Q&A - PSLE Science

[tianzhu]

atutor2001:

Ask farmers, \"How to plant carrots?' and they will tell you to use seeds.


Ask a Singapore PSLE student the same question and they will tell you to use a carrot.

Both are right.

However, planting carrot using carrot doesn't make sense because we will get back the same carrot, perhaps a bigger one after some time (but the carrot will be too old). Technically speaking we are growing back the old plant so I don't think it is really a reproduction process. So if we really need to show that carrot can reproduce from its roots, we should use only the top part of the carrot (the bottom part of the carrot can be our meal).

Hi atutor2001

I agree with your first statement. However for the second one, I’ve my reservations. From the highly popular PSLE Science Guide, first edition (MC), pg 133, students learned that carrots are grow from seeds.I think the revised second edition has included vegetative propagation as a form of reproduction for carrots.

We can grow carrots from cutting the top of an existing carrot.However,this method is not frequently used.

http://www.doityourself.com/stry/different-carrot-propagation-methods

Best wishes

[P5G]

tianzhu:

Hi P5G


Let’s us revisit this question again.

My answer is same as you .It is water vapour. James has a different answer.
Have you checked with your science teacher? For the benefits of PSLE 2010 kiasu kids, please let us know the correct answer.

Best wishes

My personal notes after discussions with my Science teacher.

Before boiling -- Air bubbles (air dissolved in the water)

During boiling - Water bubbles (water in the gaseous state, that is water vapour)

When water is heated to 100 degree C -- it refers to before boiling. So Worksheet answer is correct.
(Time when water is below 100 degree C to 100 degree C)

Confusion - 100 degree C.

Hope that my personal notes are accurate and correct and are useful to all.

[tianzhu]

P5G:

My personal notes after discussions with my Science teacher.

Before boiling -- Air bubbles (air dissolved in the water)

During boiling - Water bubbles (water in the gaseous state, that is water vapour)

When water is heated to 100 degree C -- it refers to before boiling. So Worksheet answer is correct.
(Time when water is below 100 degree C to 100 degree C)

Confusion - 100 degree C.

Hope that my personal notes are accurate and correct and are useful to all.

Hi P5G

Thank you for your quick reply.

You’ve brought up a very interesting point regarding the definition of when.

We are given the understanding that
When water is heated to 100 degree C -- it refers to before boiling.

This means water has not reached its boiling point of 100 degree C according to your discussion with your teacher.
Should we interpret it in this way? I am not so sure, maybe, some members who are more proficient in English may help to clarify?

Best wishes

[P5G]

tianzhu:

Hi P5G


Thank you for your quick reply.

You’ve brought up a very interesting point regarding the definition of when.

We are given the understanding that
When water is heated to 100 degree C -- it refers to before boiling.

This means water has not reached its boiling point of 100 degree C according to your discussion with your teacher.
Should we interpret it in this way? I am not so sure, maybe, some members who are more proficient in English may help to clarify?

Best wishes

The water is heated to 100 degree C, its boiling point.

According to my teacher to see water bubbles, we need to continue to supply heat. The heat will be used to change water from liquid to gaseous state. It also explains why the temperature remains at 100 degree during boiling.

[tianzhu]

P5G:

The water is heated to 100 degree C, its boiling point.

According to my teacher to see water bubbles, we need to continue to supply heat. The heat will be used to change water from liquid to gaseous state. It also explains why the temperature remains at 100 degree during boiling.

Hi P5G

Thank you for your quick response.

You’ve now clarified that water has reached its boiling point of 100 degree C .Based on one of your earlier statement,

During boiling - Water bubbles (water in the gaseous state, that is water vapour)

I am wondering why water vapour is not the answer.

This is an interesting article about misconceptions about boiling water.
http://www.csun.edu/~ms4288/SED%20690/Misconceptions.pdf

Best wishes

[P5G]

Please help.


Q1. Our body uses the respiratory system to ____

(1) carry out breathing

(2) circulate blood

(3) make its food

(4) produce energy



Q2. Which of the following are agents of water pollution?

A. Acid rain

B. Disposal of rubbish into canals

C. Spillage of petroleium from ships


(1) A and B

(2) B and C

(3) A and C

(4) All of the above

TIA

[P5G]

tianzhu:

P5G:

The water is heated to 100 degree C, its boiling point.

According to my teacher to see water bubbles, we need to continue to supply heat. The heat will be used to change water from liquid to gaseous state. It also explains why the temperature remains at 100 degree during boiling.

Hi P5G

Thank you for your quick response.

You’ve now clarified that water has reached its boiling point of 100 degree C .Based on one of your earlier statement,

During boiling - Water bubbles (water in the gaseous state, that is water vapour)

I am wondering why water vapour is not the answer.

This is an interesting article about misconceptions about boiling water.
http://www.csun.edu/~ms4288/SED%20690/Misconceptions.pdf

Best wishes

Mr Tianzhu,

My Science teacher actually drew a Temperature - Time graph to explain.

The graph starts from Point A (Room temperature at Time 0) to point B (Boiling point at time 10 minute) (as an example). It then remains horizontal at 100 degree C till Point C for another 5 minute.

She explained that from

Point A to B, the bubbles in the water are Air bubbles.

Point B to C, the bubbles in the water are Water bubbles.

When water is heated to 100 degree -- refers to any Point between AB to the Point B -- so Air bubbles (answer as given in worksheet).


Additional information discussed.

From Point A to B
- Heat supplied raises the temperature of water.
- Evaporation takes place only at the surface of water, so bubbles seen in the water are not water bubbles but air bubbles.

From Point B to C
- Heat supplied does not raise the temperature of water.
- Heat is used to change water from liquid state to gaseous state, so bubbles seen in the water are water vapour.

Hope that it is now clearer.

[pecalis]

P5G:

My personal notes after discussions with my Science teacher.

Before boiling -- Air bubbles (air dissolved in the water)

During boiling - Water bubbles (water in the gaseous state, that is water vapour)

I thought water at 100 deg C is called steam? Water can be changed to water vapour at any temp during evaporation but at 100 Deg C, it is NOT water vapour but steam?

A little confused...Sorry to add more confusion...

[Dbdad]

Hi everyone,


Thank you for the help.

DB

[CoffeeCat]

P5G:

Please help.


Q1. Our body uses the respiratory system to ____

(1) carry out breathing

(2) circulate blood

(3) make its food

(4) produce energy



Q2. Which of the following are agents of water pollution?

A. Acid rain

B. Disposal of rubbish into canals

C. Spillage of petroleium from ships


(1) A and B

(2) B and C

(3) A and C

(4) All of the above

TIA

hi P5G, if i am not wrong the answer is (1) and (2) respectively. My science resources from eons ago revealed that acid rain is not an agent of water pollution. unless of course , the syllabus changed...