Q&A - PSLE Science

[P5G]

Please help.


Q6: When water is heated to 100 degree C, bubbles can be seen rising through the water. What do these bubbles contain?

(1) Hot water vapour
(2) Hot water droplets
(3) Air dissolved in the water
(4) Only oxygen is released from the hot water

Worksheet's answer is (3) and my answer is (1).
Should the bubbles be hot water vapour or air dissolved in the water? How do I decide which should be the answer? What are the key factors?


Q21: Which of the following statements about yoghurt making are true? You may refer to the link for the picture given:
http://www.orlesson.org/orp/09Sc/2009-Sc-CA1-MGS.pdf

(A): Bacteria are added
(B): Fermentation of milk takes place
(C): Oxygen is needed
(D): Yeast cells are added

(1) A and B only
(2) B and D only
(3) A, B and C only
(4) B, C and D only

Worksheet's answer is (1) and my answer is (3).
Please advise if oxygen is needed ?

Q43b) Name the two stages that the butterfly can be harmful to plants.
c) Describe how this is so.

Worksheet's answer b) Larva and Adult
c) They feed actively on the leaves leaving the plant with few or no leaves to make food for itself.

Is it true that adult butterfly feeds actively on leaves? I thought butterfly feeds on sap and nectar. Any comments?

TIA.

[tianzhu]

Hi


For Q6, your answer is correct. It is water vapour. A similar type of question has been discussed earlier in this thread.

For Q21, the WS’s answer is correct. Fermentation is anaerobic which means no oxygen is required.

As for Q43b, at the larval stage, caterpillars eat leaves. Therefore, they are harmful to plants.

http://www.flmnh.ufl.edu/butterflies/qanda.htm
One interesting find from this site is that some species vary their nectar diet to include rotting fruit, pollen, excrement and carrion.Pollens are carried by the wind or insects to cross pollinate other same type of plants for reproduction. If large quantities of pollen grains are consumed by adult butterflies, it’ll reduce the chances of pollination and affect the continuity/survival of plants in the long run. I hope I am leading you to the right direction and suggest that you check with your science teacher and let us know the answer.

Best wishes

[P5G]

tianzhu:

Hi


For Q6, your answer is correct. It is water vapour. A similar type of question has been discussed earlier in this thread.

For Q21, the WS’s answer is correct. Fermentation is anaerobic which means no oxygen is required.

As for Q43b, at the larval stage, caterpillars eat leaves. Therefore, they are harmful to plants.

http://www.flmnh.ufl.edu/butterflies/qanda.htm
One interesting find from this site is that some species vary their nectar diet to include rotting fruit, pollen, excrement and carrion.Pollens are carried by the wind or insects to cross pollinate other same type of plants for reproduction. If large quantities of pollen grains are consumed by adult butterflies, it’ll reduce the chances of pollination and affect the continuity/survival of plants in the long run. I hope I am leading you to the right direction and suggest that you check with your science teacher and let us know the answer.

Best wishes

Thanks Mr Tianzhu.

So answer for

43c) Larva feed actively on leaves leaving no leaf or few leaves for the plant to make food.
Adult butterfly may feed on pollen leaving no pollen grain or few pollen grains for pollination.

[James Ang]

P5G:

Please help.


Q6: When water is heated to 100 degree C, bubbles can be seen rising through the water. What do these bubbles contain?

(1) Hot water vapour
(2) Hot water droplets
(3) Air dissolved in the water
(4) Only oxygen is released from the hot water

Worksheet's answer is (3) and my answer is (1).
Should the bubbles be hot water vapour or air dissolved in the water? How do I decide which should be the answer? What are the key factors?



TIA.

I reasoned that the correct answer is (3) and not (1) for the below reasons;

1. Water vapour escape from the surface of the water rather than from the bottom of the container. (kinetic particle theory - where the active particles leave the surface of the liquid and become gas, leaving the remaining particles to have less average energy per particle)
2. Water contains dissolved air which is necessary for the survival of living things that live in water. Boiling will expel the dissolved air from the water. That's why water animals cannot live in boiled water that has cooled down as the water does not contain dissolved oxygen.

