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1:​ ​PHYSIOLOGICAL​ ​PLAYERS

2

2&3:​ ​NUTRITION

4

4:​ ​METABOLISM​ ​AND​ ​ENERGY​ ​SUPPLY

14

5:​ ​THERMAL​ ​RELATIONS

18

6:​ ​GAS​ ​EXCHANGE

22

7:​ ​CIRCULATION

25

8:​ ​THE​ ​ENDOCRINE​ ​SYSTEM

27

9&10:​ ​OSMOREGULATION

31

11:​ ​REPRODUCTION

36

12:​ ​THE​ ​IMMUNE​ ​SYSTEM

39

13:​ ​THE​ ​NERVOUS​ ​SYSTEM

43

A-LEVEL​ ​NOTES

46

14:​ ​SENSORY​ ​SYSTEMS

47

15:​ ​MOTOR​ ​MECHANISMS​ ​AND​ ​LOCOMOTION

51

16&17:​ ​PLANT​ ​PHYSIOLOGY

56

18:​ ​PHYSIOLOGY​ ​IN​ ​HOT​ ​AND​ ​DRY​ ​HABITATS

61

19:​ ​PHYSIOLOGY​ ​OF​ ​GLOBAL​ ​CHANGE

64

A-LEVEL​ ​NOTES

55

Joanna​ ​Griffith​ ​(2017)

1:​ ​PHYSIOLOGICAL​ ​PLAYERS
Organisms
● Form​ ​and​ ​function​ ​are​ ​closely​ ​correlated
○ Anatomy:​ ​study​ ​of​ ​the​ ​biological​ ​forms​ ​of​ ​organisms​ ​(eg
...

respiration)
● Organisms​ ​are​ ​structurally​ ​dynamic
○ The​ ​atoms​ ​that​ ​make​ ​up​ ​organisms​ ​are​ ​in​ ​dynamic​ ​exchange​ ​with​ ​atoms​ ​in
the​ ​environment​ ​(unlike​ ​inanimate​ ​objects)
■ Eg
...
​ ​temperature​ ​regulators​ ​(endotherms)​ ​and​ ​temperature​ ​conformers
(ectotherms​ ​and​ ​poikilotherms)
○ Homeostasis:​ ​maintenance​ ​of​ ​a​ ​‘steady​ ​state’
■ Walter​ ​Cannon
● Argued​ ​that​ ​homeostasis​ ​is​ ​a​ ​signature​ ​of​ ​highly​ ​evolved​ ​life,
with​ ​mammals​ ​ranked​ ​highest
○ However,​ ​one​ ​could​ ​argue​ ​that​ ​insects​ ​are​ ​extremely
successful,​ ​so​ ​homeostasis​ ​is​ ​only​ ​one​ ​road​ ​to​ ​success
■ Negative​ ​feedback:​ ​control​ ​system​ ​opposes​ ​deviations​ ​from​ ​set​ ​point
■ Positive​ ​feedback:​ ​control​ ​system​ ​reinforces​ ​deviations​ ​from​ ​set​ ​point
● Eg
...
​ ​minutes​ ​or​ ​hours
○ Chronic​ ​response:​ ​following​ ​prolonged​ ​exposure,​ ​biochemical​ ​or​ ​anatomical
restructuring​ ​occurs
○ Organisms​ ​must​ ​have​ ​phenotypic​ ​plasticity​ ​(the​ ​ability​ ​of​ ​an​ ​organism​ ​to
change​ ​its​ ​phenotype​ ​in​ ​response​ ​to​ ​changes​ ​in​ ​the​ ​environment)
■ Eg
...
​ ​summer​ ​and​ ​winter,​ ​high​ ​and​ ​low​ ​altitude
● Size​ ​and​ ​shape​ ​affect​ ​interactions​ ​with​ ​the​ ​environment
○ Many​ ​different​ ​body​ ​plans​ ​have​ ​evolved,​ ​and​ ​are​ ​determined​ ​by​ ​the​ ​genome
○ Physical​ ​laws​ ​constrain​ ​size,​ ​strength,​ ​diffusion,​ ​movement,​ ​and​ ​heat
exchange
■ Evolutionary​ ​convergence​ ​reflects​ ​different​ ​species’​ ​adaptations​ ​to​ ​a
similar​ ​environmental​ ​challenge
● Eg
...
​ ​length​ ​of​ ​gestation​ ​period
○ Can​ ​help​ ​us​ ​to​ ​identify​ ​specialisations​ ​of​ ​particular
species
Environments
● Temperature
○ The​ ​majority​ ​of​ ​species​ ​are​ ​temperature​ ​conformers
(ectotherms/poikilotherms)
○ The​ ​lowest​ ​temperature​ ​at​ ​which​ ​seawater​ ​is​ ​liquid​ ​is​ ​-1
...
​ ​desert​ ​iguanas​ ​can​ ​survive​ ​tissue​ ​temperatures​ ​as​ ​high​ ​as​ ​48
...
​ ​woodlice)
○ Some​ ​terrestrial​ ​animals​ ​have​ ​evolved​ ​exceptional​ ​tolerance​ ​of​ ​water​ ​loss
(eg
...
​ ​seek​ ​shade​ ​or​ ​damp)
Evolutionary​ ​processes
● Traits​ ​of​ ​organisms​ ​often​ ​appear​ ​well-suited​ ​to​ ​their​ ​environments
○ Evolution:​ ​a​ ​change​ ​in​ ​gene​ ​frequencies​ ​over​ ​time​ ​within​ ​a​ ​population​ ​of
organisms
■

Joanna​ ​Griffith​ ​(2017)

A​ ​trait​ ​is​ ​an​ ​adaptation​ ​if​ ​it​ ​has​ ​come​ ​to​ ​be​ ​present​ ​at​ ​a​ ​high​ ​frequency​ ​in​ ​a
population​ ​because​ ​it​ ​enhances​ ​fitness
● Mechanisms​ ​(proximate)​ ​and​ ​origins​ ​(ultimate)
○ Mechanisms:​ ​components​ ​and​ ​workings​ ​(eg
...
​ ​light​ ​production​ ​by​ ​fireflies​ ​(Photinus)
■ Mechanism:
● Firefly​ ​luciferin​ ​+​ ​ATP​ ​=​ ​luciferyl-AMP​ ​+​ ​O​2​​ ​=​ ​electron-excited
product​ ​=​ ​ground-state​ ​product​ ​+​ ​photons​ ​(all​ ​catalysed​ ​by
firefly​ ​luciferase)
■ Origin:
● Species​ ​recognition
● Mate​ ​choice
○ Knowledge​ ​of​ ​a​ ​physiological​ ​mechanism​ ​doesn’t​ ​imply​ ​knowledge​ ​of
adaptive​ ​significance​ ​(origin)
○ Structures​ ​that​ ​have​ ​similar​ ​adaptive​ ​significance​ ​(origin)​ ​can​ ​have​ ​very
different​ ​mechanisms
■ Eg
...
​ ​fish​ ​eye​ ​vs
...
​ ​comparative​ ​method
■ Convergence​ ​in​ ​evolution​ ​of​ ​invaginated​ ​breathing​ ​organs
○ Eg
...
​ ​rapid​ ​evolution​ ​of​ ​lactase​ ​synthesis​ ​in​ ​cattle-farming​ ​tribes​ ​in
Africa
Essential​ ​nutrients
● “Essential”​ ​because:
○ Animals​ ​cannot​ ​synthesise​ ​them
○ Must​ ​be​ ​acquired​ ​fully​ ​formed​ ​in​ ​the​ ​diet
Joanna​ ​Griffith​ ​(2017)

●

●

○ Necessary​ ​for​ ​life
Proteins
○ Essential​ ​amino​ ​acids
○ Uniquely​ ​important​ ​for​ ​animal​ ​structure​ ​and​ ​function
○ Diverse,​ ​vital​ ​roles
○ Strings​ ​of​ ​20-22​ ​amino​ ​acids
○ All​ ​amino​ ​acids​ ​contain​ ​nitrogen
○ Protein​ ​limitation
■ Animals​ ​require​ ​nitrogen​ ​in​ ​‘fixed’​ ​forms
● Nitrate​ ​(NO​3​-​)​ ​and​ ​ammonium​ ​(NH​4​+​)​ ​are​ ​often​ ​limiting​ ​in​ ​food
chains
■ Essential​ ​amino​ ​acids
● Animals​ ​cannot​ ​synthesise​ ​around​ ​10​ ​of​ ​the​ ​standard​ ​amino
acids
■ Amino​ ​acids​ ​are​ ​not​ ​usually​ ​stored​ ​in​ ​large​ ​quantities
● Stored​ ​as​ ​lipids​ ​instead,​ ​which​ ​are​ ​not​ ​as​ ​bulky
● When​ ​food​ ​is​ ​assimilated,​ ​excess​ ​nitrogen​ ​is​ ​excreted
● Some​ ​animals​ ​do​ ​store​ ​amino​ ​acids​ ​in​ ​muscles​ ​to​ ​fuel​ ​periods
of​ ​high​ ​demand
○ Eg
...
​ ​small​ ​passerines)​ ​can’t
store​ ​sufficient​ ​nutrients​ ​to​ ​fuel​ ​reproduction
● Depletion​ ​of​ ​pectoral​ ​muscle​ ​to​ ​fuel​ ​egg
production
○ Eg
...
​ ​phospholipids,​ ​cholesterol
■ Reduce​ ​permeability​ ​of​ ​integument​ ​to​ ​water
■ Pheromones,​ ​steroid​ ​hormones
Joanna​ ​Griffith​ ​(2017)

●

■ Influence​ ​assimilation​ ​of​ ​macronutrients
○ Fatty​ ​acids​ ​mostly​ ​consist​ ​of​ ​carbon​ ​and​ ​hydrogen
○ Relatively​ ​nonpolar
○ Hydrophobic
○ Great​ ​diversity​ ​in​ ​structure​ ​(and​ ​function),​ ​influenced​ ​by:
■ Number​ ​of​ ​carbon​ ​atoms​ ​(usually​ ​8-24)
■ Degree​ ​of​ ​unsaturation​ ​(number​ ​of​ ​double​ ​bonds)
● 1​ ​or​ ​more​ ​double​ ​bonds​ ​=​ ​unsaturated
● Bonds​ ​increase​ ​flexibility​ ​and​ ​affect​ ​the​ ​permeability​ ​of​ ​cells​ ​to
water
■ Position​ ​of​ ​double​ ​bonds
○ System​ ​for​ ​symbolising​ ​fatty​ ​acids:
■ Eg
...
2​ ​(number​ ​of​ ​double
bonds)w6​ ​(position​ ​of​ ​the​ ​first​ ​double​ ​bond​ ​when​ ​scanned​ ​form​ ​methyl
(-CH​3​)​ ​end
○ Lipid​ ​limitation
■ Animals​ ​synthesis​ ​lipids​ ​by​ ​using​ ​carbon​ ​chains​ ​obtained​ ​from​ ​a​ ​range
of​ ​dietary​ ​sources
● This​ ​biochemical​ ​flexibility,​ ​and​ ​the​ ​fact​ ​that​ ​animals​ ​store
lipids,​ ​means​ ​that​ ​lipids​ ​are​ ​rarely​ ​physiologically​ ​limiting,​ ​with
the​ ​exception​ ​of​ ​essential​ ​fatty​ ​acids
○ Many​ ​animals​ ​lack​ ​the​ ​enzymes​ ​needed​ ​to​ ​create
double​ ​bonds​ ​at​ ​the​ ​omega-3​ ​and​ ​omega-6​ ​positions,
so​ ​must​ ​obtain​ ​these​ ​compounds​ ​in​ ​their​ ​diet​ ​(eg
...
​ ​lack​ ​of​ ​vitamin​ ​C​ ​can​ ​cause​ ​scurvy
● Eg
...
​ ​neural​ ​tube​ ​defects​ ​in​ ​infants​ ​were​ ​found​ ​to​ ​be​ ​the​ ​result​ ​of
a​ ​folic​ ​acid​ ​deficiency​ ​in​ ​pregnant​ ​mothers
○ Vitamin​ ​excess
■ Excess​ ​intake​ ​of​ ​water-soluble​ ​vitamins​ ​is​ ​usually​ ​harmless​ ​as​ ​they
are​ ​readily​ ​excreted
■ Excess​ ​intake​ ​of​ ​fat-soluble​ ​vitamins​ ​can​ ​be​ ​harmful​ ​due​ ​to​ ​the
accumulation​ ​of​ ​vitamins​ ​in​ ​body​ ​fat
■ Eg
...
​ ​B-carotene)​ ​are
selectively​ ​converted​ ​to​ ​retinoids
○ High​ ​intake​ ​is​ ​harmless​ ​but​ ​may​ ​result​ ​in​ ​carotenosis
(orange​ ​skin)
● Excess​ ​intake​ ​of​ ​fully​ ​formed​ ​retinol​ ​may​ ​be​ ​harmful
Minerals
○ Inorganic​ ​nutrients​ ​required​ ​in​ ​small​ ​amounts
■ Eg
...
​ ​herbivores​ ​grazing​ ​plants​ ​growing​ ​in​ ​soil​ ​that​ ​lacks
phosphorus​ ​may​ ​develop​ ​fragile​ ​bones
Joanna​ ​Griffith​ ​(2017)

Eg
...
​ ​excess​ ​salt​ ​(sodium​ ​chloride)​ ​intake​ ​can​ ​result​ ​in​ ​high
blood​ ​pressure
● Eg
...
​ ​carnivorous​ ​mammals​ ​grasp​ ​prey​ ​with​ ​teeth​ ​and
typically​ ​reduce​ ​it​ ​to​ ​smaller​ ​pieces​ ​by​ ​tearing/chewing
○ Eg
...
​ ​birds​ ​of​ ​prey
● All​ ​species​ ​have​ ​a​ ​hooked​ ​bill​ ​for​ ​tearing
○ Some​ ​swallow​ ​prey​ ​whole
● Wing​ ​morphology​ ​varies​ ​greatly,
affecting​ ​how​ ​they​ ​chase​ ​down​ ​prey
■ Substrate​ ​feeders
● Animals​ ​that​ ​live​ ​in​ ​or​ ​on​ ​their​ ​food​ ​sources
● Eg
...
​ ​snails​ ​exhibit​ ​‘variations​ ​on​ ​a​ ​theme’
○ Herbivorous​ ​snails​ ​use​ ​a​ ​radula​ ​to​ ​scrape​ ​algal​ ​growth
off​ ​the​ ​substrate
○ Carnivorous​ ​drill​ ​snails
○ Harpoonlike​ ​radulas​ ​of​ ​cone​ ​snails
■ Chemical​ ​weapon​ ​used​ ​to​ ​capture​ ​fast-moving
prey​ ​by​ ​slow-moving​ ​predators​ ​by​ ​paralysing
prey​ ​(cone​ ​snails​ ​synthesise​ ​alpha-conotoxins
which​ ​bind​ ​to​ ​receptor​ ​sites​ ​on​ ​acetylcholine
receptors​ ​on​ ​the​ ​swimming​ ​muscles​ ​of​ ​fish)
■ Fluid​ ​feeders
● Animals​ ​that​ ​suck​ ​nutrient-rich​ ​fluid​ ​from​ ​a​ ​living​ ​host
● Eg
...
​ ​the​ ​enzyme​ ​chitinase​ ​is​ ​required​ ​to​ ​digest​ ​chitin
○ Digestive​ ​enzymes​ ​act​ ​in​ ​different​ ​spatial​ ​contexts
■ Most​ ​animals​ ​process​ ​food​ ​in​ ​specialised​ ​compartments
● Compartments​ ​reduce​ ​the​ ​risk​ ​of​ ​an​ ​animal​ ​digesting​ ​its​ ​own
cells​ ​and​ ​tissues
■ Intracellular​ ​digestion
● Food​ ​particles​ ​are​ ​engulfed​ ​by​ ​phagocytosis
● Food​ ​vacuoles,​ ​containing​ ​food,​ ​fuse​ ​with​ ​lysosomes
containing​ ​hydrolytic​ ​enzymes
■ Extracellular​ ​digestion
● Breakdown​ ​of​ ​food​ ​particles​ ​outside​ ​of​ ​cells
● Occurs​ ​in​ ​compartments​ ​that​ ​are​ ​continuous​ ​with​ ​the​ ​outside​ ​of
the​ ​animal’s​ ​body
Joanna​ ​Griffith​ ​(2017)

