# Geometry and nest air

**Audience:** Upper-secondary education, Biology and Physics. **Suggested time:** 40–45 min.
**Status:** technical draft; Biology and Physics teacher review pending.
**Starting lesson:** Entrances and ventilation (entradas-ar). Resources: WebGL
browser, paper or spreadsheet, and laboratory access. Follow the [common preparation](README.md).

## Objective

Distinguish concentration, gas quantity and circulation; compare two open systems
without assuming an opening guarantees homogeneous oxygenation.

## BNCC

Proposed association: EM13CNT101, EM13CNT301 and EM13CNT302. See the mapping and
official source in the [general guide](README.md). Teacher review is needed.

## Steps and records

1. In 5 min, predict how a second opening could affect chamber gases.
2. Open **Entrances and ventilation** and check **Air in the galleries**:
   A has one entrance; B has two. Both start at model O₂ 19% and CO₂ 1.2%.
3. Record the initial diagram, minimum/maximum concentration and population.
   Equal concentration does not imply equal quantity: the second segment changes volume.
4. Advance one model day, pause and record the same A/B indicators, including
   accumulated respiration. Repeat at days 3 and 5 without changing parameters.
5. In 10 min, explain a difference or its absence, distinguishing exchange with
   the atmosphere from internal redistribution. Export and restore the backup.

## Discussion questions

- Do two openings necessarily create a strong current in every chamber?
- Is comparing percentages sufficient to compare total quantity?
- Can a nest receive oxygen and still contain lower-oxygen regions?

## Annotated answer guidance

Circulation depends on the network, resistance and gradients; an extra entrance
does not ensure uniform improvement. Percentages require volume to indicate
model quantity. Respiration consumes O₂ and produces CO₂ while boundaries allow
exchange. Accept conditional results supported by extremes and the diagram.
The pair changes both opening and local geometry, so it does not separate those effects.

## What the model does not represent

An approximate compartment network, without molecular dynamics or full CFD.
Prepared percentages are not real nest measurements, safety references or
recommended animal-rearing conditions.

## Learning evidence

Submit a hypothesis, comparable records with days/units, a data-supported
conclusion and one limitation. Use the general guide’s rubric; there is no
required outcome.

## Teacher review

Pending. No teacher or class was consulted to approve this guide. Record review
and adjustments in the appropriate form before treating it as validated.