Before sitting for PSLE Science Paper, your child should be able to solve this “food chain” question. Have you ever been to a farm? If so, you might have spotted ladybugs, which look like this:
Almost a decade ago, I visited my relatives on the island of Hainan. While there, I toured a strawberry plantation and spotted many ladybugs on the strawberry plants.
From a young age, I read farmers used pesticides to eliminate insects on their farms. However, I was surprised when I learned that the farmers on the island intentionally released the ladybugs to allow them to roam free among the strawberry plants.
To explain why farmers released the ladybugs on their plants, we will look into a question on The Food Chain from the 2019 Methodists’ Girls School P6 SA1 Examination.
What I would be sharing in this Free PSLE Science Notes:
- Analysing The Question
- Effective PSLE Science Answer Tips
- Concepts Tested in Food Chain
- Common Mistakes and Misconceptions
PSLE Science (Food Chain) – Question Analysis Strategy
MGS/2019/P6/SA1/Q31
The farmer found many organisms Q on the stems of his plants, as shown below. He then released a population of organisms R in his farm and found out that the population of organism Q decreased.
(c) Based on the information provided, complete the food chain below. [1]
During summer, organism P on the island increased in population. The graph below shows the population of organisms P, Q and R.
(d) How did organism P affect the population of the farmer’s plants? Explain your answer. [2]
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This question has been appearing in other schools’ prelim papers hence this is considered a familiar exam question. However, students still find such questions difficult especially on explaining the effect on the population of an organism.
Before we learn the solution, let’s learn and remember these answer tips!
P.S. It is important for any Science student to master the above steps in order to score in open-ended section.
Question (c) Based on the information provided, complete the food chain below. [1]
Solution
Common Mistake!
Take note of the arrow direction. The arrow always points to the feeding organism.
Question (d) During summer, organism P on the island increased in population. The graph below shows the population of organisms P, Q and R.
Thought Process: From the graph, organism R decrease greatly while Organism P and Q increased. So, this shows that Organism P must be feeding on Organism R and now, there is less Organism R (predator of Q) feeding on it, Organism Q will increase.
The food chain would look like :
Plant -> Organism Q -> Organism R -> Organism P
Hence, with the increase in the population of Organism P, the effect on the populations is:
Question(d)
How did organism P affect the population of the farmer’s plants?
Explain your answer. [2]
Solution
The population of the plants will decrease as there is less Organism R feeding on Organism Q. The population of Organism Q will increase as a result and feed more on the plants.
Common Mistake!
Do not use ‘prey’ as Organism Q is not a predator.
I also spotted a few grasshoppers on some strawberry plants, and they seemed to be feeding on the stems of the plants. Occasionally, I saw birds flying above the plants and diving down to catch grasshoppers and ladybugs.
Seeing these other animals made me think of how a food chain (such as the one seen earlier) could fit into a more extensive food web. I also wondered how changes in one organism’s population could affect other organisms’ populations.
To demystify this, let’s explore a question on Food Webs from the 2019 Rosyth School P6 SA1 Examination.
PSLE Science (Food Chain) – Question Analysis Tactic
RS/2019/P6/SA1/Q34
Study the food web below.
(a) Identify one food chain from the above food web [1]
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(b) A population of bird Q was introduced into the habitat. James said that due to this introduction, the bird P population will decrease, while John said that the bird P population will increase.
(i) Explain how it is possible for James to be correct [1]
(ii) Explain how it is possible for John to be correct. [1]
Remember to use the answer tips to answer this question too! Let’s look at how similar the two questions are.
Similarity 1
Both questions have asked for a food chain to be drawn.
MGS/2019/P6/SA1/Q31
RS/2019/P6/SA1/Q34
P.S. RS question has 2 answers and requires understanding of a food web.
Common mistake! You cannot write grass -> grasshopper -> bird P as this is an incomplete food chain. You also cannot omit grass in the food chain.
Similarity 2
Both questions are testing the same concept on the effect on other organisms due to a change in population of one organism.
Question (c) A population of bird Q was introduced into the habitat. James said that due to this introduction, the bird P population will decrease, while John said that the bird P population will increase.
(i) Explain how it is possible for James to be correct [1]
(ii) Explain how it is possible for John to be correct. [1]
This question is rather interesting as it requires students to figure out both possible roles of an organism – predator and prey.
Solution:
For Bird P population to decrease, Bird Q should be its predator, as Bird Q will feed on it.
For Bird P population to increase, Bird Q should be its prey so Bird P can feed on Bird Q and have more food/ another source of food.
Similar to the MGS question, students must have the knowledge of predator-prey relationship and understand how both organisms can affect each other. It is important to identify the roles of each organism in a food chain/web correctly before answering.
I hope you have enjoyed these 2 questions as much as me. I personally like questions on food chain as they often reflect the real world and help me to be more observant of how living things interact with each other.
PSLE Science Notes: [Free Download] What Are Effects Of Forces?
