Transcript unsur hara (2)

FISIOLOGI TUMBUHAN
• 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,
AIR DAN IKATAN HIDROGEN
• Water has a number of unique physical &
chemical properties when compared with other
molecules of similar size.
• 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 eKonsekuensi 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 (— NH2) 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 (NH3) & methane (CH4).
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 (CH3OH) and ethanol (CH3CH2OH) 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
Water comes close to being the ‘universal’
solvent, more substances will dissolve in
water than in any other common liquid
due to:
- 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
33,6
- Ethanol
24,3
- Benzene
2,3
- Hexane
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
TRANSPIRATION
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
TRANSPIRATION
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
TRANSPIRATION RATE
HUMIDITY
TEMPERATURE
WIND SPEED