Water and Food Transportation

Sugars in a Plant

Sugar Form

Location in Plant Organ

Function of Sugar form

Glucose Leaf Energy (made in photosynthesis – summer, used in cellular respiration for growth-spring)

Sucrose Stem Transported, dissolved in water

maple sap

starch root Stored in cortex, not soluble in watercannot be transported

Direction of Sugar Transport Spring/night time Summer/day time

No leaves, no photosynthesis Starch stored in root broken down to sucrose, travels in water through stem broken down to glucose for growth of leaves

Leaves produce glucose through photosynthesis excess glucose become starch in chloroplasts starch to sucrose for transportation in stem starch stored in roots

#46

• In a experiment, a metal plate was placed through the middle of a tree, [sugar]was higher above the plate, [water+minerals] was higher below the plate

• the metal plate preventing upward movement of water & minerals, and downward movement of sugar (in summer)

Types of Nutrient Transport

Material being transported

Original location

Destination Vascular tissue

Water and minerals

Roots (from soil)

Leaves xylem

Newly manufactured food (glucose)

Leaves (photosynthesis)

Roots (storage)

Phloem

Stored food (Starch)

Roots Leaves phloem

Water transport in 3 Steps

1) Absorption at the roots.

2) Capillary action in the xylem vessels.

3) Evaporation at the leaf (transpiration) • Transpiration:

http://www.kscience.co.uk/animations/transpiration.htm

1) Water Absorption

• Mineral absorption has to occur first for Water absorption to occur at the roots.

Mineral Transport

• Minerals in the soil enter the root through root hairs

• There is a higher [minerals] absorbed into the xylem than in soil minerals are absorbed into the roots by active transport (against concentration gradient) requires energy (ATP) from cellular respiration

• Endodermis prevents minerals flowing back (passively diffusing) into the soil

Water Absorption in the Roots

• Hypertonic= high[solute], less water than in a cell

• Hypotonic = low [solute], more water than in a cell

• Root cells are in a hypotonic environment high[minerals] inside, more water on the outside water flows into (osmosis) the xylem cells

Hypertonic vs. Hypotonic environment environment

water flows out water flows in

2) Water Movement up the Stem

• Water and minerals accumulate in the xylem cells root pressure increases pressure pushes xylem sap up the xylem

• But this pressure pushes the sap up only a few meters

• Other factors?

• Adhesion: water molecules tend to stick to hydrophillic surfacesxylem wall

• Cohesion: polar water molecules tend to stick together due to hydrogen bonds.

Capillary Action

• Force of cohesion (water sticking together) + force of adhesion (water sticking to xylem wall)

forms a coloumn of water within the xylem

water is pushed up

• This is called the capillary action

Capillary action

• Cohesion and adhesion cause water to “crawl” up narrow tubes. The narrower the tube the higher the same mass of water can climb.

• Maximum height: 32 feet.

3) Transpiration

• As each water molecule evaporates through the stoma during transpiration

• it pulls on the next water molecules (cohesion). • As molecules are removed from the column by evaporation

in the leaf, more are drawn up from the stems and eventually from the roots

• This process of pulling water in the leaves all the way from

the roots is called the transpiration pull. • When air temperature is higher, there is more heat energy

provided for evaporation to occur rate of transpiration is higherthe xylem sap (water + minerals) rises faster (can rise 75cm per minute in a tree)

Back to the roots...

• Pressure differences created by transpiration draws water out of the roots and up the stems.

• This creates lower water pressure in the roots, which draws in more water.

• Transpiration: http://www.kscience.co.uk/animations/transpiration.htm

Food Transport (translocation)

• - In the leaves, sugar (sucrose converted from glucose) is pumped into phloem sieve tube cells by active transport, building up hypertonic solution inside the phloem

• - this causes water to move in by osmosis from xylem cells to sieve tube cells

• - this creates pressure gradient: high pressure in the leaves, low pressure in the roots

• - the high pressure in the leaves pushes the sap (water +sugars) down to the roots (low pressure) passive movement of sugar

• - sugar can end up in any parts of the plant where sugar pressure is low as it gets used up (in the leaves and stems)

• Textbook p. 569 figure 9

• HW Read p. 565 – 570 + complete# 1-4 on p. 570