BIOLOGY 2 SB025 SEMESTER 2 SESSION 2022/2023 CHAPTER 8: TRANSPORT SYSTEM
8.3: TRANSPORT IN PLANT LEARNING OUTCOMES: At the end of the lesson, students should be able to: a) State the lateral pathway of water movement through root tissue: apoplastic, symplastic and transmembrane route(C1) b) State the water and mineral movement via xylem in stem: root pressure, cohesion-tension mechanism, transpiration pull(C1) c) Define Pressure Flow Hypothesis in phloem(C1) d) Explain the lateral pathway of water and minerals is transported from surrounding soil to the root vascular system(C3) e) Describe the mechanism of water movement via xylem(C2) f) Explain the Pressure Flow Hypothesis in phloem(C3) WILL BE COVERED IN TUTORIAL WILL BE COVERED IN TUTORIAL
From surrounding soil, water enter the plant through the epidermal cells of roots cross the cortical cells of root / root cortex pass into the endodermis and flow up into stele (xylem vessels) to the shoot system Transportation of Water & Dissolved Mineral Salts From Surrounding Soil to the Whole Part of Plant
WATER & MINERAL TRANSPORT IN ROOTS
Root hair cell sap contains dissolved minerals and sugars which reduce its water potential (ψ) Results in, water potential of soil is higher than water potential in root hair cell sap Due to the water potential gradient between root hair cells and soil, water from soil diffuse into root hair cells by osmosis WATER MOVEMENT FROM SOIL TO THE ROOT XYLEM
Results in, water potential of root hair cells become higher than water potential in cortex cells Due to the water potential gradient between cortex cells and root hair cells, water from root hair cells diffuse into cortex cells by osmosis Water potential gradient is formed between cortex cells and endodermis cells Absorption of water occurs continuously by osmosis down the water potential gradient WATER MOVEMENT FROM SOIL TO THE ROOT XYLEM
Three lateral pathways help in movement of water from soil to the xylem vessels: Transmembrane route Symplastic route Apoplastic route WATER MOVEMENT FROM SOIL TO THE ROOT XYLEM
THREE PATHWAYS OF WATER TRANSPORTATION ✔ During apoplastic route, water travels along the cellulose cell wall and extracellular spaces of adjacent cells. ✔ During symplastic route, water moves across the cytosol of one cell to the next through the plasmodesmata. ✔ During transmembrane route, water move out of one cell, across the cell wall and repeatedly cross plasma membranes as they pass from cell to cell.
THREE PATHWAYS OF WATER TRANSPORTATION Symplastic route Transmembrane route 1 Apoplastic route 2 3 through cytoplasm suberin layer (waxy substance)
10 Water flow up in xylem vessels by: ROOT PRESSURE COHESION-TENSION MECHANISM WATER MOVEMENT VIA XYLEM IN STEM TRANSPIRATION PULL
SOIL Root Pressure root cells, water from soil diffuse into root cells • At night, rate of transpiration is very low • Root cells pump dissolved minerals into xylem • • Hydrostatic pressure • Accumulation of water generate root pressure (pushing force) that push water up the xylem Guttation = exudation of water droplets from hydathodes ψ H2O P ψ ψ 1 2 11 Root pressure is a water that moves into roots from the soil is pushed up through xylem toward the top of the plant
12 A pushing force that push water upward only a few meters At night, rate of transpiration is very low But, root cells still pump dissolved minerals into xylem through active transport Casparian strip of the endodermis prevents the ion from leaking back into cortex and soil. Root Pressure
The difference of water potential in soil and root cells cause water to diffuse into root cells by osmosis down the water potential gradient As water diffuse in, the hydrostatic pressure is increased The accumulation of water in root cells generate a root pressure (pushing force) that forces fluid up the xylem 13 Root Pressure
SOIL 14 Root Pressure in Short Plant
The exudation of water droplets (liquid water) from hydathodes (at the edge of the leaves) of some small, herbaceous dicots. Effect of Root Pressure: Guttation 15
Hydathode : A pore found in the epidermis of leaves of certain plants. Like stomata, hydathodes are surrounded by two crescent-shaped cells but, these cells do not regulate the size of the aperture. 17 Effect of Root Pressure: Guttation
Water is evaporate out by transpiration from palisade and spongy mesophyll cells into atmosphere through stomata. The water potential of mesophyll cells decrease. The hydrostatic pressure is also decreased due to the lost of water. Produce negative pressure (tension) in xylem of leaf and will create transpiration pull (pulling force). Transpiration Pull and Cohesion-Tension Mechanism 18
Transpiration at stomata 18
19 Thus, more water is continuously pulled into the mesophyll cells. Transpiration put the xylem vessel under negative pressure (tension) from leaf until root. As water potential in root xylem decrease, water from soil is pulled into the root xylem with the aid of cohesion and adhesion force. Transpiration Pull and Cohesion-Tension Mechanism
Water Move Down Water Potential Gradient 20
In the xylem vessel: Cohesion of water (due to hydrogen bonds between water molecules) help in continuously pulling of xylem sap from bottom without being separated ***xylem sap: water and dissolved minerals Transpiration Pull and Cohesion-Tension Mechanism 21
Adhesion between water molecules to the hydrophilic walls of xylem cells help in xylem sap pulled against the gravity Transpiration Pull and Cohesion-Tension Mechanism 22
Water lost by transpiration through stomata. Negative pressure (tension) from leaf until root Create transpiration pull (pulling force) ψ of mesophyll cells, Hydrostatic pressure root xylem, water from soil diffuse into root xylem with the aid of cohesion and adhesion force ψ ψ -ve P H2O root xylem 1 2 ψ 3 4 5 23 Transpiration Pull and Cohesion-Tension Mechanism
24 The mechanism by which dissolved sugar to be transported in phloem, caused by a pressure gradient between the source and the sink Pressure Flow Hypothesis Definition:
25 Water and solutes move through vessels (of xylem) and sieve tubes (of phloem) by mass flow. The movement of a cell sap generate a gradient of hydrostatic pressure. One-way transports of the soluble organic products of photosynthesis from source cell to sink cell. Pressure Flow Hypothesis
Pressure Flow Hypothesis 26
Mesophyll cell (osmosi s) (osmosi s) P R E S S U R E F L O W Sucro se Photosynthesis occur Utilization / storage Sucro se Sucro se Active transport Active transport Diffusio n Diffusio n ψ ψ P P P Pressure Flow Hypothesis 27