Download doc Summary 18 to 31, 2010

Temperature regulation in animals by heat exchange
Types of animal responses to change in ambient temperature
 More accurate terms
o Homeotherms
 Regulators
 Maintain constant body temperature
o Result of internal physiological
mechanisms
o Poikilotherms
 Conformers
 Body temperature fluctuates with environment
Can also regulate by changing their environment
 Most reside in a stable, colder environment
 More or less constant temperature
Based on source of heat
o Ectotherm
 Obtain heat from environment
o Endotherms
 Produce heat internally
 In cold climate  regional heterotherms
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 Reduces metabolic cost
 Still regulate!
 Temporal heterotherm
 Allow temperature to drop  hibernation
o Heterotherm
 Produce heat internally
 Not in all body parts at one!
 Regional Heterotherms
 Warm up only parts of their body
 i.e. warming up of flight muscles
During heat loss  heat moves from deep parts to skin
 Body wall thickness, conductance, temperature gradient
o Determine speed of loss or gain
Physical mechanisms of heat transfer
 Temperature is the measure of intensity of heat
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Direction of heat transfer determined by magnitude of temperature
o Higher temperature to lower temperature
Conduction
o Direct physical contact
o Rate of transfer proportional to
 Area of surface contact
 Temperature gradient
 Material
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Q
kA(T2  T1 )
l
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o contact surface area must be normal to direction of heat flow
Convection
o Transfer of heat by mass flow of fluid, gas or liquid
o STILL EMPLOYS CONDUCTION
o Very effective means of mass transfer
 Maintains steep temperature gradient
Electromagnetic radiation
o No physical contact or carrier fluid to transfer heat
o All object emit radiation energy
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 Give heat to others without contact
o Intensity increases with
 Temperature
 Frequency
 Against wavelength
o In organisms  infrared
o Q  C(T2  T1)
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Evaporation
o ONLY for lowering body temperature in hot environment
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o Evaporation of water needs a lot of energy
 Thus, it cools a lot!
o Sweat, panting, drooling on the body surface
Heat exchange between organism and the environment
 Total heat = heat produced metabolically + heat gained or lost
o Depends on mass and overall specific heat or tissues
 An organism can gain or lose heat depending on gradient
Heat exchange in cold environments
 Core body temperature of endothermic animals
o Range of 30C to 42C  birds are higher
 Thermal Neutral Zone (TNZ)
o Specific range in which temperature is kept constant
 No change in metabolic rate
o Lower critical temperature (LCT)
 Below it  maintained through metabolic regulation
o Upper critical temperature (UCT)
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 Over it  maintained by active heat dissipation
Thermal conductance
o Heat produced in core transported to surface
 By convection and conduction
o Heat escapes by conduction to environment
 Air temperature and convection and radiation affect it
o H  C(TB  TA )
b
C*  aMb mass specific conductance
o conductance per unit area decreases with mass exponent -17
 Conductance and tolerance to cold

o Specific conductance decreases with body size faster than
specific heat production
 Larger animals retain more heat than smaller animals
 Harder to dissipate heat in warmer climates
 Control of heat exchange in cold environments
o Physiological mechanisms
 Autonomic control of blood flow to skin
 Reduced through vasoconstriction  cold
 Increased through vasodilation  hot
 Countercurrent principle
 Hot arteries surrounded by cold veins
 Smallest endotherms
 Higher cardiac output  increased frequency
 Piloerector muscles
 Blubber  changing blood flow through it
o Behavioral mechanisms
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Choice of habitat
Control portion of body surface exposed to environment
Heat exchange in warm environments
 Losing heat against a temperature gradient
 Evaporative cooling
o Skin surface, lung surface, drooling
o Body water is lost
 Thick fur insulates against entry of external heat
 Deep burrows
Internal production of heat
 Metabolic reactions produce heat as a byproduct
o May be insufficient to maintain body temperature
 Shivering thermogenesis
o Contraction of antagonistic muscles
 Little net movement
o All energy released as heat
 Non-shivering thermogenesis
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o Brown fat oxidized by respiration  uncouple from ATP synth.
 Cells loaded with fat and mitochondria
 High supply of blood vessels
o All energy dissipated as heat
If it can’t keep up  Hypothermia
Ectotherms do not regulate with metabolic rate  no TNZ
Thermoregulatory processes
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Set point temperature  slight deviations are immediately sensed
Very precise switching on and off of mechanisms
o Slight deviations  adjustments of conductance
o Outside TNZ  increase in metabolic rate
o Extreme  thermogenesis pr evaporative cooling
Hypothalamus  temperature control sensor
o Group stimulates thermogenesis, vasoconstriction,piloerection
o Group stimulates vasodilation, sweating
o Group decreases thermogenesis, vasoconstrition, piloerection
Biomechanics: structural support and organismal body
Principles of mechanics
 Forces acting on a body
o 3 major forces
 Compressive force
 Tensile force
 Shear force
o Stress is caused by these forces
 Deformation it causes  strain
 Depends on magnitude of force & material
o Strength
Capacity of the body to resist force without breaking or
buckling of permanent damage
 Can be measured in compression or tension
Young’s modulus of Elasticity
o Ratio between stress and strain  constant
o E quantifies the stiffness of the material
 Rubber = lowest, Diamond = highest
 Bone is in the middle
Elastic and plastic strain
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o Strain is only proportional to stress in true hard objects
o Cartilage does not obey Hooke’s law
o Elastic strain  completely reversible
 Linear with stress in region of elastic response
o Plastic strain  permanent and non-reversible
 After the yield point, then fractures
Cantilevers  only supported at one end
o Strut is under  compressive
o Stay is over  tensile
No stress in the middle part  beam can be hollow
Skeletons
 More or less firm structures that maintain structural integrity
 Provide attachment sites for muscles
 Hydrostactic skeletons
o Fluid-filled body cavity
 surrounded by circular and longitudinal muscles
o Earthworm
o Plants also have a hydrostatic skeleton
Exoskeleton
o Generated by secretion to outer surface  hardens
o Muscles attached to inside
o Gives shape, anchorage, protects
1.135
o Mskel  0.078Mb
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o
M shell  0.0482M egg
1.132
F  50.86Mb
0.915
  Endoskeletons
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o Internal framework of bones
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o Axial and appendicular skeleton
Composition of skeleton
 2 types of connective tissue
o Dispersed cells in a extracellular matrix
o Cartilage
 Chondrocytes secrete collagen, elastin, polysaccharides
 Collagen  reinforce gel matrix
 Flexible & resistant to compression
 Lines the joints & flexible external support
o Bone
