Form and function of animals
Lecture 1: Homeostasis and ‘The Animal in its Environment’
Example: Elephants
• Ears: They use their ears to help their cooling (they don’t have sweat glands
except a few pores between their toes). The large surface area of elephant’s
ears serves as a heat radiator. In hot weather, elephants increase the blood
supply to their ears and flap them around to lose body heat (causes
convection and speeds up cooling).
• Physiology: Air permeates the thin skin of the ears, thereby cooling the blood
as it passes through a web of vessels inside the ears before returning to the
body.
• Behaviour: Elephants often spread theirs ears and face in the wind to magnify
this effect.
• Morphology: Elephants have higher surface areas to volume ratios than
expected from size and shape because of folds in skin.
o Body plans (animal’s shape and size) are constrained mainly due to its
surface area to volume ratio. Therefore, endothermic animals cannot get
too big or too small.
o With increased complexity, comes specialised organ systems and extensive
folding of external and internal surfaces. So, as to increase the surface area
relative to the volume.
Surface area to volume ratio
➔ The comparison between the size of the outside of an object and the amount
inside.
o The surface area to volume ratio gets smaller as organism/cell gets larger.
Form and function of animals 1
, o Materials are exchanged at the surface, but used to supply cells that make up
the volume. Therefore, the organism’s surface area must be large compared
to its volume for exchange to be effective.
Importance of shape
• Rounder body shapes, small ears and shorter limbs
reduces surface area to volume ratios = heat
conservation.
▪ E.g. rabbits
• Elongated bodies, longer limbs, large thin ears increase
surface area to volume ratios = heat loss.
▪ E.g. jackal
• Body’s surface = main site for heat exchange with the
environment.
Importance of size
Endotherm = use internally generated heat to maintain body temperature. Their
body temperature tends to stay steady regardless of environment.
How small?
• Shrews and hummingbirds are the smallest of terrestrial endotherms.
• With a high surface area to volume ratio, they lose metabolic heat very
quickly.
• They have metabolisms that work overtime to keep their bodies warm.
• To feed their metabolism (to maintain constant body heat) they eat hourly or
would starve to death.
• Metabolic demands met via torpor (evolutionary adaption).
• Torpor = a state of slowed body functions (reduced metabolism) used to
conserve energy and heat during the cold nights. It is an evolutionary strategy
that preserves their daily metabolic budgets.
• During torpor, hummingbirds consume up to 50x less energy and become
hypothermic.
2 levels of explanation for biological phenomena:
1. Proximate (mechanistic)
2. Ultimate (evolutionary)
Relationships between basal
metabolic rate and body size:
Form and function of animals 2
, Why regulate body temperature?
• All living organisms depend on a
complex series of chemical
reactions that are reliant on
temperature.
• Life is sustained through
regulation of body temperature.
Homeostasis
Homeostasis: The ability of organisms to
regulate the condition of their internal
environment within narrow limits.
▪ Maintaining relative constancy of
the internal environment.
▪ Involves exchanges with the
environment.
Internal environment: The extracellular fluid of a cell.
2 components of extracellular fluid (ECF):
1. Plasma: the fluid portion of blood.
2. Interstitial fluid: fluid that surrounds the cell.
Form and function of animals 3
, Factors that are regulated homeostatically:
• Nutrient concentration: Energy production by cells requires a constant
supply of nutrient molecules. The energy generated by catabolizing the nutrients is
used for basic cellular processes and any specialized activities of the cell.
• Concentration of O2: Cellular respiration, the process that generates energy from
catabolic reactions, requires a constant supply of O2 for optimal productivity.
• Concentration of CO2: The CO2 produced by the catabolic reactions of cellular
respiration must be removed as waste or the ECF would become increasingly acidic.
• Concentration of waste chemicals: Particular biochemical reactions in the cell
generate products that would be toxic to the cell if not removed as waste.
• Concentration of water and NaCl: The relative concentrations of NaCl and water in
the ECF affect how much water enters or leaves a cell’s ICF and hence determine
the cell’s volume. These concentrations must be regulated to maintain a cell volume
that is optimal for function; swollen or shrunken cells are functionally impaired.
• pH: Changes in pH of the ECF can adversely affect enzymatic activities within cells,
as well as nerve cell functions.
• Volume and pressure of plasma: Both the volume and pressure of the plasma
component of the ECF within the vessels must be maintained at levels adequate to
distribute the fluid throughout the body. This circulation is vitally important for
supplying cells with their needs and removing their wastes.
• Temperature: Body cells (of warm-blooded animals) function optimally within a fairly
narrow temperature range. Outside of that range, chemical reactions change their
rates and may be inhibited completely. If cells become too cold, the rates of
enzymatic reactions decrease too much. If cells become too hot, structural and
enzymatic proteins can be denatured and, therefore, become inactive.
Difference in outcome of a negative feedback loop vs a positive feedback loop?
▪ Negative feedback loops either increase or decrease a stimulus causing it to
not be able to have an effect in the way it did before it was detected whereas
a positive feedback loop will run to completion but in the direction of the
stimulus even accelerating the effects of said stimulus.
▪ Negative feedback loops help reduce the effect of a stimulus while a positive
feedback mechanism amplifies the effects of the stimulus.
2 different types of alterations to homeostasis that can occur:
1. Regulated changes: puberty, menstrual cycle
2. Circadian rhythms: sets of regulated changes that cycle every 24 hours e.g.
sleep/wake cycle.
Acclimatization = The ability of an organism to adapt to a new climate in which it's
been placed.
