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Chemistry Research Essay, Research Paper

CHAPTER 32

The tallest tree is the Redwood (Sequoia sempervirens) approx 110 m

The tallest Angiosperm is the Australian Eucalyptus regnans

Water Uptake and transport (Fig. 32.1)

= water is essential because: transport solute, cool the body, photosynthesis and Turgor pressure

Osmosis- movement of H2) through a semi-impermeable membrane

Osmotic potential ( o)-depend on dissolve solute: Hi concentration means more negative o.

Isoosmotic-two solution with same o; Hypoosmotic- solution that has a less negative o(more +)

Turgor Pressure -hydraulic pressure result from water up take, cell turgid; analog to air pressure in a tire

Water Potential ( )-Overall tendency of a solution or cell to take up water from pure water solution.

= o + P, P is positive and is measured in MegaPascal (MPa); loss in P means the plant will wilt.

MINERAL UPTAKE

= Mineral and ions transported across membranes by protein: Pumps and Ion channel & Symport

= Use both Facilitated (low K outside cell) and Active transport (depend on Respiration).

= Plant do not have a Na/K pump but a H pump (generate membrane potential/ gradient).

= Ion transport changes Electric potential of membrane (-120mV- can be measure by electrodes)

= The traffic of ions into/out of cell can be measure by Patch clamping technique.

Apoplast & Symplast

= Water moves into the Stele (more – ) from the cortex (less – ) from the soil (more less – )

= Mineral move by Mass flow or diffusion/Active transport (via Membrane Protein)

Apoplast-movement through cell wall and intercellular space; it is continuous

Symplast- movement through the cell and b/w cell via plasmodesmata; continuous but regulated

= H2O from the Apoplast stops at the Endodermis (Stele); have Casparian strips -made of suberin

= Strip separate Apoplast of the cortex from the Apoplast of the stele (periclcle)

= Membrane protein enable enables selective mineral uptake and uptake rate.

Transfer cells -in pericycle, transport minerals from cytoplasm back into the apoplast (MP/Mit, SA, rate)

TRANSPORT IN XYLEM

Model 1-”pumping cells” stem; ruled out by Eduard Strasburger exp-use poison pitric acid; Stop in the leaf

= Exp. demonstrate: (1) pumping cell not responsible for uptake (2) leaves important (3) root not involve

Model 2- “Capillary action” ruled out because capillary action cannot support 110 m tree (40 cm)

Model 3- ” root pressure”-based on more – in xylem & less neg in root; support by guttation

Guttation- the removal of H2O through the leaves under high humidity and a abundance of H2O in the soil

= The Oozing of sap from a cut stem of Coleus when the top is remove; not enough

= Root pressure changes, it either weaker or stronger but will not exceed 2X atm pressure

Evaporation-Cohesion-Tension mechanism (Fig. 32.8)

(1)Evaporation of H2O through stomata-increase tension &make wall more – o; H2O enter nearest vein

(2) Removal of H2O from leaf cause pull of water below; pull is send through the whole column

(3) Column is maintain by the adhesion of water to the cell wall (glass)

Summary-evaporation account for xylem transport & the resulting tension cause the cohesion

Dry Air-more – o than root–less neg than sap in xylem which is less neg in leaf–less than air

= Minerals dissolve in sap is transported to rest of the plant body by the phloem

Evaporation-Cohesion-Tension mechanism -requires tension in column or solution of the xylem

= Pressure can be measure by pressure bomb; done by Per Scholander, Fig 32.9

= In vines there is no tension in xylem until the leaves are removed; some Plants loss tension at night

TRANSPIRATION THROUGH THE STOMATA

Transpiration- is the loss of water from shoot (leaf) by evaporation; also cools the cell

= Loss is minimize by the cuticle; impermeable to CO2

Stoma- composed of specialized guard cells in the epidermis which allow passage of H2O/CO2

= In monocot it is associated with specialized epidermal cells; but mechanism is the same in dicot

= Open by pumping of K into guard cells; stretching is regulated by Microfibril

= Pumping also allow for Cl & other organic ion uptake; maintain electrical balance or neutrality

= Increase CO2 level in spaces of leaf and – (release of ABA); blue light also reduce H pumping

CAM-succulent plants-Crassulaceae-such as Kalonchoe

= Have a backward stomata cycle- opens at night; leaf tissue becomes acidic (Malic/Aspartic acid

= Adapted for environment devoid of water; loss of H2O occurs in cool environment.

TRANSLOCATION

= Occur in the Phloem- transport sugars, aa, minerals from leaf to root

Model: bi-directional, up and down the stem or petioles (2) Arrest if tissue is damage by heating

(3) Inhibited by compound that inhibit cellular respiration

Pressure Flow Model- fig. 32.14-32.16

= Involve active transport of sugar into sieve tube at source (leaf) and removal at sink (stem/root)

= Sieve tubes at source cause increase in Turgor pressure; fluid is squeeze toward the Sink ends

Sieve Plates- must be unclogged: it is regulated by protein which is randomly distributed (until cut)

= Sugars pass from cell to cell via symport, then into the apoplast (active); likewise into sieve tube

= Apoplast selectively sort out which compound is to be translocated; Sym-Apo-Sym not universal

= Sucrose is transported via secondary transport through a symport protein (H/Sugar protein)

= In

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