Plant and Animal Reponses

• plants responses to herbivory

  physical defences - thorns, stings , barbs

  chemical defences -tannins, alkaloids and terpenoids
• what is tannins?


  bitter tasting chemical compound e.g. to discourage animals from eating the plant + tannins are toxic to insects
• what are alkaloids?


  nitrogenous, bitter tasting chemicals alkaloids affect the metabolism of the herbivore sometime resulting in death e.g =. nicotine, cocaine , morphine
• what are terpenoids?

  essential oils that can be toxic to insects and fungi
• what are pheromones? 


  Chemicals product by an organism which affect the behaviour of other members of that species
• Response to abiotic stress

  • leaf loss - trees will lose their leaves in countries that have cold winters
  • Daylength sensitivity - Photoperiodism is the term for plants being sensitive to a lack of light
  • Abscission - light levels decrease causing enzymes that digest to weaken
  • Preventing freezing - chemicals that naturally stop freezing
  • stomata control - open stomata = cooling effect
• abiotic stress


  stresses that plants are exposed to include e.g. high winds, excess water, lack of water, temperature changes
• tropism 


  when plants respond, via growth to stimuli
• what types of tropism is there?

  Phototropism, gravitropism, thigmotropism, chemotropism.

  • postive and negative
• what stimuli does the plant respond to?

  Light, water, gravity, touch, temperature, chemicals.

  • controlled by specific growth factors
• what is IAA?


  a type of auxin that controls cell elongation + inhibits growth of cells in the roots

  • made in the tip or the roots + shoots but can diffuse to to other cells
• Phototropism in shoots

  • light needed the LDR in photosynthesis = plant grows towards light = positive phototropism

  1. shoot tip cell produce IAA causing cell elongation
  2. IAA diffuses to other cells
  3. IAA will diffuse towards the shaded side = higher conc there
  4. the cells of the shaded side elongate more + results in plant bending towards light source
• Phototropism in roots

  • roots do not require light they anchor the plant in the soil
  • high conc of IAA inhibits cell elongation causing roots cells to elongate more on the lighter side = bend away from light
  • negative phototropism
• Gravitropism in shoots

  • IAA will diffuse from the upper side to the lower side of a shoot
  • plant is vertical this causes the plant cells to elongate + plant grows upwards
  • plant is on its side it will cause the shoot to bend upwards
  • negative gravitropism
• Gravitropism in roots

  • IAA moves to the lower side of roots so that the upper side elongates and the root bends down towards gravity + anchors the plant in
  • positive gravitropism
• what are plant hormones?


  hormones control responses in the plant such as ripening of fruit, germination of seeds, lengthening of stems + when leaves drop
• auxins 


  cause cell elongation in stems + inhibits growth in roots

  • prevents leaves from dropping and maintains apical dominance
• Ethene 


  a gas that causes fruit to ripen
• Gibberellin 


  stimulates seed germination, stems elongation + pollen tube growth fertilisation
• Abscisic acid (ABA)


  stimulates stomatal closing and maintains dormancy of seeds
• Ethene is used to control ripening of fruit and vegetables.
• rooting powder is used to help the plant grow faster and stronger, and to help the plant absorb water and nutrients from plant cuttings
• Auxins are used in rooting powders
• ausins have been used as weedkiller + to make seedless fruit
• what nervous systems is the mammalian nervous system made of?

  peripheral + central nervous system
• PNS (peripheral nervous system)

  includes the receptors, sensory and motor neurones
• CNS (central nervous system)


  is the coordination centres, such as the brain and spinal cord
• autonomic nervous system 


  works constantly, subconsciously e.g. digestion
• somatic nervous system 


  consciously controlled e.g. you decide to move/stand up
• Cerebrum 


  largest part of the brain

  • outer layer known as cerebral cortex made of folds and split into two hemispheres = conscious thoughts, language, intelligence, personality
• cerebellum 


  looks like a mini cauliflower

  • coordinates movement, muscles + balance
• Medulla Oblongata 


  above the spinal cord

  • control for unconscious activities such as breathing + heart rate
• Hypothalamus 


  small part of brain is responsible for homeostasis e.g. temperature + water balance
• Pituitary gland 


  small lobed structure known as the master gland because it secretes many hormones to coordinate several responses such as the oestrous cycle and osmoregulation
• Response + Reflexes

  reflex arc is made up of three neurones

  • synapses slow down responses as electrical energy is converted to chemicals that diffuse across synapse
  • no conscious decision - rapid + prevent brain from being overloaded
  • stimuli detected by receptor = impulse passed along sensory neurone to relay neurone
  • relay - motor connected to effector (muscles in hand) = muscles contract + move away from dangerous hot object
• what does the autonomic nervous system do?

  detects potential threat and sends impulse to hypothalamus = impulses sent to sympathetic nervous system + adrenal-cortical system

  • effectors = adrenal glands = more adrenaline + noradrenaline
  • = hormones trigger the hypothalamus to stimulate the release of (ACTH) from pituitary gland
• blood gluc low = adrenaline secrete = increase glucose:

  • adrenaline attaches to receptors = (G protein) activated = ATP to cAMP
  • cAMP activate an enzyme = hydrolyse of glycogen to glucose
  • second messenger model of adrenaline = process forms cAMP = second messenger
• what does the medulla oblongata control?

  brain controls the heart rate via the autonomic nervous system

  there are two parts:

  1. a centre linked to the sinoatrial node to increases heart rate via the sympathetic nervous system
  2. Another that decreases heart rate via the parasympathetic nervous system
• The heart rate changes in response to pH and blood pressure + stimuli detected by chemoreceptors + pressure receptors in aorta + carotid artery
• Response to pH

  • pH blood decreases = high respiratory rate due to CO2 + lactic acid
  • acid must removed or enzymes denaturing
  • more impulses via sympathetic nervous system to SAN so CO2 can diffuse out into alveoli more rapidly