2019 PSLE Science Split Stem Question Reboot

Updated: Feb 18

How would you teach your child to break down the following past year PSLE Science MCQ and analyse the answer options?


Give the question a go with your child before reading on.

Laura cut the lower stem of a white flower into two equal parts. She placed them into containers with different coloured water as shown.

After a short time, she observed that some parts of the flower turned red, some turned blue, while the rest remained white.


Laura made four statements:

A The food made by the plant was red and blue in colour.

B The stem transported the different coloured water to the flower.

C No coloured water was transported to the flower parts that remained white.

D There were no water tubes in the flower parts that remained white.


Which statements can be concluded from her observations?

(1) A and D only

(2) B and C only

(3) B and D only

(4) B, C and D only

This is what teachers at Joyous Learning would instruct our students to do.


Step 1: Highlight/circle/underline the keywords or key phrases in the question stem.


Key phrase #1: "white flower"

This tells us the original colour of the flower.


Key phrase #2: "some parts of the flower turned red, some turned blue, while the rest remained white"

This tells us that the flower was observed to be in three different colours at the end.


Key phrase #3: "from her observations"

This tells us that whatever conclusions that are drawn need to be based on "observations" either stated explicitly in the question or inferred implicitly from the diagrams.


Step 2: Dissect the options one by one.


Statement A: The food made by the plant was red and blue in colour. The flower was originally white, but turned red and blue in some parts at the end of the experiment. So we know the change must have been caused by the absorption of red and blue water.


This begs the question: if a plant uses coloured water to make its food, would the food be coloured? Fortunately, that is a question we do not have to answer!


In plants, food is made in the leaves. Note however in the diagram, that there are no leaves attached to the stem. Therefore, food cannot be a factor.


Statement B: The stem transported the different coloured water to the flower.

From the analysis of statement A, we know that the coloured water was a factor in causing the white flower to turn coloured. So, can we reasonably assume that the change in the colour of the flower was caused by the stem transporting the different coloured water to the flower? Yes, we can because we know that one of the functions of the stem is to transport water to all other parts of the plant.


Statement C: No coloured water was transported to the flower parts that remained white.

By inverse logic, since statement B is true, statement C has to be true too.


Statement D: There were no water tubes in the flower parts that remained white.

If a part of the flower remained white, that means coloured water did not reach that part of the flower. There are two possibilities that can account for this, though.

Possibility 1: There were no water tubes in that part of the flower.

Possibility 2: There were water tubes in that part of the flower, but coloured water did not reach that part of the flower.

Since we cannot rule out possibility 2, we cannot conclude that statement D is definitely true.


There you have it!

Statements B and C are true, so (2) is the correct answer!


To do well for MCQ, a student needs to have a crystal-clear understanding of the scientific concepts and be able to make sound scientific deductions based on the information given in the questions. So it's not enough to just know the scientific facts and principles like the back of your hand. Students need to have strong deductive reasoning skills to help them dissect tricky options so that they can zoom in on the correct answer.


Want to sharpen your child's scientific reasoning skills?

Sign up for Science enrichment classes at Joyous Learning and let our experienced MOE Science Specialist teachers be your whet steel.


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