After the 'amphibian, fish and reptile' question, second in the list of questions that stumped PSLE candidates last year is probably the one about epiphytes.
One of the difficulties of setting a challenging question is making sure that students have a fair chance of answering it. For example, a well-set PSLE question should draw upon only knowledge a student would have acquired in Primary School Level Science syllabus, and not require any Secondary School Level Science knowledge.
Question 8 of Booklet A is an example of a well-set Primary School Level question that tests various aspects of a student's mastery in PSLE Science.
These aspects include
Understanding of scientific concepts (Reproduction in Plants)
Ability to pick out key information from the question stem
Ability to evaluate options
Ability to think critically
The question runs thus:
The diagram shows plant P growing on a tree trunk. Its roots grip the surface of the trunk but do not reach the ground.
When tiny, dust-like substance from plant P land on other tree trunks, they grow into new plants.
Which statement about plant P is correct?
Wind is used for the dispersal of its spores.
P grows on a tree trunk so that it can avoid insects.
Its roots can absorb water droplets formed from condensation.
Fertilisation takes place after the dust-like substance are dispersed.
Let's consider each option in turn.
Wind is used for the dispersal of its spores. Spores are almost always dispersed by wind, but the key to this question lies in recognising that the question is not really about whether P's spores are dispersed by wind, but whether P reproduces through spores in the first place. The answer to this is sneakily revealed in the diagram in the form of flowers. Since P bears flowers, it reproduces through seeds, not spores.
P grows on a tree trunk so that it can avoid insects. Many insects can fly, and those that can't can easily crawl up tree trunks, so growing on a tree trunk wouldn't help P avoid insects.
Its roots can absorb water droplets formed from condensation There are two clues in the question that allude to this. First is that P's roots do not reach the ground. Second is that its roots only grip the surface of the trunk, as opposed to penetrating the bark (in which case it can siphon water from the xylem of the tree). P has to obtain water somehow, so the suggestion that it gets it from water droplets formed from condensation cannot be dismissed at this point. Primary School students don't learn anything about epiphytes (a plant that grows on another plant, especially one that is not parasitic) and how they obtain water, so while they cannot dismiss this option outright, they would (understandably) be hesitant in confirming this option at this point.
Fertilisation takes place after the dust-like substance are dispersed When 'dust-like substance' and 'fertilisation' are mentioned in the same sentence, the first thing that comes to mind is that the 'dust-like substance' refers to pollen. However, the question states that the 'dust-like substance' grow into new plants when they land on other tree trunks. This tells us that the 'dust-like substance' cannot be pollen, since pollen do not germinate into new plants. The purpose of dispersed pollen is seeking the stigma of the same species of plant for fertilisation. Since P bears flowers, this dust-like substance must be tiny seeds.
It takes a student who is crystal clear and confident in her concepts to conclude that option 3 has to be the answer (even though they have not learnt anything about epiphytes) because the rest of the options are not valid. [In fact, some epiphytes can absorb water vapour directly from the air!]
It's important to go through the thinking process for such questions with students so they know how to make intelligent decisions based on critical analysis of available information. Besides being useful in Science, learning how to solve problems systematically is also an important real-life skill!
Many 2017 PSLE candidates found the Science paper challenging. Relative to the 2016 paper, that's definitely true. We'll analyse more interesting 2017 PSLE Science questions in the coming weeks, so keep a lookout for our newsletter!
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