Factors Affecting Osmosis In Plant Tissue

Authors Avatar

Factors Affecting Osmosis In Plant Tissue

Aim:

        To observe how concentration affects Osmosis by calculating the difference of length, weight and diameter before and after the experiment.

Plan:

        Osmosis is the transportation of water through a plant membrane. This membrane allows water molecules through but not sugar molecules, as they are larger, this is called a semi-permeable membrane. The sugar molecules are scientifically named solutes as they dissolve in the water, which is the main purpose for osmosis. As the more water that is transported through the semi-permeable membrane the more sugar dissolves, which can then be transported through the plant for photosynthesis to occur. The water also gives support for young plants that would wilt without it. The solute molecules are already in the plant cells but need the water from the surroundings, so the semi-permeable membrane allows transportation from a low to a high concentration. This may seem illogical until a microscopic view of the process of osmosis is shown and explained below.

This process is possible because of the difference in kinetic energy, as the water molecules have a high kinetic energy to pass through the membrane, but when they react with the sugar they join there energy so have less. This gives an idea on why osmosis can occur as the low concentration has more energy to transport than the high concentration. As the high concentration has more particles within it, it so in turn has a higher pressure, which means that osmosis increases the concentration and the pressure of the plant cells. This would be a problem if it were not for the sufficient strength of the cell wall to withstand the change in pressure, as it is this pressure that keeps the cells rigid. Osmosis maintains the turgor of the cells.

However if the concentration were stronger in the surroundings of the plant cells, as this was submerged in a stronger solution, then the water from inside the plant cells would transport into the higher concentration. This is known as plasmolysis as the process is similar in the fact that there is a transportation of a low to a high concentration through a permeable membrane, but instead all the water that makes the cells turgid flows out into the surroundings.

With both these transportations in mind, depending on how the molarity in the surroundings of the plant cells changes the direction of the transportation of the water. This is known as the osmotic potential.

Factors that affect osmosis are temperature, concentration of the solute, surface area, different types of plant tissue, the PH and the time within the solutions. The decision on what variable to change and what others to keep constant was the fact on whether the factor was discrete or continuous. This is because a quantitative prediction could only be made with the continuous factors, which would reach higher marks. This narrowed the factors slightly, and then the next consideration was the resources available and the consistency or accuracy of the results. This came to a conclusion of using concentration, surface area or time. With the purpose of the experiment in mind, time is a dependant on any factor so can be used as a consistent factor to compare with. This left surface area or concentration, which with the fact that osmosis is based on the difference in concentrations and this was also the easier of the two to change, so made this factor the variable within the experiment. This means that all other factors will be kept constant for a fair result.

The other factors that are stated above change different aspects of osmosis as they affect the cell membrane or the movement of water molecules. Temperature affects the amount of kinetic energy that is transferred in the reaction and therefore the movement through the semi-permeable membrane. If the temperature increases too much, this could also affect the enzymes in the cell membrane- denaturalisation. This factor would be useful if it were easier to keep at a constant rate for a long enough time, but as it depends on the external environment, it is not an easy variable to contain. Surface area can change the movement of water molecules as a larger surface area of the solute means more water molecules passing through the membrane to counteract the change. Different types of plant tissues change the movement of water molecules and the cell membrane as every plant is unique, even when from the same species. This means the same potato should be used throughout the experiment and cannot be the variable as the resources are limited within the laboratory. The PH of the solute that plant tissues will be submerged in could be changed but this would break down the cell membrane and affects the enzymes. This means that changing the PH is a very destructive factor to make a variable and the resources limit this type of variable.

Join now!

Preliminary Experiment

        

Method:

        The preliminary experiment is to accurately understand and discover the best quantities, time etc. to use to give the best results in the main experiment. In this experiment we will use two cored pieces of potato of the same length, mass and diameter in two different concentrations. One of the pieces will be placed in a beaker of pure, 100% sugar solution and the other piece will be placed in a ...

This is a preview of the whole essay