Q&A - PSLE Science

[meimeitan]

Hi! Please help,


(A) Which of the following are possible reasons why aquatic plants and
animals cannot survive in a pond that contains mud particles?

a The water carries diseases.
b Sunlight cannot reach the aquatic plants
c The aquatic animals cannot get enough dissolved oxygen.
d There is not enough clean water for the aquatic plants and animals.

(1) a and c only
(2) b and c only
(3) b, c and d only
(4) a, b, c and d

(B) The population of bullfrogs near a pond. The number of bullfrogs
incresed in the first few weeks. However, it stopped increasing the
following weeks. Which of the following events are possible causes
for the change in the population of bullfrogs from point A to point B?

a a great drop in the water level of the pond
b A great decrease in the number of fish in the pond
c A great decrease in the number of dragonfly nymphs in the pond
d A great decrease in the number of diseaseinfecting organisms that
kill the prey of the bullfrogs

(1) a and c only
(2) b and d only
(3) a, c and d only
(4) b, c and d only

Thanks.

[tianzhu]

meimeitan:

(A) Which of the following are possible reasons why aquatic plants and
animals cannot survive in a pond that contains mud particles?

a The water carries diseases.
b Sunlight cannot reach the aquatic plants
c The aquatic animals cannot get enough dissolved oxygen.
d There is not enough clean water for the aquatic plants and animals.

(1) a and c only
(2) b and c only
(3) b, c and d only
(4) a, b, c and d

Hi

If I remember correctly, this question comes under the topic, Negative impact of the environment. Under soil erosion, students learned that sunlight cannot reach the water plants and they will eventually die when the waters become cloudy.

Applying this concept, one may infer that no/less sunlight is reaching the aquatic plants due to the mud particles. Therefore, the plants cannot photosynthesise and give out oxygen. Hence(b) and (c) are logical answers.

I am more inclined to go for option (2).

Best wishes

[tianzhu]

Hi


Your second question should be covered in the topic, Food chains and Food webs.

Let’s take a look at (d) — A great decrease in the number of disease infecting organisms that kill the prey of the bullfrogs will result in the increase of prey for the bullfrogs. Hence the bull frog will have more food. This’ll not stop the frogs from increasing.
Therefore, (d) is incorrect.

There are three options with (d), going through elimination, I’d go for option (1).

Best wishes

[meimeitan]

Hi TianZhu


Understood! Thank you. :lol:

[tianzhu]

meimeitan:

Hi TianZhu


Understood! Thank you. :lol:

Hi

You're welcome.

Best wishes

[tianzhu]

Tang:

Hi,

Here are some terms:

Heat flows, heat travels

Heat gains, heat loss

temperature

good conductor of heat / poor conductor of heat

slows down heat loss / slows down heat gain

hot region / cold region

melting point / freezing point

boiling point

solid / liquid / gas

gains heat and expands

loses heat and contracts

.......

Hi Tang

Thank you for your response.
I am sure future PSLE students will appreciate it.

Best wishes

[tianzhu]

Hi


According to OMY, this advanced technology toilet bowl system is found at the public toilet in Raffles City S.C
http://fun.omy.sg/common/media/popup/?code=section%3Dcj%26artID%3D18625%26type%3Dimage%26&section=cj&artID=18625&type=image

They are commonly found in airports, hotels, etc in Japan.

If are keen to find out the science behind the toilet bowl, you may google for more information.

How about thinking of some related PSLE Science questions?

Best wishes

[youngtay]

Hi, please help


Which statement about the circulatory system is correct?

1) It consists of the nose, windpipe and lungs.
2) It carries water to different parts of the body.
3) It digests food and passes it to the blood.
4) It removes carbon dioxide from our body.

TIA

[tianzhu]

youngtay:

Hi, please help


Which statement about the circulatory system is correct?

1) It consists of the nose, windpipe and lungs.
2) It carries water to different parts of the body.
3) It digests food and passes it to the blood.
4) It removes carbon dioxide from our body.

TIA

Hi

In PSLE Science, students learned that the blood transports digested food, oxygen, water, carbon dioxide and other waste materials to different parts of the body.

Option(1) and (3) are out.

Carbon dioxide is transported from the heart to the lungs to be breathed out or removed from the body. This rules out option(4).

I'd like to go for option (2).

Best wishes

[Vanilla Cake]

Compare the following differences between the respiratory and circulatory system in plants and in human beings. Which of them is wrong?


Option 1
Plant: Exchange of gases takes place in the leaves
Human: Exchange of gases takes place in the lungs

Option 2
Plant: Oxygen is pumped to all parts of the plant
Human: Oxygen is pumped to all parts of the body

Option 3
Plant: Carbon dioxide is not returned to leaves
Human: Carbon dioxide is returned to the lungs.

Option 4
Plant: There is no blood to carry food around the plant
Human: Blood carries food around the body

Answer given is option (2).
Is this correct?
Option (1) and option (4) are obviously correct.
Pls help to explain why option (2) is chosen instead of option (3) for this question.
TIA for your time and effort.