Q&A - PSLE Science

[Tang]

P5G:

kittycat01:

sorry, atutor, the description is not that accurate. it's actually in the psle science paper this year. According to my daughter, the plant is in a sealed beaker of water (no soil) but only the root part is immersed in the sealed beaker. and it's placed under the lamp, not the sun. The rest of the details are correct. Sorry for the confusion. I should have clarified with her first before putting the question down on this forum.


Anyway, just to comment - lots of dd's classmates put CO2 being the answer but others put water.

Hi,

My answer is carbon dioxide as the plant is in a container with limited air. Air only contains 0.03% carbon dioxide. Most of my classmates also choose carbon dioxide as their answer.

Hi,

I think the correct answer is \"water\" because when carbon dioxide is used up, the plant can replenish it through respiration and photosynthesis can continue until the water in the beaker is depleted.

[atutor2001]

Tang:

Hi,

I think the correct answer is \"water\" because when carbon dioxide is used up, the plant can replenish it through respiration and photosynthesis can continue until the water in the beaker is depleted.

I will agree that the answer is \"water\" if the question is, \"what caused the photosynthesis to finally STOP?\" However, the quesion says the rate of photosynthesis is decreasing.....and is due to what? Since the DECREASE in the rate of photosynthesis is initiated by the lack of CO2, the answer will be CO2. (Plant stores CO2, a process known - carbon sequestration. Therefore, the amount of CO2 released will be less and less. Finally, there is no more CO2 and part of plant will die, leading to decomposition and CO2 is released and the cycle continues)

[kittycat01]

atutor2001:

Tang:

Hi,

I think the correct answer is \"water\" because when carbon dioxide is used up, the plant can replenish it through respiration and photosynthesis can continue until the water in the beaker is depleted.

I will agree that the answer is \"water\" if the question is, \"what caused the photosynthesis to finally STOP?\" However, the quesion says the rate of photosynthesis is decreasing.....and is due to what? Since the DECREASE in the rate of photosynthesis is initiated by the lack of CO2, the answer will be CO2. (Plant stores CO2, a process known - carbon sequestration. Therefore, the amount of CO2 released will be less and less. Finally, there is no more CO2 and part of plant will die, leading to decomposition and CO2 is released and the cycle continues)

Thank you very much, atutor. It's a pleasure reading your explanation. Very detailed and clear.

[Verysuperkiasu]

atutor2001:

Tang:

Hi,

I think the correct answer is \"water\" because when carbon dioxide is used up, the plant can replenish it through respiration and photosynthesis can continue until the water in the beaker is depleted.

I will agree that the answer is \"water\" if the question is, \"what caused the photosynthesis to finally STOP?\" However, the quesion says the rate of photosynthesis is decreasing.....and is due to what? Since the DECREASE in the rate of photosynthesis is initiated by the lack of CO2, the answer will be CO2. (Plant stores CO2, a process known - carbon sequestration. Therefore, the amount of CO2 released will be less and less. Finally, there is no more CO2 and part of plant will die, leading to decomposition and CO2 is released and the cycle continues)

yes, i remember this question - my ds put CO2 as the answer as he also said the issue is decreasing rate of that photosynthesis. And rate of respiration is slower than rate of photosynthesis. I checked with my ds - indeed the question did ask why the rate of photosynthesis is decreasing not stop. wow these days psle question so tricky....

[Tang]

Verysuperkiasu:

atutor2001:

[quote=\"Tang\"]
Hi,

I think the correct answer is \"water\" because when carbon dioxide is used up, the plant can replenish it through respiration and photosynthesis can continue until the water in the beaker is depleted.

