1 SCI 355B: Lecture 7 Size, Success, & Build-A-Bug Size • Small size of insects has both advantages & disadvantages. • The advantages are numerous, but there is one major disadvantage = water loss • Water loss (or prevention of..) is especially critical in organisms with a high surface area to volume ratio. Surface Area and Volume • Surface area (SA) = the “exposed” area of the body expressed in squared 2 units. • Volume (V) = the three dimensional space occupied expressed in mL or cm 3 • The problems insects face can be traced back to one relationship: • The surface area/volume ratio (SA/V)
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SCI 355B: Lecture 7Size, Success, & Build-A-Bug
Size
• Small size of insects has both advantages &disadvantages.
• The advantages are numerous, but there isone major disadvantage = water loss
• Water loss (or prevention of..) is especiallycritical in organisms with a high surfacearea to volume ratio.
Surface Area and Volume
• Surface area (SA) = the “exposed” area ofthe body expressed in squared2 units.
• Volume (V) = the three dimensional spaceoccupied expressed in mL or cm3
• The problems insects face can be tracedback to one relationship:
• The surface area/volume ratio (SA/V)
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SA/V Ratio
• Transpiration (water loss) increases as afunction of an increased SA/V ratio.
• The smaller the animal, the less its volumeand the greater the SA to V ratio
• In other words, small animals can maintainlittle water reserves, yet the evaporativesurface is high.
EXAMPLE
• Consider two cubes: one is 2 cm and theother is 4 cm
• SA=height x width x number of sides• SA of the 2-cm cube = 2cm x 2cm = 4cm2 x 6
sides = 24cm2.• SA of the 4-cm cube = 4cm x 4cm = 16cm2 x
6 sides = 96cm2
EXAMPLE
• Consider two cubes: one is 2 cm and theother is 4 cm
• V = height x width x depth• V of 2-cm cube = 2cm x 2cm x 2cm = 8cm3
• V of 4cm cube = 4cm x 4cm x 4cm = 64cm3
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EXAMPLE
• 2-cm Cube• SA = 24cm2
• V= 8cm3
• SA/V= 24/8 = 3:1
• 4-cm Cube• SA= 96cm2
• V= 64cm3
• SA/V= 1.5:1
Transpiration increases as a function of an increased SA/V ratio. There is a much larger difference between SA and V in smaller animals compared to larger animals
Why are insects so successful?
• Small size (huh?) - can exploit a greaternumber/variety of habitats and muscle strength isproportional to cross-sectional area. Insectmuscles are very powerful since they are moving avolume that is relatively small.
• The alimentary canal extends from the mouth to the anus• Food is acquired & processed in the foregut, midgut & hindgut to
breakdown organic material into absorbable molecules and excretenon-usable products of digestion
Salivary Glands
• in addition to digestive enzymes, salivary glands may secrete silk(caterpillars & Hymenoptera) and anticoagulants (blood feeders)
Foregut (Stomodeum)
• The foregut extends from the mouth to the end of the proventriculus &is lined with a layer of cuticle, the intima, which is shed with each molt& serves as mechanical protection
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Foregut (Stomodeum)
•Food taken into the cibarium (preoral cavity), ground, pushed into themouth by maxillae, bathed & lubricated with saliva, & moves down theesophagus via peristalsis, a series of muscular contractions, then maybe stored in a crop.
• midgut - - main site of digestion & absorption of food, where gastriccaecae increase surface area for digestion.
(cardiac)
Midgut(Mesenteron)
Proctodeum (Hindgut)
•from pyloric valve to anus, resorption of H2O, salts & amino acids•lined with cuticle = little absorption•Malpighian tubules, anterior intestine, and rectum
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•Open system consisting of:•dorsal vessel – elongate tubeextending length of the body•hemocoel – body cavity where thehemolymph flows