SECTION 13.4: TRANSPORT IN PLANTS

How it works…

Essentially a plant is a tube with its base embedded in the ground (the roots), and leaves are at the top of the tube

Materials like sugars which are made in the leaves must get carried all over the plant

Water dissolves the carbohydrates (energy) and moves up it and down the plant via the _____________

Water and dissolved nutrients in the ground must be taken up by the roots to the cells in the leaves and other parts via the _____________

Water and Nutrients in and out of Cells… Particles move according to concentration

gradients - the difference in concentration between two areas

______________________ - the movement of particles from an area of high concentration to an area of low concentration until a balance is achieved.

“moving down the gradient” Diffusion of WATER across a membrane down

its concentration gradient is called _________________

Diffusion

Diffusion and Osmosis occur naturally and ____________________ require energy to move down the gradient

Sugars and other nutrients must move across cell membranes and _________ require energy

This is called ACTIVE TRANSPORT

Transport in the Xylem

Roots contain more dissolved nutrients than surrounding soil so water moves into roots via osmosis

Xylem transports water up from roots into the stem and some water moves by diffusion to other tissues

Xylem branches into numerous veins as it enters leaves. Water and minerals diffuses into the leave at the end of each vein

Up to 90% of water that reaches the leaf is lost to the atmosphere as it evaporates through the ___________________. This is called ________________________

What about Tall Trees?

How can water travel through Xylem up to the top of trees that are a hundred feet tall??

Long Distance Transport in Xylem

1. Root Pressure• Pushes water and minerals up the plant,

against gravity• Water enters the roots and creates a positive

pressure that pushes water upward• Minerals are moved into the roots via active

transport, which increases the concentration in the xylem and causes more water to move by osmosis

• Root pressure can sometimes be seen as tiny droplets on leaf edges – called _______________________

(Figure, 13.21 on p.561)

Long Distance Transport in Xylem2. Transpiration Pull

Negative pressure (pulling) from above is the strongest force for long distance transport in plants

____________________________________ accounts for the majority of water movement in plants

The loss of water from leaves via transpiration creates a pull, or negative pressure, that moves water up the plant to replace the water that was lost

Three Factors of Cohesion-Tension Model

1. Transpiration• Negative pressure created as water exits leaves

through the stomata.• Negative pressure exerts tension on the water

confined in xylem’s conducting tubes all the way to the roots

2. Cohesion• The force of attraction between water in each

narrow xylem tube provides a force that keeps the water column unbroken while it is being pulled up under tension

3. Adhesion• Causes water molecules to adhere to xylem walls

and keeps water column from breaking

Factors Affecting Transpiration1. Temperature: high temp = ______________

transpiration rate2. Light: stomata open during day =

____________ transpiration rate during day3. Humidity: high humidity = ____________

transpiration rate in humid conditions4. Wind: high wind = ___________

transpiration rate5. Number of Stomata per Leaf Surface Area:

more stomata = ____________ transpiration rate

Transport in Phloem

Photosynthesis in leaves creates glucose (sugar)

Phloem transports sugar through the plant via _______________________________.

From “source to sink” Moves sugar from where is is made to

where it is need for growth, metabolism and storage

Translocation

Phloem transports substances in ____________ directions by ACTIVE TRANSPORT

The Pressure-flow model uses osmosis and pressure dynamics to explain how sugars are pushed from where they are made (source) to where they are needed (sink)

Ex: Maple Syrup Summer - transport from leaves to roots Spring - from roots to branches

Collect sap Syrup Sugar is transported as ___________________, not

glucose