plant animal responses

• central nervous system includes the brain(non-myelinated) and spinal cord (myelinated )
• peripheral nervous system is composed of the afferent (sensory) and efferent (motors) system.
• efferent system is composed of the somatic and autonomic system
• somatic system is conscious reflexes, myelinated. There is one neurone between the CNS and effector. The effector is skeletal.
• autonomic system is involuntary movements, non-myelinated and usually 2 or more neurones between CNS and effector. This system can be split into the sympathetic and parasympathetic systems.
• sympathetic system speeds things up and employs flight or fight response. Uses noradrenaline and also long post-ganglionic neurones so meaning multiple effectors and short pre-ganglionic neurones.
• parasympathetic system slows things down, uses Ach. Has few long pre-ganglionic neurones and short post-ganglionic neurones
• to increase heart rate, the medulla oblongata sends an action potential via accelerans which releases noradrenaline which binds to receptors on SAN so increase heart rate.
• to decrease heart rate, medulla oblongata sends an action potential ia vagus nerve which releases Ach which binds to nicotine receptors on SAN which decrease heart rate
• heart rate can also increase if adrenaline binds to receptors on SAN
• endocrine system involves the hypothalamus, pituitary gland, adrenal cortex and thyroid gland
• sliding filament theory is how the actin and myosin slide over each other to make the muscles contract
• myosin is a fibrous protein with globular heads. The heads bind to actin-myosin active sites, they are hinged and contain ATPase
• actin is a globular protein made of many actin subunits ; tropomyosin, troponin and actin
• troponin has three subunits that bind to ; calcium, tropomyosin and actin
• tropomyosin covers the binding sites at rest
• sliding filament

  1. when muscle fibre depolarises calcium leaves the sarcoplasmic reticulum and binds to troponin
  2. this causes tertiary structure of troponin to change which pulls tropomyosin out of way revealing binding sites
  3. myosin heads attach and from cross-bridge
  4. myosin heads move actin over myosin = power stroke
  5. an increase in calcium stimulates ATPase which breaks ATP into ADP+Pi which releases energy to break the cross-bridge
  6. myosin heads returns to original shape and then attaches to another actin binding site and process is repeated many times
• ATP uses in sliding filament theory

  1. break cross-bridge
  2. ATP pumps calcium back into sarcoplasmic reticulum
• at the neuromuscular junction

  1. Action potential arrives at the junction and voltage gated calcium channels open so calcium enters
  2. vesicles containing Ash move to and fuse with membrane releasing Act into self via exocytosis
  3. Ach diffuses across cleft and binds to Ash nicotinic receptors and sodium then enters the muscle fibres
  4. if get to -55mv, voltage gates sodium channels open = depolarisation.
  5. depolarisation causes calcium to leave the sarcoplasmic reticulum
• examples of responses to biotic factors :

  • alkaloids = made from amino acids and have bitter taste
  • tannins = found throughout plant with horrid taste, binds to proteins in gut in herbivores so they can't digest protein and in insects they are toxic
  • pheromones = released by one organism that cause a response in another organism
• two types of growth response : tropism and nastic
• tropism is directional and examples include : phototropism, geotropism, chemotropism, thigmotropism, hydrotropism and thermotropism
• nastic growth is non-directional growth and examples are thimonasty
• auxins have four main functions ;

  1. cause apical dominance
  2. causes positive phototropism in shoots and negative phototropism in roots
  3. causes positive geotropism in roots and negative e geotropism in shoots
  4. inhibits leaf loss (abscission) in deciduous plants
• causes apical dominance

  1. apical bud/tip produces IAA which stimulates growth of apical tip
  2. IAA then diffuses down and inhibits growth in lateral shoots
  3. in talks plants IAA at bottom is low so lateral shoots may grow here
• causes positive phototropism in shoots

  1. IAA binds to receptors and hydrogen ions are pumped from cytoplasm to cell walls
  2. pH decrease and stimulates enzymes to break hydrogen bonds in cellulose and increase hydrogen ions and decrease water potential causing water to enter
  3. causing the cell to elongate
• causes negative phototropism in roots

  1. IAA produced in root
  2. IAA acclimates on shady side
  3. and inhibits cell elongation so root bends away from light
• causes positive geotropism in roots

  1. IAA produced by root tip
  2. IAA accumulates on underside and inhibits cells elongation
  3. root then bends down
• causes negative geotropism in shoots

  1. IAA is produced in bud
  2. IAA accumulates on underside and stimulates cell elongation
  3. so shoot bends up
• evidence of geotropism

  • happens in dark
  • put in klinostat which spins seedlings and inhibits effect of gravity roots/shoots grow horizontally
  • put shoots and roots in Petri dishes at different angles and all the shoots will bend up and roots will bend downwards
• inhibits leaf loss in deciduous plants

  • happens to prevent excess water loss as water is frozen
  • leaf loss is triggered hen day length decrease and light intensity decreases
• in spring young leaves produce auxins to inhibit leaf loss and cytokinins
• cytokinins inhibit senescence and stimulate cell division and help shoots and roots develop quicker in tissue culture and also stimulate lateral shoot formation
• in autumn cytokinin levels drop which causes senescence, causes auxins levels to drop ad cause ethylene to increase which stimulates cellulase to breakdown cells in the abscission layer meaning leaves fall off
• ethylene causes fruits and flowers to ripen by positive feedback
• gibberellins are produced by young leaves and seeds and stimulate seed germination, elongation, lateral shoot formation and flowering
• when seeds absorb water in spring they produce gibberellins which stimulate amylase and protease production causing growth
• to make gibberellins a precursor and an enzyme are needed
• abscisic acid inhibits seed germination and growth and stimulate stomatal closure when less water is available
• ABA

  1. when water levels are low, ABA binds to receptors on guard cells which causes calcium to leave vacuoles and enter cytoplasm
  2. this causes ion channels in cell wall to open and potassium to leave guard cell
  3. this decreases water potential outside guard cels and so water leaves by osmosis and guard cells become flaccid and stomata close