 Osteoblasts
 Secrete extracellular matrix  collagen + Calcium
 When trapped  osteocytes
 Osteoclast resorbs matrix (erodes bone)
 Bone is constantly replaced and remodeled
 Perceive stress imposed on them & strengthen structure
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Calcium is also a reservoir for the body
Marrow cavity in the center
Cancellous ends  spongy looking
Compact bone  Haversian systems (osteon)
 Series of concentric layers with canal in center
 Occupied by blood vessels and nerve
 Canals parallel to long axis
 Interconnected by Wolkmann’s canals
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Orientation of collagen alternate between lamellae
Osteocytes present in central canal
The skeleton as a supporting system
 Strength and design of bones
o Can take more compressive than tensile stress
o Ends are wider than the main shaft
o Forms joints with other bones
 Lined with cartilage for smoothness, lubrication,
stiffness and resiliency
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o Spongy material  trabeculae
 Struts going from one edge to the other
o Thin bones  compact on outside & cancellous on inside
Allometry of bones
o Bones of large animals scaled out of proportion to dimensions
o Area of bones has to increase in proportion to weight
o Large vertebrates must be aquatic  buoyancy of water
o Skeleton has to support static weight and locomotion
Bones as beams and columns
o Only true for graviportal animals  very large and heavy
 More or less vertical columns  solid without marrow
 Made for supporting not running
o In eursorial animals  successive limb bones at an angle
 Subjected to multidirectional stress
 Hollow or marrow cavity
 Distal end  compressive stress
 Proximal end  tensile stress
Skeleton as a balanced structural frame
 Keeps the animal from collapsing and protects against toppling
 Cantilevered mass is balanced out by the other side
 Neck and head cantilever supported by nuchal ligament
o Most elastic part of the body
Allometry of trees
 Base diameter has to increase to 1.5 power of height
 Heights of all trees are below critical buckling line  sense stresses
Terrestrial Locomotion
Muscle and motion
 3 types of muscles
o Cardiac muscle
 Looks striated
 Arrangement of actin and myosin filaments
 Criss-crossing network
 Protects heart from tearing
 Can withstand high pressure
 Electrical contact with each other
 Pacemaker cells
o Smooth muscle
 Not striated
 Ling and spindle-shaped with one nucleus
 Force of contraction of internal organs
 Arterioles & veinules wrapped by single muscles cells
 Nerve cells between muscle layers
 Direct control by nervous system
o Skeletal muscles
 Involved in all voluntary movement
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Striated and have several nuclei
Formed by fusion of cells
Much larger than 2 other types
Several bundles of muscle fibers
 Many myofibrils
 Bundle of thin actin and thick myosin
 Divided into contractile units  sarcomeres
o Cylindrical with Z-line at both ends
o Contraction  sarcomere shortens
o Mimimum contraction  twitch
Contraction by firing of motor neurons
 Depends on number firing and frequency of firing
 Spatial and temporal summation
Slow-twitch fibers  red muscle
 Lots of myoglobin, mitochondria and blood vessels
 High level of ATP, glycogen and fat
 Long term aerobic work
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 Maximum tension is lower
 Fast-twitch fibers  white muscle
 Less myoglobin, mitochondria and blood vessels
 Develop higher tension and quicker
 Cannot sustain it for long  sprinting
 Powered by glycolysis (anaerobic respiration)
Muscle-bone attachment
o Attached to bone by tendons
o Bone to bone by ligaments
Principle of lever and bone-muscle machines
 Principle of levers
o 3 point of a lever
 Fulcrum  pivoting point
 Effort arm
 Load arm
o Class-1 lever
 Fulcrum between effort and load arm
 See-saw
o Class-2 lever
 Load arm between fulcrum and effort arm
 Wheelbarrow
o Class-3 lever
 Effort arm between fulcrum and load arm
o Effort x Effort Arm = Load x Load Arm
o Lever rotates in direction of greater torque
o Effort needed inversely proportional to length of effort arm
o Effort arm short compared to load arm  quicker!
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effort velocity x load arm = load velocity x effort arm
Structural adaptations for fast running
 Cursorial animals  adapted for high-speed running
 Non-cursorial animals  adapted for walking not running
 Speed of running  determined by stride length & frequency
 Limb length and foot posture
o Speed can be increased by increasing limb length
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 Elongation of foot bones
o Plantigrade  whole foot
o Digitigrade  ball of foot
o Unguligrade  toe tips
Shoulder position
o Non-cursorial  scapulas horizontal with clavicle
o Cursorial  vertical scapulas without clavicle
 Rotation in same plane and direction as limb
 More freedom of movement without clavicle
 Carnivore have a reduced clavicle
Movement of the spine
o Legs are under the body
 spine is free to flex in vertical plane
o Stride length is increased with right flexion and extension
 Allows extra rotation of hip and shoulder girdles
 Legs reach out farther, front and back
o Bounding also adds to stride length
Angle and speed of motion
o Greater swing of the limb when muscle attached close to joint
o Higher load arm to effort arm ratio  more speed, less power
Limb mass
o Limbs move forward and backwards during locomotion
 Inertia affects them
 Proximal distribution of limb mass decreases inertia
o All muscles involved in running located near the torso
o Some bones at distal end reduced or eliminated completely
Special locomotion modes in hot desert
o As small a body part as possible touching hot surface for as
little
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time as possible
Tiptoe stance in lizards
Sidewinding snakes
Cartwheeling spider
Swimming and Flying
Principles of fluid dynamics
 Forces against forward motion
o Drag
o Cross-sectional area perpendicular to flow  resistance
 Laminar and turbulent flow
o Laminar flow  smooth flow pattern
 Parallel to direction of flow
 Narrow and short wake
o Turbulent flow  rough and disorganized flow pattern
 Perpendicular to direction of flow
o
o
o
o
 Swirling eddies behind plate
Pressure drag
 Against the forward movement
 Depends on cross-section, density and velocity
Fiction drag
 Depends on surface properties of plate & viscosity
Streamlining
 Tapering of the trailing surface of a sphere
Fitness ratio
Ratio of maximum thickness to chord length
Turbulence results when flow separates from surface of
body
Reynolds Number (Re)
length  speed  density
o Re 
dimensionless number
density
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Boundary layer
o Velocity flow is zero at interface between fluid and surface
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o Boundary layer thickness inversely proportional to flow speed
Lift to Drag Ratio, Angle of Attack and Aspect Ratio
o Fluid moving past bottom  positive pressure +upward thrust
o Fluid moving past upper surface  low pressure
o Center line or camber line
 Equidistant from upper and lower of the airfoil
o Chord line
 Connects centre of leading edge to that of trailing edge
o Camber
o
o
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o
o
High
o
o
 Distance between center line and chord line
Magnitude of lift depends on angle of attack
 Maximum lift at 10-20 degrees
lift : drag ratio
 can’t be increased only by surface area  arrangement!
