Internal and external stimuli

• What are plant growth factors and why are they produced

  ~Chemicals produced that regulate plant growth responses to directional stimuli

  ~Produced in plant growing regions

  ~Diffuse from cell to cell/ phloem mass transport
• Explain why shoots show a postive phototropism

  ~Indoleacetic acid (IAA) diffuses to shaded side of root tip

  ~As IAA diffuses down shaded side, it causes active transport of H+ ions into cell wall

  ~Disrtuption to H-bonds between cellulose molcecules and action of expansins make cell more permeable to water

  ~Cells on shaded side elongate faster due to higher turgor pressure

  ~Shoot bends towards light
• Explain why roots show positive gravitropism

  ~Gravity causes IAA to accumulate on lower side of the root

  ~IAA innibits elongation of root cells

  ~Cells on the upper side of the root elongate faster, so the root tip bends downwards
• Define taxis and kinesis

  ~Taxis = directional movement in response to external stimulus

  ~Kinesis = non directional response to presence and intensity of external stimulus

  ~Maintain mobile organism to optimum environment
• Many organisms respond to temperature and humidity via kinesis rather than taxis, why

  ~Less directional stimuli

  ~Often no clear gradient from one extreme to the other
• How could a student recognise kinesis in an organism's movement

  ~Organism crosses sharp division between favourable and unfavourable environment = turning increases

  ~If organism moves considerable distance into favourable envronment: turning slowly decreases, begins to move in long straight lines, sharper turns
• Give the advantages of a simple reflex

  ~Rapid response to potentially dangerous stimuli since only three neurons involved

  ~Instinctive
• Suggest a suitable statistical test to determine whether a factor has a significant effect on the movement of an animal in a choice chamber

  Chi squared
• What features are common to all sensory receptors

  ~Act as energy transducers which establish a generator potential

  ~Repond to sepcific stimuli
• Describe the basic structure of a pacinian corpuscle

  ~Single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule

  ~Stretch mediated Na+ channels on plasma membrane

  ~Capillary runs along base layer of tissue
• What stimulus does a pacinian corpuscle respond to and how

  ~Pressure deforms membrane, causing stretch mediated Na+ ion channels to open

  ~If influx of Na+ raises membrane to threshold potential, a generator potential is produced

  ~Action potential moves along a sensory neuron
• Name the two types of photoreceptor cell located in the retina

  ~Cone cells

  ~Rod cells
• Where are rod and cone cells located in the retina

  Rod = evenly distributed around perophery but not in central fovea

  Cone = mainly central fovea no photoreceptors at blind spot
• Define mycogenic

  Contraction of heart is initiated within the muscle itself rather than by nerve impulses
• State the name and location of the two nodes involved in heart contraction

  Sinoatrial node (SAN) = within the wall of the right atrium

  Atrioventricular node (AVN) = near lower end of right atrium in the wall that separates the two atria
• Describe how heartbeats are initiated and coordinated

  ~SAN initiates wave of depolarisation (WOD)

  ~WOD spreads across both atria = atrial systole

  ~Layer of fibrous, non-conducting tissue delays impulse while ventricles fill and valves close

  ~ANV conveys WOD down septum via bundle of HIS, which branches into purkinje fibres along ventricles

  ~Causes ventricles to contract from apex upwards
• State the formula for cardiac output

  Cardiac output = Stroke volume x heart rate
• What is the autonomic nervous system


  ~System that controls involuntary actions of glands and muscles

  ~Two subdivisions = sympathetic and parasympathetic
• State the difference between the sympathetic and parasympathetic nervous system

  ~Sympathetic involved in flight or fight response and stimulates effectors to speed up activity

  ~Parasympathetic involved in normal resting conditions and inhibits effectors to slow down activity
• Name the receptors involved in changing heart rate and state their location

  Baroreceptors = carotid body

  Chemoreceptors = carotid and aortic body
• How does the body respond to an increase in blood pressure

  ~Baroreceptors send more impulses to cardioinhibitory centre in the medulla oblongata

  ~More impulses to SAN down vagus nerve via parasympathetic nervous system

  ~Stimulates release of acetylcholine, which decreases heart rate
• How does the body respond to a decrease in blood pressure

  ~Baroreceptors send more impulses to cardioacceleratory centre in the medulla oblongata

  ~More impulses to SAN via sympathetic nervous system

  ~Stimulates release of noradrenaline, which increases heart rate and strength of contraction
• How does the body responds to an increase in carbon dioxide concentration

  ~Chemoreceptors detect pH decrease and send more impulses to cardioacceleratory centre of medulla oblongata

  ~More impulses to SAN via sympathetic nervous system

  ~Heart rate increases, so rate of blood flow to lungs increases = rate of gas exchange and ventilation rate increase