Animals​ ​with​ ​simple​ ​body​ ​plans​ ​(eg
...
​ ​some​ ​animals​ ​have​ ​a​ ​crop​ ​filled​ ​with
ingested​ ​grit/stones​ ​that​ ​help​ ​to​ ​further
break​ ​down​ ​food
○ Spatial​ ​and​ ​functional​ ​organisation​ ​of​ ​an​ ​alimentary
canal
■ Extracellular​ ​digestive​ ​system​ ​consists​ ​of​ ​an
alimentary​ ​canal,​ ​and​ ​accessory​ ​glands​ ​that
secrete​ ​digestive​ ​juices​ ​through​ ​ducts
● Mammalian​ ​accessory​ ​glands​ ​include
the​ ​salivary​ ​glands,​ ​the​ ​pancreas,​ ​liver,
and​ ​gallbladder
■ Food​ ​is​ ​pushed​ ​along​ ​by​ ​peristalsis,​ ​rhythmic
contractions​ ​of​ ​the​ ​wall​ ​of​ ​the​ ​canal
■ Valves​ ​called​ ​sphincters​ ​regulate​ ​the​ ​movement
of​ ​material​ ​between​ ​compartments
Carbohydrate​ ​digestion
■ Disaccharides​ ​are​ ​obtained​ ​through​ ​the​ ​digestion​ ​of​ ​polysaccharides
or​ ​directly​ ​in​ ​the​ ​diet​ ​(eg
...
​ ​lactase,​ ​sucrase)​ ​split​ ​disaccharides​ ​into
monosaccharides​ ​or​ ​oligosaccharides​ ​(chains​ ​of​ ​3​ ​or​ ​more
monosaccharides)
● Two​ ​enzymes​ ​typically​ ​work​ ​in​ ​sequence​ ​-​ ​the​ ​first​ ​splits​ ​the
polysaccharide,​ ​and​ ​the​ ​second​ ​splits​ ​the​ ​products​ ​of​ ​the​ ​first
into​ ​monosaccharides
Protein​ ​digestion
■ Poses​ ​a​ ​problem,​ ​as​ ​organisms​ ​must​ ​avoid​ ​digesting​ ​their​ ​own​ ​tissues
● When​ ​acting​ ​intraluminally,​ ​proteases​ ​are​ ​typically​ ​synthesised
as​ ​inactive​ ​forms​ ​called​ ​proenzymes​ ​which​ ​only​ ​become​ ​active
when​ ​they​ ​reach​ ​the​ ​place​ ​they​ ​are​ ​needed
■ Proteins​ ​contain​ ​a​ ​large​ ​diversity​ ​of​ ​different​ ​chemical​ ​bonds,​ ​therefore
many​ ​enzymes​ ​are​ ​needed​ ​for​ ​hydrolysis​ ​(typically​ ​8​ ​or​ ​more)
■ Protein​ ​digestion​ ​in​ ​vertebrates​ ​typically​ ​begins​ ​in​ ​the​ ​stomach
● Parietal​ ​cells​ ​secrete​ ​hydrogen​ ​and​ ​chloride​ ​ions
● Chief​ ​cells​ ​secrete​ ​the​ ​proenzyme​ ​pepsinogen,​ ​which​ ​is
activated​ ​to​ ​pepsin​ ​when​ ​it​ ​mixes​ ​with​ ​hydrochloric​ ​acids​ ​in​ ​the
stomach
○

○

○

Joanna​ ​Griffith​ ​(2017)

●

● Mucus​ ​protects​ ​the​ ​stomach​ ​lining​ ​from​ ​gastric​ ​juice
■ When​ ​proteins​ ​and​ ​fragments​ ​arrive​ ​in​ ​the​ ​vertebrate​ ​midgut,​ ​they​ ​are
subjected​ ​to​ ​further​ ​intraluminal​ ​digestion​ ​by​ ​enzymes​ ​from​ ​the
pancreas
● The​ ​pancreas​ ​secretes​ ​proenzymes,​ ​which​ ​are​ ​transported​ ​to
the​ ​midgut​ ​via​ ​pancreatic​ ​juice,​ ​then​ ​are​ ​activated​ ​by​ ​cleavage
reactions​ ​to​ ​yield​ ​peptidases
■ As​ ​a​ ​result​ ​of​ ​intraluminal​ ​digestion​ ​in​ ​the​ ​stomach​ ​and​ ​midgut,​ ​a
mixture​ ​of​ ​free​ ​amino​ ​acids​ ​and​ ​short​ ​amino​ ​acid​ ​chains​ ​called
oligopeptides​ ​are​ ​produced
● Oligopeptides​ ​undergo​ ​further​ ​hydrolysis​ ​in​ ​the​ ​epithelial
membranes​ ​of​ ​the​ ​midgut,​ ​resulting​ ​in​ ​free​ ​amino​ ​acids,
dipeptides​ ​and​ ​tripeptides
■ Ultimately,​ ​the​ ​products​ ​passed​ ​to​ ​blood​ ​are​ ​mostly​ ​free​ ​amino​ ​acids
○ Lipid​ ​digestion
■ Digestive​ ​enzymes​ ​are​ ​hydrophilic,​ ​while​ ​lipids​ ​are​ ​hydrophobic
● Emulsification​ ​is​ ​needed​ ​to​ ​break​ ​up​ ​lipids​ ​into​ ​smaller​ ​droplets
with​ ​relatively​ ​large​ ​surface​ ​area,​ ​on​ ​which​ ​lipases​ ​can​ ​act
■ Lipids​ ​are​ ​mainly​ ​digested​ ​in​ ​the​ ​midgut​ ​due​ ​to​ ​the​ ​presence​ ​of
chemical​ ​emulsifiers​ ​such​ ​as​ ​intraluminal​ ​pancreatic​ ​lipases​ ​and​ ​liver
bile​ ​(acts​ ​like​ ​a​ ​detergent)
■ Products​ ​are​ ​mostly​ ​free​ ​fatty​ ​acids,​ ​glycerol,​ ​and​ ​its​ ​esters
Absorption
○ Absorption​ ​in​ ​vertebrates​ ​involves​ ​the​ ​transport​ ​of​ ​chemically​ ​simple
compounds​ ​across​ ​the​ ​epithelial​ ​cells​ ​that​ ​line​ ​the​ ​gut,​ ​into​ ​blood​ ​or​ ​lymph
○ Surface​ ​area​ ​is​ ​important
■ The​ ​gut​ ​has​ ​a​ ​huge​ ​surface​ ​area​ ​due​ ​to​ ​villi​ ​and​ ​microvilli​ ​that​ ​are
exposed​ ​to​ ​the​ ​intestinal​ ​lumen​ ​and​ ​form​ ​a​ ​brush​ ​border​ ​that​ ​greatly
increases​ ​the​ ​rate​ ​of​ ​nutrient​ ​absorption
○ Transport​ ​across​ ​epithelial​ ​cells​ ​can​ ​be​ ​passive​ ​or​ ​active​ ​depending​ ​on​ ​the
nutrient
○ Fatty​ ​acid​ ​absorption
■ Epithelial​ ​cells​ ​readily​ ​absorb​ ​hydrophobic​ ​fatty​ ​acids​ ​and
monoglycerides,​ ​and​ ​recombine​ ​them​ ​into​ ​triglycerides
■ Triglycerides​ ​are​ ​coated​ ​with​ ​phospholipids,​ ​cholesterol,​ ​and​ ​proteins
to​ ​form​ ​hydrophilic​ ​chylomicrons
■ Chylomicrons​ ​are​ ​transported​ ​into​ ​a​ ​lacteal,​ ​a​ ​lymphatic​ ​vessel​ ​in​ ​each
villus
■ Lymphatic​ ​vessels​ ​deliver​ ​chylomicron-containing​ ​lymph​ ​to​ ​large​ ​veins
that​ ​return​ ​blood​ ​to​ ​the​ ​heart
○ Hepatic​ ​portal​ ​veins​ ​carry​ ​nutrient-rich​ ​blood​ ​from​ ​the​ ​capillaries​ ​of​ ​the​ ​villi​ ​to
the​ ​liver​ ​(then​ ​to​ ​the​ ​heart)
■ The​ ​liver​ ​regulates​ ​nutrient​ ​distribution,​ ​interconverts​ ​organic
molecules,​ ​and​ ​detoxifies​ ​many​ ​organic​ ​molecules
○ Hindgut

Joanna​ ​Griffith​ ​(2017)

■
■
■
■

A​ ​major​ ​function​ ​of​ ​the​ ​colon​ ​is​ ​to​ ​recover​ ​water​ ​that​ ​has​ ​entered​ ​the
alimentary​ ​canal
Houses​ ​microbes​ ​(used​ ​in​ ​digestion)
Faeces,​ ​including​ ​undigested​ ​material​ ​and​ ​bacteria,​ ​become​ ​more
solid​ ​as​ ​they​ ​move​ ​through​ ​the​ ​colon
Faeces​ ​are​ ​stored​ ​in​ ​the​ ​rectu,​ ​until​ ​they​ ​can​ ​be​ ​eliminated​ ​from​ ​the
body

●

Elimination
○ Undigested​ ​material​ ​leaves​ ​the​ ​body​ ​through​ ​the​ ​anus
Evolutionary​ ​adaptations​ ​of​ ​vertebrate​ ​digestive​ ​systems
● The​ ​digestive​ ​systems​ ​of​ ​vertebrates​ ​are​ ​variations​ ​on​ ​a​ ​common​ ​plan
○ Specialist​ ​adaptations​ ​related​ ​to​ ​diet
■ The​ ​success​ ​of​ ​mammals​ ​is​ ​partly​ ​due​ ​to​ ​their​ ​specialised​ ​dentition
● Non-mammalian​ ​vertebrates​ ​have​ ​less​ ​specialised​ ​teeth,
though​ ​there​ ​are​ ​exceptions​ ​to​ ​this
○ Eg
...
​ ​the​ ​oesophagus​ ​and​ ​stomach
■ Eg
...
​ ​kangaroos,​ ​hippos,​ ​colobus​ ​monkeys,​ ​sloths,​ ​hoatzin
● The​ ​hoatzin​ ​(“stinkbird”)​ ​has​ ​a​ ​large​ ​muscular​ ​crop​ ​(an
esophageal​ ​pouch)​ ​that​ ​houses​ ​mutualistic​ ​microorganisms
which​ ​help​ ​break​ ​down​ ​cellulose
○ Microbes​ ​also​ ​have​ ​additional​ ​functions​ ​in​ ​foregut​ ​fermenters
■ Synthesis​ ​of​ ​limiting​ ​nutrients​ ​such​ ​as​ ​B​ ​vitamins​ ​and​ ​essential​ ​amino
acids
■ Recycling​ ​of​ ​nitrogen
● In​ ​ruminants,​ ​urea​ ​can​ ​diffuse​ ​into​ ​the​ ​rumen,​ ​where​ ​it​ ​is
broken​ ​down​ ​to​ ​make​ ​ammonia​ ​(NH​4​),​ ​which​ ​is​ ​useful​ ​for
synthesising​ ​amino​ ​acids
○ Many​ ​other​ ​vertebrates​ ​are​ ​hindgut​ ​fermenters,​ ​in​ ​the​ ​caecum​ ​or​ ​colon
■ Eg
...
​ ​petrel​ ​chicks​ ​become​ ​obese,​ ​as​ ​in​ ​order​ ​to​ ​consume​ ​enough​ ​protein​ ​for
growth​ ​from​ ​high-fat​ ​food,​ ​chicks​ ​need​ ​to​ ​consume​ ​more​ ​calories​ ​than​ ​they
burn
○ Obesity​ ​in​ ​humans​ ​may​ ​have​ ​been​ ​an​ ​advantage​ ​in​ ​our​ ​evolutionary​ ​past
■ Individuals​ ​who​ ​ate​ ​fatty​ ​food​ ​and​ ​stored​ ​energy​ ​as​ ​adipose​ ​tissue
may​ ​have​ ​been​ ​more​ ​likely​ ​to​ ​survive​ ​famines
--------------------------------------------------------------------------------------------------------------------------●

4:​ ​METABOLISM​ ​AND​ ​ENERGY​ ​SUPPLY
Energy​ ​acts​ ​as​ ​a​ ​‘common​ ​currency’​ ​for​ ​all​ ​metabolic​ ​processes​ ​(eg
...
​ ​disorder​ ​in​ ​a​ ​room​ ​happens​ ​spontaneously,​ ​ordering​ ​the​ ​room
requires​ ​energy
Energy​ ​use
● Biosynthesis
● Maintenance
● Generation​ ​of​ ​external​ ​work
Oxidative​ ​metabolism
● Cellular​ ​respiration
● The​ ​set​ ​of​ ​metabolic​ ​processes​ ​that​ ​animals​ ​use​ ​to​ ​convert​ ​chemical​ ​energy​ ​from
food​ ​into​ ​adenosine​ ​triphosphate​ ​(ATP),​ ​which​ ​is​ ​used​ ​to​ ​fuel​ ​work
○ The​ ​chemical​ ​energy​ ​in​ ​food​ ​can’t​ ​be​ ​used​ ​directly,​ ​so​ ​catabolic​ ​reactions
break​ ​down​ ​chemical​ ​bonds​ ​in​ ​food​ ​to​ ​release​ ​the​ ​energy
● Aerobic​ ​metabolism:​ ​requires​ ​O​2​​ ​to​ ​generate​ ​energy
● Potential​ ​energy​ ​stored​ ​in​ ​chemical​ ​bonds​ ​can​ ​be​ ​transferred​ ​from​ ​one​ ​molecule​ ​to
another​ ​by​ ​way​ ​of​ ​electrons
○ Catabolism:​ ​chemical​ ​reactions​ ​that​ ​harvest​ ​energy​ ​when​ ​bonds​ ​are​ ​broken
○ Oxidation:​ ​loss​ ​of​ ​electrons
○ Reduction:​ ​gain​ ​of​ ​electrons
○ Redox​ ​reactions
● ATP
○ Energy​ ​from​ ​food​ ​is​ ​used​ ​to​ ​form​ ​adenosine​ ​triphosphate​ ​(ATP)​ ​from
adenosine​ ​diphosphate​ ​(ADP)​ ​and​ ​inorganic​ ​phosphate​ ​ions​ ​(Pi)
■ ADP​ ​+​ ​Pi​ ​+​ ​energy​ ​--->​ ​ATP
○ Structure:
■ Ribose​ ​sugar
■ Adenine
■ Three​ ​phosphates
● Phosphates​ ​are​ ​negatively​ ​charged,​ ​so​ ​normally​ ​repel​ ​each
other,​ ​but​ ​the​ ​energy​ ​stored​ ​in​ ​the​ ​bonds​ ​between​ ​them​ ​keep
them​ ​together
○ The​ ​ATP​ ​cycle
■ Couples​ ​the​ ​cell’s​ ​energy-consuming​ ​(endergonic)​ ​processes​ ​and
energy-yielding​ ​(exergonic)​ ​processes
○

Joanna​ ​Griffith​ ​(2017)

