Transport in Plants

Photosynthesis

is limited by available water which can be swiftly depleted by transpiration.

Bulk flow

can be achieved either through a positive hydrostatic pressure gradient (e.g., a garden hose) or a negative hydrostatic pressure gradient (e.g., suction through a straw)

mycorrhiza

A(n) is a symbiotic association of a fungus with a root system.

special proteins

In facilitated diffusion help move substances across membranes without the expenditure of ATP energy.

turgidity increases

When within the two guard cells flanking each stomatal aperture or pore, the thin outer walls bulge out and force the inner walls into a crescent shape.

water potential gradient

Loading of the phloem sets up a(n) that facilitates mass movement in the phloem.

Root pressure

can, at best, only provide a modest push in the overall process of water transport.

plant cells

The behavior of the (or tissues) with regard to water movement depends on the surrounding solution.

vascular tissues

As various ions from the soil are actively transported into the of the roots, water follows (its potential gradient) and increases the pressure inside the xylem.

fungus

The provides minerals and water to the roots, in turn, the roots provide sugars and N- containing compounds to the mycorrhizae.

Transpiration

is affected by several external factors: temperature, light, humidity, and wind speed.

mineral solutes

Water is absorbed along with , by the root hairs, purely by diffusion.

hyphae

The have a very large surface area that absorbs mineral ions and water from the soil from a much larger volume of soil that perhaps a root can not do.

Imbibition

is also diffusion since water movement is along a concentration gradient; the seeds and other such materials have almost no water hence they absorb water easily.

small diameter

In plants, capillarity is aided by the of the tracheary elements- the tracheids and vessel elements.

Symplast pathway

The is the system of interconnected protoplasts.

major constituent

The diffusion of any substance across a membrane also depends on its solubility in lipids, the of the membrane.

process of plasmolysis

The is usually reversible.

Symplastic movement

may be aided by cytoplasmic streaming.

Elements

most readily mobilized are phosphorus, sulfur, nitrogen, and potassium.

tonoplast

In plant cells, the cell membrane and the membrane of the vacuole, and the together are important determinants of the movement of molecules in or out of the cell.

stoma

The opening of the is also aided due to the== orientation of the microfibrils in the cell walls of the guard cells.

Pumps

are proteins that use energy to carry substances across the cell membrane.

Water

is essential for all physiological activities of the plant and plays a very important role in all living organisms.

Osmosis

is the term used to refer specifically to the diffusion of water across a differentially- or selectively permeable membrane.

channels

The proteins form in the membrane for molecules to pass through.

high concentration

Facilitated diffusion can not cause net transport of molecules from a low to a(n) - this would require the input of energy.

Adhesion

: attraction of water molecules to polar surfaces (such as the surface of tracheary elements)

liquid

In and gaseous form they are in random motion that is both rapid and constant.

external solution

If the is more dilute than the cytoplasm, it is hypotonic and if the is more concentrated, it is hypertonic.

Plasmolysis

occurs when water moves out of the cell and the cell membrane of a plant cell shrinks away from its cell wall.

random fashion

In diffusion, molecules move in a(n) , the net result being substances moving from regions of higher concentration to regions of lower concentration.

symport

In a(n) , both molecules cross the membrane in the same direction.

Cellulose microfibrils

are oriented radially rather than longitudinally making it easier for the stoma to open.

Diffusion

is a slow process and is not dependent on a ‘ living system.

dry matter

A watermelon has over 92 percent water; most herbaceous plants have only about 10 to 15 percent of their fresh weight as .

process of photosynthesis

The requires water.

molecule

When a(n) moves across a membrane independent of other , the process is called uniport.

They do not set up a concentration gradient

a concentration gradient must already be present for molecules to diffuse even if facilitated by the proteins

Facilitated diffusion cannot cause net transport of molecules from a low to a high concentration

this would require the input of energy

Facilitated diffusion is very specific

it allows cells to select substances for uptake

The transport protein then rotates and releases the molecule inside the cell, e.g., water channels

made up of eight different types of aquaporins

But diffusion whether facilitated or not

take place only along a gradient and does not use energy

Of course, the distribution of water within a plant varies

woody parts have relatively very little water, while soft parts mostly contain it

A seed may appear dry but it still has water

otherwise, it would not be alive and respiring

Osmosis is the term used to refer specifically to the diffusion of water across a differentially

or selectively permeable membrane

During symplastic movement, the water travels through the cells

their cytoplasm; intercellular movement is through the plasmodesmata

Transpiration is affected by several external factors

temperature, light, humidity, and wind speed

Cohesion

Mutual attraction between water molecules

Adhesion

attraction of water molecules to polar surfaces (such as the surface of tracheary elements)

Surface Tension

water molecules are attracted to each other in the liquid phase more than to water in the gas phase

In plants, capillarity is aided by the small diameter of the tracheary elements

the tracheids and vessel elements

Again active transport is necessary to move the sucrose out of the phloem sap and into the cells which will use the sugar

converting it into energy, starch, or cellulose