chemical control in mammals and plants

• what is the purpose of a negative feedback system?

  a way to maintain a condition to keep equilibrium in the body
• how does a negative feedback system work?

  a change in conditions is recognised by receptors so effectors respond to restore the equilibrium
• what is the main form of chemical control in plants?

  hormones and the endocrine system
• what is the pituitary gland?

  a gland in the brain that releases hormones that affect all other endocrine glands
• what controls the pituitary gland?

  hypothalamus
• what are the 6 hormones the pituitary gland produces?

  oxytocin, ADH, prolactin, LH, FSH, ACTH, growth hormone, TSH
• how does light affect plants?

  they respond to the direction it came from and grow in different directions
• what is a tropism?


  directional growth response of a plant based on a certain stimulus
• what are auxins?


  hormones that are involved in plant growth and apical dominance
• what is apical dominance?


  when the growth of lateral buds is repressed so the main stem grows faster
• where are auxins found?

  the shoots, and then they move down to the roots
• what do auxins promote?

  root growth
• how do auxins cause growth??

  auxins bind to receptor sites on cell membranes, causing H ions to pump into cell wall, which breaks bonds and causes the cell wall to be flexible
• how do auxins cause the plant to respond to light?

  auxins move to side of plant that isn't affected by light, which stimulates cell elongation so the plant bends towards the light
• why is it beneficial for a plant to bend towards the light?

  more chance of receiving light energy, maximises rate of photosynthesis
• what are giberellins?


  hormones that stimulate cell elongation and growth of fruit
• what do giberellins stimulate?


  the production of amylase, which breaks down starch stores to make glucose available for respiration
• what are cytokinins?

  hormones that promote cell division and lateral bud growth
• how do auxins and cytokinins work together?

  work antagonistically to supress growth of lateral buds
• what type of light promotes germination in seeds?

  red light
• what type of light inhibits germination of seeds?

  far red light
• what is the active form of phytochrome?


  Pfr
• what is the inactive form of phytochrome?

  Pr
• what happens if Pr is exposed to red light?

  it will convert to Pfr
• what happens if Pfr is exposed to far red light?

  it will convert to Pr
• what is a long day plant?

  a plant that needs red light and Pfr to germinate, so it needs a long period of daylight
• what is a short day plant?

  a plant that needs far red light and Pr to germinate, so it needs a long period of darkness
• what is a photoperiod?


  the amount of light a plant is exposed to in a day
• what are plants that are unaffected by the length of day?

  day neutral plants
• what does red light inhibit?

  the flowering of short day plants
• what does far red light inhibit?


  the flowering of long day plants
• what is photomorphogenesis?


  the process by which the development of a plant is controlled by the types of light