plant tropism

Question 1

stimulus

Answer 1

• a signel that triggers a response
  A stimulus in plants can cause plants to grow towards or away from it

Question 2

tropisim/ tropic response

Answer 2

• tropism is a plants growth response to an external stimulus
  -positive tropism: plant grows towards the stimulus
  -negative tropism: a plant grows away from the stimulus

Question 3

phototropism

Answer 3

-plants growth response to a lighgt source caused by distrubution of auxin
-if lightsource is directly above a plant, auxin if distrubuted evenly and plant grows upwards
-if light source is hitting one side of a plant, then the auxin moved towards the shaded side, causing elongation of cells in shaded side and stem curves towards light course
–> stems show postive phototropism
–> roots show negtaive phototropism cause they grow towards light source (supposed to grow downwards)

Question 4

gravitropism

Answer 4

plant growth responds to ‘evil’ gravity
-roots show positive gravitropism since they grow downwards
-stems grow upwards against gravity
–> good, cause they have to support leaves and flowers

Question 5

Thigmotropism

Answer 5

plant’s growth response to mechanical tropism (object touching the plant, organism, wind, etc)
-if an object is touching one side of a plant, auxins move to the non-touched side
-stems show positive thigmotropism since they grow around the object.
–> Usually monocots do this
-Roots show negative thigmotropism since they move away from the object touching them

Question 6

Nastic respone

Answer 6

• a plant’s response to a stimulus that is independent of the direction of the stimulus
  -not a growth response since it is reversible and can be repeated

Question 7

nastic reponse example

Answer 7

• Queen of the Night
  –> not strongly colored petals but has a strong smell and opens petals at night to attract pollinators but closes in the morning
• Venus flytrap
  –> When an organism touches the hair in the Venus fly trap (such as insect), signals are sent for the Venus fly trap to snap and close.
  –> Venus fly trap has digestive enzymes to break down the insects and absorb nutrients (mainly nitrogen)
  –> Venus fly trap opens back up
  -Mimosa Pudica
  –> When leaves are touched, they start to close to protect the plant

Question 8

If phototropism doesnt work

Answer 8

-plant may grow in wrong direction
-reduced photosynthesis, plant is weaker and slower growth
-seedling may die

Question 9

If gravitropsim doesnt work

Answer 9

roots may grow sideways or upwards, unstable anchoring, poor nutrient uptake from soil into roots
stems won’t provide support to leaves and flowers since they grow down (may bend in strange directions)

Question 10

If thigmostropism doesn’t work

Answer 10

plants wont grow around object (vines wont wrap around structures), and insetad by grow on ground and be more siked to damage

Question 11

nastic response vs tropism

Answer 11

1. Both are responses to external stimulus
   - For trospim the response to stimulus leads to permanent change in plant growth (like in phototropism the stem curves towards the light source)
   - Nastic responses happen fast (within seconds to minutes) in response to movment and can be reveresed and repeated
2. Both responses are automic plant responses after triggered by stimulus
   -Tropism is slow; growth response takes hours or days (since it’s growth-based).
   -Nastic response is fast, seconds to minutes. (movement-based)