Q&A - PSLE Science

[Muffins]

lalala123:

StudentABC:

If a question shows the life cycles of a grasshopper and mosquito,


and ask:

Based on the diagrams above, which of the following statements between animals X(mosquito) and Y(grasshopper) is/are true?

A Both the adults do not have wings
B Both the young do not live in water
C Both the adults do not give birth to their young alive
D Both are pests in at least one stage of their life cycles

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

what should the answer be? Should we use the info given in diagram to derive the answer or use our general knowledge??? Would greatly value help!

and if pollination takes place between 2 different types of flowers, will the flowers develop into fruits????

Please help!!! :?:

my answer will be C and D. its so called commom sense

Hi lalala123, the answer for Q1 is C & D, but sometimes it is not using common sense, as StudentABC has said above. I do not think you can derive that the two animals were pests in their life cycles, as it might be helpful to the environment, but in the diagram, you cannot come to that conclusion easily. Sometimes, you have to remember what you have learnt from textbooks and assessment books.

And for Q2, seldom will nature itself do this, but sometimes, the flower may become a hybrid, but Science syllabus says that the flower will not be pollinated. So, I'm going with the Science books on this one and I would say, the flower would not be pollinated.

Hope I helped!

[chk707]

Muffins:

lalala123:

[quote=\"StudentABC\"]If a question shows the life cycles of a grasshopper and mosquito,


and ask:

Based on the diagrams above, which of the following statements between animals X(mosquito) and Y(grasshopper) is/are true?

A Both the adults do not have wings
B Both the young do not live in water
C Both the adults do not give birth to their young alive
D Both are pests in at least one stage of their life cycles

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

what should the answer be? Should we use the info given in diagram to derive the answer or use our general knowledge??? Would greatly value help!

and if pollination takes place between 2 different types of flowers, will the flowers develop into fruits????

Please help!!! :?:

my answer will be C and D. its so called commom sense

Hi lalala123, the answer for Q1 is C & D, but sometimes it is not using common sense, as StudentABC has said above. I do not think you can derive that the two animals were pests in their life cycles, as it might be helpful to the environment, but in the diagram, you cannot come to that conclusion easily. Sometimes, you have to remember what you have learnt from textbooks and assessment books.

And for Q2, seldom will nature itself do this, but sometimes, the flower may become a hybrid, but Science syllabus says that the flower will not be pollinated. So, I'm going with the Science books on this one and I would say, the flower would not be pollinated.

Hope I helped! :)[/quote]I agree for both answers! :udaman:

[PlasmaStorm]

tianzhu:

Thank you for your help.


Two interesting questions.What's your view?

Q1)When water boils at 100 degree C, bubbles can be seen. What is inside these bubbles? (1) Air (2) Steam (3) Water (4) Water vapour

My guess is it is either water vapour or steam.

Q2)Where does the developing embryo get its food from?
Is it the yolk only or both the yolk and the egg white?

According to the person who posted this question, his answer of yolk only was marked wrong.

Best Wishes

Hi I'm a P6 student and for question 1 I think it is option 1. My mother (kohjl) taught me that if you want to remove the oxygen from the water, I should boil it.

For question 2, I was not very sure so I researched and saw this:

The egg white serves to protect the egg yolk and provide additional nutrition for the growing embryo. It is composed of several proteins, primarily ovalbumin (54%) dissolved in water.

So I guess the answer is both the egg white and the egg yolk.

From: PlasamaStorm

(Formerly: kohjl Jr )

[PlasmaStorm]

emerald:

Very impressed with the answers given here. Maybe someone could help ans this observation by my girl during mealtime :


Why does pepper(powdered) when added to a bowl of soy sauce float and 'move' on the surface before they finally 'settle down'?
:? What caused the 'move'?

Hi I'm a P6 student. What caused the motion could be because of the brownian motion. This is the random movements of tiny particles called atoms.

