B3.3 Muscle and motility

Question 1

B3.3.1—Adaptations for movement as a universal feature of living organisms

Answer 1

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

Question 2

B3.3.2—Sliding filament model of muscle contraction

Answer 2

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

Question 3

B3.3.3—Role of the protein titin and antagonistic muscles in muscle relaxation

Answer 3

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.

Question 4

B3.3.4—Structure and function of motor units in skeletal muscle

Answer 4

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

Question 5

B3.3.5—Roles of skeletons as anchorage for muscles and as levers

Answer 5

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

Question 6

B3.3.6—Movement at a synovial joint

Answer 6

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.

Question 7

B3.3.7—Range of motion of a joint

Answer 7

Application of skills: 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

Question 8

B3.3.8—Internal and external intercostal muscles as an example of antagonistic muscle action to facilitate
internal body movements

Answer 8

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.

Question 9

B3.3.9—Reasons for locomotion

Answer 9

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

Question 10

B3.3.10—Adaptations for swimming in marine mammals

Answer 10

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.