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Chapter 29: Animal movement

29-2Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University

Locomotion as a key to animal life• All animals move at some stage in their life cycle

– example: sponges are sessile as adults but have motile larvae

• Locomotion requires the exertion of force on the surrounding environment– land, air, water

• Two categories– muscular– non-muscular (cilia, flagella)

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Living in water• Buoyancy

– tendency for an object to float– interaction between upthrust () and gravity ()

• Positive buoyancy– object rises ( > )

• Negative buoyancy– object sinks ( < )

• Neutral buoyancy– object remains in position ( = )

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Positive and negative buoyancy• Positive buoyancy

– overall density of organism lower than that of water– example: Physalia with gas-filled float

• Negative buoyancy – overall density of organism greater than that of water– example: benthic organisms

• Both require organisms to expend energy to remain at a constant depth– not rise or sink

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Neutral buoyancy• Neutrally buoyant organisms have an overall

density the same as that of water• Neutrally buoyant animals have mechanisms for

changing overall body density• Reduces the energy expenditure associated with

maintaining vertical position

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Neutral buoyancy (cont.)• Gas-filled structures

– Nautilus shell chambers– fish swim bladders

• Gases can be excreted or secreted to allow animal to vary buoyancy

• Some sharks have high levels of lipid in liver to reduce overall density– slight negative buoyancy

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Fig. 29.1: Nautilus(a)

(b)

Copyright © Mike Tinsley/AUSCAPE

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Non-muscular locomotion• Cilia and flagella only effective in small organisms

– protists– many invertebrate larvae

• Extensions of cytoplasm exert force on water– multiple cilia– one flagellum or several flagella

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Fig. 29.2: Beating of a cilium

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Muscular locomotion• Jet propulsion

– expelling water to push animals in opposite direction

• Rowing – moving forelimbs backwards and forwards in oar-like

movements

• Body undulations– trunk muscles and tail fin used to propel animal

• Underwater flying– flapping forelimbs in flight movements

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Travelling through air• Flying animals use

– unpowered flight little energy expenditure gliding parachuting

– powered flight substantial energy expenditure muscle-powered flapping

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Unpowered (gliding) flight• Gliding animals extend body surface to increase lift• Force of lift depends on

– speed of flight– size of wing (aerofoil)– shape of wing– tilt (angle of attack) of wing

• Gliding requires minimal energy expenditure– maintenance of posture

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Gliding• Most gliding animals can alter shape of gliding

surface to modify performance– speed decreased for landing– speed increased in intercepting prey

• Soaring is employed by birds that use powered flight – gliding on thermals rising from warm land

• Slope soaring– soaring in wind rising along a slope, so bird remains

stationary relative to ground

Fig. 29.10: Hovering

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Fig. 29.11: Gliding

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Powered flight• Requires significant energy expenditure to flap

wings– but more efficient than terrestrial locomotion

• Downstroke acts against air to provide lift and thrust– wing fully extended to maximise lift and thrust

• Some birds and bats hover by producing lift on downstroke and upstroke– high energy expenditure– hovering restricted to small animals

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Moving on land• Techniques for terrestrial locomotion are varied

– without legs (protists, soft-bodied invertebrates) amoeboid locomotion peristalsis pedal waves

– with legs (invertebrates, vertebrates) crawling walking jumping

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Locomotion without legs• Amoeboid movement

– single-celled organisms extend finger-like pseudopodia over substrate

• Peristalsis– segmented worms typically use peristalsis to crawl and

burrow– interaction of muscles and hydrostatic fluid change shape

of segments

• Pedal waves– waves of muscular contraction on underside of snail’s

foot

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Locomotion with legs• Legs raise body off ground to decrease amount of

body in contact with ground• Reduced contact decreases stability• Stability increased by

– lower centre of mass– increased area of contact (larger feet, more limbs)– larger area enclosed by contact points

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Walking and running• Animals change gaits at different speeds

