Safety and evidence boundary
This week uses fictional signaling systems, published-style graphs, and card or digital models. It does not diagnose hormone, neurological, immune, or other medical conditions and does not require personal health information.
Explicit science instruction
Cells communicate when one cell releases or presents a signal and another cell has molecular machinery capable of detecting it. A signaling molecule that binds a receptor is often called a ligand. Receptors can be located on the plasma membrane or inside cells, depending on the chemical properties of the signal and the receptor system.
Specificity does not mean one ligand always produces one universal response. A cell may lack the receptor entirely, express a different receptor subtype, contain different downstream proteins, or be in a different regulatory state. The same signal can therefore have little effect in one cell and a strong but different effect in another.
Communication can occur over short distances, through direct cell contact, or through signals transported over longer distances. The key logic remains detection followed by intracellular interpretation.
Vocabulary: ligand; receptor; target cell; specificity; local signaling; long-distance signaling; response; receptor expression.
Worked example with reasoning
A fictional ligand L reaches Cell A and Cell B. Cell A expresses receptor R1 linked to a pathway that increases transport-protein insertion. Cell B expresses receptor R2 linked to a pathway that changes gene expression. The same ligand produces different outcomes because receptor and downstream pathway context differ. Cell C lacks a compatible receptor and shows no direct response.
Guided question
Why is “the signal tells every cell what to do” a weaker model than “cells respond according to receptors and downstream machinery”?
Independent work
- Draw Signal L interacting with three fictional cell types.
- Give each cell a different receptor or receptor status.
- Predict the response and justify it from the model.
- Identify one factor besides receptor presence that could change response.
Misconception check
A signaling molecule does not carry a complete instruction that every cell reads identically. Meaning emerges from the interaction between signal, receptor, downstream network, and cellular context.
Formative understanding check
Why might two cells exposed to the same ligand respond differently?
Show the worked response
They may express different receptors, receptor amounts, signaling proteins, transcription factors, or regulatory states, causing the ligand to activate different pathways or response strengths.
Open-book formative practice only; not an official mastery attempt or grade.
Mentor evidence conference
Ask Archaemenes to identify where your model skips a step between signal, receptor, intracellular transduction, and response. The mentor may challenge reasoning but does not provide protected assessment answers.
Open Archaemenes for this lessonTeacher guidance
Foundation: use lock-and-key only as an entry model, then identify its limits. Core: require receptor plus downstream-pathway explanation. Extended: compare membrane and intracellular receptors and discuss receptor subtype diversity.
Preserve learning evidence
Keep the signaling model, graph or data interpretation, correction note, and explanation in the matching Week 13 evidence field.
Return to monday Evidence Workspace