Q&A - PSLE Science

[atutor2001]

tianzhu:

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

Hi tianzhu

Thanks for the information.

I googled and realised that growing carrot from its top will not produce new carrot (which is why seeds must be used to get a new carrot).

It can only grow into a plant. Is this plant considered to be a new plant or a \"resurrection\" of the old plant is a question mark to me. However, this plant can flower and produce seeds. So it is interesting question as to whether producing a plant from a carrot top considered as \"a method of reproduction\" - though my kids had been thought that it is, many years ago.

Regards

[tianzhu]

Hi


In primary science, we learnt that respiration takes place in the cells when glucose reacts with oxygen to produce energy, carbon dioxide and water. I think you need the respiratory, digestive and circulatory systems to function together for respiration to produce energy.

Going by the choices in your Q1, I’d go for option (1).

As for Q2, from PSLE Science Guide, we have
Acid rain – formed when pollutants from smoke dissolve in rain
•\tPollutes our water supply
Therefore, I’d go for option (4)

PS — I am not sure if my answers are correct. For the benefits of PSLE kids, please help to confirm them when you receive the correct answers from your teacher.

Best wishes

[tianzhu]

atutor2001:

I googled and realised that growing carrot from its top will not produce new carrot (which is why seeds must be used to get a new carrot).

Hi atutor2001

You've brought up something interesting, please share the link to this information.

Best wishes

[tianzhu]

P5G:

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.

Hi P5G

Please do not be so formal and address me as Mr… I am also learning from other members in this thread. It’s a delight to have you here and I am very impressed by your diligence.

You can simply address me as tianzhu or uncle tianzhu (due to our big age difference)

When water is heated from A to B in 10 minutes, it reaches its boiling point of 100 degree C. From primary science, we learnt that water changes from liquid to gas (steam).The temperature of boiling water remains at 100 degree C until all water has turned into water vapour.

Your question on bubbles seen when boiling is not an easy one. If you do a google search, if will find many interesting articles discussing misconceptions on boiling water bubbles.

Best wishes

[atutor2001]

tianzhu:

atutor2001:

I googled and realised that growing carrot from its top will not produce new carrot (which is why seeds must be used to get a new carrot).

Hi atutor2001

You've brought up something interesting, please share the link to this information.

Best wishes

Hi tianzhu

The link is : http://www.associatedcontent.com/article/151591/growing_plants_from_garden_scraps.html?cat=32

Below is extracted from the article :

\"Carrot tops will sprout and grow into bushy plants, but will not grow another carrot.\"

Regards

[atutor2001]

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

Maybe we can change the content of the sentence so that we can get a clearer understanding :

\"When the liquid was heated to xx degree C, it turned red\".

Compare the above sentence to this one :

\"While the liquid was heated to xx degree C, it turned red\".

To me, the use of the word \"When\" means that the \"event\" happens only at xx degree C. If we want to describe the process from 0 to xx degree C, the word \"while\" should be used. My opinion is that your answer (1) hot water vapour, should be the correct one.

By the way, all the dissolved air in the water can be expelled before the water reaches 100 degree C. Therefore, if we observe carefully the heating process, we will notice that the water actually stopped bubbling a few seconds before it reaches 100 degree C as all the dissolved air has already been expelled and the water \"cannot boil yet\".

Regards

[tianzhu]

atutor2001:

\"Carrot tops will sprout and grow into bushy plants, but will not grow another carrot.\"

Hi atutor2001

Thank you for the link.

From the cut portion, it’ll first grow into a plant. Likewise from seeds, carrot plants will develop.

The carrots we eat are the roots of the plants. The taproots become swollen or fleshy due to storage of food.

Best wishes

[P5G]

Details of discussions on Bubbles


MGS Science P5 CA1 2009
Q6: When water is heated to 100 degree C, bubbles can be seen rising through the water. What do these bubbles contain?

(1) Hot water vapour
(2) Hot water droplets
(3) Air dissolved in the water
(4) Only oxygen is released from the hot water

Worksheet's answer is (3) and my answer is (1).
Should the bubbles be hot water vapour or air dissolved in the water?
How do I decide which should be the answer? What are the key factors?

For this question, are we referring to 'before boiling' or 'boiling'?

------------------------------------------------------------------------
Comments as given by Mr Chris Roger from Onsponge.com

Answer provided is correct.

We must realise that water is not just H2O but also contains gasses such as air that have been dissolved in water at lower temperatures (they are soluble in water). When the water is heated, you will notice bubbles starting to form at the point where the water is being heated even before 100 degrees C. Normally this is at the bottom of the jar / container. As this happens the dissolved Air will become less soluble and since gasses are less dense than liquid they rise up through the water.

