Support & Movement

All Cells Cellular Support System

cytoskeleton

Cytoskeleton

provides internal support; microtubule, actin microfilament, intermediate filament; allows cell movement; allows movement and positioning of internal materials and organelles; cytokinesis and movement of chromosomes; flagella and cilia

Microtubule

long, hallow, cylindrical protein filament; thickest; forms cytoskeleton; moves material within the cell

Actin Microfilament

gives cell shape, muscle contraction, thinnest, not hallow; near cell membrane/wall

Intermediate filament

not hollow; rope-like; resists tension/stretching; from one side of cell to the other side

Bacteria Cellular Support

cell membrane surrounded by peptidoglycan cell wall; provides external support; can be surrounded by an outer membrane

Archaea Cellular Support System

many use protein surface layer for support; some build cell wall of pseudo-peptidoglycan

Ancestral eurkaryotes support systems

no cell wall

Fungi Cellular Support System

secondarily evolve a cell wall; contains chitin that resists tension

Plant Cellular Support System

secondarily evolve a cell wall; contain cellulose that resists tension

Algae Cellular Support System

secondarily evolve cell walls; highly variable

Diatoms

planktonic unicellular brown algae, grow external support structures made of silicone; silicone shells of dead diatoms make up a large amount of marine sediment

Animal Cells Wall

do not have; cells can move

Hydrostat

any biological structure that uses internal fluid pressure for support, shape, or movement; support without regid structure

Adding fluid to tension resisting membrane surrounding fixed volume of space

pressurized volume of fluid pushed out; tension resisting membrane pushes in; → stiffens structure

Eukaryote cell membrane ____ elastic

is not

Plant Hydrostat

each cell bc cell walls resist tension (act as tension resisting membrane)

Animal Hydrostat

use tissues 

Tension resisting elements of plant cell wall

cellulose, hemicellulose, water

Cellulose

orange rods; strong support fibers; high tensile stiffness = resists being pulled

Hemicellulose

brown lines; cross-linking fibers; high elasticity = allows for energy storage with deformation

Water

surrounds fibers in apoplast; adhesion resists tensile pulling too

Central Vacuole

controls volume and pressure of fluid; usually large

Osmotic gradient

causes water to enter cell → increase pressure inside cell → pushes against cell wall → stiffens cell

True/False. Stiffness can be directional.

True

Orientation of cellulose fibers in cell wall

controls how cell deforms

Cellulose Fibers arranges in circular orientation

elongates (out)

Cellulose Fibers arranged in longitudinal orientation

left/right

Wilting

not enoguh water to inflate cells

Stomatal Guard Cells

open and close to control gas exchange and prevent water loss; depend on hydrostat pressure and fiber orientation

Tensino Resisting Elements of Animal Extra Cellular Matrix

collagen and elastin

Collagen

orange rods; most common protein in ECM; high tensile stiffness = resists being pulled

Elastin

brown lines; cross-linking fibers; high elasticity = allows for energy storage with deformation

Pressurized volume in animal hydrostats

gut, connective tissue with lots of water, body cavity

doesn’t allow expansion in any direction so causes a kink, failure is likely

spiral wound allows movement so less likely to fail

Muscle contractions can

increase pressure on volume (stiffen hydrostat) or apply force to hydrostat (deform or move hydrostat)

Sea Anemones Hydrostatic Support

to withstand forces of flow; contraction of muscles in column increase pressure on column tissue → stiffen body

Earth Worm Hydrostatic Locomotive

contractions elongates segments, pushing them forward; contraction of longitudinal muscles shortens segments, pulling trailing segments forward; alternating waves of muscle ocntraction

Muscular Hydrostat

muscle wrapped around muscle; highly flexible and deformable; strong; no need for rigid support

