• TRANSLOKASI – TRANSPIRASI (1-2)
•
UNSUR HARA (2)
•
FOTOSINTESIS (3-4)
Susiani Purbaningsih - 2007

UNSUR: SUATU ZAT YG TDK DPT DIBAGI LAGI MENJADI
ZAT YANG LBH SEDERHANA OLEH REAKSI KIMIA
SENYAWA, SUATU GABUNGAN DUA ATAU LEBIH UNSUR,
BERIKATAN SATU SAMA LAIN DG BERBAGAI CARA
CAMPURAN, PADUAN DUA ATAU LEBIH UNSUR DAN/ATAU
SENYAWAYANG TDK BERGABUNG SCR KIMIA
ATOM, PARTIKEL TERKECIL DARI SUATU UNSUR, YG MASIH
MEMPUNYAI SIFAT KIMIA UNSUR
MOLEKUL,

• The key to many of these properties is found in the structure of the water molecules & the strong intermolecular attractions that result from that structure.

Air terdiri atas 1 atom oksigen yang berikatan secara kovalen dengan 2 atom hidrogen
Atom oksigen bersifat elektronegatif kuat kecenderungan menangkap e -
Konsekuensi dari elektronegatif kuat, oksigen cenderung menjauhkan elektron dari hidrogen
The shared e yang menyusun ikatan O — H, on the average, closer to the oxygen nucleus than to hydrogen.
As a consequence, the oxygen atom carries a partial negative charge & a corresponding partial positive charge is shared between the two hydrogen atoms

This asymmetric electron distribution makes water a polar molecules
Overall, water remains a neutral molecule, but the separation of negative & positive charges generates a strong mutual (electrical) attraction between water & other polar molecules
This attraction is called hydrogen bonding
The energy of the hydrogen bond is about 20kJmol -1 .
The hydrogen bond is thus weaker than either covalent or ionic bonds, which typically measure several hundred kJmol -1 , but stronger than the short-range, transient attractions known as Van der Waals forces
(about 4 kJmol -1 )

Hydrogen bonding also accounts for attractions between water & other molecules or surfaces
Hydrogen bonding, for ex., is the basis for hydration shells that form around biologycally important macro molecules such as protein, nucleic acid & carbohydrates
These layers of tightly bound & highly oriented water molecules are often referred to as bound water
It has been estimated that bound water may account for as much as 30% by weight of hydrated protein molecules

Bound water is important to the stability of protein molecules
Bound water “cushions” protein, preventing the molecules from approaching close enough to form aggregates large enough to precipitate
Hydrogen bonding, although characteristic of water, is not limited to water

It arises where ever hydrogen is found between electro-negative centers. This includes:
 alcohols, which can form hydrogen bonds because of the — OH group
 Macromolecules such as proteins & nucleic acids, where hydrogen bonds between amino (— NH
2
) and carbonyl ( > C = O) groups help to stabilize structure

PHYSICAL & CHEMICAL PROPERTIES
OF WATER
1. Temperature & Physical State
2. Absorption & Dissipation of Heat
3. Melting & Vaporizing Water
4. Water as a Solvent
5. Cohesion & Adhesion cohesi – adhesi – tensil strength

1. Temperature & Physical State
Water is a liquid over the range of T ° most compatible with life
Boiling & melting points are generally related to molecular size, such that transit ° s 4 smaller molecules occur at lower T ° than for larger molecules
On the basis of the size alone, water might be expected to exist primarily in the vapor state at temperatures encountered over most of the earth. However, both melting & boiling point of water are higher than expected when compared with other molecules of similar size, especially ammonia (NH
3
) & methane (CH
4
).
Molecules such as ammonia & the hydrocarbons (methane & ethane) are associated only through weak Van der Waals forces & relatively little energy to change their state

Note
The introduction of oxygen raises the boiling points of both methanol (CH
3
OH) and ethanol (CH
3
CH
2
OH) to temperature much closer to that of water. This is because presence of oxygen introduces polarity & the opportunity to form hydrogen bonds

2.
Absorption
& Dissipation of Heat
The term specific heat is used to describe the thermal capacity of a substance or the amount of energy that can be absorbed for a given temperature rise
The specific heat of water is 4,182 Jg -1 ° C -1 , higher than that of any other substance except liquid ammonia
Because of its highly ordered structure, liquid water also has a thermal conductivity . This means that it rapidly conducts heat away from the point of application
The combination of high specific heat & thermal conductivity enables water to absorb & redistribute large amount of heat energy without correspondingly large increases in temperature

