st grd osmosis & Diffusion homework.pdf

Greenfaulds High School.
Department ofBiology.
Investigating Osmosis and Diffusion
Homework
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Class:
Teacher:
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Standard Grade Biology Sub-topic 2 Osmosis Greenfaulds High School KU PS
1. A group ofpupils was asked to investigate the effect ofosmosis on the diameter 0 discs of
potato tissue.
The procedure followed is outlined below:
1. A large diameter cork borer was used to cut a cylinder oftissue from a peeled potato.
2. Five discs, each 2mm thick, were cut from the cylinder.
3. Four discs were transferred to separate Petri dishes.
4. The diameter ofeach disc was measured from graph paper placed underneath the dish.
5. 20 cm 3 ofglucose solution, ofdifferent concentrations, was poured into each ofthree
dishes. 20 cm 3 ofwater was poured into a fourth dish.
6. The apparatus was left for 30 minutes and the diameter ofeach disc was re-measured.
Diagram 1 below shows the apparatus and Diagram 2 shows how the diameter ofa disc was
measured
DIAGRAM 1 - SIDE VIEW
DIAGRAM 2 - TOP VIEW
Glucose solution
Petri dish~'"'*.
Potato disc
The results are shown in the table below.
Solution Concentration oj Ditlf'Mter oj disc (mm)
glucosf: solution
At start
After 30 minutes
A 0·0% 14·0 16·2
B 0·5% 14·0 15·4
C 1·0% 14·0 14·0
0 1'5% 14·0 12·6
(a) Identify the variable which was altered and two variables which were kept constant in
the investigation.
Altered variable
Variables kept Constant 1.
-------------------
2.:- _
(1)
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Standard Grade Biology Sub-topic 2 Osmosis Greenfaulds High School
(b) Identify the solution which has a water concentration higher than that present in the
potato tissue.
KU
PS
Solution
(1)
(c) The fifth disc, ofinitial diameter 14.0 mm, was placed in a solution ofunknown
glucose concentration.
The diagram below shows the size ofthis disc after 30 minutes.
'ri"
DISC
~
-­ 10mm
(i) Calculate the change in diameter ofthis disc.
Space for calculation
Change in diameter _____mm (1)
(ii) The concentration ofthe unknown glucose solution lies within one ofthe following
concentration ranges.
Tick the correct box.
0%-0.5%
0.5%-1.0%
1.0% - 1.5%
1.5%- 2.0%
D
D
DD
(d) Water can enter or leave the discs by osmosis.
Describe the overall movement ofwater for the discs immersed in the t -0%
glucose solution.
(1)
______________________(1)
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Standard Grade Biology Sub-topic 2 Osmosis Greenfaulds High School
---------""'---------"--------------=-------IKU PS
2. (a) The statements in the table describe the movement ofsubstances into or out ofcells.
Number
J
Statement
glucose moves from the small intestine into the blood
2 water enters root cells from the soil
3 carbon dioxide passes from the blood into the lungs
(i) Which statement is an example ofosmosis?
Statement number -----
(ii) What term could be used to describe the movement ofsubstances in all ofthe
examples?
(1)
(b) Pieces ofpotato were weighed, placed in sugar solutions ofdifferent concentrations for
one hour, then reweighed. The graph below shows the percentage change in mass at each
(1)
Gain
30
20
Percentage
change in
mass
10
Sugar concentration
(Molar)
0·1 0·2 0·3 0·+ 0·5
10
20
Loss
30
40
(i) The movement ofwhat substance is responsible for the change in mass?
(1)
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_~_~~ ._
Standard Grade Biology Sub-topic 2 Osmosis Greenfaulds High School
(ii) What was the percentage change in mass of the piece of potato placed in the 0.15
Molar solution
~ (1)
-------.;.
(iii) What was the concentration ofthe solution which caused the potato to lose 30~ of
its original mass?
_____Molar
(iv) At what concentration was there no change in mass ofthe potato?
----- Molar
(1)
3. Several pieces ofpotato were blotted dry and weighed. Each was then placed in a different
concentration ofsalt solution.
After 2 hours the pieces ofpotato were removed, blotted dry and reweighed. The percentage
change in mass was calculated and the results plotted on a graph.
30 ~--..-------,.---r---..-------r--...,
(1)
KU
PS
Percentage
change in mass
._a.' 'j ...: __ • __ .~ _ .• _- ....' "••• ,•• ~ •• _ •• _
-20-+--.-J--I----+---+----f-.........-+--~
_.. - ~ ... -.-
- -~ .... . - ~.. ,-' - .... _.
_. __• ...! ~_I-- ........ -- -' _ ...... _0_1-. _ _ _ _ -- __ ~ .... ':'"' _ _ __--
.... _ -_....l __•__._ •• __ ._._._~ __
- - -,- _. - - _.- -- -..;. - - - - _. --- "" - - - - - - -
-30-1---+----;---+---1-.....;.-.-4----1
o 2 4 6 8 10 12
Salt concentration (gil 00 em 3 )
(a) At which salt concentration did the mass ofthe potato remain the same?
g/100 cm 3
------=-
(1)
(b) State the percentage change in mass ofthe potato at a salt concentration of 7 gllOO cm 3
after two hours.
(1)
Page S of9

