Q&A - PSLE Science

[Tang]

chrisu:

Question on population from Longman My Weekly Companion Science Book B;

http://img.photobucket.com/albums/v160/guppiesonli/Misc/QPopulation.jpg\">

I've problem explaining to my daughter on population in the sense as how to differentiate them. Anyone can explain in detail on how to derive the answer? Thank you.

Hi,

My answer is (1) - 5.

Label the animals given as follows from left to right and top to bottom.
A B C D
E F G H

A and G - same population, damselfly.
B and D - same population, mosquito.
C and E - same population, frog.

[chrisu]

Thank you Tang. Yes the answer given by the book is (1) -5


My daughter and I find it difficult to relate G to A as damselfly and also F and H. Frankly I don't even know what are F and H.

Tang:

chrisu:

Question on population from Longman My Weekly Companion Science Book B;
http://img.photobucket.com/albums/v160/guppiesonli/Misc/QPopulation.jpg\">

I've problem explaining to my daughter on population in the sense as how to differentiate them. Anyone can explain in detail on how to derive the answer? Thank you.

Hi,

My answer is (1) - 5.

Label the animals given as follows from left to right and top to bottom.
A B C D
E F G H

A and G - same population, damselfly.
B and D - same population, mosquito.
C and E - same population, frog.

[Nebbermind]

CHIM!


I thought '5' if we ignore all the 'infants'.

[reddotresident]

2011 red swastika science prelim paper. assuming you all hv the papers now, can someone help pls? thank you!


Q32b - DS says
yes, as only the no. of plants per plot should be changed. all other variables should be constant.

ans.sheet says
yes, as diff. plants bear diff amt of fruits.

Q41b.
Describe one action michael has to carry out consistently thruout the expereiment in order to get reliable results?

DS says
timing.

ans.sheet says place the car from top of the ramp.

Q43b
My ds answer is
chemical potential energy -electrical energy - kinetic energy-sound energy.

alhtough ans.sheet is
kinetic energy-electrical energy - kinetic energy-sound energy.

[Tang]

reddotresident:

2011 red swastika science prelim paper. assuming you all hv the papers now, can someone help pls? thank you!


Q32b - DS says
yes, as only the no. of plants per plot should be changed. all other variables should be constant.

ans.sheet says
yes, as diff. plants bear diff amt of fruits.

Q41b.
Describe one action michael has to carry out consistently thruout the expereiment in order to get reliable results?

DS says
timing.

ans.sheet says place the car from top of the ramp.

Q43b
My ds answer is
chemical potential energy -electrical energy - kinetic energy-sound energy.

alhtough ans.sheet is
kinetic energy-electrical energy - kinetic energy-sound energy.

Hi,

All the answers provided by the worksheet are correct.

Q32b. Question asks whether the same type of types should be used, so there is no need to talk about the number and other variables.

Q41b. Timing is the results, so cannot be kept constant.

Q43b. Point A - Kinetic energy, as the point moves to make contact to close the circuit. [Question does not ask for the source of energy which is chemical potential energy]
Note: Answer to Q43b is incorrect and has been amended in subsequent reply.

[reddotresident]

Tang:

reddotresident:

2011 red swastika science prelim paper. assuming you all hv the papers now, can someone help pls? thank you!


Q32b - DS says
yes, as only the no. of plants per plot should be changed. all other variables should be constant.

ans.sheet says
yes, as diff. plants bear diff amt of fruits.

Q41b.
Describe one action michael has to carry out consistently thruout the expereiment in order to get reliable results?

DS says
timing.

ans.sheet says place the car from top of the ramp.

Q43b
My ds answer is
chemical potential energy -electrical energy - kinetic energy-sound energy.

alhtough ans.sheet is
kinetic energy-electrical energy - kinetic energy-sound energy.

Hi,

All the answers provided by the worksheet are correct.

Q32b. Question asks whether the same type of types should be used, so there is no need to talk about the number and other variables.

Q41b. Timing is the results, so cannot be kept constant.

Q43b. Point A - Kinetic energy, as the point moves to make contact to close the circuit. [Question does not ask for the source of energy which is chemical potential energy]

You are my saviour ::thankyou: yet again..

[Verysuperkiasu]

CHIJ prelim 2011 Section A Q6.


Picture shows a pot of soil with a lime plant (absolutely no leaves).

Ling Ming decided to pluck off all the leaves on her lime plant as shown in the diagram below because it was full of pests. She continued to water the plant daily. What do you think will happen to her plant?

(1) The plant will die.
(2) The plant will produce new shoots.
(3) The plant will take in more food from the soil.
(4) The plant will not be able to absorb water and mineral salts.

Son’s answer is (1) - because no leaves, plant can’t make food, so it will die.
but answer is (2). Why? Stem cutting? But even stem cutting needs to remove only 50% of the leaves to reduce transpiration, not all the leaves?!

