IBO International Baccallaureate Programme

School: Druga gimnazija Sarajevo

Candidate name: Asja Čehajić

BIOLOGY LAB REPORT

TOPIC: OSMOSIS

OUTLINE (TITLE) OF INVESTIGATION/EXPERIMENT: POTATO OSMOSIS

AIM: Prove presence of osmosis and its effects in different solutions

(hypertonic and hypotonic) on plant cell

Date: 31th October 2012 Teacher: Elvira Kukuljac

DESIGN ASPECT 1:

Theoretical background:

For osmosis we can say that is diffusion of water which we can see in water movement through

semi-permeable membrane of plant cell. When water is between different concentracion, water

is going from hypotonic to hypertonic solution, through semi-permeable membrane. Osmolarity

is the measure of solute concentration around where a cell is placed. Osmosis is happening

because of the difference of osmolarity inside the cell, in cytoplasm and a solution around the

cell, what makes the cell swell. Water is moving through plant with osmosis. Water from root is

going up to the leaves by the osmosis. When roots are surrounded by water, they have to

“accept” water to themselves, because water is hypotonic solution and solution inside of plant is

hypertonic, so, with osmosis, plant is getting water- which is unavoidable for plant survival.

Problem question: The thing we have to deal with is, how potato cells will react in different

solutions. What will happen in hypertonic and hypotonic solution? Manipulative variables are

NaCl & water and responding variables are potato strips that will change because of MV.

Differences between groups: We had 5 types of potatoes. Potato 1 – 4 spoons of salt, 0 ml of

water, potato 2 – 3 spoons of salt, 50 ml of water, potato 3 – 2 spoons of salt, 75 ml of water,

potato 4 – 1 spoon of salt, 100 ml of water, potato 5 – no salt, 125 ml of water.

What do we expect of our experiment? We expect that the potato in hypertonic solution will lose

mass, and that the potato in hypotonic solution will gain mass. If a cell is in a hypertonic

solution, it means that the environment outside of the cell has a high concentration of solutes,

compared to inside the cell. This means that water will exit the cell. And if a cell is in a hypotonic

solution, it means that the environment outside of the cell has a less concentration of solutes,

compared to inside the cell.

CONTROLLED VARIABLES WHY in must be controlled HOW it was controlled

1. TEMPERATURE

Because potatoes may be frozen

or may be too hot for

experiment. If it was frozen,

then, it would take longer for

potato to react. If it was too hot,

it will react too soon, so we

would not have real effect.

We kept potato on room

temperature.

2. WATER Because water in Bosnia is full of

scale and chlorine. And it could

have affect on our experiment.

We put destilled water in our

experiment.

3. SALT

Because we have to control

concentration of salt in our

experiment. Thats the main

reason of doing an experiment.

We had 5 different situations,

and we put salt to make

hypotonic or hypertonic

solutions.

4. STRIPS

Because we have to have

samples in same lenght, mass

and everything, so we could

have real results.

We cut all of the strips in 4 cm.

DESIGN ASPECT 2:

DESIGN ASPECT 3:

List of materials:

Warm destilled water 350ml

7 potatoes cut to five strips (same size)

NaCl/Salt 91,6g (five table spoons)

5 glasses

550 ml beaker

Scale

Ruler

Two spoons

Three kitchen knives

In our experiment, we defined osmosis through potatoes. By our hypothesis we are going to see

that potatoes with hypotonic solution are going to swell, and in hypertonic they’re going to lose

mass.

So, our MVs are water and NaCl, and RV is mass of potato stripes. How did we manipulate with

water and NaCl? We had 5 situations. From first to fifth, level of salt is increasing. Now, I have to

explain our experiment.

First, we had to get all of our materials. Then, cut potatoes in stripes, same size, same thickness.

We took 5 stripes for our experiment.

We had to measure stripes length and mass before experiment.

Then, we filled five cups with different measure of water. In first cup we put 0 ml of water, or we

didn’t put it at all. Second cup, 50 ml. Third, 75 ml.

Fourth, 100 ml. Fifth, 125 ml. In first cup, with no water, we put 4 spoons of salt. Second, 3

spoons of salt. Third, 2 spoons. Fourth, 1 spoon. In fifth, we didn’t put salt at all. In those cups,

we put our potato stripes. We left them in solutions for 16 hours. After 16 hours we got our

potatoes out. First thing that we noticed was that potato from cup that didn’t had water at all

had change his colour. Beside colour he shrunk.

After that we noticed that potato from cup which didn’t have salt at all had swollen. From that,

we see that potato from hypotonic solution had swollen, and one from hypertonic had shrunk.

So, that completely confirmed our hypothesis, and we can say that our experiment was

successful.

VALIDITY MEASURES: Validity measures that we used in our experiment are: ruler, water, scale.

We used ruler for measuring length of potato strips, all of them were 4 cm. In our experiment

water was very important, because of scale and chlorine we could have different reactions in

experiment. Scale had, also, one of the most important roles. We used it for measuring potatoes

before and after solutions.

We used the same ruler for every potato. Same scale and same water.

This experiment was done with small number of samples. We didn’t have to use more because,

actually, we needed just hypotonic and hypertonic solutions. We did more of it because we

needed stronger proof of osmosis.

Initial mass/ g

Mass after the solution/g

Initial length/mm

Length after the solution/mm

Concentration of NaCl

Potato 1 1.94 1.43 40 35.6 10,66%

Potato 2 2.02 1.41 40 36.6 11,10%

Potato 3 2.06 1.43 40 37.3 11,32%

Potato 4 2.00 1.94 40 40.0 10,99%

Potato 5 2.01 2.37 40 44.3 11,04%

QUALITATIVE DATA: From table, we can conclude that Potato 1 and Potato 3 didn’t have same

mass at the beginning, but, after the solution they did. Concentration difference between them is

0.66% so, that would be enough to change potato from 1.94g to the same mass of 2.02g –after

solution, so difference at the beginning is 0.12g but after solution, we have the same mass. Also,

we can see that Potato 4 behaves like it is in isotonic solution. Isotonic solution is one where

concentration of, in our example, salt and water are the same. We concluded that because

Potato number 4 didn’t changed length at all. Mass changed, but not for too much. Only for

0.37g.

Potato 1 Potato 2 Potato 3 Potato 4 Potato 5

Mass before (g) 1.94 2.02 2.06 2 2.01

Mass after (g) 1.43 1.41 1.43 2.37 2.37

Lenght before (cm) 4 4 4 4 4

Lenght after (cm) 3.56 3.66 3.73 4 4.43

0.250.751.251.752.252.753.253.754.254.75

Percentage of NaCl and mass

Len

ght

and

mas

s of

pot

atoe

s

CONCLUSION AND EVALUATION ASPECT 1:

Our experiment completely supports our hypothesis. As we already said, potatoes from

hypotonic should swell, and potatoes from hypertonic should shrink. From our graph, we have

seen that we had one potato which behaved like it is in isotonic solution.