module 5 - 16.4 tropisms in plants & 16.5 the commercial uses of plant hormones Flashcards
what is a tropism?
- the growth or turning movement of a plant in response to an environmental stimulus
- directional growth responses
what are phototropisms?
movement or growth in response to light
what are chemotropisms?
movement or growth in response to chemicals
what are geotropisms?
movement or growth in response to gravity
what are heliotropisms?
seasonal motion of plants in response to direction of the sub e.g. sunflower
what do plant roots show?
- positive phototropism
- plant shoots will grow towards unidirectional light
what is a coleoptile?
- the pointed protective sheath covering the emerging shoot in monocotyledenos e.g. grass
- contain cells that are all specialised to fast stretch growth but they do not divide
what does unilateral mean?
unidirectional
what does the tip contain?
photoreceptor cells, and the bending takes place lower down on the coleoptile
what is etiolation?
process in flowering plants grown in partial or complete absence of light
what is etiolation characterised by?
- elongation of stems and leaves due to auxins and lack of light
- weakening of ell walls in stems and leaves due to auxins
- longer internodes so fewer leaves per unit of stem due to gibberellins and lack of light
- chlorosis, pale-yellowish colour due to lack of chlorophyll
what are statoliths?
dense amyloplasts (organelles that synthesise and store starch involved in perception of gravity)
where are statoliths?
located near vascular tissue in shoots and caps of roots
what is the composition of the denser amyloplasts?
denser than cytoplasm and can sediment according to gravity
what is a clinostat?
device which uses rotation to negate effects of gravitational pull on plant growth