From: PlasmaStorm

Fomerly: kohjl Jr

[Tang]

PlasmaStorm:

Hi I'm a P6 student and for question 1 I think it is option 1. My mother (kohjl) taught me that if you want to remove the oxygen from the water, I should boil it.


For question 2, I was not very sure so I researched and saw this:

The egg white serves to protect the egg yolk and provide additional nutrition for the growing embryo. It is composed of several proteins, primarily ovalbumin (54%) dissolved in water.

So I guess the answer is both the egg white and the egg yolk.

From: PlasamaStorm

(Formerly: kohjl Jr )

Most past papers from Top school, put egg york as the answer and egg white as an option which was considered not correct.

[endingteen]

ChiefKiasu:

Full.Cream:

My kids were asking me similar qn, ie, how come water is in gaseous state in the air when it's not 100degC. How to answer this?

To answer this question, ask another question:
\"What is the boiling point of water in space, where there is zero atmospheric pressure?\"

the answer is because there is such a thing latent heat of vapourisation which is the amount of energy required to be overcomed in order for water to change from its liquid state to gaseous state and vice versa. it is easier for water to be heated up from liquid to gas because you are heating it and heat is a form of energy. when water is heated to water vapour there is no external agent applied to the vapour to make it lose energy to become a liquid.

[endingteen]

sorry i just realised i quoted the wrong post. i am answering full cream’s post.

[Muffins]

endingteen:

ChiefKiasu:

[quote=\"Full.Cream\"]My kids were asking me similar qn, ie, how come water is in gaseous state in the air when it's not 100degC. How to answer this?

To answer this question, ask another question:
\"What is the boiling point of water in space, where there is zero atmospheric pressure?\"

the answer is because there is such a thing latent heat of vapourisation which is the amount of energy required to be overcomed in order for water to change from its liquid state to gaseous state and vice versa. it is easier for water to be heated up from liquid to gas because you are heating it and heat is a form of energy. when water is heated to water vapour there is no external agent applied to the vapour to make it lose energy to become a liquid.[/quote]Hi ChiefKiasu,
You are going into advanced statistics of atoms and vapours and temperatres in space... Let's leave it to Earth!

Hi Full.Cream,

This is because water can evaporate at ANY temperature, not only boiling. The definition of boiling is \"the application of heat to change something from a liquid to a gas.\" The definition of evaporation is \"vapourization: the process of becoming a vapour\". This is why they say the temperature of water vapour ALWAYS varies. It never evaporates at a constant temperature...

[PlasmaStorm]

ChiefKiasu:

Full.Cream:

My kids were asking me similar qn, ie, how come water is in gaseous state in the air when it's not 100degC. How to answer this?

To answer this question, ask another question:
\"What is the boiling point of water in space, where there is zero atmospheric pressure?\"

There are two answers I can think of:
1) The diff between liquid and gaseous state is that the liquid is tightly packed together by intermolecular forces but less so if gas. So the gas has no definite volume. If you leave a bowl of water on the table, the water will start to evaporate as it has heat. Based on what my eldest brother and his secondary textbook taught me, heat is an illusion. it is actually kinetic energy. Heat causes the molecules in the substance, in this case water, to vibrate. When the water molecules vibrates, the vibration causes intermolecular forces causes the water molecules to vibrate and destroy the intermolecular forces within it, causing it to turn into a gas.

2)If you put water into a vaccum (which is where nothing is, not even air), it will turn into gas. The atmosphereic pressure helps the intermolecular forces to hold the molecules together keeping it in the liquid stage. BUT when there is no atmosphereic pressure, the intermolecular forces are too weak to hold the water molecules together. thus it boils.
(My 2nd reason was derived from what ChiefKiasu said. Thanks!)

Hope this helps!

From: PlasmaStorm

[tianzhu]

Hi

Some lighter moments after PSLE
Best wishes

http://www.youtube.com/user/hdcyt?blend=1&ob=4