Biomechanics

Question 1

How do some metazoans (e.g. turbellarians and gastropods) move?

Answer 1

Propulsive forces are generated by the movement of cellular organelles (cilia).

Question 2

What are two examples of the persistence of flagellae in metazoans?

Answer 2

Choanocytes and spermatozoa.

Question 3

What is an example of amoeboid activity in various cell types?

Answer 3

Phagocytic blood cells.

Question 4

How are most forces generated in metazoans?

Answer 4

By contraction forces, shortening of specific muscles or muscle layers.

Question 5

What are cilia and flagella formed of?

Answer 5

A cylindrical array of 9 filaments within which a complete microtubule extends to the tip of the cilium and a partial microtubule that does not extend as far into the tip. Cross-bridges of the motor protein dynein extend form the complete microtubule of one filament to the partial microtubule of the adjacent filament.

Question 6

What is the ‘9+2’ arrangement?

Answer 6

The arrangement in cilia where a pair of single microtubules run through the centre of a bundle of 9 long and short microtubules.

Question 7

What are cilia encased in?

Answer 7

A membrane that is an extension of the plasma membrane.

Question 8

What are the similarities between the sliding filament model and the sliding microtubules of cilia?

Answer 8

Both are powered by ATP.
Dyein (like myosin) is the ATPase.
Both are regulated by calcium ions.

Question 9

How do metazoan muscles work?

Answer 9

They are powered by ATP. Usually they act on some type of skeleton.

Question 10

What do muscles attach to in vertebrates?

Answer 10

They attach to and work in conjunction with a bony internal skeleton.

Question 11

What do muscles attach to in hard-bodied invertebrates?

Answer 11

A rigid exoskeleton.

Question 12

What do muscles attach to in soft-bodied invertebrates?

Answer 12

Muscle layers act on a hydrostatic skeleton (fluid-filled body compartment). The segmentation in annelids acts like boiler stays, allowing the musculature to exert much greater pressure.

Question 13

What are the different ways of swimming?

Answer 13

Cilia and flagellae propelled (protozoa, macroalgal gametes, larvae & some meiofauna).
Wave-like undulations (worms.
Fluid propulsion (medusoid coelenterates, cephalopods and pectinid bivalves)
Flattened appendages (decapod crustaceans, fish, cetaceans & pinnipeds.)

Question 14

What are the types of movement on or in a substratum?

Answer 14

Amoeboid
Ciliary creeping & gliding (platyhelminthes and molluscs)
Peristaltic waves (annelids, echiurans, sipunculans & molluscs)
Looping (hirudinea & rotifers)
Walking (polychaetes & echinoderms)
Running (arthropods)
Jumping (crustaceans & gastropods)
Burrowing (nemerteans, annelids, sipunculans & echiurans.)

Question 15

How do unicellular organisms move?

Answer 15

By changing shape using sliding elements in the cytoskeleton, e.g. amoebae crawling using psuedopodia, or swim using cilia/flagellae.

Question 16

How do organisms combine functionality of locomotion?

Answer 16

Some crustaceans use rhythmic motion of thoracic appendages for walking and gas exchange.

Question 17

Where is convergent evolution seen in locomotion?

Answer 17

Undulatory (sinusoidal) swimming is seen in certain nematode worms as well as marine polychaetes.

Question 18

What forces effect movement in water?

Answer 18

Inertial forces must be overcome to start movement. To continue, friction, drag and gravity must be overcome.

Question 19

How is the relative importance of the forces decided?

Answer 19

By size of the animal - this scales the effects.

Question 20

What are the most important constraints in terms of movement in water?

Answer 20

The two main forms of drag - viscous and pressure.

Question 21

How are drag effects quantified?

Answer 21

Using Reynolds number (Re.) Re =Vo.Lx(p/u) where Vo = incident velocity, Lx = foil length, p = density and u = viscosity.

Question 22

How do high (>200,000) Re numbers affect organisms?

Answer 22

They tend to be larger and faster moving and create turbulent flows in their wakes, which produces low pressure that tends to hold them back - pressure drag. This can be reduced by streamlining –> the classic fusiform shape.

Question 23

What flow occurs at low Re numbers, and what forces are dominant?

Answer 23

Laminar flow, where viscous drag/forces are dominant. Characterised by smooth, constant fluid motion.

Question 24

What flow occurs at high Re numbers, and what forces are dominant?

Answer 24

Turbulent flow, where pressure drag/inertia forces are dominant. They then to produce chaotic eddies, vortices and other flow instabilities.

Question 25

What is Gray’s paradox?

Answer 25

Sir James Gray calculated that the apparent power output of fast-swimming fish and cetaceans was insufficient for them to swim at the fast speeds that were observed in vivo. It was later shown that there was an error in his calculations.

Question 26

How does the skin of cetaceans reduce drag?

Answer 26

The compliance and wrinkling of their skin delays water flowing over it, reducing drag and turbulence.

Question 27

What is frictional drag?

Answer 27

The most important source of drag in fast-swimming fish e.g. sharks. It is caused by the friction created by the skin and the boundary layer. This type of drag can be reduces if the boundary layer maintains a turbulent flow.

Question 28

How do sharks reduce frictional drag?

Answer 28

They reduce it by inducing turbulence at innumerable sharp edges. All fast swimming sharks have sharp-edged riblets on their skin created by their denticles.

Question 29

What are the three types of movement through sediment?

Answer 29

Hard-bodied ‘Diggers’, e.g. crustaceans, echinoids. Soft-bodied ‘burrowers’ e.g coelenterates, molluscs and veriform taxa. Also, specialised ‘drillers’ able to bore through soft rock and wood.

Question 30

How do barnacles adhere so firmly to their substrate?

Answer 30

The shape and ribbing of the base plate increases the adhesion of a protein glue that is coded for the same gene as mammalian blood clotting Factor XIII.

Question 31

What is dynein and what does it do?

Answer 31

It is the contractile protein that links microtubules in cilia and uses ATP to produce bending of the cilium/flagellum.

Question 32

What are pseudopodia and where are they found in metazoa?

Answer 32

They are extensions of cells that have amoeboid locomotion, such as phagocytic blood cells.

Question 33

Name three types of skeleton.

Answer 33

Exo- and endo-skeletons and hydrostatic skeletons.

Question 34

What does Reynolds’ number describe?

Answer 34

Drag effects on the fluid flow over an animal. Low Re = laminar flow, high Re = turbulent flow.

Question 35

What links barnacle glue to blood clotting in mammals?

Answer 35

It is coded for by the same gene that is associated with Factor XIII.