The​ ​energy​ ​released​ ​when​ ​ATP​ ​is​ ​broken​ ​down​ ​to​ ​ADP​ ​can​ ​be
used​ ​to​ ​fuel​ ​endergonic​ ​cellular​ ​processes
● The​ ​energy​ ​released​ ​from​ ​an​ ​exergonic​ ​reaction​ ​can​ ​be​ ​used
to​ ​fuel​ ​the​ ​production​ ​of​ ​ATP​ ​from​ ​ADP+Pi
■ Glycolysis
● Preparation​ ​of​ ​carbohydrates
■ Kreb’s​ ​cycle
● Removal​ ​of​ ​“energized”​ ​electrons
■ Electron​ ​transport​ ​chain
● ATP​ ​synthesis​ ​(oxidation,​ ​phosphorylation)
● Efficiency​ ​of​ ​respiration
○ For​ ​each​ ​molecule​ ​of​ ​glucose​ ​degraded​ ​to​ ​CO​2​​ ​and​ ​water​ ​by​ ​respiration,​ ​the
cell​ ​makes​ ​up​ ​to​ ​32​ ​molecules​ ​of​ ​ATP
■ Approximately​ ​34%​ ​of​ ​the​ ​potential​ ​energy​ ​in​ ​glucose​ ​is​ ​transferred​ ​to
ATP​ ​(the​ ​rest​ ​is​ ​lost​ ​as​ ​heat)
● The​ ​most​ ​efficient​ ​car​ ​converts​ ​about​ ​25%​ ​of​ ​the​ ​energy​ ​in
petrol​ ​to​ ​movement
● Anaerobic​ ​respiration
○ Most​ ​animals​ ​can​ ​use​ ​anaerobic​ ​pathways​ ​(evolutionarily,​ ​it​ ​is​ ​the​ ​oldest
mechanism​ ​for​ ​respiration)
○ An​ ​organism’s​ ​entire​ ​metabolism​ ​may​ ​depend​ ​on​ ​it​ ​in​ ​anoxic​ ​environments
(no​ ​available​ ​O​2​)
■ Can​ ​occur​ ​in​ ​a​ ​regular​ ​cycle​ ​(eg
...
​ ​in​ ​rapid-burst
exercise​ ​or​ ​air-breathing​ ​deep-divers)
○ O​2​​ ​is​ ​not​ ​used​ ​as​ ​the​ ​final​ ​electron​ ​acceptor​ ​in​ ​the​ ​electron​ ​transport​ ​chain
■ Some​ ​sulphate-reducing​ ​bacteria​ ​use​ ​sulphate​ ​ion​ ​SO​4​2○ Most​ ​vertebrates​ ​have​ ​relatively​ ​low​ ​tolerance​ ​of​ ​anoxia/hypoxia
■ Only​ ​use​ ​anaerobiosis​ ​to​ ​any​ ​great​ ​extent​ ​for​ ​rapid-burst​ ​exercise
■ The​ ​advantage​ ​is​ ​rapid​ ​ATP​ ​generation,​ ​with​ ​the​ ​reaction​ ​taking​ ​place
entirely​ ​in​ ​cell​ ​cytoplasm
■ The​ ​disadvantage​ ​is​ ​the​ ​rapid​ ​buildup​ ​of​ ​toxic​ ​end​ ​products
Metabolic​ ​rate
● Measure​ ​of​ ​total​ ​energy​ ​metabolised​ ​per​ ​unit​ ​of​ ​time
● Enables​ ​the​ ​comparison​ ​of​ ​an​ ​individual’s​ ​energy​ ​budget​ ​in​ ​different​ ​environments,
and​ ​of​ ​different​ ​individuals​ ​or​ ​species​ ​in​ ​the​ ​same​ ​environment
● Quantifies​ ​the​ ​cost​ ​of​ ​living
● Factorial​ ​aerial​ ​scope:​ ​the​ ​ratio​ ​between​ ​basal​ ​and​ ​maximal​ ​MR
● Measuring​ ​metabolic​ ​rate
○ Direct​ ​calorimeter
■ Measures​ ​heat​ ​produced​ ​per​ ​unit​ ​of​ ​time
■ Eg
...
​ ​exercise)
○ Doubly-labelled​ ​water
■ Known​ ​quantities​ ​of​ ​unusual​ ​oxygen​ ​and​ ​hydrogen​ ​isotopes​ ​(eg
...
​ ​in
urine)
● Deuterium​ ​allows​ ​an​ ​independent
estimate​ ​of​ ​water​ ​loss
○ CO​2​​ ​does​ ​not​ ​contain​ ​hydrogen,
so​ ​all​ ​deuterium​ ​must​ ​be​ ​lost
through​ ​water​ ​loss
■ Therefore,​ ​total​ ​loss​ ​of​ ​oxygen-18,​ ​minus​ ​loss​ ​of
deuterium,​ ​equals​ ​loss​ ​of​ ​oxygen-18​ ​due​ ​to
expired​ ​CO​2
Standardised​ ​measures​ ​of​ ​metabolic​ ​rates
○ Allows​ ​comparisons​ ​amongst​ ​species,​ ​environments,​ ​etc
...
​ ​in​ ​animals​ ​that​ ​hibernate
○ Spatial​ ​heterothermy
■ Eg
...
​ ​crystallin​ ​protein​ ​in​ ​the​ ​lens​ ​of​ ​the​ ​eye
● Cold​ ​cataracts​ ​form​ ​in​ ​the​ ​eyes​ ​of​ ​cows​ ​and​ ​soldierfish​ ​after
some​ ​time​ ​at​ ​0°C,​ ​but​ ​not​ ​in​ ​the​ ​eyes​ ​of​ ​Antarctic​ ​toothfish
(adapted​ ​to​ ​life​ ​in​ ​a​ ​cold​ ​environment)
■ Eg
...
​ ​antifreeze​ ​proteins​ ​bind​ ​to​ ​ice​ ​crystals​ ​and​ ​prevent​ ​them
from​ ​joining​ ​in​ ​teleosts​ ​and​ ​insects
○ Antifreeze​ ​proteins​ ​are​ ​only​ ​synthesised​ ​as​ ​needed
● Other​ ​adaptations​ ​to​ ​cold
○ Increased​ ​expression​ ​of​ ​genes​ ​coding​ ​for​ ​proteins​ ​involved​ ​in​ ​damage
limitation​ ​of​ ​repair
■ Eg
...
​ ​pythons​ ​incubating​ ​egg​ ​clutches
Homeothermy​ ​(endothermy)
● Mammals​ ​and​ ​birds
● Homeothermy:
○ Physiological​ ​regulation​ ​of​ ​body​ ​temperature
○ Independence​ ​from​ ​environmental​ ​temperature
○ Energetically​ ​costly
● Mechanisms​ ​of​ ​heat​ ​production​ ​(thermogenesis)​ ​below​ ​thermoneutrality
○ Raised​ ​metabolic​ ​rate
○ Shivering
○ Nonshivering​ ​thermogenesis​ ​(NST)
■ Oxidation​ ​of​ ​stored​ ​fats
■ Occurs​ ​in​ ​mammals​ ​and​ ​the​ ​chicks​ ​of​ ​a​ ​few​ ​species​ ​of​ ​bird​ ​(eg
...
​ ​humans,​ ​horses,​ ​camels
○ Panting
■ Common​ ​in​ ​mammals​ ​and​ ​birds
○ Gular​ ​fluttering
■ Vibrating​ ​the​ ​roof​ ​of​ ​the​ ​mouth​ ​cavity
■ Common​ ​in​ ​birds
○ Saliva​ ​spreading
■ Done​ ​by​ ​many​ ​rodents​ ​and​ ​marsupials
● Chronic​ ​responses
○ Acclimatisation​ ​of​ ​peak​ ​metabolic​ ​rate
■ Increase​ ​in​ ​maximal​ ​rate​ ​at​ ​which​ ​heat​ ​can​ ​be​ ​produced
■ Works​ ​by​ ​burning​ ​the​ ​enlarged​ ​brown​ ​fat​ ​reserves​ ​developed​ ​by
animals,​ ​commonly​ ​small​ ​rodents,​ ​throughout​ ​summer​ ​and​ ​autumn
● Evolutionary​ ​responses
○ Escaping​ ​the​ ​costs​ ​of​ ​homeothermy​ ​by​ ​allowing​ ​body​ ​temperature​ ​to​ ​fall​ ​in​ ​a
controlled​ ​manner
■ Hibernation
● Several​ ​days​ ​or​ ​longer​ ​in​ ​winter
■ Estivation
● Several​ ​days​ ​or​ ​longer​ ​in​ ​summer
■ Torpor
● Only​ ​part​ ​of​ ​each​ ​day
● May​ ​allow​ ​organisms​ ​to​ ​save​ ​energy​ ​for​ ​hunting​ ​at​ ​preferred
periods​ ​of​ ​the​ ​day
■ Controlled​ ​hypothermia​ ​allows​ ​energy​ ​use​ ​to​ ​be​ ​drastically​ ​reduced
■ Controlled​ ​hypothermia​ ​in​ ​birds
● Many​ ​species​ ​of​ ​birds​ ​use​ ​shallow​ ​hypothermia​ ​(body
temperature​ ​remains​ ​well​ ​above​ ​ambient​ ​temperature)
○ Diet​ ​influences​ ​the​ ​dynamics​ ​of​ ​hibernation
■ Hibernators​ ​need​ ​storage​ ​lipids​ ​that​ ​are​ ​in​ ​a​ ​fluid​ ​state​ ​at​ ​low
temperatures
● Eg
...
​ ​dragonfly​ ​‘obelisk’​ ​posture​ ​to​ ​reduce​ ​heat​ ​gain​ ​by​ ​radiation
○ Many​ ​species​ ​of​ ​flying​ ​insects​ ​exhibit​ ​endothermy
■ Both​ ​temporal​ ​and​ ​spatial​ ​heterothermy
Joanna​ ​Griffith​ ​(2017)

Endothermy​ ​only​ ​when​ ​active​ ​(not​ ​when​ ​resting)
Endothermy​ ​usually​ ​in​ ​the​ ​thorax​ ​(location​ ​of​ ​flight​ ​muscles),
not​ ​abdomen
■ Many​ ​insects​ ​that​ ​demonstrate​ ​endothermy​ ​warm​ ​up​ ​by​ ​shivering
■ Some​ ​species​ ​which​ ​exhibit​ ​endothermy​ ​don’t​ ​thermoregulate,​ ​others
do​ ​(eg
...
​ ​air​ ​pressure​ ​at​ ​sea​ ​level​ ​is​ ​750mm​ ​Hg
■ Oxygen​ ​makes​ ​up​ ​21%​ ​of​ ​air
● 760​ ​x​ ​0
...
​ ​single​ ​cells
○ Large​ ​surface​ ​area​ ​to​ ​volume
○ Oxygen​ ​is​ ​removed​ ​by​ ​respiration​ ​(maintains​ ​a​ ​large​ ​difference​ ​in​ ​partial
pressure)
○ Body​ ​is​ ​only​ ​a​ ​few​ ​hundred​ ​microns​ ​(short​ ​diffusion​ ​distance)
○ Live​ ​in​ ​water​ ​or​ ​moist​ ​soil
● Eg
...
​ ​annelids
○ Segmented​ ​worm
○ Uses​ ​a​ ​circulatory​ ​system
○ No​ ​outside​ ​increased​ ​surface​ ​area,​ ​but​ ​a​ ​capillary​ ​network​ ​increases​ ​internal
surface​ ​area
●

Joanna​ ​Griffith​ ​(2017)

Oxygen​ ​is​ ​removed​ ​by​ ​respiration​ ​(maintains​ ​a​ ​large​ ​difference​ ​in​ ​partial
pressure)
○ A​ ​capillary​ ​network​ ​reduces​ ​diffusion​ ​distance
○ Lives​ ​in​ ​moist​ ​environments
There​ ​reaches​ ​a​ ​point​ ​where​ ​having​ ​just​ ​a​ ​circulatory​ ​system​ ​is​ ​not​ ​enough​ ​-​ ​a
respiratory​ ​system​ ​is​ ​needed
○ Will​ ​happen​ ​faster​ ​in​ ​water,​ ​as​ ​oxygen​ ​concentration​ ​in​ ​water​ ​is​ ​lower​ ​than​ ​in
air​ ​(30​ ​times​ ​less​ ​O​2​​ ​in​ ​water​ ​than​ ​in​ ​air)
Eg
...
​ ​crustaceans
○ Gills​ ​increase​ ​surface​ ​area
○ Partial​ ​pressure​ ​difference​ ​is​ ​maximised​ ​by​ ​ventilation
■ Aquatic​ ​animals​ ​move​ ​through​ ​water​ ​or​ ​move​ ​water​ ​over​ ​their​ ​gills​ ​for
ventilation
○ Gills​ ​have​ ​thin​ ​walls,​ ​reducing​ ​diffusion​ ​distance
○ Live​ ​in​ ​aquatic​ ​environments
Eg
...
​ ​insects
○ Use​ ​specialised​ ​gas​ ​exchange​ ​tubes​ ​called​ ​the​ ​tracheae​ ​and​ ​tracheoles
■ Liquid​ ​at​ ​the​ ​end​ ​of​ ​each​ ​tracheole​ ​provides​ ​a​ ​moist​ ​surface
■ Body​ ​movement​ ​can​ ​pump​ ​air​ ​through​ ​the​ ​tracheoles​ ​by​ ​squeezing​ ​air
sacs
● Eg
...
​ ​in​ ​mammals​ ​and​ ​amphibians
○ Vital​ ​capacity:​ ​maximum​ ​tidal​ ​volume
○ After​ ​exhalation,​ ​a​ ​residual​ ​volume​ ​of​ ​air​ ​remains​ ​in​ ​the​ ​lungs
○ Inefficient,​ ​eg
...
​ ​single-celled)
○ The​ ​organism​ ​is​ ​flat​ ​(eg
...
​ ​corals)
Specialised​ ​gas​ ​exchange​ ​organs:
○ Gills
■ Parapodia
■ External​ ​gills
■ Internal​ ​gills
○ Tracheae,​ ​tracheoles,​ ​air​ ​sacs
■ Insects
○ Lungs
■ Amphibians​ ​(positive​ ​pressure,​ ​tidal)
■ Mammals​ ​(negative​ ​pressure,​ ​tidal)
■ Birds​ ​(unidirectional)
Gas​ ​exchange​ ​organs​ ​get​ ​oxygen​ ​into​ ​the​ ​animal,​ ​but​ ​a​ ​second​ ​system​ ​is​ ​then
needed​ ​to​ ​move​ ​the​ ​oxygen​ ​around​ ​their​ ​bodies​ ​to​ ​every​ ​cell
All​ ​circulatory​ ​systems​ ​have:
○ A​ ​muscular​ ​pump​ ​or​ ​heart(s)
○ A​ ​network​ ​of​ ​vessels
○ A​ ​transport​ ​fluid
Open​ ​circulatory​ ​system
○ Found​ ​in​ ​arthropods​ ​and​ ​most​ ​molluscs
○ One​ ​or​ ​more​ ​pumps​ ​or​ ​hearts
○ Haemolymph​ ​and​ ​tissue​ ​fluid​ ​are​ ​the​ ​same​ ​liquid
○ Vessels​ ​open​ ​directly​ ​into​ ​tissues
○ The​ ​heart​ ​or​ ​pump​ ​relaxes​ ​and​ ​contracts​ ​(+​ ​body​ ​movement)
○ Valves​ ​keep​ ​the​ ​flow​ ​in​ ​one​ ​direction
○ Require​ ​less​ ​energy
Closed​ ​circulatory​ ​system
○ Found​ ​in​ ​annelids,​ ​cephalopods,​ ​and​ ​all​ ​vertebrates
○ One​ ​or​ ​more​ ​pumps​ ​or​ ​hearts
○ Vessels​ ​not​ ​open​ ​to​ ​tissue​ ​fluid
○ Higher​ ​pressure
○ More​ ​efficient​ ​for​ ​larger​ ​animals​ ​with​ ​high​ ​oxygen​ ​demand
○ Allows​ ​greater​ ​control​ ​over​ ​the​ ​flow​ ​of​ ​blood​ ​to​ ​different​ ​parts​ ​of​ ​the​ ​body
○ More​ ​efficient​ ​than​ ​open​ ​circulatory​ ​systems​ ​at​ ​transporting​ ​circulatory​ ​fluids
to​ ​tissues
○ Blood​ ​vessels​ ​have​ ​more​ ​muscular​ ​walls​ ​to​ ​withstand​ ​high​ ​blood​ ​pressure
○ Capillaries​ ​are​ ​needed​ ​to​ ​enable​ ​gas​ ​exchange
Joanna​ ​Griffith​ ​(2017)

