Q&A - PSLE Science

[Verysuperkiasu]

Picture shows an glass aquarium with aquatic plants and some animals like fish, waterboatman and water fleas. Tank is sealed with a glass plate and whole aquarium placed in a brightly lit room the whole day.


Qn : Which of the following statements is correct about the organisms after several months?

1) All the organisms will die as there is hardly any air in the tank
2) The plants can survive longer than the larger animals in the tank
3) The animals will all die in less than a day as there is insufficient air
4) The organisms could still survive as there is a continuous supply of air.
Answer is 2)

Son’s answer is 4) as there is a constant exchange of gases between the plants and animals - plants give out oxygen (during photosynthesis as the glass aquarium is placed in the light whole day) for the animals to take in and animals breathe out CO2 for the plants to take in. But my question is 'can this exchange of gases take place forever in a sealed container - is there a time limit to this? Note the question says ‘after several months’.

[Nebbermind]

stary:

Hi all, need explanation...


A bar magnet, QP, with poles denoted as shown, is suspended in the air. If another magnet, SR, shown in the diagram is brought near P, how would the bar magnet, QP move?

http://www.flickr.com/photos/64113082@N03/6089207068/in/photostream

1) A
2) B
3) C
4) D

Ans: 3

Fact is that the question did not state the poles of the magnet. They might be like poles and then repelled... Why?

Many thanks!

Since QP is suspended freely, it will rotate to align the unlike poles (like the compass needle), and then it will be attracted to the fixed magnet.

[Nebbermind]

Verysuperkiasu:

Picture shows an glass aquarium with aquatic plants and some animals like fish, waterboatman and water fleas. Tank is sealed with a glass plate and whole aquarium placed in a brightly lit room the whole day.


Qn : Which of the following statements is correct about the organisms after several months?

1) All the organisms will die as there is hardly any air in the tank
2) The plants can survive longer than the larger animals in the tank
3) The animals will all die in less than a day as there is insufficient air
4) The organisms could still survive as there is a continuous supply of air.
Answer is 2)

Son's answer is 4) as there is a constant exchange of gases between the plants and animals - plants give out oxygen (during photosynthesis as the glass aquarium is placed in the light whole day) for the animals to take in and animals breathe out CO2 for the plants to take in. But my question is 'can this exchange of gases take place forever in a sealed container - is there a time limit to this? Note the question says 'after several months'.

FOOD?!

[stary]

Verysuperkiasu:

stary:

Hi all, need explanation...


A bar magnet, QP, with poles denoted as shown, is suspended in the air. If another magnet, SR, shown in the diagram is brought near P, how would the bar magnet, QP move?

http://www.flickr.com/photos/64113082@N03/6089207068/in/photostream

1) A
2) B
3) C
4) D

Ans: 3

Fact is that the question did not state the poles of the magnet. They might be like poles and then repelled... Why?

Many thanks!

Could there be some missing info on the diagram coz the question states 'with its poles denoted as shown'?

Nope... No info's gone...

[stary]

stary:

Hi all, need explanation...


A bar magnet, QP, with poles denoted as shown, is suspended in the air. If another magnet, SR, shown in the diagram is brought near P, how would the bar magnet, QP move?

http://www.flickr.com/photos/64113082@N03/6089207068/in/photostream

1) A
2) B
3) C
4) D

Ans: 3

Fact is that the question did not state the poles of the magnet. They might be like poles and then repelled... Why?

Many thanks!

Question is from (MGS/CA1/2009/Primary 5/Qns 1)

[Verysuperkiasu]

Nebbermind:

FOOD?!

Yah hor, forgot abt the animals' food part. but plants will survive coz they can make their own food right? But I need to know :

1) option 2 says 'plants will survive longer than larger animals'. Why only larger animals?

2) Assuming food is given to the animals, then can the answer be (4) - will this constant exchange of gases between the plants and the animals be able to last for several months?

Thanks

[Sun_2010]

stary,


It will move in the direction of C
Nebbermind had given the reason above.

[stary]

Thanks guys for the prompt reply!

[stary]

Hi all, need explanation again.


Refer to (SCGS/Prelim/P6/2010/Booklet B/Question 40)

Samantha put up the 3 set-ups below. All the set-ups had similar plants and 250ml of water each but differnt humidity levels. She conducted the experiment for 3 days. She wanted to find out if humidity level affects the amount of water lost by the plant through its stomata.

Set-up A (Humidity: 90%)
Set-up B (Humidity: 29%)
Set-up C (Humidity: 57%)


...........

a)What......... plants through its stomata?
My answer: The higher the humidity level, the lesser the amount of water lost by the plants through its stomata.
Ans sheet: The higher the humidity level, the more the amount of water lost by the plants through its stomata.

Many thanks!

[mother777]

stary:

Hi all, need explanation again.


Refer to (SCGS/Prelim/P6/2010/Booklet B/Question 40)

Samantha put up the 3 set-ups below. All the set-ups had similar plants and 250ml of water each but differnt humidity levels. She conducted the experiment for 3 days. She wanted to find out if humidity level affects the amount of water lost by the plant through its stomata.

Set-up A (Humidity: 90%)
Set-up B (Humidity: 29%)
Set-up C (Humidity: 57%)


...........

a)What......... plants through its stomata?
My answer: The higher the humidity level, the lesser the amount of water lost by the plants through its stomata.
Ans sheet: The higher the humidity level, the more the amount of water lost by the plants through its stomata.

Many thanks!

Hi Stary,

I agree with your answer too.

Just to confirm again, I searched the internet and found the below explanation:

\" Relative humidity: As the relative humidity of the air surrounding the plant rises the transpiration rate falls. It is easier for water to evaporate into dryer air than into more saturated air.\"

This is from the link below.
http://ga.water.usgs.gov/edu/watercycletranspiration.html

This link also explain other factors affecting plant transpiration.

Hope this helps (lets also wait for other KS parents to reply back too and enlighten us)