in a jar directly from the oven, the bread may also turn mouldy. But given the fact that the condensed droplets are of very small amount and the moulds had been killed under heat from the oven, this may not be likely. You may want to carry out an experiment to satisfy your curiosity.

Well, talking about lovely mothers and wives, I wish to take this opportunity to wish all mothers
Happy Mother’s Day

Best wishes

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[kitty2]

:thankyou: for all the replies,all of you are great!!!!!

[Puffer]

A question on Life Cycle:


There are 3 and 4 stages in a life cycle. True or False?

[tutormum]

False. There are 2 stages, 3 stages and 4 stages life cycles.

[Puffer]

First, my apologies to KS Chief and monitors for posting this wrongly - should have posted under P3/4 Science.


My DS’ Science teacher seems to have mentioned that presently, the PSLE people have ‘agreed’ that there will be no 2-stage cycles for man and most mammals. They have argued that the egg contained in the human body is considered one stage. I need experts’ advice please.