A team of microbiologists investigated the impact of synthetic micro-plastic additives (P_… — ACT

A team of microbiologists investigated the impact of synthetic micro-plastic additives ( $P_1$ and $P_2$ ) on the rate of nitrogen fixation by *Rhizobium* bacteria in soil culture vessels. Four identical culture vessels were prepared and incubated at $22^\circ\text{C}$ with $15\%$ baseline soil moisture for 14 days under the following conditions:

- Vessel 1: Standard nutrient medium + live *Rhizobium* bacteria (no plastic additives)
- Vessel 2: Standard nutrient medium + sterile (non-viable) *Rhizobium* bacteria + additive $P_1$
- Vessel 3: Standard nutrient medium + live *Rhizobium* bacteria + additive $P_1$
- Vessel 4: Standard nutrient medium + live *Rhizobium* bacteria + additive $P_2$

Match each experimental vessel on the left with its intended role in establishing control conditions or testing experimental variables on the right.

Vessel 1Negative control establishing baseline nitrogen fixation rate of live Rhizobium without plastic contamination
Vessel 2Control group ruling out non-biological abiotic nitrogen fixation attributable to plastic additive P1 alone
Vessel 3Experimental treatment group evaluating the specific effect of additive P1 on Rhizobium nitrogen fixation
Vessel 4Experimental treatment group evaluating the specific effect of additive P2 on Rhizobium nitrogen fixation

Answer

Vessel 1 matches the negative control establishing baseline nitrogen fixation without additives. Vessel 2 matches the control group ruling out abiotic nitrogen fixation from additive P1. Vessel 3 matches the treatment group testing additive P1 on live bacteria. Vessel 4 matches the treatment group testing additive P2 on live bacteria.

Each vessel is correctly paired based on variable isolation principles: Vessel 1 lacks plastics to establish baseline performance; Vessel 2 uses dead bacteria to rule out abiotic chemical artifacts from additive P1; Vessels 3 and 4 isolate the effect of additives P1 and P2 on live bacterial function.

Step-by-Step Solution

Identify the baseline control group that measures normal biological activity without experimental manipulation.

Vessel 1 contains live *Rhizobium* in standard medium without plastic additives (

P_1

P_2

), serving as the negative baseline control.

A baseline control requires normal biological components without the test variable.

Identify the control group designed to isolate abiotic (non-biological) effects of the independent variable.

Vessel 2 contains sterile (non-viable) bacteria alongside additive

P_1

, isolating any non-biological reaction caused by

P_1

Using non-viable organisms ensures any observed nitrogen fixation in this vessel is non-biological.

Distinguish between the active experimental treatment vessels.

Vessels 3 and 4 combine live bacteria with additives

P_1

and

P_2

respectively, acting as active experimental treatment groups.

Experimental treatment groups combine the active biological agent with the manipulated independent variables.

Key Concept

Distinguishing between baseline negative controls, abiotic controls, and active experimental treatment groups in experimental design.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic