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2.8.6Inquiry Process

Locomotion in Organisms — IB Biology HL Revision Notes & Topical Questions

5 min read 4 parts Lesson 91 of 160

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Part 1 of 4Swimming and Flying

2.8.6 Locomotion in Organisms
Fish swimming
  • Streamlined bodies, blocks of muscle (myotomes) on each side and a flexible backbone produce side-to-side waves that push against the water.
Buoyancy in fish
  • Many bony fish have a swim bladder whose gas content can be adjusted to control depth.
Bird flight
  • Wings with feathers form an aerofoil, and large flight muscles attach to a keeled breastbone.
Light skeleton
  • Birds have hollow bones and a lightweight body, which lowers the weight lifted in flight.
FeatureFishBird
MediumWaterAir
Main musclesMyotomesPectoral muscles
Key adaptationStreamlined bodyWings, light bones

Part 2 of 4Walking, Running and Burrowing

Walking, Running and Burrowing
Human walking
  • An upright posture on two legs, with strong leg muscles and a spine curved to balance the trunk over the hips.
Running quadrupeds
  • Long limbs and powerful muscles at the top of the limb increase stride length and speed.
Earthworm
  • A hydrostatic skeleton in which circular and longitudinal muscles contract in turn, so segments lengthen or shorten.
Chaetae
  • Bristles on earthworm segments anchor the body to soil during movement.

Part 3 of 4Earthworm Movement Step by Step

1
Circular muscles contract at the front segments, making them long and thin and pushing the front forwards.
2
Chaetae at the back segments grip the soil and prevent slipping backwards.
3
Longitudinal muscles then contract in the front part, making it short and fat and anchoring it.
4
The rear chaetae release and the back segments are pulled forward.
5
A repeating wave of contraction, called peristalsis, moves along the body and carries the worm forward.

Part 4 of 4Exam Checklist & Tips

2.8.6 – Key Points for the Exam

  • Locomotion Movement of an organism from one place to another.
  • Myotome A block of muscle on each side of a fish body that bends the body.
  • Aerofoil A shape that generates lift when air flows over it.
  • Peristalsis A wave of alternating muscle contraction and relaxation that moves along a body or tube.

Common Mistakes

  • Saying the earthworm has no skeleton; it has a hydrostatic skeleton.
  • Stating that muscles move fish fins only; the body wave provides most of the thrust.
  • Describing bird bones as empty tubes;
    • they are lightweight and air-filled but strengthened by internal struts.
  • Forgetting to link each feature to how it helps locomotion.

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Physics 0625 & 9702 SUVAT Mastery Graph Interpretation

Constant Acceleration Equations (SUVAT) & Slopes

v = u + at  |  s = ut + ½at2  |  v2 = u2 + 2as  |  s = ½(u + v)t

  • Displacement-Time Graph: Gradient = Velocity (curve = accelerating).
  • Velocity-Time Graph: Gradient = Acceleration; Area under curve = Distance travelled / Displacement.
  • Free Fall in vacuum: a = g ≈ 9.81 m/s2 downwards (air resistance negligible).