Sensitivity in plants Flashcards

1
Q

Explain why a plant may have not flowered

A
  • 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
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2
Q

What do the phytochrome convert into

A
  • 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
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3
Q

What light does daylight contain

A
  • red light

- Pr turns to Pfr

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4
Q

What light stimulates germination

A
  • red light stimulates germination
  • far red light inhibits germination
  • Pr turns to Pfr in red light, indicating higher levels of Pfr stimulate germination
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5
Q

What phytochrome stimulates flowering in long day plants

A
  • require Pfr

- plants flower in summer when nights are short so there is less time for Pfr to convert to Pr

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6
Q

What phytochrome stimulates flowering in short day plants

A
  • requires Pr

- plants flower in autumn when nights are long so there is more time for Pfr to convert to Pr

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7
Q

Suggest benefits to plants being able to respond to changes in day length

A
  • 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
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8
Q

What is the control of flowering

A
  • 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
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9
Q

Describe the mechanism that causes bending of shoots

A
  • 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
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10
Q

How do auxins cause cell elongation

A
  • 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
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11
Q

Compare response of shoot to light with hormonal coordination in animals

A
  • 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….
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