Q&A - P3 Science

[tianzhu]

Hi


In primary science, students learn that plants photosynthesise in the presence of light to make food. They also respire at all times. During photosynthesis, oxygen is given out and carbon dioxide is taken in. Plants take in oxygen and give out carbon dioxide when they respire. When stomata open, water is lost through a process called transpiration (evaporation of water through the leaves).The gaseous exchanges are done through tiny openings called stomata. There are more stomata on the undersides of leaves.

In answering Q8, we’ve to note the key words.

Under very strong sunlight for a long time, these openings will eventually close.

On a hot sunny day plants could become dehydrated as they lose water. Therefore, stomata close to prevent the plants from losing too much water.
Option(4) is correct.

What I’ve covered is very basic, the opening and closing of stomata is far more complex.You can find out more by reading books on Biology and Botany. Also try doing searches on Yahoo/Google.

Best Wishes

[Dharma]

tianzhu:

Hi, Dharma and Full.Cream


There are some missing information in one of my previous post.Here is the revision.Please follow this link.

http://www.oldschool.com.sg/index.php/module/PublicAccess/action/Wrapper/sid/a1d5550a35132f7d768a9cd73d70318e/mcq_id/15658

I am sorry for the inconvenience.

SorryTianzhu, I missed this out earlier.

When the cardboard is removed, the light brown gas will spread to fill up the whole of the jar and flask.

This tells us that
1.\tGas has no definite shape – it takes up the shape of the container that it is in.
2.\tGas has no fixed volume – it spreads to fill up the space in the flask in addition to the space it has already filled in the jar.

The answer is Option C – B & C

# Although air can be compressed but the experiment does not demonstrate this property of air.

[MdmKS]

Got this problem from my P3 child worksheet.


A conical flask contain some water and a plant with its roots submerged in the water. A stopper is fixed at the mouth of the flask holding the stem of the plant with its leaves hanging outside the conical flask. Sorry, I am not sure how to upload the image file here.
Question : how to reduce the rate of water being absorbed by the roots? Give 2 methods, without changing the setting of the experiments.

T!A

[tianzhu]

Hi Dharma


I’ve been looking at this question for quite a number of times. It’s a pretty interesting one.

The first diagram shows the brown gas in a jar.
The second diagram shows the brown gas occupying the volume of the jar as well as the flask. It expands.
From the first diagram, the brown gas take up a smaller space in the jar .Therefore it can be compressed. After the cardboard is removed, it expands to take up the combined capacities of the jar and flask.

So this experiment shows that air has no definite shape, volume and is compressible. What’s your view on this?

[Full.010894Cream]

Dharma:

The answer is Option C – B & C

# Although air can be compressed but the experiment does not demonstrate this property of air.

agreed with u on this as the demo is now complete.

i dun think it's inconclusive to say it is compressible coz both the air + the brown gas still occupy the same combined volume

[Full.010894Cream]

MdmKS:

Got this problem from my P3 child worksheet.


A conical flask contain some water and a plant with its roots submerged in the water. A stopper is fixed at the mouth of the flask holding the stem of the plant with its leaves hanging outside the conical flask. Sorry, I am not sure how to upload the image file here.
Question : how to reduce the rate of water being absorbed by the roots? Give 2 methods, without changing the setting of the experiments.

T!A

for plants, i believe the answers will always revolve around water, air & sunlight. the answer is probably to reduce the (i) sunlight & (ii)CO2 which will slow down photosynthesis (sun + CO2 + water = starch). Not sure how this can be achieve, tho. :oops:

[watmekiasu]

Full.Cream:

MdmKS:

Got this problem from my P3 child worksheet.


A conical flask contain some water and a plant with its roots submerged in the water. A stopper is fixed at the mouth of the flask holding the stem of the plant with its leaves hanging outside the conical flask. Sorry, I am not sure how to upload the image file here.
Question : how to reduce the rate of water being absorbed by the roots? Give 2 methods, without changing the setting of the experiments.

T!A

for plants, i believe the answers will always revolve around water, air & sunlight. the answer is probably to reduce the (i) sunlight & (ii)CO2 which will slow down photosynthesis (sun + CO2 + water = starch). Not sure how this can be achieve, tho. :oops:

Tricky one. My answer would be :
i - pluck out all the leaves
ii - keep plant in a dark, damp place

[Full.010894Cream]

watmekiasu:

i - pluck out all the leaves

A typical answer from a GEPer!

[atutor2001]

MdmKS:

Got this problem from my P3 child worksheet.


A conical flask contain some water and a plant with its roots submerged in the water. A stopper is fixed at the mouth of the flask holding the stem of the plant with its leaves hanging outside the conical flask. Sorry, I am not sure how to upload the image file here.
Question : how to reduce the rate of water being absorbed by the roots? Give 2 methods, without changing the setting of the experiments.

T!A

My answers are :
1. Cover the leaves with vaseline (but will this change the setting? )
2. Keep in a dark place to stop photosynthesis
3. Keep in a cold place to reduce transpiration

[watmekiasu]

Full.Cream:

watmekiasu:

i - pluck out all the leaves

A typical answer from a GEPer!

I wasn't raised here. Not even sure if I cld hv gotten into Express Stream, not to mention GEP.