Physiology

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  • Topic: Xylem, Vascular plant, Phloem
  • Pages : 6 (706 words )
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  • Published : May 3, 2013
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Chapter 2 : Circulatory system
Focus:
Plants transport systems Water and mineral uptake Xylem and transport Phloem, sugar and translocation

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An overview of plant transport system

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Water and minerals uptake
1. Bulk Flow Transport via Xylem. 2. Transport of Water and Minerals into Xylem. 3. Absorption of Water and Minerals by Root Cells Keong BP

3. Absorption of Water and Minerals by Root Cells

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Water and mineral uptake by the root hairs through apoplastic and symplastic route

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Transmembrane route, water and solutes move in and out along the continuum

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Movement of water and mineral via apoplastic route is blocked by Casparian strip but movement of water and mineral via symplastic route continues and ended in xylem vessels.

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Water and mineral are now ready for upward transport into the shoot system.

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2. Transport of Water and Minerals into Xylem.
Cohesion of water molecules and adhesion of water molecules with hydrophilic walls of xylem cells assists in movement of sap from down to upward in the stem. Keong BP

1. Bulk Flow Transport via Xylem.

The air in these spaces is saturated with water vapour, that is higher water potential.

c b

a Air outside leaf is drier, that is, it has lower water potential

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a. Water vapour diffuses from the moist air spaces of the leaf to the drier air outside via stomata. b. The loss of water is compensated by drawing water from mesophyll cells into the spaces of mesophyll. c. Subsequently, loss of water in the mesophyll cells are replenished by drawing out of water from xylem.

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Low water potential

Transpiration pull

Adhesion and Cohesion

High water potential

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Xylem and transport
Xylem: There are two types of water-conducting cells of xylem, tracheids and vessel element. Tracheids could be found in nearly all of the vascular plants. Vessels element could be found in seedless vascular plant. Both tracheids and vessel elements are tubeshaped, non-living portion of the vascular system in plants. They carry water and minerals from roots to the rest of the plant. Keong BP

Water conducting cells of xylem

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Phloem and transport
Phloem: In the phloem, nutrients are transported through long narrow cells joined to form a tube that is called sieve-tube element. The end walls between sieve-tube element is called sieve plates. Sieve plates are having pores that facilitates flow of fluid. Alongside with sieve-tube element, is a nonconducting cell called companion cell. Companion cells help to load sugar into sievetube elements. Keong BP

Sugar conducting cells of phloem

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An overview of sugar and translocation
Sugar produced through photosynthesis

Uni-directional flow of sugar

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How does sugar transported in a plant?
Sugar produced through photosynthesis

Uni-directional flow of sugar

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How does sugar transported in a plant?
Sugar produced through photosynthesis

Translocation

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Movement from Sugar Source to Sugar Sink
Sugar source is the plant organ that is a net producer of sugar (i.e. plant leaf). Sugar sink is a net consumer or depository of sugar (i.e. plant stem, root, flower, seeds or fruit). The role of plant organ as sugar source and sugar sink might differ according to: a. Plant growth stages b. Environmental conditions Keong BP

Which is the sugar source and sugar sink?

A

B

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Which is the sugar source and sugar sink?

Sugar source (net producer of sugar)

Sugar sink (net consumer of depository)

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Which is the sugar source and sugar sink?

A

B

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Which is the sugar source and sugar sink?

Sugar sink (net consumer or depository) Sugar source (source of sugar)

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An overview of sugar transport in plants

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Bulk flow of sugar in sieve tubes
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