Recall from last lesson that living things depend on their habitat for food, water, shelter and space. Pose the driving question: "What happens when those conditions change?"
Distinguish two sources of change and model an example of each:
Think aloud through one cause-and-effect chain: "Land is cleared → fewer hollow trees → fewer nesting sites → possum numbers fall." Emphasise that the effect ripples — removing one thing changes survival for many living things.
Then bridge to the practical: "Today we'll set up a fair test to watch how changing ONE condition affects how seeds grow." Revisit change / measure / keep-the-same from Lesson 1.
As a class, choose the question for the seed investigation, e.g. "Does the amount of water change how tall cress seedlings grow?"
Build the plan together on the board using the three roles:
- Change: the amount of water each day (e.g. 5 mL vs 20 mL);
- Measure: the height of the seedlings after one week;
- Keep the same: same seeds, same soil, same pot, same light and warmth.
Have students predict aloud, with reasoning, and write the class prediction. Then model setting up one pair of pots, labelling each clearly with the group name and water amount.
In groups, students set up their own seed pots following the agreed plan:
- plant the same number of seeds in each pot;
- label each pot with the variable being changed;
- record the starting conditions and their prediction on the recording sheet;
- agree who will water and measure each day.
Circulate and verify each group has changed exactly one variable and listed at least three controlled variables before they finish.
Exit ticket: students write one human activity and the effect it could have on a local living thing's survival.