Length : width ratio  aspect ratio
Streamlined body has less drag than rectangular body
lift and anti-stalling devices
Lift force can be increased increasing camber, thickness, SA
Lift increases then decreases with angle of attack
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Stall  decrease of air flow slow over airfoil
 Flow separates from surface
Coefficient of drag exponentially increases with a of a
Coefficient of lift increases then decreases
and gaps as anti-stalling devices
Redirects air flow from lower to upper surface
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o Slots
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o Bird
 Have alula which pops up just before landing
 Also have slots
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Stability and control  yaw, pitch and roll
o Yaw
 Side turning around vertical axis
 Corrected by vertical rudder
o Pitch
 Up and down rotation around horizontal axis
 Corrected by horizontal stabilizer
o Roll
 Turning movement around longitudinal axis
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Corrected by ailerons
Speed and drag
 Re determines relation between drag, speed and body size
o Low Re  friction drag predominant
o High Re  pressure drag predominant
Swimming
 Size, speed and metabolic cost
o Fish have same density as water  naturally buoyant
 Only have pressure and friction drag as resistance
o Df  0.5SU 2C f
 Drag increases with square of velocity
o U  19.5(length) 0.5  M 0.17
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 larger fish swim faster than smaller fish
 MSMC decreases with increase in body mass
  Propulsion mechanisms in fish swimming: Undulatory swimming
o Zigzag lines separate muscle blocks  myotomes
 Segments along length of fish with vertebrae
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 Cause a wave of undulation along sides of body
 Start at anterior end and passes down to tail
o Tail propulsion
 Shows largest displacement  specialized organ
Adaptations for maintaining buoyancy and reducing drag
o Swim bladders
 Beneath vertebral column
 Expels and absorbs gasses  regulates volume
 Always match density of surroundings
o Fish slime and drag
 Secrete mucus on outer surface of skin
 Protects against parasites and reduces drag!
o Tuna as super-streamlined body
 Smoothness of skin  no mucus
 Fins are thin and can be tucked into a groove
 Eyes flush with surface
 Narrow caudal fin is good for cruising
Flying
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Flying ability and body size
o Wing-loading is proportional to length
o Stalling speed proportional to square-root of wing-loading
 Larger birds  higher stalling and take off speed
 Running start, wind, higher launch, etc
 Effortless flight  thermal air masses
 Small fliers (bees)  rapid wing beat + vertical take off
 Some can hover at will
o Wing characteristics
 Aspect ratio
 Length and width of wing
 High aspect ratio = high lift to drag ratio
 Can glide at more acute angles close to ground
 Flapping of wings
 Downward and forward power stroke
 Counteracts gravity and drag
 Backward recovery stroke
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 Wing partially retracted
 In hummingbird  lift also generated
 Wings rotate during recovery
 Wing-loading
 Ratio between weight and wing SA
 Lower wing loading
o Lower stalling speed
o Enables tighter turns
Soaring and gliding
o Soaring
 Altitude is gained or conserved thanks to thermals
 Metabolic cost  adjustment of tail & wing position
o Gliding
 Altitude is lost, however slowly
Hormones in animals
Cellular secretions
 Hormones are chemical messengers and regulators
o Produced at on location and act on another
o Effective at very low concentrations
 Autocrine secretions
o Act on the cells which produces them
o Secreted outside and bind to receptor on plasma membrane
 Paracrine secretions
o Secretions from one cells affect cells surrounding
 Endocrine secretions
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o Poured into and transported by blood stream
o Act on cells of distant organs and tissues
o Clustered together to form  gland
Exocrine secretions
o Release outside the body of the organism
 Skin, epithelial surface of the gut, etc
o Secreted from a gland
 Duct that carries the secretion
Neurosecretory cells
o When secreting cells are hormones
o Almost all hormones
o All neurosecretory hormones are proteins
 Neuropeptides
Types of hormones
 Peptide hormones
o 3-4 AA residues to very large proteins
o water soluble  cannot diffuse into cell
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o specific membrane-anchored receptors
o initiate cascade of signaling events
Steroid hormones
o synthesized from cholesterol
o lipid soluble  can diffuse into cell
o receptors in cytoplasm
o sex hormones  testosterone & progesterone
o Receptor-hormone stimulates or inhibits gene expression
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Catecholamine hormones
o Derived from modification of amino acids
o Stress response  epinephrine and norepinephrine
o Hormone binding causes change in membrane potential or
triggers second-messenger pathway
 Eicosanoid hormones
o Prostaglandins
 Lipid-soluble and lipid-insoluble hormones
o Signaling mechanism depends on solubility and partitioning
SEE PAGE 92 OF COURSE PACK!!! AND MEMORIZE
Hypothalamus and Pituitary gland – A major control center
 Hypothalamus is lower region of the brain  pituitary right beneath
o Anterior and posterior pituitary
 Neurosecretory cells of hypothalamus  axons into posterior
o Main cell bodies in the hypothalamus
o Synthesize hormones
 Control synthesis and secretions of hormonespituitary
 Tropic hormones
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Hormones released by hypothalamus
o Stimulatory and inhibitory effect on anterior pituitary gland
o TRH, GnRH, Prolactin-IH, ProlactinRH, etc… P.94
Hormones released by pituitary gland
o Many are tropic in nature
o Main function of posterior
 Secrete 2 hormones
 Oxytocin  labor in mammals
 ADH  water balance
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osmoreceptors in hypothalamus
pressure receptors in aorta
Vertebrate endocrine glands and other hormone secretors
 Adrenal Glands
o Adrenal medulla  inner part
 Develops from nervous tissue
 Controlled by nervous system
Secretes epinephrine and norepinephrine
 Epinephrine also acts as neurotransmitter
o Adrenal cortex  outer part
 Secretes aldosterone, cortisol and cortisterone
 Play roles salt and carbohydrate metabolism
 Controlled by tropic hormones
Heart atrium
o Secretes atril natriuretic peptide (ANP)
 Controls salt and water excretion by kidney
Kidney
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o Secrete hormone calcitrol
 Regulates Ca level in blood, bone formation and
absorption of calcium and phosphate in intestine
Pancreas
o Alpha cells secrete glucagon
o Beta cells secrete insulin
o Regulate blood level of glucose in opposite manner
Parathyroid gland
o Secretes hormone parathormone
 Regulates blood levels of calcium and phosphate
Pineal or epiphysis
o Secretes melatonin
 Role in photoperiodic effects
 Anti-gonadotropic action
Thymus gland
o Secretes thymic hormones
 Regulate proliferation and differentiation of lymphocytes
Thyroid gland
o Follicular cells secrete 2 hormones
 Thyroxine and tri-iodothyronine
 Regulation of growth and differentiation,
metabolic rate and consumption of O2 and heat
production
o Parafollicular cells  clusters called ultimobrachial glands
 Secrete calcitronin
 Down regulates calcium levels in blood
Hormones involved in digestion
SEE PAGE 99
Pheromones, allomones and kairomones
 Pheromones
o Used to communicate with members of same species
o Pheromones evolved into hormones
o Exocrine secretions
o Involved in mate location, alarm and alerting, defense
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behavior and establishment of caste system
o First pheromone identified  bombykol
o Can respond to a single molecule
o Quite unique molecules
o Odor-plume is produced and travel down wind several km
 Active space
o Can be used as odor-trails
Allomones
o Adaptively favourable to the animal that produces them
o One-way chemical weapons which attack receiver
o 2-way where both the receiver and emitter benefit
Kairomones
o Favourable to receiver but harmful effects on emitter
 If becomes attractant to predators or parasites
Evolutionary perspectives on hormones
o Much biochemical unity in different life forms
o Similarity in amino acid sequence
o
Hormones in plants
Special
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features of plant hormones
Major differences with animals on sources and actions of hormones
