Transport in Vascular Plants

Adaptations for land

The problems:

• Conserve water

• Structure

• Transport nutrients

and water

The solution:

• Vascular system!!!!!

Transport occurs on three levels

• Within cell-root hairs

• Between cells-sugar from mesophyll to seive tube member

• Long Distance-water from roots to leaves

Quick Review

• Diffusion

• Passive transport

• Active transport

• Transport proteins

• Proton pumps

Water Potential

• Animal cells absorb water until they burst

• Plant cells have a cell wall only absorb water until the pressure inside the cell is greater than the pressure outside the cell.

• Turgor pressure- pressure against cell wall• Water potential(Ψw )=solute potential (Ψs)+ pressure potential (Ψp)

Water moves from high potential to low potential

• Adding solutes decreases solute potential– Adding salt to the water decreases the solute

potential, which makes water move out of the cell to the area of lower potential

• Adding pressure increases pressure potential– Cells that are full of water will give up water to

empty cells

How does water get around?

• Cell walls and Cytoplasm of neighboring cells are connected

• Plasmodesmata- pores in cell wall that connect cytoplasm

water

• Root epidermal cells are hydrophilic

• Water and minerals diffuse into epidermal cells

• Mycorhizae- symbiosis between root and hyphae

Bulk Flow

• Diffusion is too slow for long distance transport

• Bulk Flow= movement by pressure through trachieds, vessels and sieve tubes

• Pressure is created by manipulating solute potential (sugar)

• Tension pulls water from root to leaf

Long distance transport

• Water is pushed at night– Minerals are pumped into apoplast, creates

root pressure– Guttation- more water enters leaves than can

be transpired

• Water is pulled during the day– Transpiration-evaporation from leaves

• Air outside leaf is drier than air in spongy mesophyll

• Lower water potential outside, water moves out of leaf

• Xylem mesophyll environment

Adhesion and cohesion

• Cohesion– =water molecules stick to each other

• Adhesion– = water molecules stick to hydrophilic

surfaces

(cellulose)

• Hydrogen bonds!!!!!

Unbroken chain of water molecules

• Tension pulls water molecule chain upwards

• Pulls vessels in (trunk shrinks on hot days)

• Decreases water potential, water moves into roots passively

Broken water molecule chain

• Cavitation- air bubbles in xylem, caused by freezing

• Air bubbles expand when sap thaws, become embolisms

• Water can’t get through

blockage, can’t

reform chain

Fixing embolisms

• Small, young, nonwoody plants can fix embolisms with root pressure in spring.• Trees can’t fix embolisms• Water can detour around ruined vessel• New xylem is added every year, replaces damaged vessels

• What would be the effect of fertilizing a plant during a drought?

• A tip for helping cut flowers last longer without wilting is to cut off the ends of the stems underwater and then transfer the flower to a vase while water droplets are still present on the cut ends of the stems. Explain why this works.

Stomata

• Leaves have a large surface area

• Balance water loss and sugar requirement

• Closing stomata reduces water loss

• Plant wilts when cells lose turgor pressure

• Evaporative cooling

prevents denatuation of

photosynthetic enzymes

Stomata density

• Up to 20,000 stoma/cm (desert, rainforest)

• Plastic feature

• Fossil evidence of CO2 levels

– More stomata = lower CO2

– Less stomata = higher CO2

– WHY???

Xerophytes

• Adapted to dry climates– Thick cuticle– Less surface area– Stomata on bottom of leaf– Recessed stoma (crypts, leaf hairs)

– C4 and CAM photosynthetic pathways

• Some leaf molds, which are fungi that parasitize plants, secrete a chemical that causes guard cells to accumulate potassium ions. How does this adaptation enable the leaf mold to infect the plant?

Translocation=movement of sugars

• Sugar source sugar sink

• Source=sugar producer– Leaves, green stems

• Sink=sugar consumer– Growing stems, flowers, buds

• Bulb? Tuber?

• Direction of flow depends on source and sink

Pressure Flow

Pressure Flow

• Positive pressure (opposite of transpiration)

• Sugar loading at source decreases water potential of sieve tube

• Water moves into phloem cell from adjacent xylem, increases pressure

• Sugar is removed at sink, releases pressure, water moves back into xylem

• Potatoes break down starch into sugar at low temperatures. (this is a problem for the potatoe chip industry because the sugar in chilled potatoes turns dark brown during processing) What effect would cooling the soil around an expanding potato tuber have on sugar import into the tuber?