Osmosis in Potato Tissue

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Biology

Aim:

My objective is to plan and conduct an experiment from which I should be able to draw a firm conclusion that will either prove or disprove any predictions I make. This essay aims to assess and investigate the effect of various solution concentrations on the activity of osmosis in plant tissue.

Background scientific theory:

Plants exchange gases (CO2 and O2) in maintaining vital respiratory processes and in carrying out photosynthesis; they absorb certain minerals and sugars so to use as a source of energy and eradicate wastes in order to maintain specific requirements for survival. Large amounts of water are absorbed by root hairs and are then distributed across the cells of plants by the process of osmosis; water being essential to life, assists cells in executing crucial chemical processes. Molecules travel by two means; active transport or passive transport.

Active transport is the movement of a substance from a low to high concentration against the norm concentration gradient. Hence, the process requires expenditure of energy, and the support of a carrier protein. Passive transport, however, does not require energy but occurs spontaneously instead. It is a form of transport by which molecules move along a concentration gradient, from an area of higher concentration to an area of lower concentration. Passive transport includes osmosis and facilitates diffusion. Osmosis is a special case of diffusion; it describes the passage of a solvent from a weaker solution, where there is higher water potential, to that of a more concentrated solution that has a lower water potential through a partially permeable membrane in order to achieve the state of equilibrium. A partially permeable membrane acts as a barrier to some substances but allows others to penetrate through freely.

Within any plant cell the cytoplasm and cell sap within the vacuoles are of a variety of substances such as salt, sugars and proteins. In theory, water will diffuse into the cell by osmosis if the solution surrounding the cell is weaker but when enclosed by a stronger more concentrated solution than its contents than water is drawn from it by the same process. As a result it becomes flaccid; the turgor pressure falls, the vacuole collapses and the cytoplasm shrink away from the cell wall. This may result in its wilting or death.

Plant cells have a cell wall as well as a plasma membrane. The cell wall is a strong and rigid structure that is used by the cell to create osmotic pressure within the cell. This pressure can build because of the rigidity of the cell wall. The cells within a plant that contain high water pressure act as the plant supportive structure, helping to give it its shape. When gaining, the vacuole will expand and press outwards on the cytoplasm and cell wall but since this cannot be over stretched there is a resistance on the inflow of water by the un-stretchable cell wall. This resistance results in turgor pressure exerted by the vacuole on the cell walls.

When the vast majority of the cells within the leaves and stem of plant are turgid, its stem will be firm and upright and the leaves straight therefore providing mechanical strength. Similarly a flaccid celled leaf will be limp and the stem will droop; such plants are thought to be wilting.

Factors that affect the rate of osmosis (potential variables)

The rate of osmosis is much dependent upon a number of factors; the temperature, the nature of the solute, the difference in concentration of solute on either side of the membrane, and any external pressure applied against the direction of flow.

Concentration: -
The concentration of a chemical solution refers to the amount of solute that is dissolved in a solvent. The concentration of any solution or plan tissue is directly linked to its water potential; the higher the concentration the lower it...
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