VI. TRANSPORT SYSTEMS IN VASCULAR PLANTS
A. CELL TYPES
1. XYLEM
2. PHLOEM
B. TRANSPORT FROM SOIL TO XYLEM
C. TRANSPORT OF XYLEM SAP
D. TRANLOCATION OF PHLOEM SAP
CELL TYPES IN VASCULAR TISSUE
1. XYLEM
a. TRACHEIDS
DEAD WHEN MATURE.
HARDENED WITH LIGNIN.
FLUIDS PASS VIA PITS.
ALL VASCULAR PLANTS.
b. VESSEL ELEMENTS
DEAD WHEN MATURE
FLUIDS PASS VIA END-WALL PERFORATIONS.
FIBER CELLS AID SUPPORT.
ANGIOSPERMS.
CELL TYPES IN VASCULAR TISSUE
2. PHLOEM
a. SIEVE TUBE MEMBERS
LIVING WHEN MATURE.
FLUIDS PASS VIA END-WALL
PORES = SIEVE PLATES.
b. COMPANION CELLS
LIVING WHEN MATURE.
CONNECTED WITH SISTER SEIVE TUBE MEMBER VIA PLASMODESMATA.
CONTAINS NUCLEUS, ORGANELLES.
SIMILAR SYSTEM IN ALL SEED PLANTS.
TRANSPORT FROM SOIL TO XYLEM
OVERVIEW
SOIL => EPIDERMIS OF ROOT
=> ROOT CORTEX
=> ENDODERMIS
=> XYLEM
3 ROUTES THRU EPIDERMIS & CORTEX
i. TRANSMEMBRANE ROUTE
THRU CYTOSOL & CELL WALLS
ii. SYMPLASTIC ROUTE
THRU CYTOSOL
iii. ANOPLASTIC ROUTE
THRU CELL WALLS
TRANSPORT FROM SOIL TO XYLEM
CORTEX => XYLEM
CONTROLLED BY ENDODERMIS.
CASPARIAN STRIP
= WAXY BARRIER IN WALLS.
FORCES FLOW THRU CYSTOL.
= CELLULAR CONTROL OF DISSOLVED MATERIALS
CONTINUES ON VIA APOPLASTIC ROUTE
TRANSPORT OF XYLEM SAP
MECHANISMS INVOLVED:
i. PHYSICAL PROPERTIES OF WATER
ii. TRANSPIRATION
= EVAPORATIVE LOSS OF WATER FROM PLANT SURFACES
LEAF STOMATA OPEN TO COLLECT CO2
LOSE WATER VAPOR
= INCREASED WATER TENSION
DRAW XYLEM SAP UPWARD
CONTROLLED BY GUARD CELLS
= IONIC PUMP
TRANLOCATION OF PHLOEM SAP
PHLOEM SAP
CONTAINS SUCROSE, MINERALS, AMINO ACIDS, HOROMONES, ETC.
MOVES IN DIVERSE DIRECTIONS
MOVEMENT IS
FROM SOURCE OF SUCROSE =
PHOTOSYNTHETIC STRUCTURE
= LEAVES.
TO SINK = CONSUMES OR STORES SUCROSE
= FRUITS, STEMS, ROOTS.
TRANLOCATION OF PHLOEM SAP
MECHANISMS INVOLVED:
i. PHLOEM LOADING
= ACTIVE TRANSPORT
ii. PHLOEM PRESSURE FLOW
COUNTER-CURRENT FLOW
PHLOEM & XYLEM.
CONCENTRATION GRADIENT.
AT SUCROSE SOURCE
WATER FLOWS FROM XYLEM TO PHLOEM.
WATER PRESSURE PUSHES PHLOEM SAP TO SINK
AT SUCROSE SINK
WATER FLOWS FROM PHLOEM TO XYLEM.
TOPIC 5 - TRANSPORT SYSTEMS IN VASCULAR PLANTS
READINGS: PAGES 38 - 40; 700 - 711.
FIGURES: 3.1; 30.5; 35.10; 35.20, 36.1, 36.5; 36.6; 36.8; 36.10; 36.11; 36.13; 36.14
Glossary - anoplastic, Casparian strip, companion cell, counter current flow, cystol, hydrogen bond; mesophyll, phloem sap, plasmodesma, pressure flow, root cortex, root endodermis, root epidermis, sieve tube member, sink, source, stoma, sucrose, symplastic, tracheid, transmembrane route, transpiration, vessel element, xylem sap.