chapter 35: transport in plants chapter 35 transport in plants

Chapter 35: Transport in Plants

CHAPTER 35Transport in Plants


Chapter 35: Transport in PlantsUptake and Transport of Water and MineUptake and Transport of Water and Mineralsrals

Transport of Water and Minerals in the Transport of Water and Minerals in the XylemXylem

Transpiration and the StomataTranspiration and the Stomata

Translocation of Substances in the Translocation of Substances in the PhloemPhloem


Uptake and Transport of Water and Minerals• Plant roots take up water and minerals Plant roots take up water and minerals

from the soil.from the soil.

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Uptake and Transport of Water and Minerals • Water moves through biological Water moves through biological

membranes by osmosis, toward cells membranes by osmosis, toward cells with more negative water potential. with more negative water potential.

• The water potential of a cell or solution The water potential of a cell or solution is the sum of the solute and the is the sum of the solute and the pressure potentials. pressure potentials.

• All three parameters are expressed in All three parameters are expressed in megapascals (MPa). Review Figure megapascals (MPa). Review Figure 35.135.1

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Figure 35.1

Figure 35.1Figure 35.1

figure 35-01.jpg


Uptake and Transport of Water and Minerals • Mineral uptake requires transport Mineral uptake requires transport

proteins. proteins. • Some minerals enter the plant by Some minerals enter the plant by

facilitated diffusion; others by active facilitated diffusion; others by active transport. transport.

• A proton pump facilitates active A proton pump facilitates active transport of many solutes across transport of many solutes across membranes.membranes.

Review Figure 35.2Review Figure 35.2

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Figure 35.2


figure 35-02.jpg


Uptake and Transport of Water and Minerals • Water and minerals pass from the soil Water and minerals pass from the soil

to the xylem via the apoplast and to the xylem via the apoplast and symplast. symplast.

• In the root, water and minerals may In the root, water and minerals may pass from the cortex into the stele pass from the cortex into the stele only via the symplast because only via the symplast because Casparian strips in the endodermis Casparian strips in the endodermis block movement in the apoplast.block movement in the apoplast.

Review Figures 35.3, 35.4Review Figures 35.3, 35.4

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Figure 35.3


figure 35-03.jpg


Figure 35.4


figure 35-04.jpg


Transport of Water and Minerals in the Xylem• Early experiments established that sap Early experiments established that sap

does not move via pumping action of does not move via pumping action of living cells.living cells.

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Transport of Water and Minerals in the Xylem • Root pressure is responsible for Root pressure is responsible for

guttation and oozing of sap from cut guttation and oozing of sap from cut stumps, but cannot account for the stumps, but cannot account for the ascent of sap in trees.ascent of sap in trees.

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Transport of Water and Minerals in the Xylem • Xylem transport is the result of Xylem transport is the result of

combined effects of transpiration, combined effects of transpiration, cohesion, and tension. cohesion, and tension.

• Evaporation in the leaf produces Evaporation in the leaf produces tension in the surface film of water on tension in the surface film of water on the moist-walled mesophyll cells, thus the moist-walled mesophyll cells, thus pulling water and dissolved minerals pulling water and dissolved minerals up the xylem from the root. up the xylem from the root.


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Figure 35.7


figure 35-07.jpg


Transport of Water and Minerals in the Xylem • Support for the transpiration–Support for the transpiration–

cohesion–tension model came from cohesion–tension model came from studies using a pressure bomb. studies using a pressure bomb.


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Figure 35.8


figure 35-08.jpg


Transpiration and the Stomata• Water evaporation cools leaves, but a Water evaporation cools leaves, but a

plant cannot afford to lose too much plant cannot afford to lose too much water. water.

• Transpirational water loss is minimized Transpirational water loss is minimized by the leaves’ waxy cuticles.by the leaves’ waxy cuticles.

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Transpiration and the Stomata • Stomata allow compromise between water Stomata allow compromise between water

retention and carbon dioxide uptake. retention and carbon dioxide uptake. • Guard cells controls size of stomatal opening. Guard cells controls size of stomatal opening. • A proton pump, activated by blue light, A proton pump, activated by blue light,

pumps protons from guard to epidermal pumps protons from guard to epidermal cells. cells.

• Guard cells take up potassium ions, causing Guard cells take up potassium ions, causing water to follow osmotically, swelling the cells water to follow osmotically, swelling the cells and opening the stomata. and opening the stomata.

• Carbon dioxide level and water availability Carbon dioxide level and water availability also affect stomatal opening. also affect stomatal opening.

Review Figures 35.9, 35.10Review Figures 35.9, 35.10

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Figure 35.9


figure 35-09.jpg


Figure 35.10


figure 35-10.jpg


Transpiration and the Stomata • In most plants the stomata are open In most plants the stomata are open

during the day and closed at night. during the day and closed at night. • CAM plants have an inverted stomatal CAM plants have an inverted stomatal

cycle, enabling them to conserve cycle, enabling them to conserve water. water.


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Figure 35.11


figure 35-11.jpg


Translocation of Substances in the Phloem• Products of photosynthesis, and some Products of photosynthesis, and some

minerals, are translocated through minerals, are translocated through sieve tubes in the phloem via living sieve tubes in the phloem via living sieve tube members. sieve tube members.

• Translocation proceeds in both Translocation proceeds in both directions in the stem, although in a directions in the stem, although in a single sieve tube it goes only one way. single sieve tube it goes only one way.

• Translocation requires a supply of ATP.Translocation requires a supply of ATP.

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Translocation of Substances in the Phloem • Translocation in the phloem proceeds Translocation in the phloem proceeds

in accordance with the pressure flow in accordance with the pressure flow model: model:

• Difference in solute concentration Difference in solute concentration between sources and sinks allows a between sources and sinks allows a difference in pressure potential along difference in pressure potential along sieve tubes, resulting in bulk flow. sieve tubes, resulting in bulk flow.

Review Figure 35.14, Table 35.1Review Figure 35.14, Table 35.1

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Figure 35.14 – Part 1

Figure 35.14 – Part 1Figure 35.14 – Part 1

figure 35-14a.jpg




figure 35-14b.jpg


Table 35.1Table 35.1Table 35.1

table 35-01.jpg


Translocation of Substances in the Phloem • The pressure flow model succeeds The pressure flow model succeeds

because sieve plates are normally because sieve plates are normally open, allowing bulk flow, and because open, allowing bulk flow, and because neighboring cells load organic solutes neighboring cells load organic solutes into sieve tube members in source into sieve tube members in source regions unloading them in sink regions unloading them in sink regions. regions.


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figure 35-15a.jpg




figure 35-15b.jpg


Translocation of Substances in the Phloem • The distribution and properties of The distribution and properties of

plasmodesmata differ between source plasmodesmata differ between source and sink tissues. and sink tissues.

• It may become possible to regulate It may become possible to regulate plasmodesmata in crop plants.plasmodesmata in crop plants.

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chapter 35: transport in plants chapter 35 transport in plants

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