REQUIRED PRACTICAL 3: Osmosis on plant tissue

Question 1

in steps, describe how we can study the effects of osmosis on a plant tissue (potato e.g)

Answer 1

1. peel the potato
   potato skin can affect osmosis
2. use a cork borer to produce 3 cylinders of potato.
   to make all cylinders same diameter
   3.use a scalpel to trim the cylinders to the same length (around 3cm)
   4.measure the length of each cylinder using a ruler
   5.measure the mass of each cylinder using a balance
3. we place each cylinder into a test tube
   7.add 10cm^3 of 0.5 molar sugar solution to the first test tube
   8.add 10cm^3 of 0.25 molar sugar solution to the second test tube
   9.add 10cm^3 of water to the third test tube
   Add DISTILLED water (not tap water)
4. leave the potato to simmer overnight to allow osmosis to take place
5. we remove the potato cylinders and GENTLY roll them on paper towel to remove any surface moisture
   12.measure the length and mass of the cylinders again
   13.calculate the percentage change in length and mass using this equation
   % change = change in value/original value x 100

Question 2

why do we peel the potato firstly?

Answer 2

the potato skin can affect osmosis

Question 3

why do we use a cork borer to make 3 potato cylinders?

Answer 3

it makes all of the cylinders the same diameter

Question 4

why do we use a scalpel to trim the cylinders to around 3cm?

Answer 4

if we use shorter cylinders, then we might be unable to measure the effects of osmosis

Question 5

when placing each cylinder into a test tube, what measurements of what things do we put in the 1st test tube, the 2nd test tube, and 3rd test tube?

Answer 5

10cm^3 of a 0.5 molar sugar solution to the FIRST test tube

10cm^3 of a 2.5 molar sugar solution to the SECOND test tube

10cm^3 of DISTILLED WATER to the THIRD test tube

Question 6

why do we add 10cm^3 of distilled water instead of tap water to the 3rd test tube?

Answer 6

distilled water contains no dissolved substances, dissolved suvstances can affect the rate of osmosis

Question 7

when removing the potatoes from the cylinders, why do we roll them gently on paper towel?

Answer 7

to remove any surface moisture

Question 8

why is it important to roll the potatoes gently onto the paper towel and not press on them?

Answer 8

we gently roll them because we want to remove surface water but NOT force water out of the cells

Question 9

how do we calculate percentage change?

Answer 9

% change = change in value/original value x 100

Question 10

A potato cylinder has a starting mass of 1.56g. This increases by 0.25g. Calculate the percentage change.

Answer 10

increased by 16.03% to 2 dp

change in value/original value x 100
0.25/1.56= 0.16025641 x 100 = 16.03% increase to 2 dp

Question 11

A potato cylinder has a starting mass of 1.32g. This decreases by 0.19g. Calculate the percentage decrease.

Answer 11

-14.39%

change in value/original value x 100
0.19/1.32 x 100 =-14.39%

Question 12

after the experiment, what can we expect of the mass of the potato cylinder?
how?

Answer 12

the potato cylinder would gain mass as water moves into it by osmosis.

Question 13

after the experiment, what can we expect of the cylinders mass change in a concentrated sugar solution?
how?

Answer 13

the cylinder loses mass as water moves out by osmosis

Question 14

in a graph, the results of the concentrated sugar solution are plotted. would the line be in a positive or negative colleration?
why?

Answer 14

a negative colleration

the change in mass would decrease in a concentrated sugar solution as water moves out of the cell by osmosis

Question 15

what is the point where the line crosses the x axis,in the graph plotted with the results?
why?

Answer 15

this point where it crosses the x axis means that the approx concentration inside the cell is the same concentration outside the cell.
that is because the concentration outside the cell is the same as the concentration inside so no overall osmosis takes place.