Nothing comes from a gland
Some are synthesized in particular part of body
Specific action is not well defined for most
o Interact with each other to produce spectrum of effects
o Some are more specific than others
 Concentration in cell determined by
o Rate of synthesis
o Rate of degradation
o Rate of sequestration
 Binding to other cell molecules or compartmentalization
Auxins
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3 types of auxins exist in plants
Stimulation of growth by elongation
Formation of adventitious and side roots
Maintenance of apical dominance
o Growth inhibition of lateral branches from main axis of stem
Inhibition of leaf abscission
Coleoptile tip exposed to light makes shoot bend toward light
o Auxin mediates phototropism
o Auxin is transported to shaded side
 Cells grow faster and cause bending towards light
Transported basipetally
o From morphologically upper to morphologically lower
Polar transport mediated by auxin efflux carriers
o Anchored in PM only on morphological lower side of each cell
Gibberellins (GAs)
 Terpenoid compounds
 More than 100 gibberellins are known
o Only a few have potent biological activity (GA3 is most used)
 Role in seed germination and stem growth
o Dwarf pees have mutation in GA production gene
o Applying GA will restore wild type phenotype
Cytokinins
 Stimulation of cell division
 Lateral-shoot induction
 Retardation of senescence
Abscisic acid (ABA)
 Synthesized in response to dehydration of plant tissues
 Seed MUST dehydrate and accumulate ABA
o Without ABA  vivipary
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 Precocious germination on the mother plant
Immediate precursor  ABA aldehyde
o Inability to produce  reduced drought resistance
Ethylene
 Synthesized from methionine
 Fruit-ripening hormone
 Autocatalytic
o Any ripe fruit will make other fruits ripen faster
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Can be oxidized to ethylene oxide
Brassinolide
 Only truly steroid hormone in plants
 Multiple effects on growth and development
Systemide
 Protein hormone
 Synthesized in response to insect attacks
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Initiates synthesis of protease inhibitors I and II
o Prevent digestion of proteins by insect
Salicylic acid and Jasmonic acid
 Response to fungal, bacterial and nematode pathogens
 Can become volatile by methylation
Growth and development 1 – General considerations
Atomic size and organismal size
 Biological systems have predictable and accurate activities
o Very small margin or error
 governed by sqrt(n)
 largers numbers = larger accuracy, stability, predictable
 Measurable number of proteins are defective
o Mechanisms to evolve and degrade them and recycle AA
Growth
 Irreversible increases in size or volume or an organism
o Unlimited resources
 N t  N oe kt
 ln Nt  kt  ln No
o Limited resources
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dN
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 kN(N max  N)  Nmax-N = growth to be achieved

dt
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S-shaped curve
 Lag period
 Log phase
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Stationary phase
Dynamic nature of organisms
 Organism is constantly changing
o Starts as single cell
 Undergoes morphologically different and increasingly
complex stages of development
 Haploid gametes  diploid organism
Cellular basis of growth and development (Cell division and enlargement)
 Multicellular organisms also build body structures
 Cell division is basis for growth AND development
o Provides growth through increasing cell numbers
o Provides basis for cell commitment and determination
o Complex and highly regulated process
o Initiated by signals received by the cell
o Karyokinesis  division of nucleus
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o Cytokinesis  division of cytoplasm
Rest of time  interphase (between divisions)
o Cells receives & responds to biochemical signals
 Regulate the progression of cell division process
o Cell enlarges before it divides!
Development: Cell commitment and cell differentiation
 Division then differentiation basis of organismal development
 Continuous supply of cells is needed
o Repair and replaced of worn out cells
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Stem cell (meristematic)
o Unspecialized or uncommitted cell
o Capable of cell division
o Can differentiate into any type of cell
Differentiation
o Cell commitment, determination & specialization
 Has specific structure and function
o Incapable of cell division
o 3 levels
Structural
 Morphology and anatomy
 Biochemical
 New enzyme activity or gene products
 Molecular
 Gene activation or repression
Development
o Qualitative changes during the life cycle
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Molecular genetic basis of development
 Genetic constitution determines everything in organism
 Gene products are present in cytoplasm
o Long-lived and stable
Generation of polarity as a basis for development
 Used to achieve a specific shape
 Unequal cell division
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o Results in smaller and bigger cell
o Common in plants
Position of nucleus
o Common in lower plants
Gradient of morphogens
o Proteins, mRNAs, other biochemical factors
o Bicoid  anterior and nanos  posterior
Sperm point of entry
o Makes that part of egg ventral half of embryo
Incident light
o Fucus  shaded side produces rhizoid cell
Positional information and intercellular communication
 Tissues  cells belong to same type & have identical features
 Cells under influence of neighbours
 Cell signaling!
o Diffusible chemicals
 Released from one & bind to receptors on other
 Generates second messenger  info to nucleus
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o Direct contact between surface proteins
 Leads to generation of second messenger
o Gap junctions or plasmodesmata
 Opening between 2 cells  cytoplasms in contact
 Can transfer large molecules  proteins
Growth regulators and hormones  crucial part
o Communication and development
Reversibility of differentiation, totipotency of cells and regeneration of
missing part
 Cells cannot de-differentiate
o If they did
 No signals to guide it
 Become a cancerous mass of cells
 Uncontrolled cell proliferation
Growth and development 2 – Plants
Plants growth and it’s measurement
 Higher plants are fixed in soil
o 70% of growth is cell expansion & 30% is cell division
 Growth can be measure as increase in height or dry weight
o Growth curve is typical S-shaped curve
LogL2  LogL1
o Relative growth rate 
t 2  t1
o Rate of cell growth (G)  E(P Y)
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Growth regulation by hormones
 growth in major way
 2 hormones regulate
o Gibberellin (GA)
 Only to intact plant
 Increasing growth with increasing concentration
 GA3 is rapidly metabolized
 Cause hydrolysis of starch
 Increases glucose concentration
 Lower water potential
 Water influx!
 Increases the term P in equation
o Auxin (IAA)
 Stimulates growth of only excised segments
 Low concentration stimulates, high inhibits
 Short lag-time before growth is observed
 Activates proton-pumping ATPase
 pH in cell walls declines  activates certain enzymes
 expansins  hydrolyze acid-labile bonds
 cell wall more extensible
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 less pressure needed to expand cell
Increases E and decreases Y
Growth regulation by environmental factors
 Inhibitory effects of light on growth
o Blue and red are inhibitory
 Red light can be inhibited by far-red light flash or GA
 Light receptor  phytochrome
Effect of blue light is more rapid
 Cannot be countered
 Light receptor  cryptochrome
Regulation of plant growth by plant water status
o Water deficit is strong inhibitor
o Rapid, direct and reversible effect
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Plant development: Seed dormancy and germination
 Seed dormancy
o NOT DEAD!
o Many seeds unable to germinate right after formation
 Too strong or impervious seed coat
 Hormonal or chemical inhibitors
 Leaks out during rain or water intake
o Soaks up water but does not germinate
 Becomes metabolically active
o Activated embryo produces GA  promotes germination
o Germination balanced by ratio of GA:ABA
o Can also require environmental conditions  light or chilling
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 Light could mean near soil surface  photosynthesis
 Red light promotes germination, far-red counters
 Last type of light will determine germination
Seed germination
o Sequence of events
 Water absorption, increase in energy charge,
mobilization of food reserves, protrusions of root, etc.