●

●

●

Single​ ​circulation
○ Found​ ​in​ ​bony​ ​fish,​ ​rays,​ ​and​ ​sharks
○ Two-chambered​ ​heart
○ Blood​ ​leaving​ ​the​ ​heart​ ​passes​ ​through​ ​two​ ​capillary​ ​beds​ ​before​ ​returning​ ​to
the​ ​heart
Double​ ​circulation
○ Found​ ​in​ ​amphibians,​ ​reptiles,​ ​and​ ​mammals
○ Oxygen-poor​ ​and​ ​oxygen-rich​ ​blood​ ​is​ ​pumped​ ​separately​ ​from​ ​the​ ​opposite
sides​ ​of​ ​the​ ​heart
○ Three-chambered​ ​heart
■ Found​ ​in​ ​amphibians
■ Two​ ​atria,​ ​one​ ​ventricle
● The​ ​ventricle​ ​pumps​ ​blood​ ​into​ ​a​ ​forked​ ​artery​ ​that​ ​splits​ ​the
ventricle’s​ ​output​ ​into​ ​the​ ​pulmocutaneous​ ​circuit​ ​and​ ​the
systemic​ ​circuit
■ When​ ​underwater,​ ​blood​ ​flow​ ​to​ ​the​ ​lungs​ ​is​ ​nearly​ ​shut​ ​off
○ Three-chambered​ ​heart​ ​with​ ​partial​ ​septum
■ Found​ ​in​ ​reptiles​ ​(except​ ​birds)
■ Pulmonary​ ​circuit​ ​(lungs)​ ​and​ ​systemic​ ​circuit
■ In​ ​turtles,​ ​snakes,​ ​and​ ​lizards,​ ​the​ ​three-chambered​ ​heart​ ​is​ ​partially
divided​ ​by​ ​a​ ​septum​ ​(but​ ​blood​ ​can​ ​still​ ​cross​ ​through​ ​into​ ​the​ ​two
“halves”​ ​of​ ​the​ ​ventricle
■ In​ ​crocodilians,​ ​a​ ​septum​ ​fully​ ​divides​ ​the​ ​ventricle,​ ​and​ ​the​ ​pulmonary
and​ ​systemic​ ​circuits​ ​are​ ​connected​ ​in​ ​the​ ​aorta​ ​instead​ ​of​ ​through​ ​the
ventricle
○ Four-chambered​ ​heart
■ Found​ ​in​ ​mammals​ ​and​ ​birds
■ Two​ ​atria,​ ​two​ ​ventricles
● The​ ​left​ ​side​ ​of​ ​the​ ​heart​ ​pumps​ ​and​ ​receives​ ​only​ ​oxygen-rich
blood​ ​going​ ​to​ ​the​ ​body,​ ​while​ ​the​ ​right​ ​side​ ​receives​ ​and
pumps​ ​only​ ​oxygen-poor​ ​blood​ ​going​ ​to​ ​the​ ​lungs
■ Mammals​ ​and​ ​birds​ ​are​ ​endotherms,​ ​so​ ​they​ ​require​ ​more​ ​oxygen
than​ ​ectotherms
The​ ​mammalian​ ​heart
○ 4​ ​chambers:​ ​2​ ​atria,​ ​2​ ​ventricles
○ Three-step​ ​cardiac​ ​cycle
■ The​ ​heart​ ​contracts​ ​and​ ​relaxes​ ​in​ ​a​ ​rhythmic​ ​cycle
● Contraction​ ​is​ ​called​ ​systole
● Relaxation​ ​(filling)​ ​is​ ​called​ ​diastole
■ Atrial​ ​and​ ​ventricular​ ​diastole​ ​(0
...
1s)
● Pushes​ ​blood​ ​from​ ​the​ ​atria​ ​to​ ​the​ ​ventricles​ ​to​ ​fully​ ​fill​ ​them
■ Ventricular​ ​systole​ ​and​ ​atrial​ ​diastole​ ​(0
...
​ ​muscles)
○ Neuroendocrine:​ ​neurons​ ​cause​ ​hormones​ ​to​ ​be​ ​released,​ ​and​ ​these
neurohormones​ ​travel​ ​via​ ​the​ ​circulatory​ ​system​ ​to​ ​cells​ ​anywhere​ ​in​ ​the​ ​body
Signalling​ ​by​ ​pheromones
○ Instead​ ​of​ ​being​ ​released​ ​inside​ ​the​ ​body,​ ​hormones​ ​are​ ​released​ ​into​ ​the
environment
○ Used​ ​for​ ​mate​ ​attraction,​ ​path​ ​marking,​ ​etc
...
​ ​oestradiol​ ​triggers​ ​vitellogenin​ ​synthesis​ ​(used​ ​to​ ​form​ ​egg​ ​yolk)
One​ ​hormone​ ​can​ ​have​ ​multiple​ ​effects
○ Eg
...
​ ​oestradiol​ ​also​ ​triggers:
■ The​ ​reproductive​ ​system​ ​to​ ​synthesise​ ​proteins​ ​that​ ​form​ ​egg​ ​albumen
The​ ​endocrine​ ​and​ ​nervous​ ​systems​ ​act​ ​in​ ​concert​ ​to​ ​control​ ​reproduction​ ​and
development
○ Eg
...
​ ​in​ ​mammals,​ ​oxytocin​ ​causes​ ​the​ ​release​ ​of​ ​milk,​ ​causing​ ​greater
suckling​ ​by​ ​young,​ ​resulting​ ​in​ ​the​ ​release​ ​of​ ​more​ ​oxytocin
Endocrine​ ​pathways​ ​are​ ​subject​ ​to​ ​regulation​ ​by​ ​the​ ​nervous​ ​system,
including​ ​the​ ​brain​ ​(particularly​ ​the​ ​hypothalamus​ ​and​ ​pituitary​ ​gland)
■ Hypothalamus
● Receives​ ​information​ ​from​ ​the​ ​nervous​ ​system​ ​and​ ​initiates
responses​ ​through​ ​the​ ​endocrine​ ​system
■ Pituitary​ ​gland
● Attached​ ​to​ ​the​ ​hypothalamus
● Composed​ ​of​ ​anterior​ ​and​ ​posterior​ ​glands
○ Posterior​ ​pituitary​ ​gland
■ The​ ​two​ ​hormones​ ​released​ ​from​ ​the​ ​posterior
pituitary​ ​gland​ ​act​ ​directly​ ​on​ ​nonendocrine
tissues
● Oxytocin​ ​regulates​ ​milk​ ​production
(among​ ​other​ ​things)
● Antidiuretic​ ​hormone​ ​(ADH)​ ​regulates
many​ ​aspects​ ​of​ ​physiology​ ​and
behaviour
○ ADH​ ​and​ ​social​ ​behaviour
■ Eg
...
​ ​the​ ​release​ ​of​ ​thyroid​ ​hormone​ ​involves​ ​the​ ​hypothalamus,​ ​anterior
pituitary,​ ​and​ ​thyroid​ ​gland
○ Hormone​ ​cascade​ ​pathways​ ​typically​ ​involve​ ​negative​ ​feedback
Functions​ ​of​ ​specific​ ​hormones​ ​can​ ​diverge​ ​during​ ​evolution
○ Eg
...
​ ​prolactin​ ​and​ ​melanocyte-stimulating​ ​hormone​ ​(MSH)​ ​are​ ​both​ ​products
of​ ​the​ ​anterior​ ​pituitary​ ​and​ ​have​ ​a​ ​broad​ ​range​ ​of​ ​activities​ ​in​ ​vertebrates
Stress
○ Adrenal​ ​hormones​ ​as​ ​a​ ​response​ ​to​ ​stress
■ Adrenal​ ​glands​ ​are​ ​adjacent​ ​to​ ​kidneys
● Each​ ​adrenal​ ​gland​ ​consists​ ​of​ ​the​ ​adrenal​ ​medulla​ ​(inner
portion)​ ​and​ ​adrenal​ ​cortex​ ​(outer​ ​portion)
○ Adrenal​ ​medulla​ ​secretes​ ​catecholamines​ ​(adrenaline
and​ ​noradrenaline)
■ Adrenal​ ​hormones​ ​are​ ​released​ ​in​ ​response​ ​to​ ​stress-activated
impulses​ ​from​ ​the​ ​nervous​ ​system
● Mediate​ ​fight-or-flight​ ​(acute​ ​stress)​ ​responses
● Stressful​ ​stimuli​ ​cause​ ​the​ ​hypothalamus​ ​to​ ​secrete​ ​a​ ​releasing
hormone​ ​that​ ​stimulates​ ​the​ ​anterior​ ​pituitary​ ​to​ ​release​ ​ACTH
(a​ ​tropic​ ​hormone)
○ ACTH​ ​reaches​ ​the​ ​adrenal​ ​cortex​ ​via​ ​the​ ​bloodstream,
where​ ​it​ ​stimulates​ ​the​ ​release​ ​of​ ​corticosteroids
■ Glucocorticoids​ ​promote​ ​glucose​ ​synthesis​ ​from
noncarbohydrate​ ​sources​ ​(eg
...
​ ​catecholamines​ ​and​ ​glucocorticoids​ ​at​ ​low​ ​levels​ ​in​ ​the
early​ ​stress​ ​response​ ​act​ ​to​ ​stimulate​ ​the​ ​immune​ ​system,
allowing​ ​a​ ​wounded​ ​animal​ ​to​ ​survive​ ​without​ ​succumbing​ ​to​ ​a
bacterial​ ​infection
○ Later​ ​in​ ​the​ ​stress​ ​response,​ ​the​ ​same​ ​hormones​ ​at
higher​ ​levels​ ​suppress​ ​the​ ​immune​ ​system​ ​to​ ​prevent​ ​it
from​ ​overreacting​ ​and​ ​causing​ ​self-harm
■ Chronic​ ​immunosuppression​ ​causes​ ​increased
susceptibility​ ​to​ ​infections​ ​and​ ​disease
Endocrine​ ​signalling​ ​has​ ​important​ ​implications​ ​for​ ​pest​ ​control
○ Eg
...
​ ​feminisation​ ​of​ ​fish​ ​due​ ​to​ ​oestrogen​ ​in​ ​water
--------------------------------------------------------------------------------------------------------------------------○

9&10:​ ​OSMOREGULATION
Osmoregulation:​ ​the​ ​balance​ ​of​ ​salts​ ​and​ ​water​ ​between​ ​an​ ​organism​ ​and​ ​its
environment
● Osmosis:​ ​diffusion​ ​of​ ​water​ ​molecules​ ​across​ ​a​ ​partially​ ​permeable​ ​membrane
○ From​ ​hypoosmotic​ ​(low​ ​solute​ ​concentration)​ ​to​ ​hyperosmotic​ ​(high​ ​solute
concentration)
Excretory​ ​systems
● Summary:
○ Gills​ ​(fish)
○ Nasal​ ​glands​ ​(seabirds)
○ Malpighian​ ​tubules​ ​(insects)
○ Filtration:
■ Protonephridia​ ​(flatworms)
■ Metanephridia​ ​(earthworms)
■ Kidneys​ ​(mammals)
● Most​ ​excretory​ ​systems​ ​produce​ ​urine​ ​by​ ​refining​ ​a​ ​filtrate​ ​derived​ ​from​ ​body​ ​fluids
● Key​ ​functions​ ​of​ ​most​ ​excretory​ ​systems:
○ Filtration​ ​(filtering​ ​of​ ​body​ ​fluids)
○ Reabsorption​ ​(reclaiming​ ​valuable​ ​solutes)
○ Secretion​ ​(adding​ ​nonessential​ ​solutes​ ​and​ ​wastes​ ​from​ ​the​ ​body​ ​fluid​ ​to​ ​the
filtrate)
○ Excretion​ ​(processed​ ​filtrate​ ​containing​ ​nitrogenous​ ​waste​ ​is​ ​released​ ​from
the​ ​body)
● Protonephridia​ ​in​ ​flatworms
○ Open​ ​circulatory​ ​system
■ Tissues​ ​are​ ​bathed​ ​in​ ​fluid,​ ​branches​ ​of​ ​protonephridia​ ​extend​ ​into​ ​the
fluid
○ Filtration:
■ Flame​ ​bulbs​ ​have​ ​small​ ​openings​ ​that​ ​allow​ ​small​ ​solutes​ ​to​ ​move​ ​in
from​ ​body​ ​fluid
■ Moving​ ​cilia​ ​draw​ ​filtrate​ ​into​ ​the​ ​tubule
○ Reabsorption:
■ Reclaiming​ ​valuable​ ​solutes
■ Occurs​ ​in​ ​the​ ​tubule
○ Secretion:
■ No​ ​evidence​ ​for​ ​secretion​ ​in​ ​this​ ​system
○ Excretion:
■ Via​ ​an​ ​opening​ ​in​ ​the​ ​body​ ​wall
● Metanephridia​ ​in​ ​segmented​ ​worms
○ Closed​ ​circulatory​ ​system
○ Filtration:
●

Joanna​ ​Griffith​ ​(2017)

●

■ Via​ ​a​ ​ciliated​ ​funnel
○ Reabsorption:
■ Active​ ​transport​ ​of​ ​valuable​ ​solutes​ ​from​ ​tubes​ ​to​ ​the​ ​rich​ ​network​ ​of
capillaries
○ Secretion:
■ Adding​ ​of​ ​waste​ ​products​ ​to​ ​the​ ​filtrate
○ Excretion:
■ Nitrogenous​ ​waste
■ Released​ ​from​ ​the​ ​body​ ​via​ ​an​ ​external​ ​opening
Nephron​ ​in​ ​mammals
○ 1​ ​million​ ​nephrons​ ​in​ ​the​ ​kidneys
○ Filter​ ​1,300l​ ​of​ ​blood​ ​per​ ​day
○ >99%​ ​of​ ​products​ ​are​ ​reabsorbed
○ 1
...
​ ​kangaroo​ ​rats
○ Live​ ​in​ ​the​ ​desert,​ ​never​ ​drink​ ​water
○ Derive​ ​a​ ​lot​ ​of​ ​water​ ​from​ ​metabolism,​ ​lose​ ​very​ ​little​ ​in
urine​ ​and​ ​faeces
■ Different​ ​types​ ​of​ ​nephron
● Juxtamedullary​ ​nephron
○ Key​ ​to​ ​water​ ​conservation​ ​in​ ​terrestrial​ ​animals
■ Mammals​ ​that​ ​inhabit​ ​dry​ ​environments​ ​have​ ​long​ ​loops​ ​of​ ​Henle
● More​ ​reabsorption​ ​of​ ​water
■ Freshwater​ ​fish​ ​have​ ​short​ ​loops​ ​of​ ​Henle
● Less​ ​reabsorption​ ​of​ ​water
■ Marine​ ​bony​ ​fish​ ​are​ ​hypoosmotic​ ​compared​ ​to​ ​their​ ​environment
● Kidneys​ ​have​ ​small​ ​glomeruli,​ ​some​ ​lack​ ​glomeruli​ ​completely
● Filtration​ ​rates​ ​are​ ​low,​ ​very​ ​little​ ​urine​ ​is​ ​excreted
Different​ ​strategies​ ​in​ ​different​ ​environments
● The​ ​balancing​ ​of​ ​salts​ ​and​ ​water​ ​will​ ​depend​ ​on​ ​the​ ​environment​ ​an​ ​animal​ ​lives​ ​in
● Most​ ​vertebrates​ ​are​ ​either​ ​hypoionic​ ​osmoconformers​ ​and​ ​osmoregulators,​ ​but
hagfish​ ​are​ ​the​ ​exception
○ Hagfish​ ​rely​ ​primarily​ ​on​ ​NaCl​ ​to​ ​maintain​ ​extracellular​ ​fluid​ ​osmotic​ ​pressure,
with​ ​amino​ ​acids​ ​and​ ​methylamines​ ​as​ ​osmolytes​ ​in​ ​the​ ​intracellular​ ​fluid
■

Joanna​ ​Griffith​ ​(2017)

■
●

Hagfish​ ​are​ ​also​ ​stenohaline​ ​(they​ ​primarily​ ​live​ ​in​ ​deep​ ​water,​ ​so
probably​ ​never​ ​face​ ​changing​ ​salinity)

Marine
○ High​ ​osmolarity
○ There​ ​are​ ​salts​ ​and​ ​water​ ​in​ ​the​ ​environment​ ​and​ ​salts​ ​and​ ​water​ ​in​ ​the​ ​cells
■ All​ ​animals​ ​have​ ​selective​ ​membranes,​ ​osmoregulation​ ​is​ ​simply
balancing​ ​water​ ​and​ ​salts​ ​across​ ​these​ ​membranes
○ Osmoconformers
■ Eg
...
​ ​magnesium​ ​in​ ​Atlantic​ ​lobster
■ Generally​ ​prefer​ ​a​ ​stable​ ​environment
○ Stenohaline:​ ​organisms​ ​that​ ​cannot​ ​tolerate​ ​substantial​ ​changes​ ​in​ ​external
osmolality
○ Euryhaline:​ ​organisms​ ​that​ ​can​ ​survive​ ​large​ ​fluctuations​ ​in​ ​external
osmolality
■ Usually​ ​found​ ​in​ ​rock​ ​pool​ ​or​ ​estuaries,​ ​inhabiting​ ​fresh,​ ​brackish,​ ​and
saltwater
■ Euryhaline​ ​osmoconformers,​ ​eg
...
​ ​bass,​ ​salmon
● Main​ ​strategies:
○ Avoiders
■ Move​ ​with​ ​the​ ​salinity​ ​(eg
...
​ ​fish​ ​gills,​ ​frog​ ​skin)
○ Varying​ ​salt​ ​uptake
■ Reduce​ ​drinking
■ Use​ ​hormones​ ​such​ ​as​ ​cortisol​ ​to​ ​control​ ​uptake
of​ ​Na​ ​in:
● The​ ​gills
● The​ ​midgut/intestines
● The​ ​kidney
○ Cellular​ ​osmoregulation
■ Cels​ ​can​ ​pump​ ​salts​ ​across​ ​their​ ​membranes,
and​ ​lose​ ​amino​ ​acids​ ​(compensatory​ ​osmolytes)
○ Osmoregulators
■ Expend​ ​energy​ ​to​ ​control​ ​water​ ​uptake​ ​and​ ​loss​ ​in​ ​a​ ​hyperosmotic​ ​or
hypoosmotic​ ​environment
Joanna​ ​Griffith​ ​(2017)

■

■

●

●

In​ ​fish,​ ​the​ ​gills​ ​are​ ​the​ ​partially​ ​permeable​ ​membrane​ ​that​ ​control​ ​the
influx​ ​of​ ​water​ ​and​ ​solutes
● In​ ​marine​ ​fish
○ Specialised​ ​salt​ ​excreting​ ​cells​ ​in​ ​the​ ​gills​ ​excrete​ ​Cl​-​,
and​ ​Na​+​​ ​follows
○ Kidneys​ ​extract​ ​calcium,​ ​magnesium,​ ​and​ ​sulphate
○ Very​ ​little,​ ​concentrated​ ​urine
● In​ ​sharks​ ​and​ ​cartilaginous​ ​fish
○ Overall​ ​internal​ ​osmolality​ ​is​ ​slightly​ ​higher​ ​than​ ​that​ ​of
seawater
■ Relatively​ ​low​ ​levels​ ​of​ ​salt​ ​in​ ​tissues​ ​compared
to​ ​seawater
○ Extremely​ ​high​ ​levels​ ​of​ ​urea​ ​in​ ​tissues
■ Trimethylamine​ ​oxide​ ​(TMAO)​ ​protects​ ​proteins
from​ ​the​ ​toxicity​ ​of​ ​urea
The​ ​energetics​ ​of​ ​osmoregulation
● Osmoregulators​ ​must​ ​expend​ ​energy​ ​to​ ​maintain​ ​osmotic
gradient
○ The​ ​amount​ ​of​ ​energy​ ​differs​ ​based​ ​on​ ​how​ ​different
the​ ​animal’s​ ​osmolarity​ ​is​ ​from​ ​its​ ​surroundings
■ Eg
...
​ ​tardigrades​ ​can​ ​be​ ​dehydrated​ ​to​ ​2%​ ​water​ ​(normally​ ​85%​ ​water)
...
​ ​humans​ ​can​ ​only​ ​lose​ ​12%​ ​of​ ​water,​ ​camels​ ​can​ ​lose​ ​24%
■ Have​ ​to​ ​balance​ ​water​ ​and​ ​salt​ ​gain/loss
● Water​ ​gain:
○ Freshwater
○ Food
○ Metabolism
● Water​ ​loss:
○ Sweat
○ Breathing
○ Urine

Joanna​ ​Griffith​ ​(2017)

○ Faeces
● Some​ ​organisms​ ​can​ ​gain​ ​water​ ​by​ ​drinking​ ​seawater
○ Eg
...
​ ​in​ ​albatrosses,​ ​insects​ ​(malpighian​ ​tubules)
● Malpighian​ ​tubules
○ In​ ​insects​ ​and​ ​other​ ​terrestrial
arthropods,​ ​malpighian​ ​tubules
remove​ ​nitrogenous​ ​wastes​ ​from
haemolymph,​ ​and​ ​function​ ​in
osmoregulation
■ Insects​ ​produce​ ​relatively
dry​ ​waste,​ ​mainly​ ​uric
acid
■ Some​ ​organisms​ ​can
absorb​ ​water​ ​from​ ​the​ ​air
through​ ​the​ ​rectum
--------------------------------------------------------------------------------------------------------------------------11:​ ​REPRODUCTION
Asexual​ ​reproduction
● Creation​ ​of​ ​offspring​ ​without​ ​the​ ​fusion​ ​of​ ​egg​ ​and​ ​sperm
● Mechanisms:
○ Fission
■ Separation​ ​of​ ​parent​ ​into​ ​two​ ​or​ ​more​ ​individuals​ ​of​ ​about​ ​the​ ​same
size
■ Applies​ ​to​ ​many​ ​invertebrates
○ Budding
■ New​ ​individuals​ ​arise​ ​from​ ​outgrowths​ ​of​ ​existing​ ​ones
■ Eg
...
​ ​some​ ​annelid​ ​worms,​ ​many​ ​sponges,​ ​sea​ ​squirts
○ Parthenogenesis
■ New​ ​individual​ ​from​ ​an​ ​unfertilised​ ​egg
■ Eg
...