3. Melting & Vaporizing Water
Energy is required to cause changes in the state of any substance, such as from solid liquid, or liquid gas, without a change in temperature
The energy required to convert a substance from the solid to the liquid state is known as the heat fusion
The heat fusion for water is 335 Jg -1 , which means that 335 J of energy are required to convert 1 g of ice to 1 g of liquid water at 0 ° C
Expressed on a molar basis, the heat of fusion of water is 6,0 kJ mol -1 (18 g of water per mole x 335 Jg -1 )

The heat fusion of water is one of the highest known, second only to ammonia
The high heat of fusion of water is attribute to the large amount of energy necessary to overcome the strong inter molecular forces associated with hydrogen bonding

4. Water as a Solvent

:
- the highly polar character of the water molecule
- water molecule has the ability to partially neutralize electrical attractions between charge solute molecule or ions by surrounding the ion or molecule with one or more layers of oriented water molecules called a hydration shells.

The polarity of molecules can be mesured by a quantity known as the dielectric constant
Dielectric constant for some common solvents at 25 ° C
- Water 78,5
- Methanol
- Ethanol
33,6
24,3
- Benzene
- Hexane
2,3
1,9

5. Cohesion & Adhesion
•The strong mutual attraction between water molecules resulting from hydrogen bonding cohesion
•* One consequence of cohesion is that water has an exceptionally high surface tension
•* Surface tension arises because the cohesive force between water molecules is much stronger than interaction between water and air
•Pr……tensile strength of water
•* Adhesion, a process of water attraction to solid surface. Adhesion is an important factor in the capilary rise of water in small-diameter conduits.

COHESION
ADHESION
TENSILE STRENGTH
Explain, why water rises in capillary tubes and exceptionally important in maintaining the continuity of water column in plants

TRANSLOCATION OF WATER
One objective of plant physiology is:
To understand the dynamic of water, as it flows into & out of cells or from soil, through the plant, into atmosphere
Movement of substances from one region to another is commonly referred to as translocation
Mechanisms: active or passive; depending on whether or not metabolic energy is expended in the process
It is sometime difficult to distinguish between active and pasive transport, but the translocation of water is clearly a passive process

Passive movement of most substances can be accounted for by one of two physical processes either bulk flow or diffusion .
In the case of water, a special case of diffusion known as osmosis

BULK FLOW
Movement of materials by bulk flow (mass flow) is pressuredriven.
Bulk flow occur when an external force, such as gravity or pressure, is applied all molecules move in a mass.
Ex. Keran, tekanan hidrostatik (krn grafitasi).

DIFFUSION
Diffusion can be interpreted as a directed movement from a region of a high concentration to a lower concentration
!!! Bulk flow is pressure-driven
!!! Diffusion is driven by concentration different
Diffusion is a significant factor in the uptake & distribution of water, gasses & solutes throughout the plant.

OSMOSIS
Diffusion of water, a process known as osmosis, will occur only when the two chambers are separated from one another by a selective permeable membrane
!!!!!!
A selective perm.memb.allows free passage of water & certain small molecules, but restrict the movement of large solute molecules,…….all cellular mb.are selectively permeable.
Osmosis, is a simply special case of diffusion through a selectively permeable membrane

•
•
The water status of plant cells is constantly changing adjust to fluctuations in the water content of the environment changes in metabolic state

Cell walls have a high elastic modulus, which means that they resist deformation

It is this property that enables cells to develop high turgor pressure while maintaining structursl integrity

ANATOMI : AKAR, BATANG, DAUN
ABSORPTION (Large qtt)
TRANSLOCATION (Large qtt, < 5% used biochemically)
LOSS AS WATER VAPOR (>>>)
The balance passes through the plant to be lost as
Water vapor, a phenomenon known as transpiration
>>>>kg water may be required
1 kg of dry matter

The principal loss of water vapor from plants occurs through pores in the leaf and is driven by differences in vapor pressure between internal leaf spaces and the ambient air
ABSORPTION (Large qtt)
TRANSLOCATION (Large qtt, < 5% used biochemically)
LOSS AS WATER VAPOR (>>>)
(lenticels, stomata, cuticle)
The balance passes through the plant to be lost as
Water vapor, a phenomenon known as transpiration
>>>>kg water may be required
1 kg of dry matter

HUMIDITY
TEMPERATURE
WIND SPEED