module 5 - 16.1 plant hormones and growth in plants Flashcards
what is a tropism?
involves differential growth of plant cells triggered by chemical messages produced in response to particular stimuli
what is an abiotic factor?
non-living components of a habitat
what is a biotic factor?
living components of an ecosystem
what does dicotyledonous mean?
plants producing seeds containing 2 cotyledons which act as food stores for developing embryos and form first leaves when seed germinates
what does monocotyledonous mean?
plants producing seeds containing 1 cotyledon which act as food stores for developing embryos and form first leaves when seed germinates
what are the main hormones a plant produced?
auxins
gibberellins
ethene
abscisic acid (ABA)
what is the sequence of seed germination?
- seed absorbs water
- enzymes produced (proteases, amylase, maltase)
- products of digestion used to generate ATP and act as monomers for new macromolecules
- gibberellins switch on genes in the embryo that code for these enzymes
- ABA acts as antagonist to gibberellins to prevent early germination
how does ABA act as an antagonist?
high levels of ABA stops gibberellins switching genes on for early germination
what is the relationship between gibberellins and ABA?
- inverse relationship
- suggests there is a regulation look that establishes balance of gibberellin and ABA
how are mutant seeds evidence for gibberellin and germination?
- mutant varieties of seeds have non-working alleles that allow for gibberellin synthesis
- mutants cannot produce giberellins
- mutants cannot germinate
how are gibberellin biosynthesis inhibitors evidence for giberelling and germination?
- when gibberellin synthesis inhibitors are applies to seeds the seeds cannot make gibberellins
- treated seeds do not germinate
- when either inhibitor is removes or gibberellins are applied, seeds then germinate
what are meristems?
- tissue in most plants containing undifferentiated cells
- found in zones of plant where growth occurs
- give rise to various organs of the plant and keep plant growing
what are the 3 types of meristems?
apical - tips, root and shoot
intercalary - middle, only in monocot stems at base of nodes, and leaf blades
lateral - at the sides
what are auxins?
- made in apical meristems
- translocated in phloem, mainly from shoot tip to root tip
- stimulate growth of main apical shoot
how do auxins stimulate growth of main apical shoot?
- bind to receptors in cell membrane
- causes fall in cellular pH to pH5
- optimum pH for enzymes that keep cell walls flexible
- cells mature and move aware from the meristem, auxins also destroyed
- pH rises and inhibits enzymes that were keeping cell wall flexible
- cell wall now becomes inflexible and rigid, cell size is fixed
