Download General plant M. Sc. Huda Jasim Al-Tamimi Lab- 8

General plant
M. Sc. Huda Jasim Al-Tamimi
Lab- 8- Cell Physiology
The membrane of the cell or of various subcellular organelles (chloroplasts,
mitochondria) serves as a regulatory structure by controlling the entry or exit of
substances into and out of the cell. The membrane may be permeable, impermeable or
partially permeable to a given substance.
1- Diffusion— is the net movement of molecules or ions from an area of higher
concentration to an area of lower concentration. Think of it as a
rebalancing. Diffusion will continue until a state of equilibrium is reached.
Rates of diffusion are affected by temperature and the density of the
involved molecules among other things. In the leaves, water diffuses out
via the stomata into the atmosphere.
2- Osmosis— in plant cells is basically the diffusion of molecules through a
semipermeable, or differentially permeable, membrane from a region of
higher solute concentration to a region of lower solute concentration. The
application of pressure can prevent osmosis from occurring. Osmotic
potential is the minimum pressure required to prevent fluid from moving
as a result of osmosis. Fluid will enter the cell via osmosis until the
osmotic potential is balanced by the cell wall resistance to expansion. Any
water gained by osmosis may help keep a plant cell rigid or turgid. The
turgor pressure that develops against the cell walls as a result of water
entering the cell’s vacuole. This pressure is also referred to as the pressure
potential. If there are two cells next to each other of different water
potentials, water will move from the cell with the higher water potential to
the cell with the lower water potential. Water enters plant cells from the
environment via osmosis. Water moves because the overall water potential
in the soil is higher than the water potential in the roots and plant parts. If
the soil is desiccated then there will be no net movement into the plant
cells and the plant will die.
3- Plasmolysis— is the loss of water via osmosis and accompanying shrinkage of the
protoplasm away from the cell wall. When this occurs, the cell is said to be
plasmolyzed. This process can be reversed if the cell is placed in fresh
water and the cell is allowed to regain its turgor pressure. However, as
with anything living, there is a point of no return and permanent or fatal
damage to the cell can occur.
4- Imbibition— is the swelling of tissues, alive or dead, to several times their original
volume. This is a result of the electrical charges on materials in suspension
(colloidal) such as minerals, cellulose and starches attracting highly polar
water molecules which then move into the cell. This swelling process is
the initial step in the germination of seeds.
1- Active Transport— is the energy assisted movement of substances against a
diffusion or electrical gradient. This process requires enzymes and a
‘proton-pump’ embedded in the plasma membrane. The pumps are
energized by ATP molecules—a cellular energy storage molecule.
1
General plant
M. Sc. Huda Jasim Al-Tamimi
Practical parts:
1- A- Prepare three identical cubic blockes of Potatos (morphologically identical and
equal in weight).
B- Place the 1st block in isotonic solution (= 0.15 M Nacl) , the 2nd block in
hypotonic solution (<0.15 M Nacl), and the 3rd block in hypertonic solution
(>0.15 M Nacl) for 24hr.
C- Record your results depending on size of blocks whether , increased in size
(turgid) , Decreased in size (flaccid) , and remain unchanged.
2- Prepare a surface view of onion (Allium cepa) , Note the position and shape of
the cell wall, cytoplasm and vacuole. Now view an onion section which has had a
10% NaCl solution added . You will find that the cytoplasm has shrunk away
from the cell wall. The cell is said to be plasmolyzed.
2- Placed cut sections of beets in three solutions; Water , Boiling water and
Chloroform
Answer the following questions about the exercise
1- What happens to the membrane when the cell is killed by boiling?
2- Does it become leaky?
3- For what types of substances is chloroform a solvent?
4- How does chloroform affect cell membranes?
2