[atutor2001]

Verysuperkiasu:

CHIJ prelim 2011 Section A Q6.


Picture shows a pot of soil with a lime plant (absolutely no leaves).

Ling Ming decided to pluck off all the leaves on her lime plant as shown in the diagram below because it was full of pests. She continued to water the plant daily. What do you think will happen to her plant?

(1) The plant will die.
(2) The plant will produce new shoots.
(3) The plant will take in more food from the soil.
(4) The plant will not be able to absorb water and mineral salts.

Son's answer is (1) - because no leaves, plant can't make food, so it will die.
but answer is (2). Why? Stem cutting? But even stem cutting needs to remove only 50% of the leaves to reduce transpiration, not all the leaves?!

Great to hear that they are putting (2) as the answer now. In the past, the standard answer is (1) which is incorrect.

Although all the leaves are removed, the plant will still have stored food in the stems and roots to provide sufficient energy for new shoot to grow.

The main difference between stem cutting and this bare plant is that the plant has roots to take in nutrient immediately which a stem cutting does not. Therefore, nutrients taken in by the plant can be used immediately to grow new shoots, using energy from the stored food.

As for a stem cutting, the amount of water and nutrient absorbed is much less than the bare plant. So we need to remove some leaves from a stem cutting to prevent excessive water loss. The amount of stored food in a stem cutting is also much less than a plant. So we need to keep some leaves on a stem cutting to make food, hoping that there will be sufficient energy and nutrients to grow new roots first.

[Tang]

reddotresident:

Tang:

[quote=\"reddotresident\"]2011 red swastika science prelim paper. assuming you all hv the papers now, can someone help pls? thank you!


Q32b - DS says
yes, as only the no. of plants per plot should be changed. all other variables should be constant.

ans.sheet says
yes, as diff. plants bear diff amt of fruits.

Q41b.
Describe one action michael has to carry out consistently thruout the expereiment in order to get reliable results?

DS says
timing.

ans.sheet says place the car from top of the ramp.

Q43b
My ds answer is
chemical potential energy -electrical energy - kinetic energy-sound energy.

alhtough ans.sheet is
kinetic energy-electrical energy - kinetic energy-sound energy.

Hi,

All the answers provided by the worksheet are correct.

Q32b. Question asks whether the same type of types should be used, so there is no need to talk about the number and other variables.

Q41b. Timing is the results, so cannot be kept constant.

Q43b. Point A - Kinetic energy, as the point moves to make contact to close the circuit. [Question does not ask for the source of energy which is chemical potential energy]

You are my saviour ::thankyou: yet again..[/quote]
Hi,

I would like to make corrections to both our answers to Q43b. It does not make sense that Kinetic energy is converted to Electrical energy here. So when I take a closer look at the question again this morning, there are no connections (arrows) between the boxes given. So my revised answers are as follows:

Point A moved >>>> Chemical potential energy --> Kinetic energy
Wire >>>> Chemical potential energy --> Electrical energy
Steel bar and hammer >>>> Electrical energy --> Kinetic energy
Gong >>>> Kinetic energy --> Sound energy + kinetic energy

[Verysuperkiasu]

atutor2001:

Verysuperkiasu:

CHIJ prelim 2011 Section A Q6.


Picture shows a pot of soil with a lime plant (absolutely no leaves).

Ling Ming decided to pluck off all the leaves on her lime plant as shown in the diagram below because it was full of pests. She continued to water the plant daily. What do you think will happen to her plant?

(1) The plant will die.
(2) The plant will produce new shoots.
(3) The plant will take in more food from the soil.
(4) The plant will not be able to absorb water and mineral salts.

Son's answer is (1) - because no leaves, plant can't make food, so it will die.
but answer is (2). Why? Stem cutting? But even stem cutting needs to remove only 50% of the leaves to reduce transpiration, not all the leaves?!

Great to hear that they are putting (2) as the answer now. In the past, the standard answer is (1) which is incorrect.

Although all the leaves are removed, the plant will still have stored food in the stems and roots to provide sufficient energy for new shoot to grow.

The main difference between stem cutting and this bare plant is that the plant has roots to take in nutrient immediately which a stem cutting does not. Therefore, nutrients taken in by the plant can be used immediately to grow new shoots, using energy from the stored food.

As for a stem cutting, the amount of water and nutrient absorbed is much less than the bare plant. So we need to remove some leaves from a stem cutting to prevent excessive water loss. The amount of stored food in a stem cutting is also much less than a plant. So we need to keep some leaves on a stem cutting to make food, hoping that there will be sufficient energy and nutrients to grow new roots first.

Ah...so....thanks for the detailed explanation. It's clearer to me now.

But I remember coming across a similar question in the past but that was a tree stump - the tree was chopped until a stump at knee height. Question asked if the tree could still grow and the answer was 'no' coz no leaves to make food. Can your explanation apply to the tree case and hence it will grow branches and leaves???? :?