Lesson 3 • Size matters

Scientific diagrams of laboratory equipment are used to communicate experimental setups clearly and accurately. These diagrams help students record investigations, explain procedures, and interpret scientific methods. Unlike artistic drawings, laboratory equipment diagrams are simplified representations designed to show essential features and relationships between apparatus components.

When teaching students how to draw laboratory equipment, the emphasis should be placed on clarity, accuracy, and correct scientific conventions rather than artistic skill. Students should use a sharp pencil and ruler, draw equipment with clean, single lines and avoid sketching, shading, or decorative detail.

Key conventions for scientific diagrams of laboratory equipment include:

• diagrams should be large enough to show important details clearly.
• equipment should be drawn in proportion to the surrounding apparatus where possible.
• only essential features should be included.
• straight lines should be ruled neatly with a ruler.
• labels should be printed clearly and horizontally.
• label lines should be ruled, should not cross, and should touch the correct part of the apparatus.
• titles should clearly identify the experimental setup or equipment shown.

Students should also learn standard representations of common laboratory equipment such as beakers, test tubes, measuring cylinders, Bunsen burners, retort stands, thermometers, flasks, and delivery tubes. Consistency in these representations improves scientific communication and helps students interpret textbook and examination diagrams.

Modelling how to break complex setups into simple shapes and draw apparatus step-by-step can support students to avoid unnecessary detail or perspective drawing.

Common student errors include:

• drawing apparatus too small.
• using sketchy or multiple lines.
• including unnecessary shading or colour.
• allowing label lines to cross.
• drawing equipment out of proportion.
• confusing the names of common laboratory apparatus. 

Filtering is a physical separation method that separates particles in a mixture based on size. The mixture is passed through a barrier or filter with holes or pores of a specific size, allowing smaller particles to pass through while trapping larger ones. Filtering does not change the chemical composition of the substances; it only separates them physically.

For solids and liquids, filtering is commonly used to separate insoluble solids from liquids. For example, coffee grounds can be removed from water using a coffee filter, or sand can be separated from water using filter paper, cloth, or fine mesh. In these cases, the liquid that passes through the filter is called the filtrate, and the solid that remains on the filter is called the residue. The size of the filter pores must be carefully chosen so that they are smaller than the solid particles but large enough for the liquid to pass through.

Filtering can also be used to separate solid particles from gases. For instance, air purifiers and car cabin filters trap dust, pollen, and soot while allowing air to flow through. This technique is widely used in laboratory and industrial applications to clean air or remove airborne particles.

When using filtering techniques, it is important to select the appropriate filter size, because too large a pore allows solids to pass through, while too small a pore can slow down the filtration process. Often, multiple stages of filtration are used: a coarse filter first removes large debris, followed by a finer filter for smaller particles. Real-world applications of filtering include water purification, brewing, laboratory separations, and air filtration systems.

Mosquito-borne bacteria and viruses are an identified health issue in Australia, particularly in warmer months and after periods of rainfall when mosquito populations increase. These viruses are transmitted by female mosquitoes that need blood in order to breed. When biting an infected person or animal, the blood they take also contains viruses. When the mosquito bites the next person, the mosquito may pass on the virus to the person through its saliva.

One of the most common mosquito-borne illnesses in Australia is caused by the Ross River virus. This virus is widespread across the country and is maintained in a natural cycle between mosquitoes and mammals such as possums. Humans become infected when bitten by a mosquito. Symptoms typically include joint pain, fatigue, fever, and rash, and while the disease is rarely life-threatening, it can cause prolonged illness lasting weeks or even months. There is currently no vaccine, so prevention focuses on avoiding mosquito bites and reducing breeding sites.

Another significant emerging disease is Japanese encephalitis, which has recently been detected in parts of Australia after being historically confined to Asia. This virus is transmitted by mosquitoes that breed in water-rich environments, often involving birds and pigs as key hosts. Most infected people experience no symptoms, but in severe cases, it can cause inflammation of the brain (encephalitis), leading to neurological damage or death.

Preventative strategies for these viruses include using insect repellent, wearing protective clothing, and eliminating standing water, such as that found in open water tanks.

Argumentation is the process of systematically providing reasoning to support a claim. Unlike the commonly used negative term ‘argument’, argumentation involves developing a valid argument or persuasive idea.

At the simplest level, students should be able to provide a claim, evidence, and reasoning. At higher levels, students will be able to identify the limitations of a claim, the underlying assumptions that back the claim, and provide a rebuttal for any counterclaims.

In this lesson, students should use the results of their experiment to make a claim about which filter to use. The evidence from the experiment should describe how the filter residue contains particles larger than the filter pore, or that the filtrate only contains particles smaller than a mosquito. The reasoning should link the size of the selected filter pore to being smaller than the mosquito’s size.

There are many sources of information about how First Nations Australians traditionally separated mixtures through hand-picking, winnowing, yandying, filtering, and cold-pressing. When describing these techniques to students, it is important to consider that these practices are part of sophisticated and diverse knowledge systems developed over thousands of years by Aboriginal and Torres Strait Islander peoples across different regions of Australia. The techniques were carefully adapted to local environments, resources, and cultural practices, and should be recognised as examples of scientific observation, experimentation, and technological innovation rather than simply “traditional practices”. It is also important to acknowledge that knowledge and practices vary between language groups and communities, and that First Nations perspectives should be represented respectfully and accurately.

It is important to consider the language used when discussing these practices. Using the current tense acknowledges that Aboriginal and Torres Strait Islander cultures are living cultures and that many of these practices continue today in communities across Australia. Referring to these methods only in the past tense can unintentionally reinforce the misconception that First Nations cultures exist only in history.

It is also important to incorporate First Nations’ scientific knowledge into the main teaching and learning sequence rather than presenting it as an additional example or “add-on” at the end of a lesson. Embedding these examples alongside Western scientific concepts helps students recognise Aboriginal and Torres Strait Islander knowledge systems as equally valid and evidence-based ways of understanding the world.

Where possible, use examples connected to specific Countries, language groups, and environments to demonstrate the diversity of practices across Australia. Including local perspectives and consulting community-approved resources can further support culturally responsive and accurate teaching. Students should be encouraged to see these techniques not only as cultural practices, but also as practical applications of scientific principles such as particle size, density, filtration, and extraction.