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B3.3.1 (HL)—Movement adaptations

Movement in organisms ranges from cellular locomotion by cilia or flagella to whole-body movement for feeding, escape, migration and reproduction.

Syllabus
First assessment 2025
Objective
B3.3.1
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2013
Most common paperPaper3
Typical marks2

Scoring notes

Common mistake
Confusing movement of cells or body parts with whole-organism locomotion.

Recent exam appearances

May 2013Paper3 ["HL"] · TZ1F2(c)[ 2 ]B3.3.1 (HL)—Movement adaptations

Coverage 2013–2013 · Updated 15 Jul 2026

Movement Does Not Always Mean Locomotion

HL only

Movement changes position or shape; locomotion moves the whole organism from one place to another. A sessile organism remains attached yet may move body parts or grow directionally.

A side-by-side visual showing a motile animal moving its whole body and a sessile organism still showing local movement or growth toward a stimulus.

Locomotion can improve access to food, escape from predators, mate finding and migration. The benefit must outweigh its metabolic cost and exposure to risk.

Summary: From Molecular Pull to Locomotion

HL only

motor signal → ACh → muscle action potential → SR Ca²⁺ → exposed actin sites → cross-bridge cycling → sarcomere shortening → tendon tension → joint rotation

ATP detaches and re-cocks myosin; Ca²⁺ reuptake stops new bridges; titin restores passive sarcomere length, while antagonistic muscle action reverses joint movement. Whole-body form then determines whether force becomes efficient locomotion.

Movement adaptations

HL only

[ 2 ]

Microscopic eukaryotes include Euglena and Paramecium. Outline the range of cellular structures used for locomotion in these organisms.

Concept essentials

  • Euglena use a flagellum for locomotion.
  • Paramecium use cilia for locomotion.
  • Locomotion means movement of an organism from place to place.
  • Movement can support feeding, escape, migration and reproduction.