day​ ​length)
○ Some​ ​organisms,​ ​eg
...
​ ​in​ ​asexual​ ​whiptail​ ​lizards,​ ​females​ ​exhibit​ ​male-like​ ​mating
behaviours​ ​and​ ​switch​ ​roles​ ​several​ ​times​ ​a​ ​season
Variation​ ​in​ ​patterns​ ​of​ ​sexual​ ​reproduction
○ Hermaphroditism
■ Each​ ​individual​ ​has​ ​male​ ​and​ ​female​ ​reproductive​ ​systems
■ Two​ ​hermaphrodites​ ​can​ ​mate,​ ​some​ ​can​ ​self-fertilise
○ Sex​ ​reversal
■ Male-to-female
● Eg
...
​ ​bluehead​ ​wrasse
Gamete​ ​production
○ Organisms​ ​must​ ​produce​ ​gametes​ ​in​ ​order​ ​to​ ​reproduce​ ​sexually
○ In​ ​most​ ​species,​ ​individuals​ ​have​ ​gonads​ ​that​ ​produce​ ​gametes
○ Gametogenesis​ ​differs​ ​in​ ​males​ ​and​ ​females,​ ​reflecting​ ​the​ ​different,​ ​distinct
structure​ ​and​ ​function​ ​of​ ​their​ ​gametes
■ Sperm​ ​are​ ​small,​ ​motile,​ ​and​ ​pass​ ​from​ ​male​ ​to​ ​female
■ Eggs​ ​are​ ​larger​ ​and​ ​perform​ ​their​ ​function​ ​within​ ​the​ ​female
○ All​ ​gametes​ ​are​ ​produced​ ​by​ ​meiosis
■ Produces​ ​haploid​ ​cells
○ Spermatogenesis​ ​vs
...
​ ​TLR3​ ​recognises​ ​dsRNA,​ ​TLR4​ ​only​ ​recognises
lipopolysaccharides​ ​found​ ​on​ ​bacteria,​ ​TLR5
recognises​ ​flagellin​ ​(the​ ​main​ ​component​ ​of​ ​flagella)
○
○
○

●

●

●

●

●

●

●
●

Joanna​ ​Griffith​ ​(2017)

●

Binding​ ​results​ ​in​ ​a​ ​signal​ ​cascade,​ ​which​ ​results​ ​in
phagocytosis
○ Chemotaxis​ ​and​ ​adherence​ ​of​ ​the​ ​microbe​ ​to​ ​the
phagocyte
○ Ingestion​ ​of​ ​the​ ​microbe​ ​by​ ​phagocyte
○ Formation​ ​of​ ​a​ ​phagosome
○ Fusion​ ​of​ ​the​ ​phagosome​ ​with​ ​a​ ​lysosome​ ​to​ ​form​ ​a
phagolysosome
○ Digestion​ ​of​ ​ingested​ ​microbe​ ​by​ ​enzymes
○ Formation​ ​of​ ​residual​ ​body​ ​containing​ ​indigestible
material
○ Discharge​ ​of​ ​waste​ ​materials

Mast​ ​cells
■ Release​ ​histamine
● Causes​ ​vasodilation,​ ​increasing​ ​blood​ ​flow​ ​to​ ​the​ ​area​ ​and
thus​ ​increasing​ ​the​ ​number​ ​of​ ​white​ ​blood​ ​cells​ ​in​ ​the​ ​area
● Inflammatory​ ​response
○ May​ ​produce​ ​swelling,​ ​pain,​ ​redness,​ ​and​ ​heat
○ Neutrophils
■ Circulate​ ​in​ ​blood
● Make​ ​up​ ​60-70%​ ​of​ ​circulating​ ​immune​ ​cells
● Move​ ​out​ ​of​ ​blood​ ​vessels​ ​by​ ​extravasation
○ Histamine​ ​dilates​ ​blood​ ​vessels,​ ​creating​ ​slight​ ​gaps​ ​in
the​ ​walls
○ Neutrophils​ ​pick​ ​up​ ​cellular​ ​receptors,​ ​which​ ​cause
them​ ​to​ ​stick​ ​to​ ​blood​ ​vessel​ ​walls
○ Transdermal​ ​migration
■ Neutrophils​ ​can​ ​change​ ​shape​ ​and​ ​move
through​ ​tissue,​ ​following​ ​the​ ​gradient​ ​of
signalling​ ​molecules​ ​from​ ​macrophages​ ​by
chemotaxis
■ Can​ ​detect​ ​and​ ​phagocytose​ ​abnormal​ ​proteins
○ Dendritic​ ​cells
■ Antigen-presenting​ ​cells
■ Act​ ​as​ ​messengers​ ​between​ ​the​ ​innate​ ​and​ ​adaptive​ ​immune​ ​systems
Specific/adaptive
● Cells​ ​of​ ​the​ ​specific​ ​immune​ ​system
○ Lymphocytes
■ Look​ ​like​ ​neutrophils​ ​and​ ​macrophages
■ Recirculate​ ​around​ ​the​ ​body
■ Only​ ​recognise​ ​specific​ ​targets
● Each​ ​lymphocyte​ ​carries​ ​one​ ​specific​ ​receptor​ ​type
○ Lymphocytes​ ​can​ ​recognise​ ​up​ ​to​ ​10​ ​million​ ​receptors
■ Made​ ​up​ ​of​ ​V​ ​genes​ ​(50-200),​ ​J​ ​genes​ ​(5),​ ​and
C​ ​genes​ ​(1)​ ​which​ ​enable​ ​a​ ​huge​ ​range​ ​of
variation​ ​through​ ​different​ ​combinations
○

Joanna​ ​Griffith​ ​(2017)

■
■
■

Proliferate
Differentiate
Have​ ​‘memory’
● Enable​ ​a​ ​secondary​ ​immune​ ​response​ ​upon​ ​re-exposure​ ​to​ ​a
pathogen
■ Many​ ​other​ ​specialist​ ​functions
■ When​ ​a​ ​lymphocyte​ ​recognises​ ​an​ ​antigen
● Produces​ ​clones​ ​(with​ ​the​ ​same​ ​receptor​ ​type)
● Some​ ​cells​ ​differentiate​ ​into​ ​effector​ ​cells,​ ​some​ ​into​ ​memory
cells​ ​(which​ ​are​ ​longer-lived​ ​and​ ​able​ ​to​ ​respond​ ​to​ ​future
infections​ ​by​ ​the​ ​same​ ​pathogen)
■ B-lymphocytes
● Mature​ ​in​ ​bone​ ​marrow
● Once​ ​activated​ ​into​ ​plasma​ ​cells,​ ​they​ ​produce​ ​antigen-specific
antibodies
○ One​ ​cell​ ​can​ ​produce​ ​100,000​ ​molecules​ ​per​ ​minute​ ​for
4-5​ ​days​ ​before​ ​dying
● Antibodies
○ Clumping
■ Causes​ ​pathogens​ ​to​ ​clump​ ​together,​ ​restricting
movements​ ​and​ ​making​ ​them​ ​easier​ ​to​ ​deal
with
○ Blocking​ ​viral​ ​receptors
■ viruses​ ​have​ ​receptors​ ​that​ ​allow​ ​them​ ​to​ ​enter
cells​ ​and​ ​replicate​ ​inside​ ​of​ ​them
● Once​ ​coated​ ​in​ ​antibodies,​ ​they​ ​no
longer​ ​have​ ​any​ ​more​ ​exposed
receptors
○ Opsonisation
■ Coating​ ​a​ ​pathogen​ ​in​ ​antibody​ ​makes​ ​it​ ​more
visible​ ​to​ ​macrophages
■ T-lymphocytes
● Search​ ​inside​ ​cells​ ​for​ ​signs​ ​of​ ​infection​ ​(eg
...
​ ​squid
■ Have​ ​“giant​ ​axons”
● Key​ ​role​ ​in​ ​understanding​ ​how​ ​neurons​ ​work
○ Nervous​ ​systems​ ​process​ ​information​ ​in​ ​three​ ​stages
■ Sensory​ ​input
● Data​ ​from​ ​sensors​ ​travels​ ​along​ ​sensory​ ​neurons
■ Integration
● In​ ​the​ ​brain​ ​(central​ ​nervous​ ​system)
● By​ ​interneurons
■ Motor​ ​output
● Sent​ ​via​ ​motor​ ​neurons,​ ​which​ ​trigger​ ​effector​ ​activity
○ Most​ ​neurons​ ​have​ ​dendrites,​ ​highly​ ​branched​ ​extensions​ ​that​ ​receive​ ​signals
from​ ​other​ ​neurons
○ The​ ​axon​ ​of​ ​a​ ​neuron​ ​is​ ​a​ ​longer​ ​extension​ ​from​ ​the​ ​cell​ ​body​ ​that​ ​transmits
signals​ ​to​ ​other​ ​cells​ ​at​ ​synapses
○ The​ ​synaptic​ ​terminal​ ​of​ ​one​ ​axon​ ​passes​ ​information​ ​across​ ​the​ ​synapses​ ​in
the​ ​form​ ​of​ ​chemical​ ​messengers​ ​called​ ​neurotransmitters
■ A​ ​synapse​ ​is​ ​a​ ​junction​ ​between​ ​an​ ​axon​ ​and​ ​another​ ​cell
Resting​ ​potential
● Every​ ​cell​ ​has​ ​a​ ​voltage​ ​(difference​ ​in​ ​electrical​ ​charge)​ ​across​ ​its​ ​plasma​ ​membrane
called​ ​a​ ​membrane​ ​potential
○ Resting​ ​potential​ ​is​ ​the​ ​membrane​ ​potential​ ​of​ ​a​ ​neuron​ ​not​ ​sending​ ​signals
○ Changes​ ​in​ ​membrane​ ​potential​ ​act​ ​as​ ​signals,​ ​transmitting​ ​and​ ​processing
information
● Formation​ ​of​ ​the​ ​resting​ ​potential
○ In​ ​a​ ​mammalian​ ​neuron​ ​at​ ​resting​ ​potential,​ ​the​ ​concentration​ ​of​ ​potassium
ions​ ​is​ ​highest​ ​inside​ ​the​ ​cell,​ ​while​ ​the​ ​concentration​ ​of​ ​sodium​ ​ions​ ​is
highest​ ​outside​ ​the​ ​cell

Joanna​ ​Griffith​ ​(2017)

Sodium-potassium​ ​pumps​ ​use​ ​ATP​ ​to​ ​maintain​ ​K+​​ ​ ​and​ ​Na​+​​ ​gradients
across​ ​the​ ​membrane
■ These​ ​concentration​ ​gradients​ ​represent​ ​chemical​ ​potential​ ​energy
○ The​ ​opening​ ​of​ ​ion​ ​channels​ ​in​ ​the​ ​plasma​ ​membrane​ ​converts​ ​chemical
potential​ ​to​ ​electrical​ ​potential
■ A​ ​neuron​ ​at​ ​resting​ ​potential​ ​contains​ ​many​ ​open​ ​K+​​ ​ ​channels​ ​and
fewer​ ​open​ ​Na​+​ ​channels,​ ​so​ ​K+​​ ​ ​diffuses​ ​out​ ​of​ ​the​ ​cell
● The​ ​resulting​ ​buildup​ ​of​ ​negative​ ​charge​ ​within​ ​the​ ​neuron​ ​is
the​ ​major​ ​source​ ​of​ ​membrane​ ​potential
Action​ ​potential
● Changes​ ​in​ ​membrane​ ​potential​ ​occur​ ​because​ ​neurons​ ​contain​ ​gated​ ​ion​ ​channels
that​ ​open​ ​or​ ​close​ ​in​ ​response​ ​to​ ​stimuli
○ When​ ​gated​ ​K+​​ ​ ​channels​ ​open,​ ​K+​​ ​ ​diffuses​ ​out,​ ​making​ ​the​ ​inside​ ​of​ ​the​ ​cell
more​ ​negative
■ This​ ​is​ ​hyperpolarisation,​ ​an​ ​increase​ ​in​ ​magnitude​ ​of​ ​the​ ​membrane
potential
○ Opening​ ​other​ ​types​ ​of​ ​ion​ ​channels​ ​triggers​ ​depolarisation,​ ​a​ ​reduction​ ​in​ ​the
magnitude​ ​of​ ​the​ ​membrane​ ​potential
■ Eg
...
​ ​this​ ​direct​ ​transmission​ ​of​ ​action​ ​potential​ ​enables​ ​rapid​ ​coordination​ ​of
predator​ ​avoidance​ ​response​ ​in​ ​squids​ ​and​ ​lobsters
● Most​ ​synapses​ ​are​ ​chemical​ ​synapses
● Process:
○ Action​ ​potential​ ​arrives​ ​and​ ​depolarises​ ​the​ ​presynaptic​ ​membrane
○ Voltage-gated​ ​channels​ ​open,​ ​influx​ ​of​ ​calcium​ ​ions​ ​(Ca​2+​)
○ Ca​2+​ ​causes​ ​synaptic​ ​vesicles​ ​to​ ​fuse​ ​with​ ​the​ ​presynaptic​ ​membrane,
releasing​ ​neurotransmitters​ ​in​ ​the​ ​synaptic​ ​cleft
○ Neurotransmitter​ ​binds​ ​to​ ​ligand-gated​ ​ion​ ​channels​ ​in​ ​the​ ​postsynaptic
membrane,​ ​resulting​ ​in​ ​a​ ​postsynaptic​ ​potential
● Generation​ ​of​ ​postsynaptic​ ​potentials
○ Some​ ​ligand-gated​ ​ion​ ​channels​ ​permit​ ​diffusion​ ​of​ ​both​ ​K+​​ ​ ​and​ ​Na​+
■ When​ ​open,​ ​this​ ​gate​ ​causes​ ​a​ ​depolarisation​ ​called​ ​an​ ​excitatory
postsynaptic​ ​potential​ ​(EPSP)
■

Joanna​ ​Griffith​ ​(2017)

Other​ ​ligand-gated​ ​ion​ ​channels​ ​are​ ​selective​ ​to​ ​K+​​ ​ ​and​ ​Na​+
■ When​ ​open,​ ​this​ ​gate​ ​causes​ ​a​ ​hyperpolarisation​ ​called​ ​an​ ​inhibitory
postsynaptic​ ​potential​ ​(IPSP)
○ Most​ ​neurons​ ​have​ ​many​ ​synapses​ ​on​ ​their​ ​dendrites​ ​and​ ​cell​ ​body
■ A​ ​single​ ​EPSP​ ​is​ ​usually​ ​too​ ​small​ ​to​ ​trigger​ ​an​ ​action​ ​potential​ ​in​ ​a
postsynaptic​ ​neuron
● Temporal​ ​summation:​ ​two​ ​or​ ​more​ ​EPSPs​ ​are​ ​produced​ ​in
rapid​ ​succession
● Spatial​ ​summation:​ ​EPSPs​ ​produced​ ​nearly​ ​simultaneously​ ​by
different​ ​synapses​ ​on​ ​the​ ​same​ ​postsynaptic​ ​neuron​ ​add
together
● Combinations​ ​of​ ​EPSPs​ ​through​ ​spatial​ ​and​ ​temporal
summation​ ​can​ ​trigger​ ​an​ ​action​ ​potential
● Modulated​ ​signalling​ ​at​ ​synapses
○ In​ ​some​ ​synapses,​ ​a​ ​neurotransmitter​ ​binds​ ​to​ ​a​ ​receptor​ ​that​ ​is​ ​metabotropic
○ Movement​ ​of​ ​ions​ ​through​ ​a​ ​channel​ ​depends​ ​on​ ​metabolic​ ​steps,​ ​and
activates​ ​a​ ​signal​ ​transduction​ ​pathway,​ ​eg
...
​ ​tropical​ ​cone​ ​snail
■ Capture​ ​of​ ​fast-moving​ ​prey​ ​by​ ​slow-moving​ ​predator
■ Cone​ ​snails​ ​synthesise​ ​alpha​ ​conotoxins​ ​which​ ​bind​ ​to​ ​receptor​ ​sites
on​ ​acetylcholine​ ​receptors​ ​on​ ​muscles,​ ​paralysing​ ​the​ ​prey
○ Eg
...
​ ​golden​ ​poison​ ​dart​ ​frog
■ Batrachotoxin
■ Extremely​ ​poisonous
● Costly​ ​to​ ​frog,​ ​but​ ​evolved​ ​as​ ​part​ ​of​ ​an​ ​arms​ ​race
○

Joanna​ ​Griffith​ ​(2017)

