Skeletal systems and movement — A/L Biology

What must I remember about Skeletal systems and movement?

• Supporting systems in animals provide mechanical body support, maintain shape, protect vital organs, and serve as rigid anchor points for muscle attachment to enable locomotion.
• Three major skeletal architectures across Animalia: Hydrostatic skeletons (fluid enclosed under pressure in gastrovascular or coelomic cavities, e.g., Cnidaria, Annelida, Nematoda), Exoskeletons (hard external encasements, e.g., chitinous arthropod cuticle, calcium carbonate mollusk shells), and Endoskeletons (internal rigid frameworks, e.g., echinoderm calcareous ossicles, chordate cartilage and bone).
• Hydrostatic locomotion: Annelids (earthworms) use peristalsis powered by alternating contractions of circular muscles (elongates segments) and longitudinal muscles (shortens/widens segments) acting against incompressible coelomic fluid with chaetae for anchorage.
• Exoskeleton properties: Chitin-protein complex with cuticle sclerotization protects against mechanical trauma and terrestrial desiccation, but limits continuous body growth, necessitating periodic ecdysis (molting) controlled by ecdysone.
• Endoskeleton advantages: Bone and cartilage grow continuously with animal body without requiring vulnerable molting periods, supporting large body mass against gravity while serving as calcium/phosphate reservoirs and housing hematopoiesis.

Test yourself (1 minute)

1. Cartilage vs Bone

   Cartilage is non-vascularized, flexible connective tissue composed of chondrocytes in chondroitin sulfate matrix; Bone is highly vascularized, rigid tissue with osteocytes in mineralized hydroxyapatite (calcium phosphate) and collagen matrix arranged in osteons (Haversian systems).

2. Ecdysis vulnerability

   Immediately after molting, arthropods have soft, unsclerotized cuticles, rendering them highly vulnerable to predators and mechanical damage until tanning hardens the new exoskeleton.

3. Bone remodeling cellular triad

   Osteoblasts synthesize and mineralize new bone matrix; Osteocytes maintain mature bone tissue; Osteoclasts (multinucleated macrophages) resorb/dissolve bone during remodeling and calcium regulation.

Practise Skeletal systems and movement questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 5

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Where does Skeletal systems and movement fit in the syllabus?

Year 2 · Term 1