BI111 week 8

Passive Transport

• simple diffusion

• no metabolic energy

• substance moves down concentration or electrochemical gradient

• energy free load transportation

• Simple form of passive transport, not efficient or fast 10um in 0.1 sec, 100um in 1 sec, 1mm in 100 sec. (hard for larger plants cannot wait that long for nutrients) ex Hyperion coast redwood tree would take 25 years for nutrients to get there not ideal.

Active Transport

• electrochemical gradient

• requires metabolic energy (ATP)

• Based on hydrogen pumps in plasma membrane →H+ gradient maintained through ATP use → H+ diffusion into cell powers uptake of solutes

symport

• molecule moves same direction as proton

• material transported in the same direction as movement of hydrogen and solute organic uptake

antiport

• toxic products cumulates in body where it does not want it and therefore moves the opposite direction

• material transported in opposite directions to movement of hydrogen and solute sodium export

Diffusion

• spontaneous movement of molecules or particles along concentration gradient

Osmosis

• special case of diffusion (is a process where water moves through a barrier, like a cell membrane, from an area with less stuff dissolved in it to an area with more stuff dissolved in it)

Hypertonic

• high concentration solute outside cell there for water, leaves shrink, more flexible

• will shrink away from cell wall

Isotonic

• balance each other

• Isotonic solution a flaccid cell place in solute rich environment become plasmolysis

Hypotonic

• lower concentration of solute outside cell, more water inside, swells and gets rigid

• becomes turgid

Solute Potential

• always negative since it represents the reduction in free energy of water molecules due to the presence of solutes.

• causes water to move to where it is abundant to where it is rare, then cell bursts.

• Animal cells do not have cell wall plants do, plants therefore move channels to move potassium in concentrations and cell expands but cell wall prevents cell from bursting pressure potential =P the turgor pressure makes cell become rigid but not burst

Adhesive

• meniscus

• water sticks to side of the glass

Cohesive

• sticks to itself

Transpiration

• evaporation of water out of plants (draw water uproots to shoots)

• escaping from the plant into the atmosphere as plant vapour

Cohesion Tension Mechanism of water transport

• is the primary mechanism by which water is transported from the roots to the leaves in plants.

  • Evaporation from mesophyll walls

  • Replacement by cohesion (H bonded) water in xylem.

  • Tension, negative pressure gradient adhesion of water to xylem walls

Tracheid

• thin tapered tubes

• lots of things to hold onto for cohesion and adhesion

Vessel Membrane

• barrel like

• better at quickly moving water more easily backed by air bubbles in water (activation)

TACT (Transpiration, Adhesion, Cohesion, Tension)

• water always evaporating through guard cells, therefore water becomes rare inside the cell

• Water will come from adjacent cell and move to place which lack water.

• Xylem and in tracheid molecules sticking to wall

• Cells which are closer to vascular molecules will move out, all water will move other water molecules together upwards to leaves.

Guttation

• when root pressure is strong enough to force water out of leaf openings

• water is pushed up and out of veins

Stomata

• small pores found on the surface of leaves

• important for gas exchange, allowing uptake of CO2 and release of O2

• Need guard cells (location at pores) to open and close to prevent water loss or assist movement of water from high to low concentration.

• Flaccid (close guard cells), turgid (provide opening of guard cells)

Physiology of stomata

• Stomata must balance water loss and carbon dioxide uptake by responding to many signals biological clock.

• Stomata open to increase photosynthesis (increase blue light) (decrease carbon dioxide concentration in leaf)

• Stomata close under water stress

Xerophytes

• plants that adapted to survive in dry environments where water availability is limited

• thickened cuticle, sunken stomata, water storage in stems, modified leaves

Crassulacean acid metabolism (CAM)

• stomata opens at night

• Carbon dioxide fixed at night (low evaporation into malate)

• Carbon Dioxide released from malate during day when stomata is closed

Angiosperm adaptations

• angiosperms have much smaller genome then gymnosperm (selection for smaller genome size, high vein density/stomata density doesn’t have to go that far for water, large cells take up space, more efficient for growth.)

Organic Compounds

• macromolecules broken down into constituents for transport across cell membrane

Translocation

• long distance transport of substances via phloem (flows under pressure)

• phloem sap studded with pores.

• companion cells or transfer cells load to unload.