This blog is managed by Song Hock Chye, author of Improve Your Thinking Skills in Maths (P1-P3 series), which is published and distributed by EPH.

## Tuesday, January 13, 2009

### Common Errors and confusion – Cell Division

Cell division is the process where the cell splits into two new cells. What is the purpose of cell division? That depends on:

If the organism is a multi-cellular organism, (for example a cat, a mango tree, a mushroom) the purpose is for growth and replacement of old cells. A kitten needs to grow into a cat. A seedling needs to grow into an adult plant. Hence, cells need to go through the process of cell division so that the organism can grow. Cell division also helps replace older cells that die.

If the organism is a single-cellular organism, (for example paramecium, bacterium) the purpose is for reproduction. All living things reproduce more of their own kind for the continuity of their specie.

The most common confusion among students is that they erroneously think that the purpose of cell division is for growth, replacement of old cells and reproduction for all organisms. This concept is WRONG.

Below, is a table that summarises the right and wrong concepts of the function of cell division.

tianzhu said...

http://www.wendykoh.com/08/primary6-taonansa1-science.pdf

Dear Mr Song
Toanan P6 SA1 Q42

When the water filled up, the candle would be raised up closer to the spiral. Hot air rises causing the spiral to twirl/spin.
In this question, we assume that the candle must be of a reasonable distance from the spiral before the rising hot air can cause it to spin.

Let’s take it a bit further, if the candle is placed even nearer to the spiral, will the spiral spin faster or slower. Please explain your answer. I am not sure whether this has been asked before.

Excel Eduservice said...

The closer the spiral is to the candle, the hotter the air is. Theoretically, it should spin faster. In real life, it may be a different story due to wind, the configuration of the set-up etc.

tianzhu said...

Dear Mr Song

The candle must be of a reasonable distance from the spiral. Let’s say that the candle is about 3 m away, it’s unlikely to cause any movement.

But if it is placed too near, the amount of air movement between the candle and the spiral is limited due to restricted space. It leads to the spiral spinning at a slower rate. If the candle is moved slightly further away, the air space increases, so the spinning movement increases.There is an optimum distance when the spiral is revolving at its maximum speed.

What’s your opinion on this scenario?

Excel Eduservice said...

My opinion has always been the same for Science experiments. What you learn in class may be very different from what happens in real life.

In class, you learn theory. In real life, there are so many other factors. Resistance, friction, wind, improper set-up etc.

So how near is near to the spiral? 1m? 10 cm? 1 cm? The explanation never stated that.

The best way is to test it out yourself in real life. Sometimes real life experiences give much more valuable answers.

Here are 2 experiments students asked in this blog, expecting typical classroom answers, but got very different answers from those who have tried out the same experiments in real life.

Q1. Does a higher voltage rated bulb result in a brighter bulb than a lower rated voltage bulb, if both circuits have the same number of batteries?

Student’s answer based on theory – yes, because the higher voltage bulb results in higher power based on the formula P=IV.

Real life answer – no, because the internal resistance of the higher voltage rated bulb is higher than the lower voltage rated bulb.

Q2. A container containing hot water and a container containing cold water are placed in freezing temperature. Which container freezes first?

Student’s answer: The container with the cold water freezes first because it takes the hot water to cool down before it can freeze. The cold water's temperature is closer to freezing point, compared to the temperature of the hot water.

Real life answer: Hot water freezes first because a lot more evaporation takes place, taking away a lot of heat. In short, the hot water loses more heat energy than the cold water during the same period.

In conclusion, if you really want to know the answer to your spiral question, try the experiment out yourself.

Putting it very direct, if you want to pass your PSLE Science, just forget about these kind of “challenging questions” (they do not really help in your PSLE science, do they?) - and concentrate on what is being taught in your school instead.

What is important is for to you score for your PSLE Science. You can be the scientist you want after you have passed your exams.

However, you can never be that scientist if you don’t pass exams.

Tan said...

Hi, can someone help me with this question
A glass bowl contains 300 g of water. 25g of sugar was dissolved in the water. After 5 days, 225g of solution remains.
The remaining solution contains
200g of water and 25 g sugar [answer-why? Doesn't the sugar dissolve?]
Thanks