5.1.5 Plant and Animal Responses

• Why is it important for plants to respond to the environment?

  • avoid abiotic stress
  • avoid herbivory
  • maximise photosynthesis
  • ensure germination/ fertilisation
• What is phototropism?

  Plants growth response to light

  • positive; growth towards light, e.g. stem tip, maximises light for photosynthesis
  • negative; growth away from light, e.g. root tip, less chance of drying out
• What is geotropism?

  Plants response to earths gravitational field

  • positive; roots, respond by growing towards gravitational attraction
  • negative; shoots, growing away
• What is hydrotropism?

  Growth response to earth's water

  • roots positive as grow towards water
• What is thigmotropism?

  Thigmotropism is the growth or movement of a plant in response to touch or contact with a solid object.

  • e.g. venus flytrap and mimosa puddica (touch so leaves coil up, movement/ folding scare herbivores and less likely to be eaten)
• What are alkaloids?

  • nitrogenous compounds, bitter tasting
  • e.g. caffeine toxic to fungi and insects, nicotine a toxin produced in the roots of tobacco plants and highly poisonous to insects
• What are tannins?

  • bitter taste, puts animals off consuming leaves
  • toxic to insects as binds to digestive enzymes produced in saliva and inactivates them
  • tea and red wine rich
• What are terpenoids

  • form essential oils but act as toxins to insects and fungi
• What are pheromones?

  Chemicals made by organisms that affect behaviour of other members of the same species
• What does the hormone cytokinnins do?

  promote cell division

  • more mitosis> more cells> plant growth
• What does the hormone gibberellins do?

  • Causes stem elongation
  • Seed germination; triggers the breakdown of the food store to accessible monomers
  • absorbs water> hormone synthesised in the embryo> transcribes DNA to RNA> translated to amylase (polysaccharides to glucose available for aerobic respiration) and protease (proteins into amino acids which are available to make proteins in new germinating seedlings) which break down the food store
• What does the hormone abscisic acid ABA do?

  Stimulates stomatal opening

  • Water becomes limiting so root cells synthesis and release ABA
  • ABA transported to the leaves and binds to receptors on the plasma membrane of guard cells
  • Triggers ionic concentration of guard cells to decrease so WP decreases and water moves out of the cell via osmosis, reducing the turgor pressure causing stomatal closure
• What does the hormone auxin IAA do?

  • Prevent fruit fall by inhibiting ethene
  • Maintain apical dominance (high as possible quickly, opposed to growing buds)
  • Inhibit root growth at high concentrations

  Made in the shoot tip, diffuse down, sunlight breaks auxins so shaded areas have high concentrations causing more cell division, bending towards the light. For roots, there's a high concentration where gravitational pull, inhibiting cell division causing the other side to grow.
• What does the hormone ethene do?

  • Promotes fruit ripening
  • Promotes leaf fall (abscission) as more glucose is required to keep them in winter. Increase in darkness prevents auxin, allowing ethene to stimulate cells in abscission zone to produce digestive enzymes that weaken leaf petiole. Fatty deposits prevent pathogens from entering
• Auxin experiment

  • tips removed, no auxin made so stems do not grow, lateral shoots do
  • tip covered so auxin moves to all parts of stem, causing all parts to grow
  • lit from one side so auxin accumulates on shaded side causing it to grow more than illuminated side
  • tip separated by agar block, allowing auxin to diffuse down to shoot
  • mica block on tip so auxin has no impact further down and shoot doesn't bend
• How to design an experiment

  • what variable is being changed and how
  • what variables remain constant and how
  • what is being measured and how
  • repeats to identify anomalous results, calculate mean and perform statistics such as standard deviation
  • have a control group to compare effect
• Commercial use of ethene

  • fruit ripening; fruit kept unripe and gas released when ready to be sold
• Commercial use of auxins

  • rooting powders; micropropagation (ideal to produce seedless plants), applied to shoot/ leaves to stimulate root growth also through apical dominance with cytokinnins aiding
  • weed killers; synthetic auxin applied to weeds, promoting growth in broad leaved weeds until they cannot support themselves and die, leaving narrow leaved crops to grow without competition. Cheap and less harmful to the environment
• Commercial use of gibberellins

  • causing germination of seeds used in beer brewing to produce malt
  • (delay ripening and ageing in fruit)
  • (improves fruit shape and size)
• Commercial use of cytokinnins

  • prevent aging
• Commercial use of ethene

  • preserves cut flowers/ green vegetables
• Lack of auxin, cytokinnins and gibbilerins aid fruit dropping
• What is the peripheral nervous system?

  nerves go from sense organs to glands, detects stimuli and controls effectors

  • somatic; all sensory neurones, motor neurones to skeletal muscle
  • autonomic; motor neurones to viscera, sympathetic and parasympathetic
• What is the central nervous system?

