Q&A - PSLE Science
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Vanilla Cake:
Hi i think the answer would be (4). Photosynthesis requires carbon dioxide to be carried out, and it will give out oxygen during the process. Which means the level of carbon dioxide keeps decreasing as the plant carries out photosynthesis, and since carbon dioxide is needed for photosynthesis, the rate is slowed down.kittycat01:
The picture in the question shows a plant in a sealed beaker of soil (only the bottom part of the plant that means the root part is sealed in the beaker). But there's some water in the sealed beaker. The whole plant is sealed in a clear container and put out in the sun. Quesion says the rate of photosynthesis is decreasing.....and is due to what? is it carbon dioxide or water. To answer the question must ask ourselves which one is used up first - carbon dioxide or water?atutor2001:
Hi atutor2001,This is a terrible question. Lets try to list down the effects of :
1. sealing the soil
2. sealing the plant
3. placing it under the sun.
1. Sealing the soil means water condensing in the outer container cannot return to the soil. Water from the soil cannot evaporate away under the sun. It also means the roots will use up the oxygen for respiration (an additional confusing factor) and will rot (an additional confusing factor).
2. Supply of carbon dioxide to the plant is limited and will be used up eventually. Sealing the plant means water vapour given out by the plant cannot escape (but also cannot return to the soil)
3. Placing the plant under the sun means light will be converted to heat inside the set-up and is trapped (greenhouse effect). Temperature inside the set-up will rise and the plant will give out more water vapour to cool down the plant. i.e. rate of transpiration will increase. However, with bright light from the sun, the rate of photosynthesis will also increase.
From the able analysis, we can see that both the rate of usage of water and carbon dioxide have increased. Therefore, to determine which is the main cause for the rate of photosynthesis to decrease, (i.e. which is used up first), the amount of water (i.e. size of the pot) and carbon dioxide available (i.e. size of the outer enclosure) will be the determining factor.
Based on my reading of the mindset of the person who set the question, I think the answer he/she wants is \"water\" because water is used for both transpiration and photosynthesis while carbon dioxide is used only for photosynthesis.
Anyway, it is a lousily set question as I can argue that the amount of water in the pot was \"so much so\" that carbon dioxide is used up first. The saddest truth is in real life, the photosynthesis will decrease not due to lack of water nor carbon dioxide. The plant will be dying because it cannot remove heat fast enough because of the intense heat inside the set-up (like the interior of a car parked under the hot sun)
PS once I bought a pot of orchid, left it in the car (under the sun) and continued shopping for less than an hour. The orchid looks fine when I reached home. I was shocked the next morning to find all the leaves had turned brown - it was just amazing.
Here's the question (placed under a lamp and not under the sun):
Study the set-up as shown below:
![](\"http://i41.tinypic.com/2aa0t3a.png\")
http://i41.tinypic.com/2aa0t3a.png\">
After some time, the rate of photosynthesis of the plant slowed down. This was most likely caused by a lack of ________________.
(1) water
(2) oxygen
(3) chlorophyll
(4) carbon dioxide -
kittycat01:
2) picture shows a pond with frogs outside pond and tadpoles inside pond, butterflies flying and caterpillars on the leaves of some aquatic plants (there are 3 different types of plants), fishes.
How many communities in the picture above? Some argue 2 because caterpillars & butterflies belong to garden community. But by definition of community - it means DIFFERENT populations together that means at least 2 or more right? Cater. & butt belong to 1 pop right? So if there is only 1 pop, then cannot form a community. So is it 1 or 2 comm?atutor2001:
The diagram below shows a habitat with some living things.2) I think the most important word we need to consider for \"community\" is \"interaction\". A person standing at a pond community is not part of that community because he/she does not depend/interact on/with the other pollutions in the pond community for survival and vice versa.
With regard to the \"size/limit\" of a community, there is no set rule on the \"size/limit\" of a community. It is up to the person who is doing the study to decide. A pond in a garden can be broken into 2 communities i.e. pond & garden or it can also be considered as 1 single community. The important factor is that there must be interaction among the populations in the \"defined community.\"
Therefore, in your example, I will take it as 1 community (garden with pond community) because there is interation between frog and butterfly (frog eats butterfly/caterpillar)
![](\"http://i40.tinypic.com/ivlb7r.png\")
Based on the diagram shown, which one of the following statements is correct?
(1) There is one community with six populations.
(2) There is one community with eight populations.
(3) There are two communities with six populations.
(4) There are two communities with eight populations. -
Vanilla Cake:
Thanks Vanilla Cake for posting the picture. With the picture, I agree with choco05 that (4) should be the answer because carbon dioxide will be depleted before water as the roots are immersed in a flask of water.
