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Decomposition Investigation Worksheet

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Decomposition Investigation Worksheet

A restoration team is testing how leaf-litter conditions affect decomposition in a New Zealand ngahere. Use the supplied investigation and results to evaluate the evidence. Treat all values as class data; do not open or handle unknown decomposing material.

Investigation and results

Small mesh sachets each contained 10.0 g of air-dried, finely cut mānuka leaves. Replicate sachets were buried in soil for 28 days. Moisture was the independent variable: low moisture (20% water content) or high moisture (60%). Temperature (15 °C), oxygen access (same mesh), soil type, leaf mass and leaf preparation were kept as similar as possible. At day 28, sachets were retrieved, dried to constant mass and weighed. Percentage mass loss = (starting mass − final dry mass) ÷ starting mass × 100. Values below are means of five sachets.

Moisture condition

Mean final dry mass (g)

Mean mass loss (%)

Low: 20% water content

8.6

High: 60% water content

6.9

Analyse the evidence

Answer in complete sentences where appropriate. Include units and refer to specific evidence.

1.Identify the independent variable and the dependent variable in this investigation.

2.Calculate the percentage mass loss for the high-moisture sachets using their mean final mass of 6.9 g. Show your working and compare your result with the table.

3.Which condition showed greater decomposition? Select one answer and support it with a numerical comparison.

Low moisture: 14% mass loss
High moisture: 31% mass loss
Both conditions: 20% mass loss
The results do not show a difference

4.Explain how greater moisture availability could increase decomposition, referring to decomposer activity and material breakdown.

5.The sachets were placed in the same soil and used identical mesh. Explain why these controls improve the investigation, and name one factor that may still have varied between sachets.

6.Five sachets were measured in each condition. How does replication improve confidence in the results, and what additional information would help you judge variation?

7.A team member says, “The results prove that moisture alone caused all the extra mass loss.” Evaluate this claim, using one strength and one limitation of the evidence.

8.Identify two safety or environmental precautions for this investigation, and explain why each matters in a New Zealand field setting.

9.Propose one improvement to make a follow-up investigation more reliable and one improvement to make it more valid. State what each improvement addresses.

10.Design a follow-up test to investigate whether the effect of moisture depends on oxygen availability. State the treatments and the key conditions you would control.