Water absorption
o Mature seeds are dehydration  7-15% weight
o Membranes are not lipid bilayer conformation
 Take time to regain normal characteristics
 Small solutes leak out
o Membrane regain semi-permeability
 Reabsorbtion of solutes
o Bi-phasic process
 Pre-existing cells absorb water (1st phase)
 Mew cells are formed and absorb water (2nd phase)
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Increase in energy charge (EC)
o Proportion of phosphate bonds in all AMP, ATP and ADP
 ATP has 2, ADP had 1, AMP has none
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EC 
[ATP]  1 [ADP]
2
[ATP]  [ADP]  [AMP]
Production of hydrolytic enzymes and mobilization of food reserves
o Enzymes to degrade carbohydrates, lipids and proteins
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 Amylases, lipases and proteases
o Genes for these are activated by GA
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Embryo synthesizes GA
GA diffuses to aleurone cells & activates gene transcription
Enzymes secreted into endosperm
Reserves hydrolyzed into monomers  diffuse to embryo
Serve as respiratory substrates & building blocks
Plant development: Meristems (embryonic regions)
 Permanent meristems
o Continuously produce branches, leaves and roots
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o Located at particular sites
 Apical
 Tip of the shoot
 Leaves and branches
 Root apex
 Roots
 Lateral
 Cambium & cambium cork
Determinate meristems
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o Leaf primordia
o Flower primordia
Can also be intercalary  at the base of the leaf in grasses
Plant development: Organogenesis of shoot (stem, branch, leaf)
 Shoot and root apical meristems  established in embryogenesis
o First cell division unequal  long basal cell + small terminal
 Terminal cell is embryo
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o Leaves have buds in their axilsprimordial of future branches
Upper cells are organized, lower cells are random
Cells in meristem never differentiate
o Products of their division produce lateral organs & internal
o Peripheral zone produce lateral organs  leaves & branches
 Outermost  epidermis
 Inner  internal tissues
 Rib zone  vasculature
 Central zone  meristem
o Apical  no hormones
 Sub-apical  hormones
Positional information determines what a primordium is going to do
Plant development: Organogenesis of root
 No sub-apical meristem
 Root cap in meristem
o Sheds peripheral cells
o Protects root apical meristem
o Secretes many biochemicals into soil
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Quiescent center in meristem
o Reserve apical meristem
Cells elongation zone behind meristem
o Frequency of division declines
Maturation zone behind elongation zone
o Differentiation of cells
Totipotency of plant cells
 Cells can de-differentiate and grow completely new plants
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Differentiation is reversible in plants!
Hormonal regulation of differentiation into roots and shoots
 Mass of undifferentiated cells  callus
 Auxin and cytokinins levels regulate differentiation
Regeneration of missing parts
 High cytokinin (from roots)  shoots
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High auxin (from top)  roots
Growth and development 3 - Animals
4/12/2010 8:50:00 PM
Growth of the body
 Growth spurt at puberty
o On sensing of first signal of sexual maturity  rush for max
 Significant changes to relative proportions of different body parts
 Tension-driven muscle growth
o Linear growth of muscle is couple with growth of bone
 Driving force is the tension bone exerts on muscle
 Genetic basis of limb growth
o Limb contains genetic information about maximum length
Cell division and limits to cell proliferation
 Contact inhibition of cell division
 Cells have to be anchored to divide  basal membrane
 Cells away from basal layer are differentiated and don’t divide
Establishment of polarity
 Earliest acting morphogens are usually maternally produced
 Protein gradient results from polar distribution of their mRNA
o Embryogenesis proceeds with precise timing
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Morphogens are all transcription factors
o Proteins that bind to DNA and activate transcription
 Specific genes involved in developmental process
Ventral side is marked by sperm entry point
Dorsal side is marked by presence of Nieuwkoop centre
Cell commitment and determination
 How do you know?
o Take a cell and transplant it in another region
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If it forms structure it should have  differentiated
Cell type identity and unique surface features
 In every case, cells sort themselves out according to their type
o Reorganize themselves like in the embryo
 Different cell types have different surface features
o Including specific proteins and glycoproteins
Early embryogenesis: establishment of three primary embryonic cell layers
 Cleavage by cell division starts soon after fertilization
 At 16-cell stage  division without enlargement
o Blastula stage
o 3 cell types and cavity  blastocoel
 Further cell divisions and movement create gastrula
Organogenesis from the three primary embryonic cell layers
 In last stages of gastrula  blastocoel shrinks
o Archenteron takes it’s place  forms gut
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Ectoderm
o Outside layer
o Epidermis, eye lens, brain, secretory glands, spinal cord, etc
Endoderm
o Inside layer
o Bones,cartilage,connective tissue, skeletal muscles, heart, etc
Mesoderm
o Middle layer
o Liver, pancreas, gut, lungs, pharynx, thyroid, pharynx, etc
Primordial germ cells are separated from the rest
o Will form sperms and eggs
o Protects them from cumulative mutations genetic constancy
Totipotency and capacity for regeneration of missing parts
 Differentiated animal cells are totipotent in nuclear transplant
o Need a receptive female for artificial embryo
o Not exactly totipotency
 Regeneration of missing parts
o Seen in lower animals
o Flat worm will regenerate head and tail
 Morphogen gradient!
o Newt regenerate amputated limb
 Presence of nerve is regulating factor
 No nerve = no regeneration
 Unless unnerved in early embryo
Major differences between animals and plants
 Growth habit
o Animals  determinate
o Plants  indeterminate
 Development
o Partitioning of germ and somatic cell lines
 Animals  very early in embryo development
 Plants  none until flowering
o Role of gametophyte
 Animals  represented by gametes themselves
 Plants  multicellular embryo sac
o Post-embryonic development
 Animals  most adult organs formed in embryogenesis
 Plants  from meristems adult organs develop post.
o Cell movement during development
 Animals  cells migrate to where they form an organ
 Plants  cells walls cement cells in place of formation
o Regeneration and Totipotency
 Animals  cells have finite lifetime
 Plants  de-differention of cells in vitro
o Variety of Organs and cell types
 Animals  hundreds of cell types
 Plants  40 different cell types with little difference
o Hormone synthesis/action, specificity
 Animals  specific site of synthesis, action and function
 Plants  synthesized and acts at many location 
depends on relative concentration
Plant reproduction: options and timing
Asexual options for reproduction
 Through any vegetative part that can give rise to a new plant
 Does not involve chromosomal rearrangement
o Leads to inbreeding depression of fitness
Readiness to flower
 Plants will not flower in juvenile phase
 Passage to reproductive phase comes after a certain time
o Can be marked by changes in leaf shape or other things
 Plant dies after flowering and seeding
Transition of shoot apex from vegetative state to reproductive state
 Important changes in shape and activity of apical meristem
o During transition from vegetative to reproductive phase
 Increase in diameter or length or both in shoot apical meristem
Flower structure and development
 Almost all flowers have 4 flower organs
o Sepals, petal, stamens and carpels
Stamen has filament and anther on top
Carpel ovary at bottom, stigma on top, style in middle
 More than one  fusion into multi-chambered
Flower development
o Only A  sepals
o A and B  petal
o B and C  stamens
o Only C  carpel
o A & C complementary  mutually exclusive
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If C is mutated, A will take it’s place and vice versa
Regulation of flowering time – Some general comments
 Environmental cues involved in regulating time of flowering
o Not temperature  too variable in day
o Relative length of day and night!