Hi atutor2001,
Here's the question (placed under a lamp and not under the sun):
Study the set-up as shown below:
After some time, the rate of photosynthesis of the plant slowed down. This was most likely caused by a lack of ________________.
(1) water
(2) oxygen
(3) chlorophyll
(4) carbon dioxide -
Vanilla Cake:
I will pick (1) as my answer.
The diagram below shows a habitat with some living things.
Based on the diagram shown, which one of the following statements is correct?
(1) There is one community with six populations.
(2) There is one community with eight populations.
(3) There are two communities with six populations.
(4) There are two communities with eight populations. -
![](\"http://i41.tinypic.com/2602yac.jpg\")
There are 2 different books explaining the same diagram above. Their explanations are contradictory.
book 1 :
In the example below, the two bottom batteries cancel each other out. The overall effect is thus the same as using only one battery. Bulb is still able to light up.
book 2 :
bulb will not light up as the bottom 2 batteries are not connected properly.
Which is correct? IMO, i go with book 2 because if the batteries connection are wrong, then there will be a broken circuit. Want to confirm this is correct be4 telling my dd. -
I will pick the answer from Book 2ā¦
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Verysuperkiasu:
Book 1 is correct. A battery is a conductor of electricity regardless whether it is flat, connected in the wrong direction...unless the battery has \"exploded\" i.e. the chemical leak out. When the polarity are connected in the same direction in series, the voltages will add up. When connected in opposite directions, the resultant voltage is the net voltage i.e. 2 batteries of the same voltage but in opposite directions will cancel each others voltage.
There are 2 different books explaining the same diagram above. Their explanations are contradictory.
book 1 :
In the example below, the two bottom batteries cancel each other out. The overall effect is thus the same as using only one battery. Bulb is still able to light up.
book 2 :
bulb will not light up as the bottom 2 batteries are not connected properly.
Which is correct? IMO, i go with book 2 because if the batteries connection are wrong, then there will be a broken circuit. Want to confirm this is correct be4 telling my dd. -
atutor2001:
Oh, I see. So u mean even if the batteries are not connected properly, the current is still able to flow through? Just that the voltages is zero?....TIA
Book 1 is correct. A battery is a conductor of electricity regardless whether it is flat, connected in the wrong direction...unless the battery has \"exploded\" i.e. the chemical leak out. When the polarity are connected in the same direction in series, the voltages will add up. When connected in opposite directions, the resultant voltage is the net voltage i.e. 2 batteries of the same voltage but in opposite directions will cancel each others voltage.Verysuperkiasu:
There are 2 different books explaining the same diagram above. Their explanations are contradictory.
book 1 :
In the example below, the two bottom batteries cancel each other out. The overall effect is thus the same as using only one battery. Bulb is still able to light up.
book 2 :
bulb will not light up as the bottom 2 batteries are not connected properly.
Which is correct? IMO, i go with book 2 because if the batteries connection are wrong, then there will be a broken circuit. Want to confirm this is correct be4 telling my dd. -
Verysuperkiasu:
Your statement is not correct. The current can only flow if the voltage in one direction is higher than the other direction i.e. there is a net voltage in the circuit.
Oh, I see. So u mean even if the batteries are not connected properly, the current is still able to flow through? Just that the voltages is zero?....TIA
For example, if there are 5 batteries in one direction and 3 batteries in the opposite direction then there is a \"net voltage\" of 2 batteries (5 - 3 = 2). The brightness of the bulb is the same as a circuit with 2 batteries connected in series in the same direction.
If there are 5 batteries in one direction and 5 batteries in the opposite direction then there is a net voltage of 0 (5 - 5 = 0). The bulb will NOT light up because the net voltage is 0. The batteries are still conductors of electricity but NO current will flow because current can only flow if there is a \"net voltage\" from the batteries in the circuit. -
atutor2001:
sorry, I'm quite bad in understanding electricity. If batteries are conductors of electricity (then shouldn't electricity still flows) isn't flow of electricity = flow of current? that is, if batteries still can conduct electricity, shouldn't current flow as well?
Your statement is not correct. The current can only flow if the voltage in one direction is higher than the other direction i.e. there is a net voltage in the circuit.Verysuperkiasu:
Oh, I see. So u mean even if the batteries are not connected properly, the current is still able to flow through? Just that the voltages is zero?....TIA
For example, if there are 5 batteries in one direction and 3 batteries in the opposite direction then there is a \"net voltage\" of 2 batteries (5 - 3 = 2). The brightness of the bulb is the same as a circuit with 2 batteries connected in series in the same direction.
If there are 5 batteries in one direction and 5 batteries in the opposite direction then there is a net voltage of 0 (5 - 5 = 0). The bulb will NOT light up because the net voltage is 0. The batteries are still conductors of electricity but NO current will flow because current can only flow if there is a \"net voltage\" from the batteries in the circuit.
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