Note: You will notice that these bubbles start to appear before the water is actually boiling. They could in fact, start to appear around 80 degrees C. Once the water temperature reaches 100 degrees C it converts to a gaseous state - water vapour.

So what is water vapour? Water vapour is water in its gaseous state-instead of liquid or solid (ice).

------------------------------------------------------------------------
Discussions at Kiasuparents.com

Mr Tianzhu,
Your answer is correct. It is water vapour. A similar type of question has been discussed earlier in this thread.


Mr James Ang,
I reasoned that the correct answer is (3) and not (1) for the below reasons;

1. Water vapour escape from the surface of the water rather than from the bottom of the container. (kinetic particle theory - where the active particles leave the surface of the liquid and become gas, leaving the remaining particles to have less average energy per particle)
2. Water contains dissolved air which is necessary for the survival of living things that live in water. Boiling will expel the dissolved air from the water. That's why water animals cannot live in boiled water that has cooled down as the water does not contain dissolved oxygen.

I am sure the above reasons are convincing and scientific for you.


Mr Tianzhu,
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.


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.


Mr Tianzhu,
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?


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.


Mr Tianzhu,
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


P5G
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,
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?


Mr Tianzhu,
When water is heated from A to B in 10 minutes, it reaches its boiling point of 100 degree C. From primary science, we learnt that water changes from liquid to gas (steam).The temperature of boiling water remains at 100 degree C until all water has turned into water vapour.

Your question on bubbles seen when boiling is not an easy one. If you do a google search, if will find many interesting articles discussing misconceptions on boiling water bubbles.


Ms atutor2001,
Maybe we can change the content of the sentence so that we can get a clearer understanding :

\"When the liquid was heated to xx degree C, it turned red\".

Compare the above sentence to this one :

\"While the liquid was heated to xx degree C, it turned red\".

To me, the use of the word \"When\" means that the \"event\" happens only at xx degree C. If we want to describe the process from 0 to xx degree C, the word \"while\" should be used. My opinion is that your answer (1) hot water vapour, should be the correct one.

By the way, all the dissolved air in the water can be expelled before the water reaches 100 degree C. Therefore, if we observe carefully the heating process, we will notice that the water actually stopped bubbling a few seconds before it reaches 100 degree C as all the dissolved air has already been expelled and the water \"cannot boil yet\".

------------------------------------------------------------------------
Discussion at Road-to-PSLE

Bubbles:
atutor has emphasised on ‘when’ versus ‘while’ and decided that for ‘when’, the answer is hot water vapour.
To add to the confusion, I would like to emphasise on ‘to’ (when water is heated to 100 deg C) versus ‘at’ (When water is heated at 100 deg C), so for ‘to’, my answer is air dissolved in the water.
If the question has been ‘at’, my answer will be hot water vapour.

To bubbles:
Heated to 100 degree C meaning water has reached boiling point which is 100 degree C. At about 80 degree, dissolved air has been expelled, so the answer is water vapour.

------------------------------------------------------------------------
Any further comments.

[tianzhu]

Hi P5G


I am very impressed by your diligence in your pursuit of the correct answer.
So, how can we as parents leave you alone? I am inspired to do a bit of further reading.

On pg 12 of Chemistry Matters, there is a photo shows water boiling vigorously in a container, with bubbles breaking from the water surface. The caption is ---- Bubbles are seen when water boils.They contain water vapour.

You may also find this link useful.
http://nicholasacademy.com/scienceexperiment300watchedpot.html

Best wishes

[James Ang]

tianzhu:

Hi P5G


I am very impressed by your diligence in your pursuit of the correct answer.
So, how can we as parents leave you alone? I am inspired to do a bit of further reading.

On pg 12 of Chemistry Matters, there is a photo shows water boiling vigorously in a container, with bubbles breaking from the water surface. The caption is ---- Bubbles are seen when water boils.They contain water vapour.

You may also find this link useful.
http://nicholasacademy.com/scienceexperiment300watchedpot.html

Best wishes

Let's vote for the right answer based on the discussion raised so far. What is everyone's final answer?

I choose answer (3) Air dissolved in the water. The intention of the setter and primary school syllabus is to test the student's knowledge that water contains dissolved air that is required for some living things to breathe in water, and that the dissolved air can be expel through heating to boiling point.

extract from Tianzhu's link;
As the pot and water heat up, you will notice tiny bubbles forming on the bottom and sides of the pot. These first bubbles are not the start of boiling. Instead, they are from dissolved gases being driven out of the water. Still, these bubbles are important, as they will serve as starting points for the bubbles produced by boiling.