Biology Investigation - Osmosis

List of apparatus

• Test tubes

• Potato
• Chipper

• Salt
• Sugar
• Measuring cylinder
• Ruler
• Test tube rack

Method

To make the experiment safe I am going to have to be careful while chipping the potatoes to avoid injury. The key features to alter are the amount of salt and sugar in each test tube. I am going to take four readings for both salt and sugar, ranging from one to four spatulas of each substance. I am also going to take a reading with pure deionized water as a control. The key features that need to be kept the same are the amount of water (25ml.) and the size of the potato chip (2cm.x1cm.x1cm.). I must also always use deionized water. No preliminary experiments or secondary sources were necessary in the planning of this investigation.

Observing

Analysing

My results show that the weights of all of the potatoes except for the one in deionized water decreased. This means that the osmatic pressure was greater in the extracellular solution in all of my readings. I got this result because the semi-permeable membrane in the potato cells allows the passage of the water but not of the solute molecules. This helps the potato maintain a high concentration of salt and sugar.

Evaluating

I had an error in my investigation when in one of the readings for sugar the mass of the potato went up instead of down. I retook the result and it came out as expected the second time. My results support my conclusion that salt and sugar would both have a negative effect on the osmosis ability of a potato. I could have improved the experiment by taking multiple readings for each amount of salt and sugar. If I were going to extend my experiment I would carry on taking results until the effect of salt and sugar on osmosis reached saturation point.