Bio125Lec - Botany - Water Structure & Properties

understanding leads you to righteousness

In Broad meaning: Phsysis means _______; Logos means ________. Thus, Plant Physiology means _____________.

Nature; Discourse; Discourse about Nature of Plants

In Restrictive meaning: Phsysis means _______; Logos means ________. Thus, Plant Physiology means _____________.

Function; Study; Study of the how plants function

Water is the substance that makes life ________.

possible

Life on Earth began in water and evolved there for __ billion years before spreading onto land.

three (3)

Terrestrial organisms cells are about_______ % water.

70% - 95%

Is water polar or nonpolar? Explain.

Water is polar because it has a partial positive charge on one side (hydrogen atoms) and a partial negative charge on the other side (oxygen atom), allowing it to form hydrogen bonds. (difference in electronegativity between oxygen and hydrogen).

Covalent Bond vs Hydrogen Bond

A covalent bond is a strong bond formed when two atoms share electrons, while a hydrogen bond is a weaker attraction between a hydrogen atom and an electronegative atom, such as oxygen or nitrogen.

What is hydrogen bonding in water?

Hydrogen bonding in water refers to the attraction between the partially positive hydrogen atoms of one water molecule and the partially negative oxygen atom of another water molecule. This interaction is crucial for many of water's unique properties, such as high surface tension and boiling point.

Each water molecule can form hydrogen bonds with up to ______ neighbors.

four (4)

Why hydrogen bond is a weak bond? (2 reasons)

• 1/20th as strong as covalent bond

• continually forms, break ups, and reforms

Why is water more structured than most other liquids?

At any instant, a substantial percentage of all water molecules are bonded to their neighbors

__________ are responsible for many of the unusual physical properties of water.

Hydrogen bonds

WATER TRANSPORT & TRANSPIRATION

How does water transport up to transpiration happen in plants?

1. Water uptake from soil.

   • water molecule, soil particle, root hair

2. Water cohesion and adhesion in the xylem.

   • adhesion to cell wall & cohesion by hydrogen bonding

3. Transpiration

   • xylem sap -→ mesophyll cells → stoma → water molecule release to atmosphere

PROPERTIES OF WATER

Enumerate the 8 properties of water. [CATHVFST]

1. Cohesion

2. Adhesion or attraction to solid phase

3. Surface Tension

4. High Specific Heat

5. High heat of Vaporization

6. Solid water Floats

7. Solvent of life

8. High Tensile strength

What is cohesion? Why is water cohesive?

Cohesion is the tendency of water molecules to stick together due to hydrogen bonding, resulting in high surface tension and the ability to form droplets.

When water evaporates from a leaf, it is replaced by _______________.

water from the vessels in the leaf

This upward pull is transmitted to the _______.

roots

________ among water molecules plays a key role in the  __________________ in plants.

Cohesion; transport of water against gravity

Determine the Water Potential Gradient of the following.

Outside air ψ = ____________ Leaf ψ (air spaces) = ____________ Leaf ψ (cell walls) = ____________ Trunk xylem ψ = ____________ Root xylem ψ = ____________ Soil ψ = ____________

1. Outside air ψ = -10.0 to -100.0 MPa

2. Leaf ψ (air spaces) = -7.0 MPa

3. Leaf ψ (cell walls) = -1.0 MPa

4. Trunk xylem ψ = -0.8 MPa

5. Root xylem ψ = -0.6 MPa

6. Soil ψ = -0.3 MPa

Xylem Tissues extend from _______ to the _____ up to the  ______ wherein water molecule in root is replaced by _______.

leaf down; roots; root tips; water in soil

Why do people cut the lower end of the peduncle in cut flowers?

• remove air spaces, to have continuous column of water

• prevents early wilt

Define adhesion. What type of bonding is involved?

• attraction between unlike molecules

• also due to hydrogen bonding

How does water exhibit adhesion? Why?

• adhesion of water to the walls of the vessels helps counter the downward pull of gravity during water transport

How does hydrogen bonding relate to cellulose? What is cellulose?

