Factor affecting osmosis in plant cells.

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Heather Bibby

Biology Coursework – Factor affecting osmosis in plant cells

Introduction

Osmosis is the passage of water molecules from a weaker solution into a stronger solution through a partially permeable membrane.

Plant cells are surrounded by a cell wall. This is fully permeable, which means it will not let any molecules go through it, so osmosis will not occur across it. A plant cell also has a cell membrane just like an animal cell. The cell membrane is selectively permeable in the same way as an animal cell. As the water goes in the cytoplasm and vacuole will swell. However, the plant cell has a very strong cell wall around it. The cell wall is much stronger than the cell membrane and it stops the plant cell from bursting. The cytoplasm presses out against the cell wall, but the cell wall resists and presses back on the contents

Prediction

I predict that the piece of potato in the highest concentration of sucrose will lose weight or gain the least. The piece of potato in the lowest concentration of sucrose will gain the most. I predict this because the water molecules move from a weaker solution into a stronger solution. The water molecules will pass through the partially permeable wall of the potato and into the potato.

e.g. 20% sucrose = 4.7g    > 4.72g

       0% sucrose = 4.7g     > 5.02g

Planning

In my experiment I am going to keep the volume of the solution the same and the weight and mass of the potato the same. I am going to change the concentration of the sucrose solution. In my experiment the weight of the potato will change throughout the experiment. My experiment is fair because I will get the weight of the potatoes to be as accurate as possible to the same weight and I will put them in and take them out of the solution at the same time. In my experiment the equipment that I am going to need is:

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        A beaker of sucrose solution

        7 test tubes

        2 measuring cylinders

        knife

        Cork borer

        Top pan balance

        Potato

        Some water

My equipment will look like this:

The precautions that I am going to make are that I am going to wear goggles. I am going to measure the weight of the potato after being in sucrose solution for 30 minutes. I will get four measurements from each of the different concentrations. I am going to record my results in a table like this:

Method

I am going to get my equipment ...

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In this report on an investigation into the effect of sucrose concentration on percentage mass change in potato tissue, the writer follows the standard GCSE structure for practical write-ups covering all the main sections, albeit not always in sufficient detail. [1] The introduction was a little brief and could have described work carried out by other scientists on the same topic. [2] The method lacked detail with regard to numerical values (times, volumes, concentrations) but was otherwise clear and appropriate. [3] The results were quite bizarre with the four replicates generating very different data with no obvious trends. [4] Unfortunately, the student did not analyse this data in a realistic way, choosing to ignore the lack of consistency (and reliability). However, although the quality of the data collected is poor, the student makes a fair attempt at writing up the work and with the improvements listed above, would gain a middle grade at GCSE. 3 stars