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BIOL371 Comparative Biology of Plants and Animals > Theme 4 > Flashcards

Theme 4 Flashcards

1
Q

Terrestrial Animals Key Points

A

Relatively few terrestrial lineages

Requirements for a terrestrial life include:

  • Desiccation avoidance
  • Desiccation tolerance (aestivation, life cycles)
  • Excretion with limited water loss
  • Internal bulk flow of fluids and gasses
  • Gas exchange with air
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2
Q

Desiccation And The Environment – Terrestrial Animals

A
  • Constant water loss through evaporation: across the wet respiratory membrane, across the surface of the skin
  • Water loss in urine and feces
  • Some species lose water through thermoregulatory methods (sweating, panting)
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3
Q

Desiccation (terrestrial animals) requirements:

A
  • Waterproofing of outer layer of the body: (keratin, wax)

- Minimal exposure of gas-exchange and digestive surfaces to air (internal placement)

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4
Q

Loop of Henle aids in the conservation of

A

water in mammals, produces concentrated urine – hyperosmotic to blood

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5
Q

Kangaroo Rats Desiccation:

A
  • Very long Loop of Henle
  • Produces a small quantity of highly hyperosmotic urine (22.5% of daily water loss – for a human, water loss in urine is 57.7%)
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6
Q

Desiccation And The Environment – Insects

A
  • Must deal with small size (cube-square relationship favours evaporative water loss from body surface) and inevitable evaporative loss from wet respiratory surfaces in tracheae
  • Waxy outer layer of the cuticle minimizes evaporative water loss from the body surface
  • Spiracles permit closing of the tracheal system, cuts down on evaporative water loss
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7
Q

Desiccation Tolerance

A

Terrestrial tardigrades live in water films in damp environments

  • Cryptobiosis: formation of the resistant stage (tun) in response to environmental challenges (dehydration, sub-zero temperatures)
  • Anhydrobiosis: when slowly desiccated, resistant tun formed – when re-hydrated, tardigrade returns to active state
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8
Q

Nitrogenous Wastes

A
  • Toxic ammonia (NH3) is produced in every cell of the body by catabolism of amino acids and nucleic acids
  • Mammals convert NH3 to less-reactive urea and flush it away in urine = inevitable water loss in excretion of nitrogenous wastes in mammals (Loop of Henle reduces this)
  • Reptiles, birds and insects convert it to uric acid – very low water-solubility, semi-solid nitrogenous wastes can be excreted while conserving water
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9
Q

Bulk Transport

A
  • Larger and more complex animals - transport system necessary to carry fluids and solutes to within 0.01 mm of most cells in the body to support a reasonably active metabolism
  • This requires a transport fluid (blood, hemolymph) and a circulatory system to deliver it to within this distance of every cell in the body
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10
Q

Disadvantages of Breathing Air

A
  • CO2 does not diffuse into the air as easily as into water

- Inevitable evaporative water loss from internal respiratory surface, which must be kept wet

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11
Q

Advantages of Breathing Air

A
  • 21% O2 – much greater than water

- Bulk flow of air (ventilation) requires less muscular effort (low viscosity, low density)

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12
Q

Gas Exchange With Air - Insect tracheal system

A
  • Delivers air directly to tissues (via interstitial fluid)
  • Moist exchange surfaces are internal
  • Form of a bulk flow system for air
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13
Q

Gas Exchange With Air - Vertebrate Lungs

A
  • Bulk flow of air to respiratory membrane
  • Moist exchange surfaces internal
  • Requires muscular effort (ventilation)
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14
Q

More requirements for terrestrial life:

A
  • Protect gametes from desiccation
  • Protect embryo from desiccation
  • Temperature extremes
  • Constraints on sensory systems
  • Support body weight
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15
Q

Protect gametes from desiccation

A

fertilization without water (internal)

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16
Q

Protect embryo from desiccation

A
  • Aquatic larvae, thick covering on egg/embryo

- Amniote vertebrates ( birds/reptiles/mammals) – amniotic membrane

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17
Q

Temperature extremes

A
  • Avoid via thermoregulation

- Tolerate

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18
Q

Constraints on sensory systems

A
  • Chemosensors

- Mechanosensors – tympanal organ, vert. middle ear

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19
Q

Support body weight

A
  • Robust skeleton

- SA/V relationships, size, stance

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20
Q

Amphibians – Reproduction in Water

A
  • Amphibians lay anamniotic eggs in the water but metamorphose into a form that can live on land to some degree
  • Embryos can exchange gasses and wastes with the aquatic environment
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21
Q

Reasons For Thermoregulation

A
  • Most terrestrial animals regulate their body temperature when possible through metabolic activity or behaviour
  • Animal body temperature range ~4°C - 40°C
    < 0°C - ice crystals damage cells
    > 45°C – proteins denature
22
Q

Ways Of Thermoregulation

A
  • Endothermy
  • Ectothermy
  • Heterothermy
  • Homeothermy
23
Q

Endothermy

A

The production of sufficient metabolic heat to warm the tissues significantly

24
Q

Ectothermy

A

Insufficient heat from metabolic activities to warm tissues significantly; heat must come from the environment

25
Q

Heterothermy

A

Allowing body temperature to vary with the environment

26
Q

Homeothermy

A

Tightly regulating body temperature around an unvarying mean

27
Q

Distinguishing endotherms vs. ectotherms is based on metabolic rate

A
  • endotherms: metabolic rate changes with temperature in order to maintain a constant body temperature – a cost
  • ectotherms: metabolic rate changes directly with body temperature, which changes with environmental temperature
28
Q

Reasons For Thermoregulation

A
  • Performance depends upon biochemical processes

- Animals regulate temperatures within the range allowing optimal performance

29
Q

Heat Exchange With The Environment Occurs Via:

