Plant Water Relation

Plant Water Relation

PUNCHED HOLES Polar
molecules

Universal Cohesion and
solvent of life adhesion

H2O Properties

Mashitah_Teume Density – High specific
greatest at 4°C heat

Water Properties

H2O Polarity Universal solvent

2 Hydrogen atoms form Capable of dissolving more substances than any
single polar covalent other liquid.
bonds with an oxygen
atom Water potential: To determine water-deficit
stress,drought tolerance in plants,irrigation
Partial positive charge needs of different crops and how the water
status of a plant affects the quality and yield
of plants.

Each water molecule can a) Atmospheric water potential influences
form hydrogen bonds transpiration rate/water loss in plants.

with up to 4 neighbors. b) Soil water potential influences the water

Partial negative charge because more Hold water molecules available for uptake by plant roots.
electronegative together. The hydrogen
Water density
1 molecule slightly negative attracted
to nearby molecules slightly positive bonds joining water Most dense at 4oC -0oC=water
regions forming a hydrogen bond. molecules are weak, as Contracts until 4oC becomes lock in
covalent bonds. They Expands from 4oC to 0oC crystalline
form, break, and reform lattice(each
molecule
with great frequency. The density of bonded to the
maximum of 4
water: partners)
-Ice starts to
Force measure Cohesion & Adhesion (i) Prevents water melt,some
to stretch or from freezing hydrogen bonds
break the liquid from the bottom break and some
surface. Water up. water molecules
has a greater (ii) Ice forms on can slip closer
surface tension the surface first together.
than most other (the freezing of -Ice less dense
liquids because the water than water at
hydrogen bonds releases heat to 4oC.
among surface the water below
water molecules creating
resist stretching insulation)

or breaking the

surface. Some

H2O = H2O (polarity due to Clinging of one animals can
hydrogen bonds) for transport substance to another
of the water column in plants as water adheres to stand, walk, or
against gravity the vessels wall
run on water

without breaking

the surface.

• Heat amount must be absorbed/lost for 1.0g substance to change its
temperature by 1oC.

• Water stabilizes air temperatures by absorbing heat from warmer air and Specific heat
releasing heat to cooler air.

• Water can absorb or release relatively large amounts of heat with only a
slight change in its own temperature.

• Evaporative Cooling
-The surface cooling occur when liquid evaporates to moderating
earth’s,stabilizes temperature in aquatic ecosystems & prevent organisms
from overheating

Transport systems in vascular plants provide intercellular communication contain 2 types of vascular tissues: xylem & phloem that are grouped in
arrangements (vascular bundles).

• Xylem: transports water and minerals in the plants
• Phloem: transports food materials; synthesized by the leaves during photosynthesis and hormones.
Less than 1% water reaching the leaves is used in photosynthesis and plant growth. Most of water is lost in transpiration. Water enters the root
through epidermis. Then water travels in both, symplast & apoplast.
• Symplast : it crosses the plasma membrane and then passes from cell to cell through plasmodesmata
• Apoplast: in the spaces between the cells and in the cells walls themselves. This water has not crossed a plasma membrane.

Impervious to water because of a band of suberized matrix (casparian strip).

cell

root
cortex

Inner boundary of cortex In young roots, water enters
directly into the xylem
1 (Apoplastic water) Endodermal cells symplasm
2 Pass by plasmodesmata Water move upward
3 Stele by diffusion,capillary
4 Water free to move between cells as well as action & transpiration

through them. Dissolved minerals + Small
5 H2O + minerals moves along the apoplast. organic molecules + H2O = Sap
6 Transported into epidermis protoplast cells
7 Cortex cells
8 Move inward via the symplast

Access water to the apoplast: Uptake of soil
solution (H2O + minerals) of root hairs.

Access water to symplast: H2O + minerals across
the plasma membrane of root hairs

Diffusion Capillary Action Transpiration

Plant roots absorb water from the Water molecules have a strong attraction to each other Plants lose water through the leaf surface &
soil. Water enters the roots through causing the molecules to stick together to the side of the xylem stomata opening.Plants lose water through the
diffusion/osmosis. and does not fall back down. They also adhere to the surface leaf surface primarily from the stomata/pores in
of the xylem. leaf surface used for respiration & photosynthesis.
Root has a higher salt concentration
than in the soil. Water flows from the As the plant transpires, water molecule evaporates, pulling On warmer days, more water evaporates, the
low to high salt side to make salt another water molecule up through the xylem. plant draws more water from the roots & roots
concentration equal. take up more water from the soil.
Cohesion force = molecules of same kind ability to stick
Root allow water, minerals & small together. Water molecules are polar, having slight positive and Affecting factors:
organic pass from soil to the plant negative sides,causes cohesion. Inside xylem, water molecules
passively. are in a long chain extending from the roots to the leaves. (i)Temperature (iv) CO2

The membrane is semi-permeable. Adhesion force = molecules of different kinds tendency to (ii)Humidity (v) Soil Water Availability
(If the salt concentration inside root stick together. Water sticks to the cellulose molecules in the
becomes too low, it will actively xylem walls counteracting the gravity force & aiding the water (iii) Air Currents
transport salts into the root.) rise within xylem.

Picture source: https://www.howitworksdaily.com/how-do-plants-transport-water/

Radiation Some radiation reflected &
input some reradiated

Only 1-3% of Evaporative cooling depends
radiation used in upon latent heat of evaporation
photosynthesis.
If Tleaf > Tair then the
Radiation leaf warms the air.
input

TRANSPIRATION

Soil water availability

Increase of soil water availability,
the plant will have more excess
water to move through the
plant.Therefore,increasing water
availability in the soil will
increase the rate of
transpiration.

Let me
explain!

Occurs when roots continue take in
mineral and rate of transpiration is low.

Root pressure is created by the xylem

• Dissolved minerals are present in the
root cells (get there from active
transport) increases the solute
concentration inside the cell, thus
water enters through osmosis creating
pressure forcing the fluid up the xylem.

• Thus, water is forced from the high
pressure in the roots to the low pressure
in the leaves.

• Can only push water a maximum of a
few meters

Getting water to the leaves

The leaves need the water to perform
photosynthesis (without water no
photosynthesis.)

Without photosynthesis the plant will
die) but the leaves can be hundreds of
meters from the root where most of the
water uptake occurs.