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ZOOLOGY FINAL UNIT 5.1-5.2 QUESTIONS AND ANSWERS
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ZOOLOGY FINAL UNIT 5.1-5.2 QUESTIONS ANDANSWERS
1) List four functions of the integumentary system. - Answers- 1)Skin is tough and
pliable, providing mechanical protection against abrasion and puncture and forming an
effective barrier against bacterial invasions.
2)it may also provide moisture proofing against fluid loss or gain.
3)Skin helps to rpotect underlying cells against damaging action of the sun's ultraviolet
rays.
4)serves as variety of important regulatory functions
2) What is the difference between structural colors and colors based on pigments? How
do the chromatophores of vertebrate and cephalopod molluscs differ in structure and
function? - Answers- Structural colors- colors are produced by the physical structure of
the surface of the tissue, which reflects certain light wavelengths and eliminates others.
They are responsible for the most beautifully iridescent and metallic hues.
pigments- a more common and extremely varied group of large molecules that reflect
light rays.
In crustaceans and ectothermic vertebrates, these pigments are contained in large cells
with branching processes,called chromatophores. The pigment may concentrate in the
center of the cell in an aggregate too small to be visible, or it may disperse throughout
the cell and its processes, providing maximum display.
Chromatophores of cephalopod molluscs are different. Each one is a small sac-like cell
filled with pigment granules and surrounded by muscle cells that, when contracted,
stretch the whole cell into a pigmented sheet. When relaxed, the elastic chromatophore
quickly shrinks to small sphere. With such pigment cells, squids and octopuses can alter
their color more rapidly than any other animal.
3) As "naked apes" humans lack the protective investment of fur that shields other
mammals from the damaging effects of sunlight. How does human skin respond to
ultraviolet radiation in the short term and with continued exposure? - Answers-
Damaged cells in both epidermis and dermis release histamine and other vasodilator
substances that cause blood-vessel enlargement in the dermis and characteristically
red coloration of sunburn. Light skins suntan through the formation of the pigment
melanin in the deeper epidermis and by "pigment darkening," that is, the photooxidative
blackening of bleached pigment already present in the epidermis. Sunlight still ages skin
prematurely,causing skin to become dry and leathery. Sunlight also is responsible for
approximately 1 million new cases of skin cancer annually in the US alone. There is
, now strong evidence that genetic mutations caused by high doses of sunlight received
during pre-adult years are responsible for skin cancer later on in life.
4) What is keratin? What is the most abundant protein in metazoans? An animal fibrous
protein that is exported by exocytosis and assembled into fibers. - Answers- Keratin is a
scleroprotein found in epidermal tissues and modified into hard structures such as
horns, hair, nails, and reptilians scales. Collagen is the most abundant protein in
metazoans.
5) Distinguish between epidermis and dermis in vertebrate integument, and describe
structural derivatives of these two layers. - Answers- The epidermis is derived from
ectoderm, while the dermis, an inner, thicker layer is true skin, which is of mosodermal
origin. Although the epidermis is this and appears simple in structure, it gives rise to
most derivatives of the integument, such as hair, feathers,claws,and hooves. The
epidermis is a stratified squamous epithelium consisting of several layers of cells. Cells
of the basal epidermal layer undergo frequent mitosis to renew layers above it. As outer
layers of cells are displaced upwards by new generations of cells beneath, an
exceedingly tough, fibrous protein called keratin accumulates in the interior of the cells.
Gradually, keratin replaces all metabolically active cytoplasm and cells die as they
become cornified, making cells highly resistant to abrasion and water diffusion, and
form the outermost stratum conneum, which becomes especially thick in places of wear
and tear.
The dermis is a dense connective tissue layer containing blood vessels, collagenous
fibers, nerves, pigment cells, fat cells, and connective-tissue cells called fibroblast.
These elements support, cushion, and nourish the epidermis, which is devoid of blood
vessels. other cells present in the connective-tissue layer (macrophages, mast cells,
and lyphocytes) provide first line of defense if epidermis is broken. Dermis may also
contain true bony structures of dermal origin, which gave rise to antlers, scales,and the
bony core of horns.
Structures such as claws, beaks, nails, and horns contain both epidermis and dermal
components.
6) A "9+2" arrangement of microtubules is typical for both cilia and flagella. Explain how
this system is thought to function to produce a bending motion. What is the difference
between a cilium and a flagellum? - Answers- During ciliary movement, microtubles
behave as "sliding filaments" that move past one another. During ciliary flexion, dynein
arms link to adjacent microtubles, then swivel and release in repeated cycles, causing
mircrotubles on the concave side to slide outward past microtubules on the convex side.
This process increases curvature of the cilium. During the recovery stroke microtubules
on the opposite side slide outward to bring the cilium back to its starting position.
Flagellum have the same basic internal "9+2" structure, with a few exceptions: A
flagellum cell is a whip-like structure that is longer than a cilium and usually present
singly or in small numbers at one end of the cell. The main difference between a celium
and a flagellum is in their beating pattern rather than in their structure. A flagellum beats
symmetrically with snakelike undulations so that water is propelled parallel to the long
axis of the flagellum. A cilium beats asymmetrically with a fast power stroke in one
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