Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 326–340 of the course textbook. Image credits are on slide 16.
All organisms move. Motile organisms, such as whales, move from place to place. Sessile organisms, such as barnacles and corals, stay fixed but move parts of their bodies to feed, and often have motile larvae.
Animals move to forage (bees collecting nectar), escape danger (impala fleeing lions), find a mate (male moths following scent) and migrate (humpback whales moving between feeding and breeding waters).
Myofibrils are chains of sarcomeres with thick myosin and thin actin filaments. Calcium ions bind troponin, moving tropomyosin to expose binding sites on actin. Myosin heads bind, swivel and pull actin towards the centre; ATP breaks each cross-bridge and re-cocks the head. Sarcomeres shorten while the filaments stay the same length.
Muscles only exert force when they contract, so they work in antagonistic pairs, each stretching the other. The huge protein titin stores energy when stretched, helps the sarcomere recoil and prevents overstretching.
A motor unit is one motor neuron and all the muscle fibres it controls, connected at neuromuscular junctions. All fibres in a unit contract together. Small units give fine control; using more units gives more force.
The external and internal intercostal muscles have fibres running in different directions, so they move the ribcage in opposite directions. When one layer contracts it stretches the other, storing energy in its titin.
Arthropods have an exoskeleton, with muscles attached inside; vertebrates have an endoskeleton, with muscles attached to bones by tendons. Bones act as levers, with the joint as the pivot.
At the hip, the head of the femur fits a socket in the pelvis. Cartilage reduces friction, synovial fluid lubricates, ligaments join bone to bone, and muscles pull on the bones through tendons.
Ball-and-socket joints (hip, shoulder) move in three planes; hinge joints (knee, elbow) move mainly in one. Range of motion can be measured with a goniometer and is affected by training, age and injury.
Whales and dolphins have a streamlined body, forelimbs modified as flippers, a tail fluke moved up and down, and a blowhole with an airway separate from the gut, so they can breathe at the surface between dives.
Select a video to play it here. Select it again to close it.
Print this guide and complete it as you work through the slides and videos. It asks for your own explanations, so close the notes while you try each section.
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A printable worksheet covering all ten statements, from quick recall to data questions and a longer answer. It has 40 marks and takes about 40 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
You will need: Large protractor or goniometer, or a phone angle app, results table
Safety: Volunteers only. Move gently and stop at any discomfort.
Carry this out with your teacher's supervision and follow your school's lab rules.
In 1954 two independent teams, led by Andrew Huxley and Hugh Huxley, published the sliding filament idea together.
Two teams reached the same idea at the same time. Consider what this suggests about how knowledge develops.
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
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