Year 7 Science · Unit 1 · Lesson 11
Challenge Worksheet
Learning Goals
What if…?
Scenario — Great Barrier Reef marine heatwave
Water temperature in the Great Barrier Reef has risen 2°C above the long-term average for three consecutive months due to a marine heatwave in the Coral Sea. Coral polyps — tiny animals that form the physical structure of the reef — are extremely sensitive to temperature change. When water becomes too warm, the corals expel the microscopic algae called zooxanthellae that live inside their tissues. Without these algae the corals lose their colour and their main food source — a process called coral bleaching. If the warm temperatures continue, the bleached corals die.
Using what you know about biotic and abiotic factors, predict and explain what would happen next in this ecosystem. In your answer, describe at least THREE steps in the cascade — include effects on both biotic factors (living things) AND abiotic factors (non-living parts of the reef environment). Use scientific terms from the lesson.
1. A scientist studying the Great Barrier Reef says: "The reef ecosystem collapsed because of one abiotic factor changing." Evaluate this claim. Is it a complete explanation? What else would you need to consider to fully explain the ecosystem collapse?
2. Zooxanthellae algae are described as a biotic factor inside the coral polyp's tissues. Explain why losing these algae also changes the abiotic environment of the reef community — not just the coral polyps themselves. Think about light, nutrients, and the reef structure.
Wrap Up
In one sentence, what was the main idea of this lesson?