 How to measure flowering response?
o Time taken for 1st flower to appear
o Number of nodes that bear flowers or inflorescnces
o Number of flowers per plant
o Percentage of plants that flower in a population
Photoperiodic regulation of flowering time
 Short day plants (SDP)
o Flowers when day length is shorter than critical photoperiod
o Does not flower when above CP
 Long day plants (LDP)
o Flowers when day length is longer than critical photoperiod
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o Does not flower below CP
Day-neutral plants (DNP)
o Don’t respond to day length
o Flower after producing a certain number of leaves
 Related to age of the plant
Inductive photoperiod
o Combination of day and night length that induces flowering
Qualitative and quantitative photoperiodic responses
o Qualitative  not flower without inductive photoperiod
 Most SDP
o Quantitative  flowers slower and less without IP
 Most LDP
Number of induction cycles depends on plant (1 to several)
Once flowering is induced  cannot be stopped!
It is actually night that is critical for flowering response
o SDP are long night plants (LNP)
o LDP are short night plants (SNP)
Non-inductive cycle cancers an inductive cycle
Hormonal regulation of flowering time
 Effective for inducing flowering is GA
o Can make LDP flower is SD conditions
Temperature regulation of flowering time – Vernalization
 Some plants need a chilling treatment to flower
o Gene (suppresses flowering) is switched off permanently
A flowering hormone (florigen)?
 Perception of photoperiod occurs in leaf but flowering  shoot apex
o Even if single leaf exposed to IP  flowering
 Hypothetical hormone  Florigen
o Can be transported through graft union of 2 plants
Underlying mechanisms
 LDP in inductive conditions
o Gene called Flowering locus T induced in leaf phloem
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Protein coded by it transported to shoot tip by phloem
Complexes with another protein to initiate process
SDP
o Hd3a is kept repressed by another gene
o In inductive conditions  repressor gene is inactivated
 Hd3a free to express itself
 Acts like FT protein
Pollination and seed development
Sex systems in plants
 Distribution of sexes at level of flower, plant or population
 Flower
o Bisexual, female or male
 Plant
o Only bisexual flowers  hermaphrodite
o Male and female flowers on same plants  monoecious
o Male and female flowers on separate plants  dioecious
 Population
o Any combination of types of plants
Gametogenesis
 Gametes are haploid
 Stamen  diploid
 Anther  microspore mother cell diploid  microspores  haploid
 Ovary  megaspore mother cell diploid  megaspores  haploid
 Development of pollen grains
o Anther has 4 chambers
 Lining of chambers --. Tapetum payer
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 Cells lyse to provide nutrition to microspore
o Microspores mature into pollen grains
 Becomes multicellular  male gametophyte
 Vegetative and generative cell
 Shed and dispersed
Development of the egg
o Develops in the ovule
o Mother cell is differentiated
 Produces 4 megaspores  3 die
Nucleus forms 8 nuclei  3 mitotic divisions
 4 on each end
 1 from each side fuse in center  secondary nucleus
 Middle of 3 at microphyler end  egg
 Other 2 are synergids
 3 others  antipodals
 pollen tube enters through microphyle
Pollination: Self- and cross-pollination
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o Various vectors of dispersion
 Wind
 Inconspicuous or absent petals
 Large anthers and stigma
 Animals
 Large, showy, fragrant
 Bees  most efficient pollinators
 Blue or yellow
 Lines or markings as honey guides
 UV light flower markings
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Beetles
 Strong yeasty, spicy or fruity odor
 No nectar  food storing cells in petals
Moths
 Yellow or white flowers  stand out at night
Birds
 Long tubular flower structure for beak
Bats
 Forage at night
o Nectar compositions
 Sugars, org. acids, volatile oils, proteins, enzymes, etc
o Sugar concentration
 Depends on flower and time of day
o Special case  the fig and the wasp
 Male synconium
 Male flowers with mature pollen
 Just inside the ostiole
 Female synconium
Female flowers line inner wall of fruit
 Long-styled carpels and short-styled carpels
Female wasp with fertilized eggs and pollen enters
female synconium  lays eggs and pollinates flower
 Eggs in short-styled ovaries
Larvae hatch and eat short-styled flowers
Male and female wasps mate
Females leave synconium and carry pollen away
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 MALES NEVER SEE LIGHT OF DAY
o Advantages of cross-pollination
 Promotes heterozygosity and genetic diversity
 Self-pollination
 Needs self-compatibility and temporal coincidence
 Promotes homozygosity + inbreeding depression
Germination of pollen grains
o Pollination  pollen grain lands on stigma
 If compatible  absorb water and swells
 Germinates and produces pollen tube
Incompatible  no germination
 If germinatesgrow short distance and dies
Sphorophytic incompatibility
o Ligand on surface of pollen binds receptor kinases
 Complete inhibition of germination
Gametophytic self-incompatibility
o Controlled by several alleles of S-gene
o S-RNAse produced by cells lining pathway of pollen tube
 Pollen tube from self-pollen takes S-RNAse
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 Degrades the mRNAs in pollen tube  dies
Double fertilization
o Compatible pollen hydrates & germinates  pollen tube
o Generative cell divides mitotically  2 sperms
 Released into embryo sac
 One fuses with egg, other with secondary nucleus
o Resulting triploid cell forms endosperm
o Sinergids and antipodals degrade  realease nutrients
Development of embryo
o 1st division is unequal
 Smaller  embryo
 Larger  suspensor
Seed development
o Different parts of ovule and embryo sac give rise to different
parts of seed
Precocious germination
o ABA prevents germination inside the mother plant
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o 2 mutations can lead to precocious germination
 Inability to synthesize ABA
 Germinates right in fruit
 Insensitivity to ABA
 Mutation in receptor that senses ABA
o Viviparous mutants
Sequence of events in seed development
o Embryogenesis
o Seed development, growth, germination genes not repressed
 Germination is inhibited by ABA
o Seed starts drying out
 DNA synthesis stops
o Seed dries out  dormant cell
Storage food reserves
