Tropisms In Plants Flashcards
what are the different types of tropisms?
- phototropism
- geotropism
- chemotropism
- thigmotropism
what is a tropism?
plant growth in response to a stimulus
what is the importance of tropisms?
the shoot must grow towards the light for photosynthesis (positive tropism) the root must grow towards the ground so they can get minerals and water for the plant.
why are germinating seeds and young seedlings used in research?
they are easy to work with and manipulate. As they are growing rapidly, any changes to their growth are recognised quickly.
why do roots have negative phototropism?
if roots emerge from the soil due to rain, they will grow in the opposite direction of light to retain usual position.
what happens when a shoot is exposed to unilateral light?
the shoot will bend towards the light. this is because the shoot is positivly phototrophic bending occurs behind the tip.
what happens when a shoot with a removed shoot tip is exposed to unilateral light.
there is no response. this is because the tip is needed to detect the stimulus.
what happens when a lightproof cover is placed on top of the tip of a plant exposed to light?
nothing happens as the light stimulus must be detected by the tip.
what happens when a band of mica is placed on the side of the shoot where light is coming from?
auxin travels down the shaded side of the shoot and it will increase growth and bending.
what happens when a band of mica is placed on the shaded side of a shoot?
movement of auxin down the shaded side of the shoot is prohibited and therefore nothing happens.
what happens when the tip is removed and replaced after placing a gelatin block on the shoot?
auxin travels down the shaded side of the shoot as gelatin allows chemicals to pass through it but not electrical. As a resut, it must be a chemical processes.
which side of the shoot contains less auxin?
the side exposed to light.
what was the original theory about auxin?
it was suggested that auxin was destroyed by light but this was disproved as levels of auxin in shoots are similar regardless of whether they are in the dark or in the light.
how can phototropisms be investigated?
- germinate and grow seedlings in different conditions.
- germinate and grow seedlings in light with different colour filters to see which wavelength of light trigger phototropic response.
why do plants grow more in the dark?
the biological imperative is t grow upwards to reach the light and photsynthesise.
