Critical Timing Windows, When the Door Closes
Developmental domain · Lesson 15 of 20 · Principles of Biomedical Science (PBS)
Today's goal: Explain that each lip and palate fusion step has a narrow critical window, and that once a window closes the cleft cannot be undone by later development.
This is a model of the work you should turn in. Use it to check your own: match the structure and the level of detail, do not copy it. Your wording should be your own.
Timeline (human weeks):
- Weeks 4 to 6: lip fusion window (medial nasal plus maxillary).
- Weeks 6 to 12: palate fusion window (growth, elevation, fusion); fusion complete by about week 12.
Latest deadline: Mateo's lip-and-palate closure had to succeed or fail by about week 12, when the secondary palate normally finishes fusing.
Why it will not self-close: After the window the closure machinery (MEE, periderm peel-away, TGF-beta3) shuts off, so a doctor cannot expect his cleft to close on its own; the face only grows larger, and growth is not fusion (PMID:26589921).
This model shows the level of evidence and organization needed to complete: A labeled developmental timeline marking the lip and palate closure windows and an irreversibility statement.
- Name the variables and include units.
- Enter observations without changing the raw values.
- Check labels, calculations, and patterns before interpreting the data.
Keep the structure. Replace the question, facts, measurements, and evidence. Then recheck units, vocabulary, and whether the conclusion goes beyond the evidence.
The finished product above did not appear all at once. Here is the path from the question to the turned-in work, so you can follow the same steps.
- 1Start from today's question: Why does the timing of a disruption change which part of the face is affected?
- 2Work the Model and the Explore questions to reason it out before writing anything.
- 3Pull the specific evidence the product needs from the reading and any database you used.
- 4Write it up in the required format: Build a simple timeline for Mateo. Mark the lip window (weeks 4 to 6) and the window (weeks 6 to 12). Then write two sentences: (1) the latest week by which his lip-and-palate closure had to succeed or fail, and (2) why a doctor cannot expect his to close on its own after birth, using the word window and the idea that the machinery has shut off. Do not name a diagnosis.
- 5Check it against the rubric, then submit.
| Criterion | Proficient | Developing | Beginning |
|---|---|---|---|
| Complete | Every required part of the artifact is present and filled in. | Most parts are present, but one is missing or left blank. | Several parts are missing. |
| Accurate | The science and data are correct and match the evidence. | Mostly correct, with a small factual slip. | Key science or data is wrong. |
| Scientific reasoning (CER) | States a claim, backs it with specific evidence, and explains the reasoning. | Has a claim and evidence, but the reasoning is thin or missing. | Gives an answer with no evidence or reasoning. |
| Professional communication | Clear, organized, and labeled the way a clinician or scientist would write it. | Readable but disorganized or missing labels. | Hard to follow. |
| Submitted | Turned in through the route named under Submit here and confirmed. | Turned in, but in the wrong place or unconfirmed. | Not turned in. |
- CompleteProficient: Nothing is left blank: the model fills every part of "Build a simple timeline for Mateo. Mark the lip window (weeks 4 to 6) and the palate window (weeks 6 to 12). Then write two sentences: (1) the latest week by which his lip-and-palate closure had to succeed or fail, and (2) why a doctor cannot expect his cleft to close on its own after birth, using the word window and the idea that the fusion machinery has shut off. Do not name a diagnosis.".
- AccurateProficient: Every number and claim matches the case evidence.
- Scientific reasoning (CER)Proficient: It names a claim, cites the specific evidence, and explains the reasoning, not just the answer.
- Professional communicationProficient: It is organized and labeled like a real chart note.
- SubmittedProficient: It would be attached to your class form or handed in, and confirmed.
One exam-style question that uses exactly what you practiced today. Try it before you reveal the answer, then read why each choice is right or wrong.
Tap an answer to see the full explanation. Nothing is recorded or graded.
It builds this reusable test skill: Reasoning about critical-window timing and irreversibility.
- Name the concept or data pattern being tested.
- Cross out choices that violate that rule or the evidence.
- Justify the best remaining choice before checking the answer.