Life Cycles of Living Things

Hello! 

Today's summary guide is on Life Cycles of living things, a topic covered for Primary 4 Science. For my P5 and P6 students, this is a good revision for you to recap on the different animals and the number of stages of their life cycles.

You can download the summary guide on the link below, but I would first like to focus your attention on one of the most common booklet B question that is tested for this topic.

P4 Science - Life Cycles Summary

Life cycles is a pretty easy chapter, as long as you remember the group of animals in the 3-stage and 4-stage life cycle.

For animals with a 4-stage life cycle, for example the butterfly, one of the most important thing to note is that the animal consume the most amount of food and moults the most number of time during the larval stage.

4-stage life cycle of the butterfly

During the larval stage, the caterpillar moults several times and will eat the most amount of leaves compared to the other stages in its life cycle.

Let's take a look at two types of booklet B questions testing this concept.

A pot of plant is given, with several butterfly eggs placed on its leaves. The plant is left in a controlled environment where no other insects or animals are exposed to it for several weeks. After monitoring the plant for several weeks, data is collected and shown in the graph below.

Graph 1A: Amount of food eaten after several weeks

Question: Identify the larva and pupa stage of the butterfly life cycle (A, B, C or D).

Remember: LARVA EATS THE MOST FOOD

Hence, if you look at this graph, stage B is where you see the highest amount of food eaten. 

This means that stage B is the larva stage. Based on the ABCD life cycle given, stage C comes after stage B, and thus, stage C is the pupa stage. Easy, right?😊

Okay, now if I change the graph and instead give you the graph below:

Graph 1B: Number of leaves on a plant after several weeks

Now, the axis heading on the left states the number of leaves on a plant. 

Going back to the same concept that LARVA EATS THE MOST FOOD, this means that during the larva stage, you would have the least number of leaves on the plant because most of it have been eaten by the caterpillars.

Hence, in this question, stage B with the lowest number of leaves on the plant, would be the larva stage. 

It is also important to note that the eggs and pupa does not consume any food at all. Pupa does not consume food as they are in the cocoon, undergoing metamorphosis. Hence, stages A, C and D could be the pupa stage. 

But, if we look at the ABCD life cycle given, stage C is next, indicating that stage C is the pupa stage.

However, sometimes this ABCD life cycle may not be given and we have to still identify the pupa stage. The egg is the start of the cycle and since it does not consume any food, you will have the most number of leaves during the egg stage. As time passes and the larva moves on to the pupa stage, it will stop eating the leaves but the number of leaves left will decrease as compared from the start.

Therefore, from this we can conclude that stage A is the egg stage while stage C is the pupa stage.

I hope that the explanation provided is clear for you. Please let me know if you have any questions regarding this.

May the summary benefit you as you are going through or revising this topic in school. 😀