Form and function of animals 4
Lecture 1: Homeostasis and ‘The Animal in its Environment’
Example: Elephants
• Ears: They use their ears to help their cooling (they don’t have sweat glands
except a few pores between their toes). The large surface area of elephant’s
ears serves as a heat radiator. In hot weather, elephants increase the blood
supply to their ears and flap them around to lose body heat (causes
convection and speeds up cooling).
• Physiology: Air permeates the thin skin of the ears, thereby cooling the blood
as it passes through a web of vessels inside the ears before returning to the
body.
• Behaviour: Elephants often spread theirs ears and face in the wind to magnify
this effect.
• Morphology: Elephants have higher surface areas to volume ratios than
expected from size and shape because of folds in skin.
o Body plans (animal’s shape and size) are constrained mainly due to its
surface area to volume ratio. Therefore, endothermic animals cannot get
too big or too small.
o With increased complexity, comes specialised organ systems and extensive
folding of external and internal surfaces. So, as to increase the surface area
relative to the volume.
Surface area to volume ratio
➔ The comparison between the size of the outside of an object and the amount
inside.
o The surface area to volume ratio gets smaller as organism/cell gets larger.
Form and function of animals 1
, o Materials are exchanged at the surface, but used to supply cells that make up
the volume. Therefore, the organism’s surface area must be large compared
to its volume for exchange to be effective.
Importance of shape
• Rounder body shapes, small ears and shorter limbs
reduces surface area to volume ratios = heat
conservation.
▪ E.g. rabbits
• Elongated bodies, longer limbs, large thin ears increase
surface area to volume ratios = heat loss.
▪ E.g. jackal
• Body’s surface = main site for heat exchange with the
environment.
Importance of size
Endotherm = use internally generated heat to maintain body temperature. Their
body temperature tends to stay steady regardless of environment.
How small?
• Shrews and hummingbirds are the smallest of terrestrial endotherms.
• With a high surface area to volume ratio, they lose metabolic heat very
quickly.
• They have metabolisms that work overtime to keep their bodies warm.
• To feed their metabolism (to maintain constant body heat) they eat hourly or
would starve to death.
• Metabolic demands met via torpor (evolutionary adaption).
• Torpor = a state of slowed body functions (reduced metabolism) used to
conserve energy and heat during the cold nights. It is an evolutionary strategy
that preserves their daily metabolic budgets.
• During torpor, hummingbirds consume up to 50x less energy and become
hypothermic.
2 levels of explanation for biological phenomena:
1. Proximate (mechanistic)
2. Ultimate (evolutionary)
Relationships between basal
metabolic rate and body size:
Form and function of animals 2
, Why regulate body temperature?
• All living organisms depend on a
complex series of chemical
reactions that are reliant on
temperature.
• Life is sustained through
regulation of body temperature.
Homeostasis
Homeostasis: The ability of organisms to
regulate the condition of their internal
environment within narrow limits.
▪ Maintaining relative constancy of
the internal environment.
▪ Involves exchanges with the
environment.
Internal environment: The extracellular fluid of a cell.
2 components of extracellular fluid (ECF):
1. Plasma: the fluid portion of blood.
2. Interstitial fluid: fluid that surrounds the cell.
Form and function of animals 3
, Factors that are regulated homeostatically:
• Nutrient concentration: Energy production by cells requires a constant
supply of nutrient molecules. The energy generated by catabolizing the nutrients is
used for basic cellular processes and any specialized activities of the cell.
• Concentration of O2: Cellular respiration, the process that generates energy from
catabolic reactions, requires a constant supply of O2 for optimal productivity.
• Concentration of CO2: The CO2 produced by the catabolic reactions of cellular
respiration must be removed as waste or the ECF would become increasingly acidic.
• Concentration of waste chemicals: Particular biochemical reactions in the cell
generate products that would be toxic to the cell if not removed as waste.
• Concentration of water and NaCl: The relative concentrations of NaCl and water in
the ECF affect how much water enters or leaves a cell’s ICF and hence determine
the cell’s volume. These concentrations must be regulated to maintain a cell volume
that is optimal for function; swollen or shrunken cells are functionally impaired.
• pH: Changes in pH of the ECF can adversely affect enzymatic activities within cells,
as well as nerve cell functions.
• Volume and pressure of plasma: Both the volume and pressure of the plasma
component of the ECF within the vessels must be maintained at levels adequate to
distribute the fluid throughout the body. This circulation is vitally important for
supplying cells with their needs and removing their wastes.
• Temperature: Body cells (of warm-blooded animals) function optimally within a fairly
narrow temperature range. Outside of that range, chemical reactions change their
rates and may be inhibited completely. If cells become too cold, the rates of
enzymatic reactions decrease too much. If cells become too hot, structural and
enzymatic proteins can be denatured and, therefore, become inactive.
Difference in outcome of a negative feedback loop vs a positive feedback loop?
▪ Negative feedback loops either increase or decrease a stimulus causing it to
not be able to have an effect in the way it did before it was detected whereas
a positive feedback loop will run to completion but in the direction of the
stimulus even accelerating the effects of said stimulus.
▪ Negative feedback loops help reduce the effect of a stimulus while a positive
feedback mechanism amplifies the effects of the stimulus.
2 different types of alterations to homeostasis that can occur:
1. Regulated changes: puberty, menstrual cycle
2. Circadian rhythms: sets of regulated changes that cycle every 24 hours e.g.
sleep/wake cycle.
Acclimatization = The ability of an organism to adapt to a new climate in which it's
been placed.
Form and function of animals 4
