Sensitivity in plants Flashcards
Explain why a plant may have not flowered
- not enough time in dark
- not enough Pfr concerted to Pr
- Pfr levels remain too high
- once Pfr below a certain level, flowering occurs
- flowering stimulated by fall in Pfr
What do the phytochrome convert into
- Pr is converted into Pfr in red light
- Pfr is converted into Pr in far red light
- Pfr slowly turns to Pr when in darkness
What light does daylight contain
- red light
- Pr turns to Pfr
What light stimulates germination
- red light stimulates germination
- far red light inhibits germination
- Pr turns to Pfr in red light, indicating higher levels of Pfr stimulate germination
What phytochrome stimulates flowering in long day plants
- require Pfr
- plants flower in summer when nights are short so there is less time for Pfr to convert to Pr
What phytochrome stimulates flowering in short day plants
- requires Pr
- plants flower in autumn when nights are long so there is more time for Pfr to convert to Pr
Suggest benefits to plants being able to respond to changes in day length
- flowering occurs at the right time
- flowers when insects available
- seeds germinate at the right time
- day length changes to a sets pattern, short days in winter, long day in summer
- reliable compared to less regular stimuli, e.g. temperature
What is the control of flowering
- a certain period of darkness is required to cause flowering
- it is enough stimulus if only part of the plant, e.g. leaf, is in the dark for the critical period
- leaf is a photoreceptor
- phytochrome in leaves
- signal must be passed to site of flower production from leaves
Describe the mechanism that causes bending of shoots
- phototropism
- light causes auxin moves laterally away from light
- high concentration of auxin away from light
- auxin diffuses down shoot towards zone of elongation (auxin synthesised in meristem at tip of shoot)
- auxin stimulates cell elongation
- H+ pumps in membrane activated, H+ ions enter lowering pH, providing optimum pH for enzyme to break cellulose microfibrils, allowing cells to absorb water and expand
How do auxins cause cell elongation
- auxin diffuses to zone of elongation
- H+ pumps in membrane activated
- H+ ions enter
- pH lowers
- optimum pH for enzymes to break down cellulose microfibrils
- as fewer cross links, cells can absorb water and expand
- cell wall flexible
Compare response of shoot to light with hormonal coordination in animals
- both chemical
- both transported away from production site
- diffusion in plants, blood system in animals
- slower in plants, some animal hormones faster
- some animal hormones has a shorter term effect
- plant response only involves growth/cell elongation, animal hormones do not just effect growth
- comparison of stimuli, e.g….