A-LEVEL​ ​NOTES
Resting​ ​potential
● When​ ​an​ ​axon​ ​is​ ​not​ ​conducting​ ​a​ ​nerve​ ​impulse,​ ​the​ ​membrane​ ​is​ ​relatively
impermeable​ ​to​ ​sodium​ ​ions,​ ​but​ ​freely​ ​permeable​ ​to​ ​potassium​ ​ions
○ An​ ​active​ ​sodium/potassium​ ​ion​ ​pump​ ​uses​ ​ATP​ ​to​ ​move​ ​sodium​ ​ions​ ​out​ ​and
potassium​ ​ions​ ​in​ ​in​ ​a​ ​3:2​ ​ratio
○ Potassium​ ​ions​ ​gradually​ ​diffuse​ ​back​ ​out​ ​along​ ​the​ ​concentration​ ​gradient
■ Eventually,​ ​the​ ​movement​ ​of​ ​positively​ ​charged​ ​potassium​ ​ions​ ​out​ ​of
the​ ​cell​ ​along​ ​the​ ​concentration​ ​gradient​ ​is​ ​opposed​ ​by​ ​the
electrochemical​ ​gradient,​ ​leaving​ ​the​ ​inside​ ​of​ ​the​ ​cell​ ​negative​ ​(-70
mV)​ ​relative​ ​to​ ​the​ ​outside
● polarisation
Action​ ​potential
● The​ ​change​ ​in​ ​electrical​ ​potential​ ​as​ ​an​ ​impulse​ ​passes​ ​along​ ​a​ ​neuron​ ​or​ ​muscle
cell
● Occurs​ ​in​ ​response​ ​to​ ​a​ ​stimulus​ ​(from​ ​a​ ​receptor​ ​or​ ​synapse)
● When​ ​a​ ​neuron​ ​is​ ​stimulated,​ ​sodium​ ​ion​ ​channels​ ​open,​ ​making​ ​the​ ​axon​ ​permeable
to​ ​sodium​ ​ions
○ Potential​ ​difference​ ​across​ ​the​ ​membrane​ ​is​ ​reversed​ ​as​ ​the​ ​inside​ ​of​ ​the
neuron​ ​becomes​ ​positively​ ​charged​ ​(depolarisation)
○ After​ ​a​ ​brief​ ​period​ ​of​ ​depolarisation,​ ​the​ ​sodium​ ​ion​ ​channels​ ​close​ ​again​ ​and
the​ ​excess​ ​sodium​ ​ions​ ​are​ ​pumped​ ​out​ ​using​ ​active​ ​transport
■ The​ ​permeability​ ​of​ ​the​ ​membrane​ ​to​ ​potassium​ ​ions​ ​is​ ​increased,
leading​ ​to​ ​hyperpolarisation​ ​as​ ​the​ ​inside​ ​of​ ​the​ ​membrane​ ​becomes
extremely​ ​negative​ ​due​ ​to​ ​potassium​ ​ions​ ​being​ ​attracted​ ​by​ ​the
negative​ ​charge​ ​outside​ ​of​ ​the​ ​axon
● The​ ​threshold​ ​for​ ​any​ ​nerve​ ​fibre​ ​is​ ​the​ ​point​ ​at​ ​which​ ​the​ ​rush​ ​of​ ​sodium​ ​ions​ ​into​ ​the
axon​ ​is​ ​greater​ ​than​ ​the​ ​outflow​ ​of​ ​potassium​ ​ions​ ​(all-or-nothing​ ​response)
● The​ ​recovery/refractory​ ​period​ ​of​ ​an​ ​axon​ ​is​ ​the​ ​time​ ​is​ ​takes​ ​for​ ​an​ ​area​ ​of​ ​the​ ​axon
membrane​ ​to​ ​repolarise​ ​after​ ​an​ ​action​ ​potential
○ Absolute​ ​refractory​ ​period:​ ​the​ ​point​ ​immediately​ ​after​ ​the​ ​action​ ​potential,
where​ ​it​ ​is​ ​impossible​ ​to​ ​re-stimulate​ ​the​ ​fibre​ ​as​ ​the​ ​sodium​ ​ion​ ​channels​ ​are
completely​ ​blocked​ ​and​ ​the​ ​resting​ ​potential​ ​has​ ​not​ ​yet​ ​been​ ​restored
○ Relative​ ​refractory​ ​period:​ ​the​ ​point​ ​when​ ​the​ ​axon​ ​may​ ​be​ ​re-stimulated,​ ​but
only​ ​by​ ​a​ ​much​ ​stronger​ ​stimulus
○ The​ ​refractory​ ​period​ ​is​ ​necessary​ ​to​ ​limit​ ​the​ ​rate​ ​at​ ​which​ ​impulses​ ​can​ ​flow
along​ ​a​ ​fibre​ ​and​ ​ensure​ ​that​ ​they​ ​only​ ​flow​ ​in​ ​one​ ​direction
● The​ ​spread​ ​of​ ​an​ ​action​ ​potential​ ​along​ ​an​ ​axon
○ As​ ​the​ ​change​ ​in​ ​charge​ ​difference​ ​spreads​ ​from​ ​open​ ​sodium​ ​ion​ ​channels,
sodium​ ​channels​ ​further​ ​down​ ​the​ ​axon​ ​begin​ ​to​ ​open​ ​(due​ ​to​ ​reversal​ ​of
charges)
○ The​ ​original​ ​sodium​ ​ion​ ​channels​ ​close​ ​and​ ​the​ ​adjacent​ ​potassium​ ​channels
open

Joanna​ ​Griffith​ ​(2017)

○

As​ ​potassium​ ​ions​ ​move​ ​out​ ​of​ ​the​ ​cell,​ ​original​ ​charges​ ​(resting​ ​potential)
across​ ​the​ ​membrane​ ​are​ ​restored​ ​and​ ​the​ ​potassium​ ​channels​ ​close,​ ​and​ ​so
on

Synapses
● Information​ ​needs​ ​to​ ​be​ ​able​ ​to​ ​pass​ ​freely​ ​through​ ​the​ ​nervous​ ​system,​ ​through
receptors​ ​to​ ​sensory​ ​neurons​ ​to​ ​the​ ​CNS​ ​to​ ​effector​ ​organs
● Process:
○ The​ ​arrival​ ​of​ ​an​ ​impulse​ ​at​ ​the​ ​synaptic​ ​knob​ ​increases​ ​the​ ​permeability​ ​of
the​ ​presynaptic​ ​membrane​ ​to​ ​calcium​ ​ions​ ​(as​ ​calcium​ ​ion​ ​channels​ ​open),so
calcium​ ​ions​ ​move​ ​into​ ​the​ ​synaptic​ ​knob​ ​down​ ​the​ ​concentration​ ​gradient
○ The​ ​influx​ ​of​ ​calcium​ ​ions​ ​causes​ ​the​ ​synaptic​ ​vesicles​ ​(which​ ​contain
neurotransmitters)​ ​to​ ​move​ ​to​ ​the​ ​presynaptic​ ​membrane
○ Some​ ​of​ ​the​ ​vesicles​ ​fuse​ ​with​ ​the​ ​presynaptic​ ​membrane​ ​and​ ​release​ ​the
neurotransmitters​ ​into​ ​the​ ​synaptic​ ​cleft,​ ​which​ ​diffuse​ ​across​ ​the​ ​gap​ ​and
become​ ​attached​ ​to​ ​specific​ ​protein​ ​receptor​ ​sites​ ​on​ ​the​ ​postsynaptic
membrane
○ Sodium​ ​ion​ ​channels​ ​in​ ​the​ ​postsynaptic​ ​membrane​ ​open,​ ​causing​ ​an​ ​influx​ ​of
sodium​ ​ions​ ​into​ ​the​ ​axon,​ ​causing​ ​a​ ​change​ ​in​ ​the​ ​potential​ ​difference​ ​across
the​ ​membrane​ ​and​ ​an​ ​excitatory​ ​postsynaptic​ ​potential
○ If​ ​there​ ​are​ ​sufficient​ ​EPSPs,​ ​the​ ​positive​ ​charge​ ​in​ ​the​ ​postsynaptic​ ​cell
exceeds​ ​the​ ​threshold​ ​level,​ ​and​ ​an​ ​action​ ​potential​ ​is​ ​produced​ ​to​ ​carry​ ​an
impulse​ ​through​ ​the​ ​cell
Summation
● Signal​ ​summation​ ​occurs​ ​when​ ​the​ ​impulses​ ​in​ ​different​ ​neurons​ ​add​ ​together​ ​when
they​ ​synapse​ ​with​ ​the​ ​same​ ​neurons​ ​to​ ​reach​ ​the​ ​threshold​ ​of​ ​excitation​ ​and​ ​cause
an​ ​action​ ​potential​ ​in​ ​the​ ​postsynaptic​ ​neuron
○ Excitatory​ ​postsynaptic​ ​potentials​ ​result​ ​from​ ​the​ ​depolarisation​ ​of​ ​an​ ​axon,
resulting​ ​in​ ​an​ ​action​ ​potential
○ Inhibitory​ ​postsynaptic​ ​potentials​ ​occur​ ​when​ ​the​ ​postsynaptic​ ​membrane
becomes​ ​more​ ​negative,​ ​making​ ​it​ ​harder​ ​for​ ​an​ ​action​ ​potential​ ​to​ ​occur
● Temporal​ ​summation
○ When​ ​the​ ​same​ ​neuron​ ​synapses​ ​with​ ​the​ ​synaptic​ ​knob​ ​twice​ ​in​ ​quick
succession,​ ​sometimes​ ​bumping​ ​the​ ​postsynaptic​ ​membrane​ ​potential​ ​over
the​ ​threshold​ ​of​ ​excitation,​ ​resulting​ ​in​ ​an​ ​action​ ​potential
● Spatial​ ​summation
○ When​ ​two​ ​or​ ​more​ ​different​ ​neurons​ ​synapse​ ​with​ ​the​ ​synaptic​ ​knob​ ​at​ ​the
same​ ​time​ ​or​ ​in​ ​quick​ ​succession
--------------------------------------------------------------------------------------------------------------------------14:​ ​SENSORY​ ​SYSTEMS
●

Sensory​ ​receptors​ ​transduce​ ​stimulus​ ​energy​ ​and​ ​transmit​ ​signals​ ​to​ ​the​ ​central
nervous​ ​system
○ All​ ​stimuli​ ​represent​ ​forms​ ​of​ ​energy
○ Sensation​ ​involves​ ​converting​ ​energy​ ​into​ ​a​ ​change​ ​in​ ​the​ ​membrane
potential​ ​of​ ​sensory​ ​receptors
Joanna​ ​Griffith​ ​(2017)

When​ ​a​ ​stimulus’​ ​input​ ​to​ ​the​ ​nervous​ ​system​ ​is​ ​processed,​ ​a​ ​motor​ ​response
may​ ​be​ ​generated
■ This​ ​may​ ​involve​ ​a​ ​simple​ ​reflex​ ​or​ ​more​ ​elaborate​ ​processing
Sensory​ ​pathways
● Sensory​ ​reception
○ Detection​ ​of​ ​stimuli​ ​by​ ​sensory​ ​receptors
■ Sensory​ ​receptors​ ​interact​ ​directly​ ​with​ ​stimuli,​ ​both​ ​inside​ ​and​ ​outside
the​ ​body
● Transduction
○ Conversion​ ​of​ ​stimulus​ ​energy​ ​into​ ​a​ ​change​ ​in​ ​membrane​ ​potential​ ​of​ ​a
sensory​ ​receptor
■ This​ ​change​ ​in​ ​membrane​ ​potential​ ​is​ ​called​ ​a​ ​receptor​ ​potential
● Receptor​ ​potentials​ ​are​ ​graded​ ​(magnitude​ ​varies​ ​with​ ​strength
of​ ​stimulus)
● Transmission
○ After​ ​energy​ ​has​ ​been​ ​transduced​ ​into​ ​a​ ​receptor​ ​potential,​ ​some​ ​sensory
cells​ ​generate​ ​the​ ​transmission​ ​of​ ​action​ ​potentials​ ​to​ ​the​ ​CNS
■ Some​ ​sensory​ ​receptors​ ​are​ ​specialised​ ​neurons,​ ​others​ ​are
specialised​ ​cells​ ​that​ ​regulate​ ​neurons
■ Sensory​ ​neurons​ ​produce​ ​action​ ​potentials​ ​and​ ​their​ ​axons​ ​extend​ ​into
the​ ​CNS
● integration
Coding​ ​of​ ​stimulus​ ​intensity
● Sensory​ ​receptor​ ​response​ ​varies​ ​with​ ​intensity​ ​of​ ​stimulus
○ If​ ​the​ ​receptor​ ​is​ ​a​ ​neuron,​ ​a​ ​larger​ ​receptor​ ​potential​ ​results​ ​in​ ​more​ ​frequent
action​ ​potentials
○ If​ ​the​ ​receptor​ ​is​ ​not​ ​a​ ​neuron,​ ​a​ ​larger​ ​receptor​ ​potential​ ​causes​ ​more
neurotransmitters​ ​to​ ​be​ ​released
Perception
● The​ ​brain’s​ ​construction​ ​of​ ​stimuli
● Stimuli​ ​from​ ​different​ ​different​ ​sensory​ ​receptors​ ​travel​ ​as​ ​action​ ​potentials​ ​along
dedicated​ ​neural​ ​pathways
○ The​ ​brain​ ​distinguishes​ ​stimuli​ ​from​ ​different​ ​receptors​ ​according​ ​to​ ​the​ ​area
of​ ​the​ ​brain​ ​where​ ​the​ ​action​ ​potentials​ ​arrive
Types​ ​of​ ​sensory​ ​receptor
● Mechanoreceptors
○ Sense​ ​physical​ ​deformation​ ​caused​ ​by​ ​stimuli​ ​such​ ​as​ ​pressure,​ ​stretch,
motion​ ​and​ ​sound
○ Eg
...
​ ​the​ ​mammalian​ ​sense​ ​of​ ​touch​ ​relies​ ​on​ ​mechanoreceptors​ ​that​ ​are
dendrites​ ​of​ ​sensory​ ​neurons
● Chemoreceptors
○ General​ ​chemoreceptors​ ​transmit​ ​information​ ​about​ ​the​ ​total​ ​solute
concentration​ ​of​ ​a​ ​solution
○ Specific​ ​chemoreceptors​ ​respond​ ​to​ ​individual​ ​kinds​ ​of​ ​molecules
○

Joanna​ ​Griffith​ ​(2017)

When​ ​a​ ​stimulus​ ​molecule​ ​binds​ ​to​ ​a​ ​chemoreceptor,​ ​the​ ​chemoreceptor
becomes​ ​more​ ​or​ ​less​ ​permeable​ ​to​ ​ions
○ Eg
...
​ ​many​ ​animals​ ​appear​ ​to​ ​migrate​ ​using​ ​the​ ​earth’s​ ​magnetic​ ​field​ ​to​ ​orient
themselves
○ Eg
...
​ ​one​ ​of​ ​the​ ​simplest​ ​is​ ​that​ ​of​ ​planarians
● A​ ​pair​ ​of​ ​ocelli​ ​(eyespots)​ ​located​ ​near​ ​the​ ​head
● Allow​ ​planarians​ ​to​ ​sense​ ​light​ ​and​ ​move​ ​away​ ​from​ ​it
○ Compound​ ​eyes
■ Insects​ ​and​ ​crustaceans
■ Consist​ ​of​ ​up​ ​to​ ​several​ ​thousand​ ​light​ ​detectors,​ ​called​ ​ommatidia
■ Very​ ​effective​ ​at​ ​detecting​ ​movement
○ Single-lens​ ​eyes
■ Some​ ​jellies,​ ​polychaetes,​ ​spiders,​ ​many​ ​molluscs,​ ​all​ ​vertebrates
■ Work​ ​on​ ​a​ ​camera-like​ ​principle​ ​in​ ​invertebrates
● Iris​ ​changes​ ​the​ ​diameter​ ​of​ ​the​ ​pupil​ ​to​ ​control​ ​how​ ​much​ ​light
enters
● Muscles​ ​move​ ​the​ ​lens​ ​forwards​ ​and​ ​backwards​ ​to​ ​focus
objects​ ​at​ ​different​ ​distances
■ In​ ​some​ ​vertebrate​ ​taxa​ ​(eg
...
​ ​mammals),​ ​focusing​ ​differs​ ​in​ ​that
muscles​ ​change​ ​the​ ​shape​ ​of​ ​the​ ​lens​ ​rather​ ​than​ ​moving​ ​it​ ​around
● The​ ​eye​ ​detects​ ​colour​ ​and​ ​light,​ ​then​ ​the​ ​brain​ ​assembles​ ​the
information​ ​and​ ​perceives​ ​the​ ​image
● Vertebrate​ ​visual​ ​system
○ Photons​ ​of​ ​light​ ​enter​ ​the​ ​eye​ ​and​ ​strike​ ​rods​ ​and​ ​cones​ ​(photoreceptors)
○ Neurons​ ​relay​ ​the​ ​information​ ​captured​ ​by​ ​the​ ​photoreceptors​ ​to​ ​the​ ​optic
nerve​ ​and​ ​brain
○ Rods
■ Very​ ​light-sensitive,​ ​but​ ​don’t​ ​distinguish​ ​colours
○ Cones
■ Less​ ​light-sensitive,​ ​but​ ​can​ ​distinguish​ ​colours
○ Visual​ ​pigments​ ​(rhodopsin​ ​in​ ​rods)​ ​are​ ​made​ ​up​ ​of​ ​a​ ​light-absorbing
molecule​ ​(retinal)​ ​bound​ ​to​ ​a​ ​membrane​ ​protein​ ​(opsin)
■ Retinal​ ​exists​ ​in​ ​two​ ​isomers
■

Joanna​ ​Griffith​ ​(2017)

