Water and Food Transportation

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 water cannot be transported

Direction of Sugar Transport Spring/night 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 Summer/day time 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) Stored food (Starch) Leaves (photosynt hesis) Roots (storage) Phloem 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 environment water flows out vs. Hypotonic environment 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 surfaces xylem 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 higher the 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