Models Under Pressure

Overview

In lesson 2 of Skeletons: Structure in Action, students investigate how endoskeletons, exoskeletons, and hydroskeletons respond to force, weight, compression, bending, and pressure. They use simple models to collect evidence, consider fair-test conditions, and connect skeleton structure with survival in environments such as the deep sea.

Learning intentions

• WALT investigate how different skeletal frameworks respond to force, weight, and pressure.
• WALT carry out a safe, fair practical test and record observations as evidence.
• WALT compare advantages and disadvantages of endoskeletons, exoskeletons, and hydroskeletons.
• WALT connect deep-sea pressure with structural adaptations that prevent collapse.

Success criteria

• I can safely carry out a test and explain what was changed and measured.
• I can record clear observations in a shared results table.
• I can describe at least one advantage and disadvantage of each skeleton type.
• I can connect a deep-sea adaptation to the problem of increasing pressure.

Curriculum links

• Science — Biological Science: investigating how muscles and bones interact and how body structures provide support and protection.
• Science — Fluids and pressure: using models or demonstrations to interpret how pressure in fluids changes with depth, including sea pressure.
• Science — Body Systems: recognising that multicellular organisms require transport and support systems suited to their size and complexity.
• Nature of Science and the capabilities of Thinking, Managing self, and Participating and contributing.

Lesson structure (50 minutes)

1. 0–5 min · Brain starter and hook. Teacher displays a striking image of a giant wētā and a deep-sea animal using the opening image and pressure question, then leads a quick “opposite actions” brain break: students copy movements only when the teacher says “pressure”, not “release”. Students predict: “Which skeleton would cope best with a heavy load?” and briefly justify their choice to a partner.

2. 5–12 min · Build the model. Teacher introduces the three model types using the skeleton model comparison slides: a bundle of straws or craft sticks for an endoskeleton, a paper cup/card shell for an exoskeleton, and a sealed flexible bag or balloon partly filled with water for a hydroskeleton. Explain that models simplify real organisms and are useful when we state their limits. Assign groups of three roles: equipment manager, tester, and recorder/reporter. Students examine or assemble their group’s models and identify the force being tested.

3. 12–29 min · Practical pressure challenges. Teacher demonstrates safe testing and distributes the skeleton investigation recording sheet. Groups rotate through compression, bending, load, and flexibility challenges, using one model at a time where equipment allows. They record what happened rather than simply ranking models; suitable tests include adding identical masses, pressing gently between books, bending a strip through a marked angle, or observing how a fluid-filled model changes shape. Students keep the starting size, force, time, and number of attempts as consistent as possible, stop if a model leaks or breaks, and add observations to the shared class results table.

4. 29–35 min · Fair-test check. Teacher pauses the practical and asks groups to compare methods using the fair-test prompts: What was changed? What was measured or observed? What should stay the same? Students orally complete the sentence frame, “Our test was fairer because we kept ___ the same,” and identify one limitation, such as different amounts of water, uneven force, or models made from different materials.

5. 35–43 min · Wētā and deep-sea connection. Teacher presents the Giant Wētā’s moulting dilemma on the wētā dilemma and deep-sea demonstration slides: an exoskeleton protects and supports the animal but must be shed for growth, leaving the animal vulnerable while the new one hardens. Demonstrate increasing water pressure by placing an upside-down, air-filled cup or sealed container in a deep tub and pressing it down gradually; discuss that pressure increases with depth. Students read the short, chunked deep-sea text on the worksheet, or listen while following the text, and identify adaptations such as flexible bodies, reduced gas spaces, and strong internal tissues that help prevent collapse.

6. 43–50 min · Compare, share, and exit check. Teacher asks each group to contribute one evidence-based point to a class pros-and-cons matrix, then uses the comparison and exit-question slides to revisit the opening prediction. Students complete the final worksheet prompts: one advantage and one disadvantage for each skeleton type, plus “A deep-sea adaptation helps because…”. Invite two students to share different conclusions and collect the sheets for assessment.

Resources

• the Models Under Pressure slide deck
• the skeleton investigation recording sheet
• Simple endoskeleton models: straws, craft sticks, tape, or pipe cleaners
• Exoskeleton models: paper cups, card, cardboard tubes, and tape
• Hydroskeleton models: sealable bags or balloons, water, and trays
• Identical small masses, books, rulers, elastic bands, and tubs
• Shared results table on the board or digital display
• Safety glasses, towels, and waste container

Assessment

• Question groups during testing: “What is your evidence?” and “What variable are you controlling?” Check whether observations are specific and linked to the force applied.
• Review the class results table and pros-and-cons matrix for accurate comparisons rather than unsupported claims.
• Use the completed worksheet as an exit assessment, looking for a safe-testing decision, three skeleton comparisons, and a correct pressure–adaptation connection.

Differentiation

• Offer pre-built models and allow students to handle and test rather than construct; provide step-by-step visual instructions and assign clear practical roles.
• Use vocabulary cards for endoskeleton, exoskeleton, hydroskeleton, compression, pressure, depth, adaptation, and moulting. Provide sentence starters such as “The model changed when…” and “One advantage is…”.
• Provide the deep-sea reading in short chunks with large, dyslexia-friendly text, uncluttered spacing, and the option to listen while following. Accept labelled diagrams, oral explanations, or scribed responses.
• Confer orally with students who need support, pair students strategically, and use trays and towels to manage water safely. Extension students design a fairer investigation or predict how changing fluid pressure, shell thickness, or support points would affect results, explaining their reasoning.

Extension

• Design a follow-up investigation with one independent variable, one measured outcome, and at least three controlled variables.
• Predict and justify how increased fluid pressure, a thicker shell, or changed support points would alter a model’s performance.