Absorption​ ​of​ ​light​ ​causes​ ​a​ ​shift​ ​from​ ​the​ ​cis​ ​to​ ​the​ ​trans
configuration,​ ​which​ ​destabilises​ ​and​ ​activates​ ​opsin
○ Trans-retinal​ ​activates​ ​rhodopsin,​ ​which​ ​activates​ ​a​ ​G
protein,​ ​eventually​ ​leading​ ​to​ ​hydrolysis​ ​of​ ​cyclic​ ​GMP
■ When​ ​cyclic​ ​GMP​ ​breaks​ ​down,​ ​Na​+​​ ​channels
close,​ ​hyperpolarising​ ​the​ ​cell
● Signal​ ​transduction​ ​shuts​ ​off​ ​as
enzymes​ ​convert​ ​retinal​ ​back​ ​to​ ​cis​ ​form
○ Processing​ ​of​ ​visual​ ​information​ ​in​ ​the​ ​brain
■ The​ ​optic​ ​nerves​ ​meet​ ​at​ ​the​ ​optic​ ​chiasm​ ​near​ ​the​ ​cerebral​ ​cortex
■ Most​ ​ganglion​ ​cell​ ​axons​ ​lead​ ​to​ ​the​ ​lateral​ ​geniculate​ ​nuclei,​ ​and
information​ ​is​ ​relayed​ ​from​ ​there​ ​to​ ​the​ ​primary​ ​visual​ ​cortex
■ At​ ​least​ ​30%​ ​of​ ​the​ ​cerebral​ ​cortex,​ ​in​ ​dozens​ ​of​ ​integrating​ ​centres,​ ​is
active​ ​in​ ​creating​ ​visual​ ​perceptions
● Colour​ ​vision
○ Most​ ​fish,​ ​amphibians,​ ​reptiles​ ​and​ ​birds​ ​have​ ​very​ ​good​ ​colour​ ​vision
○ Humans​ ​and​ ​other​ ​primates​ ​are​ ​among​ ​the​ ​minority​ ​of​ ​mammals​ ​with​ ​the
ability​ ​to​ ​see​ ​colour​ ​well
○ Colour​ ​vision​ ​depends​ ​on​ ​the​ ​relative​ ​stimulation​ ​of​ ​two​ ​or​ ​more​ ​cone​ ​types​ ​of
different​ ​wavelength​ ​sensitivity
■ Humans​ ​have​ ​three​ ​cone​ ​types,​ ​each​ ​with​ ​a​ ​different​ ​visual​ ​pigment
● These​ ​pigments​ ​(photopsins)​ ​are​ ​formed​ ​when​ ​retinal​ ​binds​ ​to
three​ ​distinct​ ​opsin​ ​proteins
● The​ ​way​ ​we​ ​see​ ​the​ ​world​ ​differs​ ​from​ ​some​ ​other​ ​animals
○ Eg
...
​ ​bees​ ​are​ ​red-blind
--------------------------------------------------------------------------------------------------------------------------●

15:​ ​MOTOR​ ​MECHANISMS​ ​AND​ ​LOCOMOTION
The​ ​physical​ ​interaction​ ​of​ ​protein​ ​filaments​ ​is​ ​required​ ​for​ ​muscle​ ​function
Muscle​ ​activity​ ​is​ ​a​ ​response​ ​to​ ​input​ ​from​ ​the​ ​nervous​ ​system
The​ ​action​ ​of​ ​a​ ​muscle​ ​is​ ​always​ ​contraction
○ Extension​ ​is​ ​passive
Vertebrate​ ​skeletal​ ​muscle
● Characterised​ ​by​ ​a​ ​hierarchy​ ​of​ ​smaller​ ​and​ ​smaller​ ​units
○ Muscle​ ​to​ ​bundle​ ​of​ ​muscle​ ​fibres​ ​to​ ​single​ ​muscle​ ​fibre​ ​(cell)​ ​to​ ​myofibrils
○ Muscle​ ​consists​ ​of​ ​a​ ​bundle​ ​of​ ​long​ ​fibres,​ ​each​ ​a​ ​single​ ​cell,​ ​running​ ​parallel
to​ ​the​ ​length​ ​of​ ​the​ ​muscle
■ Each​ ​muscle​ ​fibre​ ​is​ ​itself​ ​a​ ​bundle​ ​of​ ​smaller​ ​myofibrils
● Myofibrils
○ Composed​ ​of​ ​two​ ​kinds​ ​of​ ​myofilaments
■ Thin​ ​filaments
● Consist​ ​of​ ​two​ ​strands​ ​of​ ​actin​ ​and​ ​two​ ​strands​ ​of​ ​a​ ​regulatory
protein
●
●
●

Joanna​ ​Griffith​ ​(2017)

Thick​ ​filaments
● Staggered​ ​arrays​ ​of​ ​myosin​ ​molecules
Sliding-filament​ ​model​ ​of​ ​muscle​ ​contraction
● Filaments​ ​slide​ ​past​ ​each​ ​other​ ​longitudinally,​ ​producing​ ​more​ ​overlap​ ​between​ ​thick
and​ ​thin​ ​filaments
● Sliding​ ​of​ ​filaments​ ​relies​ ​on​ ​interactions​ ​between​ ​actin​ ​and​ ​myosin
○ The​ ​head​ ​of​ ​a​ ​myosin​ ​molecule​ ​binds​ ​to​ ​an​ ​actin​ ​filament,​ ​forming​ ​a
cross-bridge​ ​and​ ​pulling​ ​the​ ​thin​ ​filament​ ​toward​ ​the​ ​centre​ ​of​ ​the​ ​sarcomere
● Muscle​ ​contraction​ ​requires​ ​repeated​ ​cycles​ ​of​ ​binding​ ​and​ ​release
● Glycolysis​ ​and​ ​aerobic​ ​respiration​ ​generate​ ​the​ ​ATP​ ​needed​ ​to​ ​sustain​ ​muscle
contraction
Regulation​ ​of​ ​skeletal​ ​muscle​ ​contraction
● Stimulus​ ​leading​ ​to​ ​contraction​ ​of​ ​a​ ​muscle​ ​fibre​ ​is​ ​an​ ​action​ ​potential​ ​in​ ​a​ ​motor
neuron​ ​that​ ​makes​ ​a​ ​synapse​ ​with​ ​the​ ​muscle​ ​fibre
○ The​ ​synaptic​ ​terminal​ ​release​ ​acetylcholine,​ ​which​ ​depolarises​ ​the​ ​muscle,
causing​ ​it​ ​to​ ​produce​ ​an​ ​action​ ​potential
■ Action​ ​potentials​ ​travel​ ​to​ ​the​ ​interior​ ​of​ ​muscle​ ​fibres​ ​along​ ​transverse
(T)​ ​tubules,​ ​which​ ​causes​ ​the​ ​sarcoplasmic​ ​reticulum​ ​(SR)​ ​to​ ​release
Ca​2+​​ ​into​ ​the​ ​cytosol
● The​ ​role​ ​of​ ​calcium​ ​and​ ​regulatory​ ​proteins
○ Regulatory​ ​proteins​ ​tropomyosin​ ​and​ ​troponin​ ​complex​ ​bind​ ​to​ ​actin​ ​on​ ​thin
filaments​ ​when​ ​the​ ​muscle​ ​fibre​ ​is​ ​at​ ​rest,​ ​preventing​ ​actin​ ​and​ ​myosin​ ​from
interacting
○ Myosin-binding​ ​sites​ ​are​ ​uncovered​ ​when​ ​Ca​2+​​ ​bind​ ​to​ ​the​ ​troponin​ ​complex
and​ ​cause​ ​tropomyosin​ ​to​ ​shift​ ​out​ ​of​ ​the​ ​way
● When​ ​motor​ ​neuron​ ​input​ ​stops,​ ​the​ ​muscle​ ​cell​ ​relaxes
○ Transport​ ​proteins​ ​in​ ​the​ ​sarcoplasmic​ ​reticulum​ ​pump​ ​Ca​2+​​ ​out​ ​of​ ​the​ ​cytosol
○ Regulatory​ ​proteins​ ​bound​ ​to​ ​thin​ ​filaments​ ​shift​ ​back​ ​to​ ​the​ ​myosin-binding
sites
Nervous​ ​control​ ​of​ ​muscle​ ​tension
● Extent​ ​and​ ​strength​ ​of​ ​muscle​ ​contraction​ ​can​ ​be​ ​altered​ ​(graded​ ​contractions)
○ The​ ​nervous​ ​system​ ​does​ ​this​ ​by:
■ Varying​ ​the​ ​number​ ​of​ ​fibres​ ​that​ ​contract
■ Varying​ ​the​ ​rate​ ​at​ ​which​ ​fibres​ ​are​ ​stimulated
● More​ ​frequent​ ​action​ ​potentials​ ​=​ ​summation​ ​=​ ​can​ ​lead​ ​to
tetanus​ ​(high​ ​frequency​ ​of​ ​action​ ​potentials)
Types​ ​of​ ​muscle​ ​fibres
● There​ ​are​ ​several​ ​distinct​ ​types​ ​of​ ​skeletal​ ​muscles,​ ​each​ ​adapted​ ​to​ ​a​ ​particular
function
○ Can​ ​be​ ​classified​ ​by​ ​the​ ​source​ ​of​ ​ATP
● Oxidative​ ​fibres
○ Rely​ ​mostly​ ​on​ ​aerobic​ ​respiration​ ​to​ ​generate​ ​ATP
○ Many​ ​mitochondria,​ ​rich​ ​blood​ ​supply,​ ​lots​ ​of​ ​myoglobin​ ​(an​ ​oxygen-storing
protein)
● Glycolytic​ ​fibres
○ Use​ ​glycolysis​ ​as​ ​their​ ​primary​ ​source​ ​of​ ​ATP
■

Joanna​ ​Griffith​ ​(2017)

Have​ ​less​ ​myoglobin​ ​than​ ​oxidative​ ​fibres,​ ​and​ ​tire​ ​more​ ​easily
Eg
...
​ ​in​ ​kangaroos,​ ​kinetic​ ​energy​ ​stored​ ​in​ ​the​ ​tendons​ ​after​ ​each​ ​leap
provides​ ​a​ ​boost​ ​for​ ​the​ ​next​ ​leap
■ Limbless​ ​locomotion
● Crawling​ ​is​ ​costly​ ​because​ ​much​ ​of​ ​the​ ​body​ ​is​ ​in​ ​contact​ ​with
the​ ​ground
● Eg
...
​ ​vipers)
○ Throw​ ​anterior​ ​of​ ​body​ ​sideways,​ ​then​ ​bring​ ​posterior
into​ ​line
○ Energy-efficient​ ​movement​ ​on​ ​loose​ ​ground
● Swimming
○ In​ ​water,​ ​friction​ ​if​ ​a​ ​bigger​ ​problem​ ​than​ ​gravity
■ Fast​ ​swimmers​ ​usually​ ​have​ ​a​ ​fusiform​ ​shape​ ​to​ ​minimise​ ​friction
○ Animals​ ​swim​ ​in​ ​diverse​ ​ways
■ Paddling​ ​with​ ​legs​ ​as​ ​oars
■ Jet​ ​propulsion
■ Undulating​ ​their​ ​body​ ​and​ ​tail​ ​up​ ​and​ ​down​ ​or​ ​side​ ​to​ ​side
● Flying
○ Active​ ​flight​ ​requires​ ​that​ ​wings​ ​develop​ ​enough​ ​lift​ ​to​ ​overcome​ ​the
downwards​ ​force​ ​of​ ​gravity
○ Many​ ​flying​ ​animals​ ​have​ ​adaptations​ ​that​ ​reduce​ ​body​ ​mass
■ Eg
...
​ ​European​ ​eels​ ​migrate​ ​to​ ​Bermuda​ ​to​ ​breed,​ ​then​ ​return​ ​to​ ​Europe
(3,400​ ​miles)
● Metabolic​ ​rate​ ​during​ ​migration​ ​is​ ​only​ ​twice​ ​that​ ​at​ ​rest
● WSCT​ ​is​ ​1/5th​ ​that​ ​expected​ ​for​ ​their​ ​body​ ​size
● Only​ ​20%​ ​of​ ​body​ ​mass​ ​is​ ​lost,​ ​leaving​ ​sufficient​ ​reserves​ ​for
breeding​ ​on​ ​arrival
■ Eg
...
​ ​brent​ ​goose)
● Digestive​ ​organs​ ​and​ ​flight​ ​muscles​ ​are​ ​catabolised​ ​for​ ​fuel,
which​ ​also​ ​means​ ​less​ ​weight​ ​to​ ​carry​ ​(eg
...
​ ​nodules​ ​in​ ​soybean​ ​plants
Worms
■ Aerate​ ​the​ ​soil
■ Decompose​ ​organic​ ​matter
■ Release​ ​nutrients
Other​ ​plant​ ​roots
■ Change​ ​pH​ ​of​ ​soil
■ Affect​ ​the​ ​rhizosphere
■

○

○

○

Xylem
● How​ ​is​ ​water​ ​transported​ ​around​ ​the​ ​plant?
○ ‘Free​ ​water’​ ​(not​ ​bound​ ​to​ ​solutes)
○ Osmotic​ ​potential​ ​(indicates​ ​direction​ ​of​ ​flow)

Joanna​ ​Griffith​ ​(2017)

○ Water​ ​will​ ​move​ ​into​ ​the​ ​root​ ​by​ ​osmosis​ ​when​ ​‘following’​ ​salts
○ Uncontrolled​ ​(through​ ​the​ ​membrane)​ ​or​ ​controlled​ ​(through​ ​aquaporins)
● If​ ​water​ ​were​ ​transported​ ​by​ ​diffusion,​ ​it​ ​would​ ​take​ ​1​ ​molecule​ ​1​ ​second​ ​to​ ​diffuse
through​ ​a​ ​cell,​ ​and​ ​1​ ​century​ ​to​ ​reach​ ​the​ ​top​ ​of​ ​a​ ​redwood​ ​tree
○ Bulk​ ​flow​ ​is​ ​a​ ​much​ ​more​ ​efficient​ ​method
● Xylem
○ Dead,​ ​hollow​ ​cells
○ No​ ​organelles
○ Stiff​ ​(lignified)​ ​walls
● Bulk​ ​flow​ ​in​ ​the​ ​xylem​ ​differs​ ​from​ ​diffusion
○ It​ ​is​ ​driven​ ​by​ ​differences​ ​in​ ​pressure​ ​potential,​ ​not​ ​solute​ ​potential​ ​(osmosis)
○ It​ ​moves​ ​the​ ​entire​ ​solution,​ ​not​ ​just​ ​water​ ​or​ ​solutes
○ It​ ​is​ ​much​ ​faster
● Xylem​ ​sap​ ​ascent​ ​by​ ​bulk​ ​flow
○ Against​ ​gravity
○ Transpiration-cohesion-tension​ ​mechanism
■ Water​ ​evaporates​ ​from​ ​the​ ​surface​ ​of​ ​the​ ​leaves,​ ​reducing​ ​pressure​ ​in
the​ ​upper​ ​xylem
● Controlled​ ​by​ ​guard​ ​cells
■ Adhesion
● Water​ ​molecules​ ​form​ ​weak​ ​hydrogen​ ​bonds​ ​with​ ​the​ ​sides​ ​of
the​ ​tube
■ Cohesion
● Water​ ​molecules​ ​form​ ​weak​ ​hydrogen​ ​bonds​ ​between​ ​each
other
○ When​ ​water​ ​evaporates​ ​from​ ​the​ ​top,​ ​the​ ​water
molecules​ ​below​ ​are​ ​pulled​ ​upwards
● Maintaining​ ​control​ ​of​ ​bulk​ ​flow
○ Guard​ ​cells​ ​in​ ​the​ ​leaves
○ The​ ​casparian​ ​strip,​ ​surrounding​ ​the​ ​xylem
■ Water​ ​can​ ​either​ ​take​ ​the​ ​apoplastic​ ​route,​ ​around​ ​cells,​ ​or​ ​the
symplastic​ ​route,​ ​through​ ​cells
● Water​ ​and​ ​nutrients​ ​can​ ​only​ ​pass​ ​into​ ​the​ ​xylem​ ​if​ ​they​ ​pass
into​ ​cells​ ​and​ ​take​ ​the​ ​symplastic​ ​route,​ ​which​ ​enables​ ​cells​ ​to
control​ ​water​ ​and​ ​solutes
Transpiration​ ​through​ ​the​ ​leaf
● CO​2​​ ​moves​ ​in,​ ​H​2​O​ ​moves​ ​out
● Through​ ​stomata
● When​ ​weather​ ​is​ ​hot,​ ​the​ ​plant​ ​risks​ ​losing​ ​too​ ​much​ ​water​ ​so​ ​it​ ​closes​ ​the​ ​stomata
○ Less​ ​CO​2​​ ​can​ ​be​ ​absorbed​ ​as​ ​a​ ​result
Photosynthesis
● The​ ​main​ ​role​ ​of​ ​the​ ​leaves​ ​(and​ ​any​ ​other​ ​green​ ​part​ ​of​ ​the​ ​plant)
● Most​ ​important​ ​reaction​ ​on​ ​the​ ​planet
○ All​ ​life​ ​is​ ​dependent​ ​on​ ​photosynthesis
● The​ ​average​ ​photosynthetic​ ​cell​ ​contains​ ​between​ ​30-40​ ​chloroplasts
○ A​ ​1mm​2​​ ​chunk​ ​of​ ​leaf​ ​will​ ​contain​ ​around​ ​half​ ​a​ ​million​ ​chloroplasts
Joanna​ ​Griffith​ ​(2017)

