An Investigation into Potato Tissue

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Kelly

Biology coursework

An Investigation into Potato Tissue

Aim:        To investigate how varying the sucrose concentration around piece of potato tissue affects the diffusion of water (osmosis) into or out of the cell.

Introduction:

Definition of Osmosis: This is the diffusion of water molecules from an area of high water concentration (dilute solution) to an area of low water concentration (concentrated solution) through a permeable membrane.

The rate, again, depends on the surface area, the concentration gradient and the properties of the partially permeable membrane.

A diagram of Osmosis:

 

We have looked into osmosis previously in the experiment of turgid and plasmolysed onion cells, and a visking tube.

Demonstration of Osmosis Using a Visking Experiment

The Visking tube experiment was used to demonstrate osmosis. The Visking tubing was semi-permeable, which allows small molecules (water) to pass through, but it doesn’t allow the larger ones (sugar).

Apparatus

  • a small length of capillary tubing
  • a larger amount of Visking tubing
  • 0.5 sucrose solution
  • pipette

Osmosis Experiments

Factors that will affect the rate of osmosis will be the Independent variables, the dependent variables and the external variables.

Independent variable =

Concentration of sucrose solution – If the sucrose solution is changed, osmosis will change in rate and direction.

Dependent variables =

Change in mass of potato.

(Water movement in and out)

External variables =

Size and shape of potato – If the potato is large in surface area then osmosis will occur more.

Volume of solution– If the sucrose solution is much higher this will affect osmosis.

Temperature – if it is warmer then osmosis will happen more rapidly.

Type of potato – In a fair test you must use the same potato other wise it wont be a fair test.

Things that I need to concentrate on in my experiments to keep fair tests-

Precision -   Measure everything using an electronic balance, this measures to 0.01(g).

Accuracy -   Zero the balance each time when using it. Make sure that using same units when measuring something.

Reliability -   Repeat experiment, reduce risk of anomalies.

Before we did the final experiment we did a practise one, to see if we could improve on any of these variables. Here is my investigation:

My first Experiment of Osmosis

Aim

To investigate how varying the sucrose concentration around a piece of potato tissue affects the diffusion of water (osmosis) into or out of a potato cells.

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Introduction

This is an investigation into the water movement, through a partially permeable concentration.

In this experiment Im going to use the range of sucrose solutions 0,0 (distilled water, 0,2 0,4 0,6 0,8 1,0. These shall be provided to us when we do the experiment. In future experiments I may choose different sucrose concentrations, it all depends on the results that I get back at the end of this experiment. I will not need to worry about how to make these solutions as they will all be provided.

Hypothesis

I predict that the higher the concentration solution ...

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