BSC 2011L

1
Transpiration, Tropisms, Hormones in Plants

• BSC 2011L

2
Water Transportation in Plants

• Adhesion - water molecules momentarily will
  stick to the sides of xylem vessels
• Cohesion water molecules cling together

3
Transpirational pull at leaves

• Transpiration evaporation of water from leaves
  continuous water column is pulled upward
• We will perform transpiration experiment today
• Environmental factors effecting transpiration
• Temperature as temp increases, so does
  transpiration
• Humidity as humidity increases, transpiration
  decreases
• Wind increased movement of air causes increase
  in transpiration

4
Stomata

• In leaves, lower epidermis has openings called
  stomata
• Opening and closing of these regulated by guard
  cells
• When open, gas exchange and water evaporation
  occur
• The more stomata and the more they are open, the
  greater rate of transpiration

5
Plant Growth

• Regulated by temperature, nutrients, and water
  availability
• Plants respond to environmental stimuli by
  utilizing hormones that affect growth
• Positive tropism growth of plant toward
  stimulus
• Negative tropism growth of plant away from
  stiumlus
• Look at Fig 20.1

6
Gravitropism

• Negative gravitropism of stems
• Lay potted plant on its side and it will
  eventually bend upward
• Why does this happen?
• Gravity causes amyloplasts (plastids that store
  starch) to settle in lower part of cell
• This leads to increase in hormone AUXIN in lower
  part of stem
• Auxin causes cell elongation on lower part of
  stem bending it upward

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8
Phototropism

• Bending of plants in response to light
• How does this happen?
• Auxin migrates from bright side of plant to dark
  side
• Auxin causes cells to become elongated on dark
  side, so that stem bends towards the light

9
Etiolation

• Altered growth patterns when seedling is grown
  without sunlight
• May assist seedling in reaching sunlight