Year 8 Science · Unit 1 · Lesson 12

Removing Waste

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Learning Goals

Apply the input-use-output model to a real-world scenario involving athletes sweating.
Compare the roles of two systems, one that brings things in and one that removes wastes, using the idea of system interaction.
Predict what would happen to a living system if waste removal stopped.

Warm Up

Order the steps

Number the stages from 1 to 4 to show the correct order of the input-use-output cycle in a living system. Step 1 = what happens first.

Order	Stage
	Wastes are produced as a by-product of cell processes
	The excretory system helps remove wastes from the body
	Useful materials enter the body (food, water, gases)
	Cells use the materials for their processes

Your Turn

Real-world context

During a 10 km fun run at the Sydney Olympic Park, athletes can lose over one litre of sweat per hour. Sweat contains water and dissolved substances that cells no longer need. If these substances were not removed through sweat and other excretory processes, they would build up in the body. Research by Sports Medicine Australia shows that managing both intake (hydration) and output (sweating and excretion) is essential to performance.

(a) Using what you know about inputs and outputs in living systems, explain why the sweat removed during running is an example of an output process that helps the body maintain balance.

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(b) Explain why an athlete needs to manage both drinking water (input) and sweating (output) to keep their body functioning well during a long run.

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Show What You Know

1. Imagine the excretory system stopped working completely. Predict and explain what would happen in the body over time, using the concept of balance between inputs and outputs.

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2. Compare the role of the digestive system (an input system) with the role of the excretory system (an output system). Explain why both are needed for a living system to keep functioning.

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Wrap Up

In one sentence, what was the main idea of this lesson?