Phototropism example

2.81 Phototropism

Notes

"Describing positive phototropism of stems"

Phototropism = Growth response of plant due to light
   - positive (towards light)

Stems


Uniform (all-direction) light = Stems will grow upwards/forwards in direction

Lateral light source (one side) = Stem will bend in tropism towards light
   - Direction of tropism adaptation (light from right) --> Auxin (plant hormone on left), causes more growth on left, pushing stem to right.

NOTE on Auxin: Causes cells to elongate, not divide

2.80 Geotropism

Notes


Geotropism = Growth response of plant due to gravity

Plant seed (conventional orientation)


Embryonic root will grow downwards - positive geotropism (towards gravity centre)
Embryonic shoot will grow upwards - negative geotropism


Plant seed (on it's side)


Root will still show negative geotropism (turn up)
Shoot will still show positive geotropism (turn down)

2.79 Plant response to stimuli

Notes


1. Stimuli = changes in the environment
       - Temperature
       - Light

2. Receptors detect stimuli
    Receptors ----- plant Hormones/growth regulators (e.g. Auxin) -----> Response

3. Response
       - Growth from stimuli = Tropism
          - Temperature    
          - Light                    = Phototropism
          - Gravity                 = Geotropism
          - Water/Moisture     = Hydrotropism

2.54 Transpiration

Notes


Word equation:
Liquid ---------- Heat (Sunlight) ---->  Gas

Process:
1. Water (osmosis): Root system -> Stem -> Leaf -> Stomatal pores to evaporate
2. Sunlight hits leaf surface;
       - Leftover from photosynthesis absorbed by other cell structures -> Produces Heat
       - Water from xylem: Spongy mesophyll -> Cavity 'above' stomata
          - Where phase change occurs
3. Vapor inside (100% humidity) --- Diffusion ----> Outside environment (h < 100%)

2.53 Uptake of Water

Notes

Roots:
 - Branching increases Surface Area for absorption of water
 - Smallest ends of roots have root hairs - epidermis of root shows extension (hair) of cell wall
    - Increases S.A. for absorption of water

Absorption:
 1 Active transport (against concentration gradient, with energy) of minerals --> Surface     epidermal cells & inside root hair
 2 This encourages water uptake (osmosis), dilute = soil/water -->  concentrated = by
    minerals 'moved' into root hair through active transport.

- Water: From root cortex --> root xylem (by osmosis)