Year 8 Science · Unit 1 · Lesson 19
Challenge Worksheet
Learning Goals
Find the errors
This paragraph has exactly three errors. Underline each one and correct it below.
A student’s summary
An ecosystem is made up of biotic factors, which are living, and abiotic factors, which are not. Producers, such as plants and algae, make their own food using energy from sunlight. Fungi are also producers, because, like plants, they grow out of the soil. Decomposers such as bacteria break down dead matter, but this has little effect on plants. Abiotic factors are the least important part of an ecosystem, because they cannot eat, grow or move.
1. Write the three corrections.
Real-world context: coral bleaching
Reef-building corals are animals. Tiny algae live inside each coral polyp, make food by photosynthesis and pass much of it to the coral. When the sea stays warmer than usual for several weeks, corals push the algae out and turn white (bleaching). If the water does not cool soon, many bleached corals starve and die. The Great Barrier Reef has had several mass bleaching events since 1998, including in 2016 and 2017.
| Site | Highest water temperature (°C) | Colonies counted | Colonies bleached | Bleached (%) |
|---|---|---|---|---|
| A | 28.5 | 200 | 12 | 6 |
| B | 29.5 | 200 | 46 | |
| C | 30.5 | 160 | 96 | |
| D | 31.0 | 150 | 126 |
Source: sample dive-survey results for this exercise.
2. Calculate the percentage of colonies bleached at sites B, C and D, and write them in Table 1. Show your working for site C.
Site C %
3. Describe the pattern in Table 1. A student concludes: “Every coral reef will bleach once the water reaches 30 °C.” Give two reasons why this conclusion goes further than the data.
Evaluate the claim
A student claims
“A coral is a producer, because it has algae inside it that photosynthesise.”
4. Use the definition of a producer to decide which living thing in a coral is the producer and what role the coral animal itself has. Then explain why bleaching is a problem for the coral.
5. A mass bleaching event kills many of the corals on one part of a reef. Explain how this could affect the whole reef ecosystem, not only the coral. Use the terms producer, consumer, decomposer and abiotic factor, and name at least two reef consumers.
Find the errors
1. (i) Fungi are decomposers, not producers: they cannot make their own food and feed by breaking down dead matter. (ii) Decomposers do affect plants: they return nutrients to the soil that producers need to grow. (iii) Abiotic factors are important: sunlight, water, temperature and soil decide which organisms can survive. [3 marks: 1 per correction]
Your Turn
2. B: 46 ÷ 200 × 100 = 23%. C: 96 ÷ 160 × 100 = 60%. D: 126 ÷ 150 × 100 = 84%. [3 marks: 1 per site; working shown for C]
3. Pattern: the higher the top water temperature, the greater the percentage bleached (6% at 28.5 °C up to 84% at 31.0 °C). Too far, any two: only four sites after one summer; it did not measure how long the water stayed warm; even at 30.5 °C only 60% bleached, not every colony; other reefs and coral types may respond differently; the data are a sample, not every reef. [3 marks: 1 pattern, 1 per reason up to 2]
Go Deeper
4. A producer makes its own food. The algae do this by photosynthesis, so the algae are the producers. The coral animal cannot make its own food, so it is a consumer that relies on food from the algae (it also catches tiny plankton). When it bleaches it loses its algae, so it loses most of its food and can starve. [3 marks: algae are producers; coral is a consumer; bleaching removes its food supply]
Show What You Know
5. Marking guide (points expected): 1 an abiotic factor, water temperature, rose and caused bleaching; 1 the algae (producers) are lost, so the coral loses its food and dies; 1 consumers that eat coral, such as butterflyfish, lose their food; 1 fish that shelter in coral lose their homes and decline, so predators such as reef sharks or coral trout have less prey; 1 decomposers break down the dead coral tissue, and seaweed may cover the dead coral; 1 judgement: one abiotic change spreads through the biotic community, so the whole reef is affected. [6 marks]
Common error to watch for: calling the coral a plant or a producer. The coral is an animal; its algae are the producers.