A

Conduction, radiation, convection, and evaporation

30
Q

Conduction

A
  • Direct heat transfer by contact – air conducts heat poorly, water well
  • Gill-breathing aquatic organisms tend to be isothermic with the water in which they swim
31
Q

Radiation

A
  • Transfer of heat as long-wave light – not very effective as a heat sink at biological temperatures
  • Radiative sources (the sun) are very effective for heating up
32
Q

Convection

A
  • Transfer of heat by a moving medium – air or water flowing over an organism carries heat away or brings it
33
Q

Evaporation

A

Energy consumed by the change from liquid to gas; effective way to carry heat away

34
Q

Ectothermic animals can thermoregulate by using

A

Conduction, radiation, convection, and evaporation alone for heat exchange with the environment

35
Q

Countercurrent Heat Exchange

A
  • Cold-climate terrestrial endotherms can conserve heat by using counter-current heat exchange structures – regional heterothermy
36
Q

Torpor

A
  • Reduces energy demands in small endotherms during periods of low or high environmental temperatures, or resource unavailability
  • Body temperature setpoint drops
  • Metabolic rate slows
37
Q

Hibernation

A

Seasonal version of torpor, undertaken during seasonal periods of low temperature

38
Q

Endothermy In Insects

A
  • Bees and some other flying insects are heterothermic endotherms
  • Generate sufficient heat by the action of the flight muscles to maintain a high constant temperature in the thorax
  • Tend to be furry
39
Q

Freeze Tolerance and Freeze Avoidance

A
  • Some ectotherms can supercool their ECF – goes below 0° C without freezing
  • Some terrestrial ectotherms can allow the bulk of their ECF to freeze for extended periods (high intracellular osmolality depresses the freezing point, control of ice nucleation in ECF)
40
Q

Chemosensors

A
  • Chemosensory organs – require a wet surface for adsorption of air-borne chemical particles
  • Insect antennae have minute channels lined with moist adsorptive tissue
  • Terrestrial vertebrates have moist olfactory epithelium and taste buds in the buccal cavity
41
Q

Hearing

A
  • Sound does not transmit easily from air to water
  • Sensing soundwaves by terrestrial animals must take this into account
  • Insects – tympanal organs – air on both sides, nerves pick up vibrations
  • Hearing in aquatic vertebrates – inner ear can pick up vibrations through tissues
  • In fish, hyomandibular bone suspends the lower jaw
42
Q

Hearing in Mammals

A
  • middle-ear bones transform large-amplitude eardrum vibrations to low-amplitude high-force vibrations transmitted to oval window of inner ear, which amplifies vibrations so that waves are produced in fluid-filled inner ear
43
Q

Support Body Weight

A
  • Cross-sectional area of limb (support) is a function of size squared
  • Volume (mass) is a function of size cubed
  • All else being equal, as animals get bigger body MASS would increase faster than the cross-sectional AREA of the limbs for support
  • Thus, in terrestrial animals, if body and limbs scale proportionately/linearly with size, at some point body mass exceeds the ability of the limbs to support it
  • Limbs must change disproportionately to body size as terrestrial animals get larger – allometric growth
  • Some ‘animals’ are impossibly big
  • Water supports the body mass
44
Q

Allometric growth

A
  • Produces limbs that can support increasing body weight with increasing size
  • Characteristic of most animals
  • An evolutionary phenomenon associated with trends in increasing or decreasing size in a lineage
45
Q

Hard Skeletons

A
  • Two types: exoskeletons (external) and endoskeletons (internal)

Functions:

  • Provide attachments and leverage for muscles = force transmission
  • Transmit compressive stress to the substrate
  • Provide a framework for tissues of body
  • Act as a mineral bank for physiological requirements (vertebrates)
  • Protection for delicate organs or whole body
46
Q

Endoskeletons

A
  • In vertebrates, composed of bone and cartilage
  • Bone: collagenous matrix mineralized by CaPO4 crystals
  • Highly vascularised, matrix architecture supports scattered osteocytes
  • Metabolically active
  • Bears compressive stress well, shear stress not so well
47
Q

Exoskeletons

A

The arthropod exoskeleton:

  • consists of chitin – long complex polysaccharide
  • may be impregnated with calcium carbonate

Composed of plates (tergae) with joints between them
- muscles are within the skeleton

48
Q

Hydrostatic Skeletons

A
  • Volume of fluid enclosed by 2 layers of muscle, longitudinal and circular
  • Fluid incompressible but pressurized when muscle contracts
  • Muscular “container” changes shape with the contraction of different muscle layers (organ, animal’s whole body)
49
Q

What’s good about being aquatic:

A
  • Water supports the body (affects the size, stance and skeleton)
  • Desiccation is a lesser threat
  • Stable and mild temperatures
  • Metabolic waste removed by water
  • Sound transmits well from water to the body
50
Q

Aquatic animals can become much bigger than terrestrial animals

A

The biggest aquatic animals are air-breathers

51
Q

Challenges of living in aquatic environments:

A
  • Water is dense
  • Water is viscous
  • Water has low oxygen content compared to air
  • Water has a high thermal conductance
52
Q

Being warm in aquatic environments

A
  • Water is a good heat conductor = aquatic organisms are mostly heterothermic ectotherms
  • Aquatic homeothermic endotherms must deal with rapid loss of body heat
  • Insulation: fur, feathers, fat
  • Respiratory medium: breathe air, allows higher metabolic rate; also, the air is a poor conductor of heat from the body
  • Aquatic endotherms utilize counter-current heat exchange – allows outbound blood to heat inbound blood – retains heat by maintaining gradient along parallel lengths

BIOL371 Comparative Biology of Plants and Animals (10 decks)

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