Support

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Support Movement Chap. 49 (2nd half)
I. Introduction to Skeletons
A. The problem of support in animals
1. Cell membranes lack rigidity - no cell walls
2. Life evolved in water
a. Specific gravity (density) of H20 1.0
b. Specific gravity of cells 1.02 to 1.08
c. Hence aquatic animals are essentially
weightless
d. Water supports body parts
e.g., gill filaments of fish dispersed in water,
not sticky
jellyfish tentacles as long as 3 m (jellyfish in
water becomes a blob on the beach)
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B. Plants
1. Cell walls of cellulose (impregnated w/
lignin in woody plants)
2. High turgor pressure (osmotic pressure)
3. Aquatic plants no other internal
support submerged aquatic grasses, kelp (40 ft
long) and other algae
C. Terrestrial Organisms
1. Specific gravity of air 0.075 (cf. 1.0)
2. Hence force of gravity is much greater on
terrestrial organisms
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Kelp Forest
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D. Functions of skeletons
1. Support and shape
2. Protection
a. mechanical braincase protecting soft brain
tissue
b. osmotic - bony scales, etc.
3. Movement Locomotion
a. attachment anchor points of muscles
b. mechanical levers
4. Mineral (calcium and phosphorus) homeostasis
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Figure 49.29 Posture helps support large land
vertebrates, such as bears, deer, moose, and
cheetahs
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II. Kinds of Skeletons
A. Cytoskeleton (REVIEW pp 126-132)
A meshwork of fibers gives form esp. to
animal cells determines position of
organelles within cell mechanisms of
motility and internal movement (cytoplasmic
streaming, cilia, flagella, myosin arms)
1. Microtubules
2. Microfilaments
3. Intermediate filaments
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B. Plant Cell Walls Fig 35.10, 11- pp. 727-28
1. Primary cell wall
a. usually thin and relatively flexible
b. microfibrils - chains of cellulose
(carbopolymer)
c. matrix (framework) of pectins and
hemicellulose
2. Secondary cell wall major component of wood
a. Much thicker than primary wall - layered
b. inside primary wall
c. wall matrix with lignin (another complex
carbopolymer)
d. 2 wall in growing xylem is in a spiral ring
that stretches with cell elongation
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3. Cell types - cell wall structure - See in lab
Fig 35.11
a. parenchyma and collenchyma usually lack 2
wall or partial thickening
b. sclerenchyma - xylem
1) 2 wall with much lignin present
2) two kinds of sclerenchyma cells are
sclereids - short, irregular in shape stone
cells
fiber cells - long, often dead (lack protoplast),
major support function
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C. Hydrostatic Skeletons

• Cell hydrostatic (turgor) pressure a major aspect
  of support in
• non-woody plants. (Wilting is loss of
  turgor pressure and hence of support)

2. Mainenance and control of turgor pressure
a. Osmotic gradient - plant cells, small aquatic
animals, vertebrate notochord
b. Muscular constriction - circular or diagonal
muscles act on fluid-filled compartments -
e.g., earthworm
c. Hemostatic (blood) pressure
blood pressure coupled w/ vascular shunting
varies turgor pressure for size and shape of an
organ

• e.g., chameleons tongue, mammalian penis,
• jumping spiders (leg extension by turgor pressure
  only)

3. Tight epithelia - cell junctions less leaky
than is typical
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4. Examples of hydrostatic skeletons
a. Non-woody parts of most terrestrial plants
wilting results from a loss of turgor pressure
b. earthworm
compartmentalized coelom (body cavity)
longitudinal muscles shorten segments
circular muscles constrict and elongate segments
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Figure 49.27 Peristaltic locomotion in an
earthworm
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no extensor muscles in legs
c. jumping spiders
rapid blood pressure increase effects a rapid leg
extension
d. Foot of clams push through mud or sand
e. Miscellaneous mammalian erectile organs
penis
tongues of several nectar- or ant-eaters
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D. Exoskeletons
1. CaCO3 - mollusks
1. secreted in increments by integument (mantle)
2. connected by adductor muscles in bivalves
3. conchiolin a protein layer on outer surface
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2. Arthropod Integument (epidermis cuticle)
1. living epidermis secretes non-living layers
2. cuticle
a. composition
chitin (polysaccharide) 30-50
Bound together as protein -- glycoprotein
b. layers (from outside to inside)
epicuticle - waxy, minimizes water loss or gain
exocuticle - protein cross-links (tanned) by
quinones and phenols impregnated by CaCO3 in
crabs and lobsters
endocuticle
cellular epidermis
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3. Molting - animal imprisoned inside
unexpandable cuticle
a. molt cued by and permits growth see.
Fig. 5.9, p. 68
b. fixed number of molts in some animals -
insect larvae, roundworms
c. molt initiated by hormone ecdysone
d. enzymes secreted into fluid zone at epidermal
surface
e. untanned edocuticle is digested exocuticle
decalcified
f. new cuticle is secreted

• old cuticle splits animal crawls out leaving a
  replica of body surface
• - cicada molt horseshoe crab

h. body expands by hydration
i. new cuticle hardens, tans, calcifies
j. as growth occurs new tissue replaces water
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