Osmosis, like all forms of diffusion, requires no energy, it happens somewhat automatically. It is crucial for all life, plants & animals alike. It is very useful in many ways, for example, plant roots absorb water from the soil through osmosis, our bodies absorb water from our food through osmosis, very importantly, kidneys absorb water from our blood through osmosis. If the water concentration in our blood is too high, we could die. When red blood cells are placed into pure water, the swell up and eventually explode, however, if red blood cells are placed into a concentrated solution, water leaves them through osmosis and they are unable to function. The diagram below demonstrates this As I am sure you can see, osmosis is arguably, one of the most important processes in all of nature. Plan: Potato Cell Research I also did some research into potato cells, and the effect of osmosis upon them. Here's what I found: Potato tuber cells, are plant cells, they feature many of the characteristics of the stereotypical plant cell, such as: * A cell wall * A cell membrane * Cytoplasm * A nucleus * Starch grains (tuber cells actually feature more starch grains than average plant cells) However, they do not contain chloroplasts, this is probably because they are underground, and so have no light to photosynthesize. The diagram below shows an artists impression of a potato cell: This image is a photo of a potato tuber cell taken through a microscope: Plant cells like all cells, swell when they gain water through osmosis, and shrink when they lose water through osmosis. This extract is by Nigel Purchon, a biology teacher for 31 years, he explains osmosis in plant cells for GCSE students on his website: "Plant cells always have a strong cell wall surrounding them. When the take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become "turgid" when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises, eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what make the green parts of the plant "stand up" into the sunlight. When plant cells are placed in concentrated sucrose solutions they lose water by osmosis and they become "flaccid"; this is the exact opposite of "turgid". If you put plant cells into concentrated sucrose solutions and look at them under a microscope you would see that the contents of the cells have shrunk and pulled away from the cell wall: They are said to be plasmolysed. When plant cells are placed in a solution which has exactly the same osmotic strength as the cells they are in a state between turgidity and flaccidity. We call this incipient plasmolysis. "Incipient" means "about to be". When I forget to water the potted plants in my study you will see their leaves droop. Although their cells are not plasmolsysed, they are not turgid and so they do not hold the leaves up into the sunlight." www.purchon.com Plan: Variables and Controlled Variables To keep the test fair, I will need to select my independent variable and my dependent variables and ensure that the controlled variables remain constant throughout the experiment. The variable I have selected as my independent variable is the concentration of sucrose solution that the potato chips will be placed in. The dependant variables I have chosen to measure are: The mass of potato chip after osmosis and the volume of solution remaining after osmosis. The table below shows all the controlled variables, and how I intend to ensure they are constant: Controlled Variable How it will stay constant Solution Volume at beginning of experiment To make sure each potato chip is put into the same volume of solution. I will measure the amount of solution before putting it in the boiling tube, and for each experiment use exactly 20ml of solution. Surface Area & Mass of Potato at beginning of experiment To make sure the different pieces of potato are as similar in surface area and mass as possible, I will use a scalpel to cut identical pieces of potato, and then weigh them to find their starting mass. Condition of Potato at beginning of experiment To make sure the condition of the different potato chips is near identical, I will use potatoes of the same variety treated in the same way, i.e.: Have all been cut with scalpel, and skins removed. Temperature To ensure the temperature doesn't vary, I will perform all the experiments at room temperature.
