Sensitivity in plants (2) Flashcards
What is the term for plant growth responses to environmental cues?
Tropism
List 4 plant stimuli
- light
- gravity
- water
- temperature
How do plants grow?
They grow due to cell division, assimilation and elongation.
Division - when a cell divides (duh)
Assimilation - new materials are assimilated by the divided cells
Elongation - cell elongates
What kind of tropisms are there? And which growth directions are positive and which are negative?
Geotropism - response to gravity
- Positive geotropism = grow downwards
- Negative geotropism = grow upwards
Phototropism - in response to light
- Positive phototropism = grow towards light
- Negative geotropism = grow away from light
What are photoreceptors and what are they called in plants?
Photoreceptors are proteins which are sensitive to light. In plants they are called phytochromes.
Where are they found?
many parts of the plant eg leaves
What are the two states that phytochomes exist in?
Pr (phytochrome red) and Pfr (phytochrome far-red)
What is the difference between these two forms?
Pr absorbs red light at a wavelength of 660 nm
Pfr absorbs far red light at a wavelength of 730 nm
What happens when a plant is exposed to red light?
Pr is converted to Pfr
What happens when a plant is exposed to fer-red light?
Pfr is converted to Pr
What happens when a plant is in darkness?
In darkness Pfr is slowly converted into Pr
What happens when a plant is in daylight?
Daylight contains more red light than far red light so more Pr is converted to Pfr than vice versa.
What do these phytochromes actually do?
Phytochromes can have inhibitory or stimulating affects on growth depending on the plant.
What is the term for the lenght of night and day which affects a plant’s growth?
Photoperiodism
What is a critical day length?
the minimun hours a day there must be for a plant to flower
