Microbial Misfit CER Worksheet
Antarctic Research Initiative
Project Frozen Life
CONFIDENTIAL // DATA FILE
Dossier ID: #X24-ANT
Researcher Name:
Date:
Mission Brief: The Antarctic Subglacial Specimen
A deep ice-core sample drilled 3,200 meters beneath the East Antarctic Ice Sheet has revealed a living, unicellular organism. Your lab team has been tasked with classifying this unknown specimen (designated Specimen X-24) as either a prokaryote or a eukaryote using Claim, Evidence, and Reasoning.
Laboratory Analysis Report: Specimen X-24
Digital Micrograph (4000x)
DNA_LOOP
Unicellular structure with rigid outer boundary.
| Test / Parameter | Laboratory Observation |
|---|
| Average Cell Size | 2.8 µm (micrometers) |
| Nuclear Envelope | Not Detected (Absent) |
| Genetic Material | Single, circular DNA molecule |
| Organelles | Ribosomes present; No mitochondria/ER |
| Outer Cell Wall | Present (Peptidoglycan composition) |
Scientific Investigation Prompt
Is Specimen X-24 a prokaryote or a eukaryote? Justify your decision using CER.
C
Claim
(Directly answer the prompt in a single complete sentence)
E
Evidence
(State at least two specific, measurable facts or observations from the data table)
R
Reasoning
(Explain the biological principles that link your evidence to your claim)
* Link evidence back to biological definitions (e.g., cell wall composition, nucleus role, DNA organization).
High School Biology Core Curriculum // Cell Structure & Function Page 1 of 1
Microbial Misfit Teacher Guide
Teacher Guide & Answer Key
Microbial Misfit Key
BIOLOGY CORE
Focus: Prokaryotes vs. Eukaryotes
Suggested Pacing (15-20 Minutes)
- Min 0-3 (Hook): Introduce the subglacial discovery. Emphasize that extreme environments like Antarctic Lake Vostok harbor microbes that challenge traditional definitions.
- Min 3-6 (Analyze): Have students read the data table silently. Point out units like micrometers (µm) and review what peptidoglycan is.
- Min 6-15 (Drafting): Students draft their CER arguments individually.
- Min 15-20 (Debrief): Call on students to share claims and discuss why circular DNA and absent nuclei point definitively to prokaryotes.
Misconceptions
Students may think cell walls are exclusive to eukaryotes (plants/fungi). Remind them that bacteria (prokaryotes) also possess cell walls, specifically made of peptidoglycan.
Exemplar Student Response (Model Work)
C Model Claim
Specimen X-24 is a prokaryotic organism.
E Model Evidence
Evidence 1: The laboratory analysis states that a nuclear envelope was "Not Detected (Absent)."
Evidence 2: The specimen contains a single, circular DNA molecule and has no membrane-bound organelles like mitochondria or endoplasmic reticulum.
Evidence 3: The cell wall is composed of peptidoglycan, and the overall size is very small (2.8 µm).
R Model Reasoning
By definition, prokaryotes are unicellular organisms that lack a membrane-bound nucleus and membrane-bound organelles, whereas eukaryotes contain their DNA inside a nuclear envelope and have specialized organelles like mitochondria. Since Specimen X-24 lacks a nuclear envelope and has only ribosomes, it must be prokaryotic. Furthermore, its genetic material is organized in a single, circular loop, which is a key characteristic of prokaryotic DNA (eukaryotes have linear chromosomes). Finally, peptidoglycan cell walls are unique biological structures found exclusively in bacteria, which are prokaryotes.
Quick-Grading CER Rubric (4-Point Scale)
| Component | Proficient (1 Point) | Developing (0.5 Points) |
|---|
| Claim (1 pt) | Clearly and correctly states that the specimen is a prokaryote. | State is vague, or incorrectly identifies the cell type. |
| Evidence (1 pt) | Provides at least 2 specific pieces of data (e.g., circular DNA, lack of nuclear envelope). | Provides only 1 piece of data, or uses generalized/unsupported statements. |
| Reasoning (2 pts) | (2 pts) Fully explains the scientific biological definition linking prokaryotes to absent nuclei and circular DNA. | (1 pt) Mentions biological rules but does not connect the evidence directly to the definitions. |
High School Biology Core Curriculum // Cell Structure & Function Teacher Resource Sheet