I am sure the above reasons are convincing and scientific for you.

[James Ang]

P5G:

So answer for

43c)

1. Larva feed actively on leaves leaving no leaf or few leaves for the plant to make food.
2. Adult butterfly may feed on pollen leaving no pollen grain or few pollen grains for pollination.

Statement 1 is correct, Statement 2 seems wrong.

Adult butterfly is known to be an agent of pollination and is attracted by colourful sweet smelling flowers to collect nectar from flowers and helps to pollinate the flowers in the process. Therefore it seems generally wrong to say that butterflies feed on the pollen grains and disrupted the pollination process although some sources may suggest so. I stand by the general fact that butterfly is an agent of pollination.

[atutor2001]

Ask farmers, "How to plant carrots?’ and they will tell you to use seeds.


Ask a Singapore PSLE student the same question and they will tell you to use a carrot.

Both are right.

However, planting carrot using carrot doesn’t make sense because we will get back the same carrot, perhaps a bigger one after some time (but the carrot will be too old). Technically speaking we are growing back the old plant so I don’t think it is really a reproduction process. So if we really need to show that carrot can reproduce from its roots, we should use only the top part of the carrot (the bottom part of the carrot can be our meal).

[P5G]

Please help.


Q1) Jason immersed two fresh green leaves from the same plant into two beakers of water A and B. The beakers were placed at different locations as shown below. Jason observed that more bubbles were seen escaping from the leaf in Beaker a than the leaf in Beaker B.

Diagrams given:

Beaker A - In the Sun … more bubbles in the water

Beaker B - In the shade … less bubbles in the water

She concluded that _____________________.


1) hot air rises while cold air sinks

2) respiration takes place in Beaker A only

3) photosynthesis is more intense in Beaker A

4) transpiration occurs at a faster rate in the Sun



Q2) The statements A to D describe the breathing process of the human body but they are not arranged in the correct order. Arrange them in the correct order.

A. The lungs expand.

B. The diaphragm contracts.

C. Air is taken in through the nose.

D. Exchange of gases takes place in the lungs.


1) A, C, D, B

2) B, A, C, D

3) C, D, B, A

4) D, A, C, B


Please advise what are the correct answers.


TIA.

[tianzhu]

Hi P5G


For Q1, try to recall what you’ve learned in your science lessons.

This question touches on the concepts of photosynthesis and respiration. Gases exchanges take place through tiny openings called stomata found on both the surface and underside of the leaves.In the presence of light, plants photosynthesise to produce food. The higher the intensity of light, the higher the rate of photosynthesis. Oxygen is released and carbon dioxide is taken in.During respiration which happens in the day as well as night, oxygen is taken in and carbon dioxide is released to the surroundings.

Going back to your question, option (1) is offside. Option (2) is also incorrect. Respiration takes place in both Beaker A and Beaker B.
As for option (4), transpiration refers to the evaporation of water from plants. I am not sure if it’s covered in primary science syllabus.

Option (3) is my choice. Why? In the presence of light, plants photosynthesise. Oxygen is produced and it appears as bubbles in the water.The more bubbles you see, the more intense is the rate of photosynthesis.

For your Q2, I remember seeing detailed explanation in the i- science textbooks and PSLE Guidebook when my boy was doing his PSLE.Please refer to your science books .

Best wishes

[P5G]

Pl help.


Q. The statements below explain how you get the pins and needles.

Rearrange them in the correct order.

a: When the blood rushes to the feet, the nerves respond with sharp stabs which feel like pins and needles.

b: Less blood and oxygen flow to the feet.

When you move your feet, the nerves become normal and blood rushes to the feet.

d: Hence the muscles of your feet get weak.

e: Your feet’s nerves are squashed and begin to lose their feeling.


_____ –> _____ –> _____ –> _____ –> _____.


TIA.

[tianzhu]

Hi P5G


http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Pins_and_needles

e --> b --> d--> c-->a

Hope I am right. Please check with your teacher and let us know the correct answer.

Best wishes