– example: horses walk trot gallop

• Energy expenditure increases with increasing speed

• Within each gait there is a speed at which energetic cost is minimal

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Jumping• Kangaroos use pentapedal (four limbs + tail)

locomotion at low speeds• Hopping is more efficient than pentapedal

locomotion at higher speeds

Fig. 29.12: Metabolic costs of transport

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Skeletons• Skeletons provide

– support for muscles– support against gravity

• Types of skeletons– hydrostatic

fluid-filled

– exoskeleton rigid, external

– endoskeleton rigid, internal

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Hydrostatic skeletons• Soft-bodied animals (deformable body wall)• Fluid-filled body cavity• Action of muscles shunts water around one or

more cavities, changing shape of body• Body capable of extension and contraction

– example: annelid (segmented) worms

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Exoskeletons• External skeleton of chitin (+ minerals in some

species)• Thick and rigid plates (sclerites), thin and flexible

between plates• Muscles attached to inside of skeleton• Must be moulted periodically to allow growth

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Endoskeletons• Internal skeleton of cartilage and/or bone

– bone can be remodelled to accommodate changed loads– increases in mass in response to increased loads– decreases in mass in response to decreased loads

• Muscles attached to outside of skeleton• Endoskeleton grows with the organism

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Joints• Exoskeletons and endoskeletons both have rigid

components• Joints allow flexibility between the components

– muscle produces force– bones or other skeletal elements act as levers

• Joints can be classified by degree of mobility– sutures are fixed and immovable (e.g. skull)– slightly movable joints (e.g. intervertebral discs)– freely movable joints (e.g. elbows, shoulders)

Fig. 29.20: Joint structure

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Muscle structure• Skeletal muscle cells (fibres) are cylindrical,

multinucleate and have a striated (striped) appearance– striations due to arrangement of actin and myosin

filaments in sarcomeres

• Infoldings of sarcolemma (muscle fibre plasma membrane) ramify through fibre– transverse (T) tubule system

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Fig. 29.22a: TEM of mammalian skeletal muscle

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How skeletal muscle works• Mechanism of skeletal muscle contraction is

explained by the sliding filament model• Actin filaments slide relative to myosin filaments

– draw Z-discs towards centre– shorten sarcomere– muscle contracts

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Sliding filaments• When resting, myosin heads are unable to form

cross-bridges with actin• Myosin binding sites blocked by tropomyosin• When an action potential depolarises sarcoplasmic

reticulum, Ca2+ binds to troponin-tropomyosin complex, exposing myosin binding sites

• Myosin binds to actin filament

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Sliding filaments (cont.)• Change in shape of myosin head draws actin

filament towards centre of sarcomere• Binding of ATP to myosin head causes it to detach

and return to ‘primed’ state• It reattaches at another binding site further along

actin filament

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Fig. 29.24 (top): Mechanism of muscle contraction

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Fig. 29.24 (bottom): Mechanism of muscle contraction (cont.)

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Skeletal muscle fibre types• Type I fibres

– slow oxidative or slow-twitch fibres

• Type IIA fibres– fast-oxidative or fast-twitch, fatigue-resistant fibres

• Type IIB fibres– fast glycolytic or fast-twitch, fatigable fibres

• Type IIX fibres– intermediate between IIA and IIB

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Slow- and fast-twitch fibres• Force-production of characteristics of a fibre in

response to stimulation• Fast twitch fibres

– contraction lasts about 10 ms

• Slow-twitch fibres– contraction lasts about 100 ms

• Distribution of muscle types depends on function of muscle– Type I (slow-twitch) fibres in postural muscles– Type IIB (fast-twitch) fibres in arms and shoulders

Summary• Various forms of locomotion have evolved in

animals• Aquatic locomotion is achieved by an animal

exerting a force on the surrounding water • All types of flight employ some type of aerofoil of

which its size, shape and orientation determine performance

• Support and stability are important for animals whose bodies are raised off the ground

• Movement requires muscles to work against skeletons

29-38Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University