Year 7 Science · Unit 1 · Lesson 14
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Learning Goals
Read the graph — Energy pyramid for an Australian grassland
Study the energy pyramid below, then answer the questions.
Data: adapted from Lindeman (1942) trophic efficiency model; values representative of Australian grassland ecosystems.
(a) Describe the pattern in energy as you move from producers to tertiary consumers.
(b) Calculate the percentage of energy that passes from producers (10 000 kJ) all the way to tertiary consumers (10 kJ). Show your working.
(c) Use the 10% rule to explain why food chains rarely have more than 4–5 trophic levels.
Predict + reason
Scenario
A farmer in rural New South Wales wants to feed a growing family using the same area of farmland. They have two options. Option A: grow wheat grain and eat it directly as bread, pasta, and cereal. Option B: feed all the wheat to cattle, then eat the beef. The farm produces 100 000 kJ of energy in wheat each season.
(a) Predict: Which option will provide more food energy for the family — eating the wheat directly (Option A) or eating the beef (Option B)?
(b) Justify your prediction. Use the 10% rule and energy flow to explain your answer. Include a calculation to support your reasoning.
1. An energy pyramid shows 50 000 kJ at the producer level. How much energy would you expect at the secondary consumer level? Explain your reasoning.
2. A student says: "Energy pyramids can sometimes be inverted (wider at the top) if there are more predators than prey." Do you agree? Explain using the 10% rule.
Wrap Up
In one sentence, what was the main idea of this lesson?