• H-Bond is responsible for adherence of water molecules to cellulose on vessels or tracheids walls

• Cellulose is a repeating glucose units; the exposed oxygen atoms on its surface can form H-bonds with water as water moves thru xylem

Which is stronger, interaction of water to water or water to air? To increase the area of an air-water interface, ______________________.

• water to water is stronger

• H-bonds must be broken

Surface tension is a force exerted by __________at the___________ resulting from the _______. Is energy required?

• water molecules; air-interface; cohesion

• yes, energy is required

Surface tension is a measure of __________________________________.

What results in an unequal attraction of water and air?

• an air-water interface minimizes the surface area of water

In terms of surface tension level, is Water greater than Mercury?

Mercury

Water molecules are __________ bonded with one another and the _________. This makes the water behave as _______.

hydrogen; ones below; though it is coated with invisible film

Surface tension influences the ________________ especially in ____________.

• shape of the surface in mesophyll

• in spongy layer

What happens as the surface tension creates pressure in the rest of the liquid?

• at the evaporative surfaces of the leaves generates the physical forces that pull water thru the plant’s vascular system

Define specific heat. Does water have high specific heat?

• heat required to increase the temperature of a substance by a specific amount (1 degree centigrade)

• yes

What does the high specific heat of water do? What bond causes it?

• stabilizes temperature

• hydrogen bonding

Why does the investment of heat cause relatively little change to the temperature of water?

• because much of the energy is used to disrupt the hydrogen bonds, not move molecules faster

How does water resist temperature changes? (2 reasons)

• High specific heat -→ takes a lot to heat it up, takes a lot to cool it down

• When it changes temp, it either absorbs or loses a relatively large amount of heat

How does high specific heat relate to the earth? (3)

• stabilize ocean temp creating favorable environment for marine life

• keep temp fluctuations within limits that permit life

• water makes up most organisms and this moderates changes in temp better

Does water have high thermal conductivity? Give an advantage.

• Yes, localized overheating so heat is dissipated thruout the cell

_________ is the quantity of heat that a liquid must absorb for 1 gram of it to be converted from the liquid to the gaseous state at constant temp

• Heat of Vaporization

• simple terms, energy required to change from liquid to gas

For water, at 25 degrees centigrade, the heat of vaporization is ___ kilojoules per mole. _____ volume for any liquid.

• 44 kJ per mole

• Highest volume

Hydrogen bonds must be ______ before a water molecule can evaporate from the liquid.

broken

Evaporation from the moist surface _______ the surface. Why is that?

• cools

• most energetic molecules escape the surface, leaving behind the lower energy hence cooler molecules

Energy is required to change from liquid to gas. High Energy: _______. Medium Energy: ______. Lower Energy: _____.

Evaporating; Pulled back into water; Remain as liquid

_______________ moderates temperature in lakes and prevents terrestrial organisms from overheating.

Evaporative cooling

Plants may undergo ____________ as water evaporates from leaf cell surfaces. An important mechanism for _________ in leaves of terrestrial plants that are often exposed to intense sunlight.

• substantial heat loss

• temperature regulation

Solid water ___. Water is unusual because it is ____ as a solid rather than as a liquid. Allows life to exist under the ___________.

• floats

• less dense

• frozen surfaces

Water is the ________ of life.

solvent

Many of the ________ of importance to plants like mineral nutrients are ________.

solutes; charged

Water is the ____________ of molecules within and between cells.

medium for movement

Water forms the environment in which most of the ________________ of the cell occur.

biochemical reactions

Cells are made up of _________% water.

70%-95% water

______ makes water a good solvent. _____ water molecules surround ______ and ______.

Polarity; Polar; Cations; Anions

Solvents dissolve solutes creating _____________. Relate NaCl and H₂O.

solutions

____________ is the maximum force per unit area that a continuous column of water can withstand before breaking.

Tensile Strength

Water has ___ tensile strength.

high

__________ gives water high tensile strength. Such water property must exist for water to be ___________ in a tall tree.

• Cohesion

• Pulled up