Calculating the Area of a Triangle

Area of a triangle = ½ x base x height

A very common mistake students make is extending the base outside the triangle.
Example -
Question – Find the area of the shaded triangle.


Common Mistake (Wrong solution)

A common mistake students make in the above question is:-

Area of triangle = ½ x base x height
= ½ x 6cm x 3cm = 9 square cm (wrong)

The base should be 4 cm and not 6 cm. The question asks you to calculate the area of the SHADED triangle. The base of the shaded triangle is 4 cm.

If you put the base as 6 cm, you will calculate the area of the WHOLE figure as shown below.



The correct answer is as follows:

Area of triangle = ½ x base x height
= ½ x 4cm x 3cm = 6 square cm (correct answer)

In order to avoid making the mistake above, always remember that the base of the triangle must never extend outside the triangle.

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 species. 

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.

  

The Three States of Water

Most PSLE students know that water exists in three states – solid, liquid and gas. Most students also know that the ‘magic numbers’ are ‘0’ and ‘100’ deg Celsius, because that is the temperature at which water changes its state.

Students also know that ice exists at 0 deg C and below, while steam exists at 100 deg C and above.

However, quite a few students get confused, when the temperature is at or between 0 and 100 deg Celsius. Some students get the impression that water exists in liquid form only when the temperature is at or between 0 and 100 deg C. This concept is wrong.

At or between 0 to 100 deg C, water can exist in two forms – liquid (as in lakes, rivers) and gas (water vapour). Below is a diagram to illustrate the states of water, in relation to the temperature.



Simply put,
Solid - At 0 deg C and below.
Liquid – At and between 0 and 100 deg C.
Gas – At 0 deg C and above.


Important and useful point to note –

Because water can exist in 2 forms (liquid and gas) from 0 to 100 deg C, we have evaporation, condensation in this world and hence, the very critical Water Cycle, which is so important to life on earth.

If water exists only as liquid between 0 to 100 deg C, it will not evaporate to form water vapour, then condense to form clouds, and eventually fall back to earth as rain.

This wide range of 0 to 100 deg C, where water exists in 2 forms is unique, unlike many other substances, where at a given temperature, it exists only in one form.

Summary – Water exists in two forms (liquid and gas) from 0 to 100 deg C and NOT in liquid form only.

Common Errors and Confusion – “ovary” and “spores”

It is a bit unfortunate that both the reproductive parts of the female human and the female part of the flower have the same name, “ovary”. Because both have the same name, spelling and the same way they are pronounced, some students end up confused.

Ovary in a flower refers to the female reproductive part of the flower. The ovary in this case, will develop into the fruit after fertilization. The ovary of the flower is illustrated as shown below.



Ovary in the human female on the other hand, is the reproductive part of the female where eggs are produced. The ovary in the human female is illustrated as shown below.



Another confusion which is caused by the same term, is “spores”. Spores are produced by ferns and mushrooms for the purpose of reproduction. Again, because of the same name, some students get confused that mushrooms and ferns are plants. This is not correct. Ferns are plants but mushrooms are fungi. Only plants make their own food. Mushrooms feed on dead matter - eg rotting logs.

Common Mistake - Perimeter of Partial Circles

Common Science Mistake – Internal and External Fertilisation

Fertilisation (in animals) is the process where the male sperm cell fuses with the female egg cell.

Internal fertilisation occurs when the male sperm cell fuses with the female egg cell, in the female’s body.

External fertilisation occurs when the male sperm cell fuses with the female egg cell, outside the female’s body.

The most common mistake made by students is that they believe internal fertilisation occurs in animals that give birth (example mammals) and external fertilisation occurs in animals that lay eggs (example birds and reptiles etc). This concept is wrong.

Internal fertilisation occurs in mammals, birds and reptiles.

In the case of mammals, fertilisation occurs in the female’s body. The new life develops inside the mother’s womb for most mammals.

In the case of birds and reptiles, fertilisation occurs inside the female’s body, and the fertilised egg is then laid. The new life develops outside the mother’s body.

In the case for amphibians and most fishes, fertilisation occurs outside the female’s body and the new life develops outside the mother’s body.

Below are some examples of internal and external fertilisation.