Transpiration/Translocation

Transpiration

when water moves through a plant from the roots to the leaves through vessels called xylem

4 factors that affect transpiration

1. temperature

   1. warmer weather = higher rate because of faster/more evaporation

2. humidity

   1. high humidity = lower rate because more water outside and a lower conc gradient

3. airflow

   1. high air flow = higher rate because more water is swept away so higher conc gradient

4. light intensity

   1. high light intensity = higher rate because more photosynthesis means open stomata

cohesion tension theory

water is pulled up through a plant by airs evaporative drying power, which creates a continuous negative pressure called “tension”

• cohesive/adhesive properties of water maintain transpiration

lignin

xylem have lignin to reinforce the walls

• woody texture and handle extreme pressure

  • sucking water wouldve collapsed the walls

xylem structural adaptations

1. strong hollow tube with cell walls

2. no plasma membrane —> constant stream

3. helical structure —> resists inward pressure

   1. like vacuum

guard cells

swell or shrink to open and close the stomata

• swollen = turgid = open

• shrunken = flaccid = shut

water conserving adaptations

1. waxy cuticle

   1. limits evaporation and shield the top leaf from the sun

2. guard cells open and close

   1. helps choose when water leaves —> open with water

3. guard cells are light sensitive

   1. close at night w/ no photosynthesis

translocation

the movement of organic compounds through the phloem tissue of plants

• osmosis is important

phloem

has two cell types to move sugars

1. sieve tubes

   1. need companion for energy+nutrients

2. companion tubes

goes up and down the sieve tubes and gets nutrients from the companion cell

translocation needs __ transport

translocation needs active transport and osmosis

• to move sugars from outside and water from xylem

process of translocation

sugars move from a source (high sugar) to a sink (low sugar storage area)

1. loads sucrose into phloem

2. osmosis moves water into the phloem to build pressure

3. the sucrose moves up/down the tube

4. the sucrose moves into the sink

5. water moves back into the xylem through osmosis

when does translocation happen

fall/winter: moves sugars down to roots to store energy

spring/summer: moves sugars up to leaves to help with growth

pressure flow hypothesis

osmosis increases hydrostatic pressure which moves sucrose from source to sink

cuticle

upper epidermis

lower epidermis

palisade mesophyll

stomata + guard cells

vascular bundle

spongy mesophyll