Osmosis, What is the effect of sucrose concentration on the rate of osmosis in a potato cell? What is the concentration inside a potato?

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Investigation - Biology Coursework

What is the effect of sucrose concentration on osmosis in a potato cell?

What is the concentration inside a potato?

PLANNING 2

AIM 2

WHAT IS OSMOSIS? 2

FAIR TEST 3

PREDICTION 4

PREDICTION GRAPH 4

RISK ASSESSMENT 4

APPARATUS 4

DIAGRAM 5

METHOD 6

BLANK RESULTS TABLE 6

PILOT TEST 7

PILOT TEST RESULTS TABLE 7

PILOT TEST ANALYSIS 7

PILOT TEST GRAPH 8

OBTAINING EVIDENCE 9

RESULTS TABLE 9

GRAPH OF RESULTS 9

ANALYSIS 10

SCIENTIFIC EXPLANATION OF RESULTS 10

CONCLUSION 10

PREDICTION CONFIRMED? 10

EVALUATION 11

QUALITY OF RESULTS 11

ANOMALOUS RESULTS 11

QUALITY OF THE METHOD USED 12

METHOD IMPROVEMENTS 12

IDEAS FOR COLLECTING FURTHER EVIDENCE 12

BIBLIOGRAPHY 16

PLANNING

Aim

What is the effect of sucrose concentration on the rate of osmosis in a potato cell?

What is the concentration inside a potato?

What is Osmosis?

Osmosis is the net movement of water from a high water concentration (high water potential, a dilute solution) to a place of lower water concentration (low water potential, a concentrated solution) through a partially permeable membrane.

This is a diagram to show how osmosis works:

When sugar dissolves in water...

This diagram, I sourced from [www.gcsesciencehelp.co.uk/concepts/osmosis]

I have edited it slightly

Hypertonic Solution

Hypotonic Solution

Concentrated Sugar Solution - A low water concentration or low water potential

Dilute Sugar Solution - A high water concentration or high water potential

A low concentration of free water molecules

A high concentration of free water molecules

Sugar molecules pass through the pores more slowly

Water molecules are free to move through the pores in the membrane

Selectively permeable membrane

Sugar molecules attract some of the water molecules and stop them from moving freely. This, in effect, reduces the concentration of water molecules. In the diagram above, the molecules on the left have "captured" about half of the water molecules. There are more free water molecules on the right of the membrane than on the left, so water will diffuse more rapidly from right to left across the membrane than from left to right. This creates a net movement of water from a high water potential to a low water potential.

The partially permeable membrane does not act as a sieve in this case. The sugar molecules can diffuse from left to right but, because they are bigger and surrounded by a cloud of water molecules, they diffuse more slowly than the water

This information was sourced from "A Level Biology" Jones and Jones

Fair Test

Factors affecting osmosis and how I will control them in my investigation:

) Surface Area: The surface area of the potato piece affects the amount of sucrose surrounding the potato. The larger this surface area is, the faster the rate of osmosis occurs. I will control this variable by making all of the potato pieces have the same surface area. I will do this by using a corer to cut the potatoes into tubes instead of cutting them into cubes. This way, all the pieces will have the same cross sectional area. Then I will cut each piece to 3 cm long using a scalpel. The potato pieces will now have an equal surface area. In addition, any traces of skin will have to be removed. The potato skin is not a partially permeable membrane, and therefore water cannot travel through it by osmosis.

2) Mass of Potato Piece: As the potato piece gets larger, more water can go into the potato out of it. Using the cutting method approved above, the mass of the pieces should be approximately equal. However, I feel that another measure should be taken. The potatoes will be weighed before and after the experiment to gain a mass change during incubation. The mass change will vary slightly from potato to potato. Therefore, I will calculate the percentage mass change (Mass Change (g) / Mass Before (g)). This will eliminate any minor errors

3) Time of Incubation: As the time of incubation grows, the rate of osmosis speeds up. For this experiment, all the pieces of potato will be subjected to 30 minutes of submersion. I feel that this is a good time because...

At two hours all possible osmosis will have stopped for the test tubes will the highest and lowest concentrations because they will have conducted osmosis the fastest due to their high water potential gradient between the potato cells and the solution. In addition, the concentrations below the two extremes will begin to catch up with the boundaries creating an awkward graph.

At 5 minutes, hardly any osmosis will have taken place. Even a small anomaly in one measurement could result in an experimental failure because the values will be so small.

Therefore, I will conduct my experiment over a period of 30 minutes, a time when none of the above problems will occur.

4) Temperature: As temperature increases, the rate of osmosis increases. As temperature increases, the particles have more energy and move faster. They move faster through the partially permeable membrane and therefore the rate of osmosis speeds up. To solve this problem I will conduct my experiment within one hour on the same day. Therefore, temperature will not fluctuate significantly to ruin the results
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5) Potato (age, type, size, plant): Different types of potatoes have different concentrations. Baking potatoes are bitter. They have a low sucrose concentration. New potatoes are sweeter. They have a high sucrose concentration. Small young potatoes are sweeter than larger, older ones. To solve this problem, I will just use a single large potato for all of my potato pieces to prevent shifts in the graph line from occurring as I change to a different potato.

6) Concentration of surrounding solution: The concentration of the solution is the variable that I am measuring. It is my independent ...

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