AHL Content Statements

• B3.3.1

  Adaptations for movement as a universal feature of living organisms
  

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  Students should explore the concept of movement by considering a range of organisms including one motile and one sessile species.
  

• B3.3.2

  Sliding filament model of muscle contraction

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  Students should understand how a sarcomere contracts by the sliding of actin and myosin filaments.
  

• B3.3.3

  Role of the protein titin and antagonistic muscles in muscle relaxation

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  The immense protein titin helps sarcomeres to recoil after stretching and also prevents overstretching. Antagonistic muscles are needed because muscle tissue can only exert force when it contracts.
  

• B3.3.4

  Structure and function of motor units in skeletal muscle

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  Include the motor neuron, muscle fibres and the neuromuscular junctions that connect them.
  

• B3.3.5

  Roles of skeletons as anchorage for muscles and as levers

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  Students should appreciate that arthropods have exoskeletons and vertebrates have endoskeletons.
  

• B3.3.6

  Movement at a synovial joint

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  Include the roles of bones, cartilage, synovial fluid, ligaments, muscles and tendons. Use the human hip joint as an example. Students are not required to name muscles and ligaments, but they should be able to name the femur and pelvis.
  

• B3.3.7

  Range of motion of a joint

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  AOS: Students should compare the range of motion of a joint in a number of dimensions. Students should measure joint angles using computer analysis of images or a goniometer.
  

• B3.3.8

  Internal and external intercostal muscles as an example of antagonistic muscle action to facilitate internal body movements

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  Students should appreciate that the different orientations of muscle fibres in the internal and external layers of intercostal muscles mean that they move the ribcage in opposite directions and that, when one of these layers contracts, it stretches the other, storing potential energy in the sarcomere protein titin.
  

• B3.3.9

  Reasons for locomotion
  

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  Include foraging for food, escaping from danger, searching for a mate and migration, with at least one example of each.
  

• B3.3.10

  Adaptations for swimming in marine mammals
  

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  Include streamlining, adaptation of limbs to form flippers and of the tail to form a fluke with up-and-down movement, and changes to the airways to allow periodic breathing between dives.
  

• B2.3.9

  Adaptations of cardiac muscle cells and striated muscle fibres

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  Include the presence of contractile myofibrils in both muscle types and hypotheses for these differences: branching (branched or unbranched), and length and numbers of nuclei. Also include a discussion of whether a striated muscle fibre is a cell.