Tension Resisting Membrane in Muscular Hydrostat

circular muscle; muscle action and connective tissues

Pressurized Volume of fluid in Muscular Hydrostat

longitudinal muscle; muscle cells mostly in water

Contract circular muscle

hydrostat gets long and skinny; lengthens longitudinal muscles

Contract Longitudinal muscle

hydrostat gets short and wide; lengthens circular muscles

Contract circular and longitudinal muscle

muscles contract and bulge (increase pressure), push out against elastic membrane of circular muscles that are also contracting → stiffens hydrostat

examples of muscular hydrostats

octopus & squid tentacles; elephant trunks; most vertebrate tongues

Hydrostatic skeletons work great when

the organism is small and/or supported by water or some other external forces

Larger organisms on land with hydrostatic skeletons

body weight; increases regional tension concentrates force in smaller area; increase stress on body walls

Organisms need stiff structures to 

resist external loads

Hydrostats stiffen via

tension-resisting membrane; pressurized volume of fluid

Organisms need rigid structures to

support larger body weight; protect soft tissue

Composite materials

composed of different types of materials to resist different types of forces

Tension

resist pulling loads

compression

resist squishing loads

Rigid Structures

resist deformation; typically subject to bending loads & must resist tension and compression

Arrangement of materials in composite

controls how material resists different types of loads

Plant Rigid Support

Xylem

Plant Rigid Support Structure

parallel cylindrical columns; resist compression within tube as water is pulled upmaterials arranged far from neutral axis → resistant to bend; yearly growth adds tubes in parallel → increases strength

Plant Rigid Structure Material

composite cell walls; hemicellulose and cellulose hold things together; primary cell wall → cellulose; secondary cell wall → cellulose & lignin

Woody Plants Secondary Cell Wall

cellulose (resists tension) & lignin (resists compression)

Early Land Plants used

hydrostatic support; limited to small size and close proximity to water

Early Trees possible thanks to

evolution of specialized vascular tissues for support & transport

Animal Rigid Support

skeletons

Animal Rigid Support structure

highly variable morphologies; external → shells or exoskeletons; internal → ossicles or bones

Animal Rigid Support Materials

highly variable composites; tension resisting fibers and compression resisting minerals

External Shells as Skeletons Examples

mollusca (reduced/lost in some); brachiopoda

External Shells as Skeleton Materials

very rigid → brittle; secreted by ectodermal cells; mostly mineral; some proteins; arrange materials to ocntrol fialure/crack formation

Exoskeleton Structure

body is fully enclosed; limits movement → material thinner at joints; limits growth → ecdysis

Exoskeleton Material

stiffness varies with components; secreted by ectodermal cells; tensile: chitin fibers cross-linked by proteins; compression (minerals)

Ecdysis

molting; grow new exoskelton under old; pre-weakened regions → controlled failure; new exoskeleton not stiff; organisms needs to increase size, make protein crosslinks, add minerals; in between expanding and hardening, they make their body hydrostats

Ossicles Structure

grow within body wall surround body cavity and covered by soft tissue; size and number may vary

Ossicles as Skeletons Examples

echinodermata

Exoskeleton as Skeleton Example

arthropoda

Ossicles Material

connected by mutable connective tissue (MCT); formed by ectodermal cells

Ossicles

mineral crystals

Mutable connective tissue

specialized collagen, stiffness under active control

Bone Skeleton Structures

varies with function; long, cylindrical (materials arranged far from neutral axis → resistant to bending)

Bone as Skeleton Example

vertebrata

Bones as Skeleton Material

mineralized composite; formed by mesoderm and/or ectoderm; tensile (collagen fibers); compression (minerals- likely first evolved as chemical storage mechanism)

Metazoan Rigid Support

protection and movement; hydrostatic support and fossilized poorly

Protection in Metazoan Skeletons

prevent damage to soft tissues

Movement in Metazoan Skeletons

mucles can only shorten, need antagonist to lengthen; rigid structures act as levers to change muscle output

How do rigid structures act as levers?

transmit force from one point to another; translate output from force to movement; transform direction of force

Cambrian Explosion

result of increased fossilization of rigid support