Biology Coursework - Osmosis

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Osmosis Coursework        


Contents

Pg. 3 – Plan: Introduction & Aims

Pg. 4 – Plan: Osmosis Research

Pg. 6 – Plan: Potato Cell Research

Pg. 8 – Plan: Variables & Non-Variables

Pg. 9 – Plan: Proposed Method

Pg. 10 – Plan: Hypothesis

Pg. 11 – Preliminary: Introduction and Aim

Pg. 12 – Preliminary: Variable and Controlled Variables

Pg. 13 – Preliminary: Method

Pg. 15 – Preliminary: Results

Pg. 17 – Preliminary: Graphs

Pg. 18 – Preliminary: Conclusion & Evaluation

        Pg. 19 – Experiment: Equipment

        Pg. 20 – Experiment: Safety

        Pg. 21 – Experiment: Method

        Pg. 22 – Results: Table

Plan: Introduction & Aims

In this coursework, I will be studying the process of Osmosis. To do so I will carry out an experiment, this will look at the effects of Osmosis on chips of potato in a sucrose solution.

The experiment will involve placing identical potato chips into different sucrose solutions with varying concentrations, after 45 minutes, I will take the potato chips out of the solutions and weigh them, changes in mass would indicate Osmotic activity.

My aim is as follows:

“To investigate the effect of varying concentrations of sucrose solution on the amount of osmotic activity between the solution and a potato chips, identical in size”

I hope that by the end of the investigation, I will have a better understanding of osmosis and a conclusion that demonstrates that knowledge.

Plan: Osmosis Research

To help me plan my investigation better, I have decided to do some background research on Osmosis, this is what I found:

Osmosis is simply a special type of diffusion; the movement of water molecules from a high water concentration (low solute concentration, said to be high water potential), to a lower water concentration (high solute concentration, said to be low water potential) through a partially permeable membrane.

This diagram shows the process of osmosis:

“During osmosis, more water particles pass from the pure water into the dilute solution than pass back the other way. This is because there is a higher concentration of water molecules in the pure water than in the solution. This results in more water molecules diffusing across the concentration gradient from the water to the solution. Eventually, the level on the more concentrated side of the membrane rises, while the level on the less concentrated side falls. When the concentration is the same on both sides of the membrane, the movement of water molecules will be the same in both directions. At this point, the net exchange of water is zero and there is no further change in the liquid levels.”

Bitesize -  

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.”

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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 ...

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***** This is a detailed and full write up of a well planned and conducted investigation. A high level of scientific knowledge and understanding is evident.