●
●

●

○ RuBisCo​ ​is​ ​thought​ ​to​ ​be​ ​the​ ​most​ ​abundant​ ​protein​ ​on​ ​earth
6CO​2​​ ​+​ ​6H​2​O​ ​→​ ​C​6​H​12​O​6​​ ​+​ ​6O​2
Light-dependent​ ​step
○ Takes​ ​place​ ​within​ ​the​ ​thylakoid​ ​membrane​ ​of​ ​chloroplasts
○ Summary:
■ Light​ ​energy​ ​dissociates​ ​water,​ ​splitting​ ​it​ ​into​ ​H+​​ ​ ​ions,​ ​electrons,​ ​and
oxygen
■ Light​ ​energy​ ​excites​ ​electrons​ ​so​ ​that​ ​they​ ​move​ ​down​ ​an​ ​electron
transport​ ​chain,​ ​providing​ ​the​ ​energy​ ​necessary​ ​to​ ​produce​ ​NADPH
and​ ​ATP​ ​(which​ ​are​ ​required​ ​in​ ​the​ ​light-independent​ ​reaction)
○ Cyclic​ ​phosphorylation
■ Within​ ​the​ ​thylakoid​ ​membrane,​ ​series​ ​of​ ​electron​ ​carrier​ ​proteins​ ​form
an​ ​electron​ ​transport​ ​chain
● Each​ ​molecule​ ​is​ ​able​ ​to​ ​be​ ​oxidised​ ​(takes​ ​up​ ​an​ ​electron)​ ​or
reduced​ ​(gives​ ​an​ ​electron​ ​away)
● Each​ ​protein​ ​has​ ​a​ ​slightly​ ​lower​ ​energy​ ​level​ ​than​ ​the​ ​one
preceding​ ​it​ ​in​ ​the​ ​chain
■ The​ ​excited​ ​electron​ ​passes​ ​from​ ​one​ ​carrier​ ​to​ ​the​ ​next​ ​through​ ​a
series​ ​of​ ​redox​ ​reactions
■ As​ ​the​ ​electron​ ​moves​ ​down​ ​the​ ​chain,​ ​it​ ​releases​ ​some​ ​energy,​ ​which
is​ ​used​ ​to​ ​take​ ​in​ ​the​ ​H+​​ ​ ​ions​ ​from​ ​the​ ​stroma​ ​into​ ​the​ ​thylakoid​ ​space
■ The​ ​electron​ ​returns​ ​to​ ​the​ ​chlorophyll​ ​molecule
■ The​ ​H+​​ ​ ​ions​ ​that​ ​have​ ​been​ ​pumped​ ​into​ ​the​ ​thylakoid​ ​space​ ​travel
back​ ​across​ ​the​ ​membrane​ ​down​ ​an​ ​electrochemical​ ​gradient​ ​through
ATP​ ​synthase​ ​(a​ ​protein​ ​channel​ ​that​ ​also​ ​acts​ ​like​ ​an​ ​enzyme)
● The​ ​energy​ ​released​ ​as​ ​the​ ​ions​ ​move​ ​is​ ​used​ ​by​ ​ATP
synthase​ ​to​ ​phosphorylate​ ​(add​ ​phosphate​ ​to)​ ​ADP​ ​to​ ​make
ATP
○ Non-cyclic​ ​phosphorylation
■ There​ ​are​ ​two​ ​chlorophyll-containing​ ​complexes​ ​within​ ​the​ ​thylakoid
membrane,​ ​photosystem​ ​I​ ​and​ ​photosystem​ ​II
● Electrons​ ​excited​ ​by​ ​light​ ​energy​ ​from​ ​PSII​ ​pass​ ​to​ ​an​ ​electron
acceptor​ ​and​ ​down​ ​an​ ​electron​ ​transport​ ​chain,​ ​and​ ​are​ ​taken
in​ ​by​ ​PSI
○ The​ ​energy​ ​released​ ​is​ ​used​ ​to​ ​generate​ ​ATP
■ Light​ ​energy​ ​releases​ ​an​ ​electron​ ​from​ ​PSI,​ ​which​ ​passes​ ​to​ ​an
electron​ ​acceptor​ ​called​ ​NADP​ ​with​ ​a​ ​H+​​ ​ ​ion
● NADP​ ​is​ ​reduced​ ​to​ ​NADPH
● NADPH​ ​is​ ​used​ ​in​ ​the​ ​LIR​ ​as​ ​a​ ​source​ ​of​ ​H+​​ ​ ​ions​ ​to​ ​reduce
carbon​ ​dioxide
Light-independent​ ​step
○ The​ ​Calvin​ ​cycle
○ Takes​ ​place​ ​in​ ​the​ ​stroma​ ​of​ ​chloroplasts
○ Uses​ ​the​ ​chemical​ ​energy​ ​of​ ​ATP​ ​and​ ​NADPH​ ​from​ ​the​ ​light-dependent​ ​step
to​ ​reduce​ ​CO​2​​ ​to​ ​sugar
○ Carbon​ ​fixation:
Joanna​ ​Griffith​ ​(2017)

A​ ​carbon​ ​dioxide​ ​molecule​ ​is​ ​fixed​ ​to​ ​ribulose​ ​bisphosphate​ ​by
RuBisCo
● Produces​ ​an​ ​unstable​ ​intermediate,​ ​which​ ​splits​ ​into​ ​two
glycerate​ ​3-phosphates
○ Reduction:
■ ATP​ ​joins​ ​a​ ​phosphate​ ​group​ ​to​ ​each​ ​glycerate​ ​3-phosphate​ ​molecule,
and​ ​NADPH​ ​leaves​ ​two​ ​electrons​ ​with​ ​each,​ ​forming​ ​glyceraldehyde
3-phosphate​ ​(high​ ​energy,​ ​3-carbon​ ​compounds​ ​that​ ​plants​ ​can​ ​turn
into​ ​carbohydrates​ ​such​ ​as​ ​glucose,​ ​starch,​ ​and​ ​cellulose)
○ Regeneration​ ​of​ ​CO​2​​ ​acceptor:
■ 3​ ​RuBPs​ ​can​ ​be​ ​converted​ ​in​ ​6​ ​GALPs,​ ​but​ ​only​ ​on​ ​GALP​ ​can​ ​leave
the​ ​cycle​ ​as​ ​the​ ​other​ ​five​ ​are​ ​needed​ ​to​ ​regenerate​ ​RuBPs​ ​for​ ​the
next​ ​round​ ​of​ ​the​ ​cycle
Photorespiration
○ Closing​ ​the​ ​stomata​ ​results​ ​in​ ​increased​ ​O2​​ ​ ​and​ ​reduced​ ​CO​2
○ Photorespiration​ ​consumes​ ​O​2​​ ​and​ ​ATP​ ​and​ ​releases​ ​CO​2​​ ​without​ ​producing
sugar
■ Provides​ ​enough​ ​CO​2​​ ​for​ ​photosynthesis
○ Photorespiration​ ​can​ ​drain​ ​as​ ​much​ ​as​ ​50%​ ​of​ ​the​ ​carbon​ ​fixed​ ​by​ ​the​ ​Calvin
cycle​ ​on​ ​a​ ​hot​ ​dry​ ​day
■ May​ ​be​ ​an​ ​evolutionary​ ​relic​ ​because​ ​RuBisCo​ ​first​ ​evolved​ ​at​ ​a​ ​time
when​ ​the​ ​atmosphere​ ​had​ ​far​ ​less​ ​O​2​​ ​and​ ​more​ ​CO​2
■ Some​ ​plants​ ​have​ ​evolved​ ​solutions​ ​to​ ​photorespiration
● C4​ ​plants
○ Eg
...
​ ​desert​ ​plants
○ Use​ ​crassulacean​ ​acid​ ​metabolism​ ​to​ ​fix​ ​carbon
■ Open​ ​their​ ​stomata​ ​at​ ​night,​ ​incorporating​ ​CO​2
into​ ​organic​ ​acids,​ ​which​ ​are​ ​then​ ​stored​ ​in
vacuoles
● Stomata​ ​close​ ​during​ ​the​ ​day​ ​(when​ ​it​ ​is
hot)​ ​and​ ​CO​2​​ ​is​ ​released​ ​from​ ​organic
acids​ ​and​ ​used​ ​in​ ​the​ ​Calvin​ ​cycle
Translocation
○ Transport​ ​of​ ​the​ ​products​ ​of​ ​photosynthesis
■

●

●

Joanna​ ​Griffith​ ​(2017)

Plant​ ​may​ ​transport​ ​sugars​ ​to​ ​a​ ​growing​ ​stem​ ​tip,​ ​growing​ ​root​ ​tip,​ ​or​ ​a
storage​ ​tissue​ ​(eg
...
​ ​in​ ​insects)
○ Offloading​ ​excess​ ​salts​ ​via​ ​nasal​ ​salt​ ​glands​ ​(eg
...
​ ​reptiles,​ ​birds,​ ​insects,​ ​arachnids,​ ​and
some​ ​snails​ ​and​ ​frogs)
■ Voiding​ ​(egesting)​ ​waste​ ​nitrogen​ ​in​ ​poorly-soluble​ ​forms​ ​(eg
...
​ ​Arabian​ ​oryx
■ Elite​ ​water​ ​conservationists
■ Store​ ​heat​ ​gained​ ​during​ ​the​ ​day,​ ​use​ ​it​ ​to​ ​keep​ ​warm​ ​at​ ​night
■ Minimise​ ​water​ ​use​ ​for​ ​thermoregulation
■ When​ ​their​ ​body​ ​temperature​ ​goes​ ​up​ ​during​ ​the​ ​day,​ ​the​ ​temperature
difference​ ​between​ ​them​ ​and​ ​the​ ​surrounding​ ​air​ ​decreases,​ ​so​ ​they
gain​ ​less​ ​exogenous​ ​heat
○ Eg
...
​ ​ostriches​ ​lay​ ​eggs​ ​in​ ​a​ ​shallow​ ​scrape,​ ​rely​ ​on​ ​high​ ​thermal​ ​inertia,
panting,​ ​and​ ​piloerection
○ Eg
...
​ ​kangaroo​ ​rats
■ Exceptional​ ​water​ ​conservationists
■ Low​ ​cutaneous​ ​permeability​ ​to​ ​water
■ Concentrated​ ​urine​ ​and​ ​dry​ ​faeces
■ Nasal​ ​countercurrent​ ​heat​ ​exchange
■ Can​ ​survive​ ​with​ ​basically​ ​no​ ​pre-formed​ ​water​ ​in​ ​their​ ​diet
● In​ ​contrast,​ ​all​ ​large​ ​herbivores​ ​(eg
...
​ ​oryx​ ​behaviourally​ ​maximise​ ​intake​ ​of​ ​pre-formed​ ​water​ ​by​ ​eating​ ​a​ ​few
hours​ ​before​ ​dawn,​ ​when​ ​plants​ ​contain​ ​the​ ​most​ ​water
○ Eg
...
​ ​in​ ​Serengeti​ ​ungulates
■ Wildebeest​ ​and​ ​zebra​ ​are​ ​drinking​ ​water-dependent​ ​so​ ​cannot​ ​move
more​ ​than​ ​15​ ​miles​ ​from​ ​water,​ ​while​ ​Grant’s​ ​gazelle,​ ​common​ ​eland,
and​ ​dik​ ​dik​ ​are​ ​drinking​ ​water-independent
Evasion​ ​via​ ​migration
○ Following​ ​the​ ​water​ ​source
Evasion​ ​via​ ​estivation
○ Eg
...
​ ​termites
● ‘Compass​ ​termites’​ ​build​ ​nests​ ​with​ ​the​ ​long​ ​axis​ ​running
north-south​ ​so​ ​that​ ​the​ ​nest​ ​warms​ ​up​ ​at​ ​dawn,​ ​but​ ​there​ ​is
minimal​ ​surface​ ​exposed​ ​at​ ​midday
○ Vertical​ ​shafts​ ​provide​ ​ventilation
Joanna​ ​Griffith​ ​(2017)

--------------------------------------------------------------------------------------------------------------------------19:​ ​PHYSIOLOGY​ ​OF​ ​GLOBAL​ ​CHANGE
Anthropogenic​ ​threats​ ​to​ ​ecosystems
● Can​ ​be​ ​localised​ ​or​ ​globalised
● Conservationists​ ​must​ ​be​ ​selective​ ​and​ ​pragmatic
○ Not​ ​everything​ ​can​ ​be​ ​preserved
○ To​ ​be​ ​effective,​ ​conservation​ ​requires​ ​a​ ​sound​ ​evidence​ ​base
■ Urgent​ ​need​ ​to​ ​understand​ ​cause​ ​and​ ​effect
■ Physiology​ ​often​ ​provides​ ​the​ ​link​ ​between​ ​cause​ ​and​ ​effect
● Human​ ​activity​ ​modifies​ ​abiotic​ ​and​ ​biotic​ ​components​ ​of​ ​the​ ​environment
○ The​ ​most​ ​obvious​ ​threat​ ​is​ ​direct​ ​destruction​ ​of​ ​habitats,​ ​but​ ​there​ ​are​ ​also
more​ ​subtle,​ ​and​ ​potentially​ ​more​ ​serious​ ​anthropogenic​ ​effects
● Physiology​ ​may​ ​compensate​ ​for​ ​environmental​ ​change,​ ​up​ ​to​ ​a​ ​point
○ Developmental​ ​plasticity​ ​(during​ ​development)
○ Acclimation​ ​and​ ​acclimatisation,​ ​reversible​ ​plasticity​ ​(within​ ​the​ ​adult​ ​lifespan)
○ Genetic​ ​adaptation​ ​(between​ ​generations)
○ Eg
...
​ ​butterfly​ ​biogeography​ ​in​ ​relation​ ​to​ ​temperature
○ How​ ​do​ ​thermal​ ​tolerance​ ​limits​ ​differ​ ​amongst​ ​species?
○ Which​ ​species​ ​seem​ ​most​ ​threatened​ ​by​ ​climatic​ ​warming?
■ Eurythermal​ ​species
● Can​ ​tolerate​ ​a​ ​wide​ ​range​ ​of​ ​temperatures
● Some​ ​may​ ​be​ ​able​ ​to​ ​exhibit​ ​phenotypic​ ​plasticity,​ ​or​ ​may​ ​be
able​ ​to​ ​evolve​ ​fast​ ​enough
○ Species​ ​with​ ​high​ ​reproductive​ ​outputs​ ​and/or​ ​traits
with​ ​high​ ​heritability
● Some​ ​species​ ​may​ ​exhibit​ ​behavioural​ ​alterations​ ​to​ ​cope​ ​with
warming
○ Eg
...

porcelain​ ​crabs)
○ Ectotherms​ ​adapted​ ​to​ ​environments​ ​where​ ​they​ ​have
historically​ ​experienced​ ​a​ ​limited​ ​range​ ​of​ ​temperatures
■ Particularly​ ​polar​ ​species,​ ​which​ ​are​ ​doubly​ ​in
danger​ ​as​ ​most​ ​warming​ ​is​ ​predicted​ ​to​ ​occur​ ​at
the​ ​poles
● Eg
...
8°C
■ Have​ ​a​ ​high​ ​expression​ ​of
genes​ ​which​ ​code​ ​for
cold-adapted​ ​proteins
(cold-adapted​ ​proteins
are​ ​inherently​ ​more
stenothermal​ ​and​ ​are
likely​ ​to​ ​degrade​ ​rapidly
upon​ ​warming)
● ‘Evolvability’​ ​is​ ​also​ ​a​ ​problem​ ​as​ ​there
is​ ​little​ ​variation​ ​upon​ ​which​ ​selection
can​ ​act
● There​ ​is​ ​still​ ​a​ ​lot​ ​of​ ​uncertainty​ ​about​ ​the​ ​impacts​ ​of​ ​warming
on​ ​stenothermal​ ​species
○ Eg
...
​ ​green​ ​turtles​ ​at​ ​Ascension​ ​Island
○ Beaches​ ​just​ ​a​ ​few​ ​km​ ​apart​ ​vary​ ​drastically​ ​in
temperature​ ​due​ ​to​ ​the​ ​colour​ ​and​ ​quality​ ​of​ ​the​ ​sand
■ At​ ​both​ ​beaches,​ ​hotter​ ​sand​ ​=​ ​lower​ ​hatching
success
● But​ ​the​ ​sand​ ​is​ ​far​ ​hotter​ ​at​ ​the​ ​black
sand​ ​beaches,​ ​so​ ​how​ ​do​ ​embryos
survive​ ​at​ ​all?
■ Experiment:
● Eggs​ ​from​ ​both​ ​beaches​ ​were​ ​artificially
incubated​ ​at​ ​cold​ ​(29°C)​ ​or​ ​hot​ ​(32
...
​ ​artificial​ ​lighting
■ Widespread​ ​loss​ ​of​ ​natural​ ​unlit​ ​habitats
■ Impacts​ ​on​ ​physiology​ ​and​ ​behaviour
● Eg
...
​ ​anthropogenic​ ​noise
■ Noise​ ​from​ ​roads,​ ​ships,​ ​urban​ ​development,
sonar,​ ​etc
...
​ ​ship​ ​noise​ ​increases​ ​metabolic​ ​rate​ ​in​ ​shore
crabs
Joanna​ ​Griffith​ ​(2017)

●

Potentially​ ​part​ ​of​ ​a​ ​general​ ​stress
response

Joanna​ ​Griffith​ ​(2017)



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