  • brain and spine
  • intermediate/ relay neurones
  • many synapses
• What is a ganglion?

  a structure containing a number of nerve cell bodies, typically linked by synapses and often forming a swelling on nerve fibre
• What is the sympathetic nervous system?

  neurotransmitter is noradrenaline

  • short lightly myelinated preganglionic neurones, long post ganglionic
  • fight/ flight
  • increased breathing rate
  • increase diameter of airways
  • increase blood flow to skeletal muscle
  • dilates pupils
  • liver releases glucose
  • reduces peristalsis
• What is the parasympathetic nervous system?

  neurotransmitter is acetylcholine

  • long preganglionic neurones/ short postganglionic
  • rest and digest
  • decrease breathing rate
  • decrease diameter of airways
  • decrease blood flow to skeletal muscle
  • constricts pupils
  • liver stores glucose
  • increases peristalsis
• Reflex arc

  • receptor detects stimuli
  • impulse sent down to sensory neurone
  • sent to relay neurone in CNS (spinal cord and base of brain)
  • sent to a motor neurone
  • attached to an effector (muscle/ gland causing change/ response)
• Suggest how and why someone would react to an object coming towards them

  • they would blink/ close their eyes
  • to protect the eye from the object
• Survival importance of reflexes

  • involuntary; decision-making regions of the brain not involved
  • not having to be learnt; present at birth and therefore provide immediate protection
  • extremely fast; reflex arc short and typically involves one or two synapses, the slowest part being transmission
• What does the cerebrum do?

  • control voluntary actions such as learning, memory, personality and conscious thought
  • largest main bulk of brain matter
• What is the cerebellum?

  • at the bottom of the brain
  • controls unconscious functions such as posture, balance and non-voluntary movement
• What is the medulla oblongata

  • section branching off
  • used in autonomic control e.g. heart rate and breathing rate
• What is the pituitary gland?

  • small part in the middle/ base
  • stores and releases hormones that regulate many bodily functions e.g. FSH, LH, GH
• What is the hypothalamus?

  • middle of brain
  • regulatory centre for body temperature and balance of blood, water potential through osmoreceptors and thermoreceptors
• Fight or flight response

  • hypothalamus activates sympathetic nervous system> activates adrenal medulla to release norepinephrine and epinepherine into the bloodstream (neurotransmitters that can act as hormones)
  • hypothalamus activates adrenal-cortical system by releasing CRF> pituitary gland secretes hormone ACTH> ACTH arrives at adrenal cortex and releases approx. 30 hormones into bloodstream
  • hypothalamus activates sympathetic nervous system> impulses activate glands and smooth muscles
• Effects of norepinephrine and epinephrine

  • increases breathing rate> more oxygen available for aerobic reparation> more ATP made for muscle contraction
  • increase diameter of airways> higher volume of oxygen into lungs
  • increase blood flow to skeletal muscle> more oxygen available, takes away carbon dioxide waste product from muscles
  • dilates pupils> more light> awareness
  • liver releases glucose
• How is the heart rate increased?

  low bp detected by baroreceptors in aorta/ vena cava/ carotid sinus and muscles and low blood pH detected by chemoreceptors in carotid artery/ aorta/ brain (as HCO⁻₃ formed from bohr effect and other acidic substances)> send impulses to medulla oblongata in cardiovascular centre> activates sympathetic NS> impulses sent down accelerator nerve to SAN> increase in frequency of waves of excitation from SAN> increased heart rate> nerve impulses sent from hypothalamus activate adrenal medulla to release adrenaline and the adrenal cortex to release cortisol
• How is heart rate decreased?

  high bp detected by baroreceptors in aorta/ vena cava/ carotid sinus and muscles and high pH detected by chemoreceptors in carotid/ artery/ aorta/ brain> send impulses to medulla oblongata cardiovascular centre> activates parasympathetic NS> impulse sent down Vegas nerve to SAN> decreased frequency of waves of excitation from SAN> less nerve impulses sent from hypothalamus> less activation of adrenal medulla to release less adrenaline and adrenal cortex to release less cortisol
• What is standard deviation?

  spread of data around the mean, excluding extreme values