I will agree that the answer is \"water\" if the question is, \"what caused the photosynthesis to finally STOP?\" However, the quesion says the rate of photosynthesis is decreasing.....and is due to what? Since the DECREASE in the rate of photosynthesis is initiated by the lack of CO2, the answer will be CO2. (Plant stores CO2, a process known - carbon sequestration. Therefore, the amount of CO2 released will be less and less. Finally, there is no more CO2 and part of plant will die, leading to decomposition and CO2 is released and the cycle continues)

yes, i remember this question - my ds put CO2 as the answer as he also said the same as what atutor said above. I checked with my ds - indeed the question did ask why the rate of photosynthesis is decreasing not stop. wow these days psle question so tricky....[/quote]
I also hope that the answer is CO2, otherwise my sister will lose 2 marks.

During her revision, she was asking me about what are the factors that can be changed to get the same experimental results.
My answer was intensity of light, temperature of water, the number of hydrilla, the type of water plant or amount of CO2 (one of these is already the changed factor for the experiment), but never to put amount of water as the answer because it was a fully submerged plant and the amount of water was not going to factor the results.
So for this question, she just ruled out water, ignoring that the plant is a land plant.

[Verysuperkiasu]

Tang:

I also hope that the answer is CO2, otherwise my sister will lose 2 marks.

During her revision, she was asking me about what are the factors that can be changed to get the same experimental results.
My answer was intensity of light, temperature of water, the number of hydrilla, the type of water plant or amount of CO2 (one of these is already the changed factor for the experiment), but never to put amount of water as the answer because it was a fully submerged plant and the amount of water was not going to factor the results.
So for this question, she just ruled out water, ignoring that the plant is a land plant.

oh..but the sad truth is that we will never know how the moe mark this question, even if we have reasons to support our answer. Because we will not be given the paper back to see or check. What if they decide the answer is water?

[cimman]

kittycat01:

Thank you very much, atutor. It's a pleasure reading your explanation. Very detailed and clear.

here's what I found while trawling the web:
http://www.tomatosphere.org/teacher-resources/teachers-guide/grades-8-10/plants-and-light.cfm

Carbon dioxide is a factor in decreasing rate of photosynthesis. While there is light, rate of respiration is lower than rate of photosynthesis, so carbon dioxide produced through respiration is insufficient for photosynthesis. Thus overall volume of carbon dioxide will steadily decline. The experiment documented in the article also has a sealed container for the plant and it has a lamp as well. Seems like a popular setup for studying rate of photosynthesis in plants.

Here is another article that talks about which wavelengths of light is more effective (ie. absorbed the most) for photosynthesis. For those who have greenhouses, blue light is the best, followed by red. Yellow is the worse.
http://fhs-bio-wiki.pbworks.com/w/page/12145771/Factors%20effecting%20the%20rate%20of%20photosynthesis
So, feed your indoor plants blue light...

[atutor2001]

Thank you cimman. The sites are very informative.

[kittycat01]

1)Is it correct to say food and water are transported to all parts of the plant? I thought so too but my child argue that the food that goes out of a leaf for example cannot travel back to itself or water that travel out of the roots cannot go back to the roots or can it?


What about a leaf producing food does it also travel to the other leaves because they already producing food themselves. so is it correct to say travel to 'all' parts of plants?

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]

kittycat01:

1)Is it correct to say food and water are transported to all parts of the plant? I thought so too but my child argue that the food that goes out of a leaf for example cannot travel back to itself or water that travel out of the roots cannot go back to the roots or can it?


What about a leaf producing food does it also travel to the other leaves because they already producing food themselves. so is it correct to say travel to 'all' parts of plants?

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?

1) It is commonly used term that \"food is transported to all parts of the plant.\" Technically, this is inaccurate because a healthy leaf that is already making food on its own, need not receive food from other parts.
However, I feel it is ok. If we really want to be 100% correct then maybe we can add : \"food is transported to all parts of the plant when needed.\"

Unlike water which can only travel upwards, food can travel in all directions. As to whether can food travel back to the leaf that make it, I think it is yes. Excess food is stored as starch in different parts of a plant. If there is a prolonged period of no light (i.e. photosynthesis stopped), the leaves will draw from this stored food. This means that the food is travelling back to the leaves.

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)