o Starch, proteins, fats, phytic acid or phytate
Storage of minerals
o Phytate
 Hexaphosphoric acid ester of myo-inositol  phytin
 Insoluble mixed salts  K, Mg, Ca
o Storage proteins
 Albumins
 Globulins
 Glutelins
 Prolamins
Reproduction in animals
Reproduction and genetic recombination
 Reproduction  increase of number of individuals
o By production of offspring
 Genetics determine potential, environment determines actual
 In evolution
o Reproduction without recombination
o Then reproduction and recombination  separated in time
o Then melding of the two
 Differentiation of sexes ensures re-shuffling of gene combinations
o Enlarges repertoire or responses to given situation
Asexual reproduction
 Single cell and some multicellular  splitting in 2  binary fission
o Single celled  genetic material divided in 2
o Multicellular  no chromosomal duplication
 Genetic constancy is not disturbed
 Budding  small outgrowths produced by main body detach
o Start independent existence
 Chances for genetic innovation are slim
Resort to genetic recombination under stressful conditions
 Recombination through mating without reproduction
 Macronucleus and all but one micronucleus disintegrate
o Undergoes meiosis  4 haploid micronuclei3 die, 1 survives
 Remaining mitosis  2 micronuclei
 Exchange of 1 micronuclei between Paramecium
 Separation of organisms & fusion of micronuclei
 NO increase in number of cells
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Asexual reproduction is good under constant environment
Parthogenesis
o Sexual behavior exhibited but no egg fertilization
 Unfertilized egg is stimulated to form embryo
o Whiptail lizard
 Acts like female in high estrogen & male progesterone
 Behavior of courtship display but no sperm produced
 Essential for egg development
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Asexual reproduction important in parasites
o Tapeworm  oldest segment breaks away and becomes adult
Sexual reproduction
 Combines genetic recombination with reproduction
o Contributes to generation of genetic diversity
o Formation of haploid gametescrossing-over in chromosomes
o Assortment of chromosomes is also independent
 Hermaphroditism
o Organism is both female and male  both sex organs
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Origin of internal sex organs
o Common origin and represent 2 extremes of hormonal ratios
o Structural deviations are due to hormonal balances
o 3 major steps
 Gametogenesis  haploid cells produced
 Mating  gametes are brought together
 Fertilization  gametes fuse to form zygote
Gametogenesis
o In early stages of embryogenesis  germ cells set apart
Migrate to gonads when later are differentiated
 Protects germ cells from mutations
 Reduces birth defects
Males  sperm, female  egg
Proliferate mitosis  oogonia (female) & spermatogonia
Spermatogenesis  spermatocytes undergo meiosis
Oogenesis  oocyte undergoes unequal meiosis
 Very small cell is 1st polar body  discarded
 Second meiosis  second polar body produced
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 Large cell forms egg
Structure of ovary and egg
o Ovary contains primary oocytes  form definite # of eggs
 Most degenerate
o Each is surrounded by layer of ovarian cells
 Follicle
o Ovarian cycle  cycle of ovulation, duration varies with specie
 Several follicles mature  only one releases ovum
Follicle cells form corpus luteum
 Produces and secretes progesterone & estrogen
o Egg is surrounded by plasma membrane
 Just inside PM, cortical granules
 Egg membrane surrounded by vitelline envelope
 In turn surrounded by coat of jelly
 Sperm has to go through both barriers
 When penetrates  changes in PM
 Highly controlled process
o Egg surrounded by zona pellucida  surrounded by cumulus
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 Cumulus  various ovary cells
 Zona pellucida  glycoproteins (like vitelline envelope)
Testis and sperm
o Elongated cell with 3 regions
 Head
 Nucleus and acrosome
 Forms cap over nucleus
 Packed with enzymatic proteins
 Midpiece
 Packed with mitochondria
 Tail
o Produced in seminiferous tubules
 Mature sperms released in the lumen
 Tissue between tubules  Ledig cells
 Secrete testosterone
 Contain Sertoli cells  nurture developing sperms
 Secrete hormone called inhibin
Fertilization
o Several distinct steps
 Species specificity in mutual recognition of gametes
 Activation of sperm
 Fusion of sperm and egg plasma membrane
 Blocking of entry by additional sperm
 Egg and sperm nuclei fuse  diploid zygote
o Species-specific recognition mechanisms located in zona
pellucida
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Activation of the sperm and the acrosomal reaction
o Sperm of same species makes contact with egg
 Biochemical in jelly trigger acrosomal reaction
 Breakdown of membrane covering acrosome
 Enzymes released
 Enzymes bore hole in jelly and vitelline envelope head
 Polymerized actin elongates & carries bindin
 Egg membrane has bindin receptors
o 2 types of actions prevent entry of more sperm
 Fast block to polyspermy  few seconds
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Slow
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Sodium ions flood eggchange electrical property
block to polyspermy  30 seconds
Bindin receptors removed
Vitelline envelope is hardened
Hormonal regulation of reproduction
 2 important hormones released by hypothalamus
o Gonadotropin-releasing hormone (GnRH)
o Prolaction releasing hormone
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o Stimulate anterior pituitary
 Follicle-stimulating hormone (FSH)
 Leutinizing hormone (LH)
Women at puberty hypothalamus increases release of GnRH
o Increase of FSH and LH  targets ovarian tissue
 Produces estrogen and progesterone
 Development of sexual characters
o Estrogen has time-dependent effect on ovarian cycle
 Menstruation is beginning of cycle
1st 12 days FSH & LH negative feedback by estrogen
on 12th day  positive feedback  increase in LH & FSH
 Stimulates follicle cells to make corpus luteum
 Endocrine gland  estrogen & progesterone
o Progesterone prepares uterus for pregnancy
 Development of endometrium on uterine lining
 If no fertilization  corpus lutem degrades on 26th day
 Endometrium degenerates without progesterone
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 Discarded through menstruation
o Decrease in estrogen & progesterone releases neg. control
o Cycle starts again!
Hormonal control of male reproductive system
o Spermatogenesis and development of sexual characters
 Depends on secretion of testosterone
 FSH and LH control testosterone release by Ledig cells
 Under the control of GnRH
 Testosterone and inhibin exert negative feedback
inhibition of hypothalamus and pituitary
Evolutionary perspectives on reproductive systems in vertebrates
 Their evolution is related to migration from water to land
 Behavioral and structural adaptations promotes proximity of eggs
and sperm  enhances chances for fertilization
 Amphibians  proximity through copulation
 Reptiles and birds  amniote egg with sufficient food and water
o Permeable to air but not water
o Fertilization before formation of shell  internal fertilization
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ALL MAMMALS PRACTICE INTERNAL FERTILIZATION
Homology between GnRH and mating alpha-factor in yeast
o Can bind to mammalian receptor for GnRH
 Needs higher concentrations for same effect
Aging, senescence and death
Life span of organisms and cells
 Potential life span  genetically determined
o Actual  organism-environment interactions
 Correlaition between life span, length of gestation and puberty age
 Life span and total number of cell doublings
o Related to number of possible divisions by the cells
 Fixed number of divisions for each cell
 Positively correlated with life span
 Cell stop dividing  telomeres not long enough
o Reduced by 50 bp at every division
Programmed cell death (PCD) or apoptosis
 Cellular/molecular basis of cell death
o Cell triggers activation of specific genes  products kill cell
o Time and place of PCD genetically programmed
 Nucleus condenses
 Nuclear DNA is cut by DNAse between nucleosomes
 Ladder pattern of DNA fragments  gel electrophoresis
PCD in normal development
 Several genes regulate  ced3 & ced4 promote, ced9 inhibits
 PCD in animal development
o Major role in limb development  carves limb bud
 Chiseling generates variation
o Pattern of selective PCD determined by mesoderm
 PCD in plant development
o Major role in development of plant body
 Xylem, leaf trichomes, egg development
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o Role in stress response
 Cell with pathogen die through PCD with pathogen
 Rest of plant is saved
Different from necrosis
o PCD  PM is intact
o Necrosis  PM deteriorates  cell lysis
Patterns of senescence in plants
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Cumulative effects of deteriorative processes  leads to death
o Genetically programmed and developmentally regulated
Whole plant senescence
o Whole plant, except seed, dies
Senescence of lateral organs in trees
o Lateral organs such as leaves die
Senescence of above-ground parts only
o Shoot dies every year but underground parts survive
When does senescence start
o At whole organism  onset of sexual maturity
o Rate of senescence related to life span of organism or organ
o In leafs
 Total protein and chlorophyll content starts declining
 Membranes become leaky
 With increase in lipid peroxidation products
Reversal of foliar senescence
o Leaf senescence also triggered by lead maturity
 Reverse senescence by removing upper part of plant
Hormonal and anti-oxidant regulation of leaf senescence
o Membrane deterioration mediated by anti-oxidants
 Ethanol, vitamin E, isobenzofuran
o Cellular levels of some hormones and anti-oxidant defenses of
the plant can regulate rate and intensity of leaf senescence
Sensing the environment – Nervous System
Nervous system – Introduction
 2 majors parts  central and peripheral nervous system
o CNS  brain & spinal chord
o PNS  nerves
 Cells in nervous system  highly excitable & conduct electricity
o Neurons
 Information transfer and storage
o Glial
 Out-number neurons 5:1
 Schwann cells
Wrap body many times around neuron in PNS
Form myelin sheet
 Insulate axon & increase conduction speed
 Maintenance and repair of damaged neurons
 Digests debris & guides re-growth
Astrocytes
 Star-shaped body in CNS
 Multiples contacts with neurons, myelinated part
of axons, blood capillaries & ependymal cells
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 Gap-junctions
 Transport nutrients & regulate extracellular space
 Remove debri from damage & guide development
Oligodendrocytes
 Myelin sheet around neuronal axons of CNS
 Can for myelin around several nearby neurons
Microglia
 Smallest glial cells  located in CNS
 Remove debris from trauma or disease
Ependymal cells
 Line ventricles of CNS
 Cavities filled with cerebrospinal fluid
 Cilia on surface circulate cerebrospinal fluid
 Processes that makes connections with Astrocytes
Cell types in nervous system: Neurons
 Wide main body called soma  rich in cell contents
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Individual branches  dendrites
o Make contacts with other neurons  synapses
Long process coming out of soma  axon
o Region of connection  axon hillock
 Information is integrated
o Axon is myelinated  narrow bare part  node of Ranvier
 Each sheath is internode
Types of neurons
o Purkinje cell  fewer but highly branched dendrites
o Many other types, see page 6 of lecture
Structural classification  position & number of dendrites + location
of integrating center
o Multipolar  many dendrites and 1 long axon (myelin)
o Bipolar  single dendrite and 1 long axon (no myelin)
o Unipolar  single long myelinated axon
o Pseudo-unipolar  2 axons
Functional classes
o Motor  efferent  take information to muscles
o Sensory  afferent  take information from sensory organs
o Interneurons  connects previous 2 to CNS
Action potential: generation and perpetuation
 Unequal distribution of charges across PM  -70 mV
o Inside more negative than outside
 Entry of positive ions  membrane depolarization
 More negative than -70 mV  hyperpolarization
 Stimuli which depolarize by causing specific ion channel to open
o Potential below threshold  graded potentials
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o Potential above threshold  active potential
 Only voltage-gated ion channels
Wave action of membrane depolarization
o Local potential arises to maintain magnitude of action
o Myelination of axon increases speed
 Nodes of Ranvier 1mm apart  potential jumps
The synapses and the neurotransmitters
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Synapse composed of presynaptic and postsynaptic cells and
synaptic cleft
Electrical synapse  electrical signal passes as electrical signal
Chemical synapse  release of neurotransmitter
Neurotransmitters
o Small molecular weight molecule
o Synthesized in neurons
o Release triggered by action potential at distal end
Neuromuscular junction
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Neurotransmitter released is acetylcholine
Neuron originates from CNS
At distal end  axons divides into several branches
o End in terminal button
 Forms a synapse with single muscle fiber
 Motor endplate
Presynaptic  voltage-gated Ca channels & Ach vesicles
Postsynaptic  Ach receptors
Action potential opens Na channels  depolarization
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Ca channels open  Ca released
Fusion of Ach vesicles with PM  Ach released in cleft
Binds to receptors  activation  open ion-gated channels
Depolarization leading to muscle action
Ach released and degraded in cleft  presynaptic recycles
Invertebrate nervous system
 Cnidarians have simplest NS
o Neurons are not specialized  impulses in all directions
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In evolution  network rearranged in pathway with defined flow
o Ganglion  cell bodies fuse together with synapses
 Integrating centers of varying complexity
Bilaterally symmetrical animals  complex groupings  brain
o Ganglia are arranged in series
o Cephalization  locating sense organs & integrating centers
at anterior end of the body
Vertebrate nervous system
 3 divisions of nervous system
o Integrating center  brain & spinal chord  CNS
o Smatosensory division  sensory neurons
o Motor division  motor neurons
 Brains
o Narrow neural groove from neurula stage results in brain
o Protected by cranium & meninges
 Dura mater, arachnoid mater & pia mater
o Forebrain, midbrain and hindbrain
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 Hindbrain leads to spinal chord
Peripheral nervous system
o Cranial and spinal nerves
o 2 main divisions
 Somatic motor nervous system  voluntary control
 Autonomic nervous system  no conscious control
 Sympathetic
 Active in stressful conditions
 Regulates blood flow and pressure
Parasympathetic
 Active in periods of rest and calm
 Redirects energy
 Enteric
 Independent  gastro-intestinal tact, etc.
Structure of vertebrate nerve
o Several bundles of axons  bundle = fascicle
 Individual neuron surrounded by endoneurium
 Fascicle surrounded by perineurium
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 Nerve surrounded by epineurium
o Forms synapse at both ends
Structure of a reflex arc
 Receptor  stimulus perceived
 Sensory pathway  sensory neurons take info to CNS
 Integrating center  decision making
 Motor pathway  info from integrating sensor to muscles
 Effector organ  organ where the action is taken
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4/12/2010 8:50:00 PM
4/12/2010 8:50:00 PM