Standard Grade Biology Sub-topic 2 Osmosis Greenfaulds High School KU PS
(c) Predict the salt concentration that will produce a 30% decrease in mass.
(1)
(d) Cells from the potato in the 8 gllOO cm 3 solution were examined with a microscope.
Which ofthe following diagrams best represents one cell from the potato?
Tick the correct box.
4. Potato cylinders ofequal mass were placed in separate test tubes, as shown in the diagram.
salt
solution
++__ potato cylinder
The tubes contained salt solutions of0.5%, 1.0%, 1.5%,2.0% and 3.0% concentrations.
After two hours the change in mass ofeach cylinder was measured. The results are shown in
the table.
Tube
Change in mass
A -0.6
B -0.5
Salt solution
(g) (0/0)
C -0.2 1.5
D +0.1
E +0.2
(a) Complete the table by adding the correct concentration ofthe salt solution in each tube.
(1)
(b) Which tube contained a solution with a water concentration closest to that ofthe potato
cell sap?
Tube
(1)
------
Page 6 of9

Standard Grade Biology Sub-topic 2 Osmosis Greenfaulds High School KU PS
(c) The original mass ofeach potato cylinder was 5 g.
Calculate the percentage change in mass for the cylinder in tube D.
Spacefor calculation
-----% (1)
(d) Underline one alternative in each bracket to explain the results for Tube C.
Water mo\"ed
{
into }
out of
the potato by osmosis from a higher water
concentration {inSide } the potato to a lower water concentration
outside
{
insid.e Ithe potato.
outsIde
(e) Why would it be good experimental technique to blot the potato cylinders dry before
each weighing?
(2)
-----------------------,(1)
(t) How could the results ofthe experiment be made more reliable?
______________________(1)
Page 7 of9

Standard Grade Biology Sub-topic 2 Osmosis Greenfaulds High School KU PS
5. In an experiment, a cylinder ofpotato (cylinder A) was kept in pure water for one hour. An
identical piece ofpotato (cylinder B) was kept in a 10% salt solution for one hour.
(a) Describe the difference you would expect to observe between the potato cylinders when
removed from the liquids.
(b) The diagram below shows cells from the potato cylinder which had been in the 10% salt
solution.
(1)
Cells from potato in 10% salt solution
Explain what has happened to the cell, in tenns ofwater concentrations.
(1)
(c) In another experiment, some strips ofskin from red onions were placed on microscope
slides in sucrose solutions ofvarious concentrations. After IS minutes, the number of
cells with shrunken contents (plasmolysed) was counted.
The results are shown in the table.
Slide A B C D E
Sucrose concentration
(g/litre)
0 40 80 120 160
Total cell number 127 132 117 125 139
Number plasmolysed 0 II 68 139
% plasmolysed 0 8.3 58.1 80 100
(i) Complete the table by calculating the missing value for the number ofcells
plasmolysed in the 120 g/litre sucrose solution.
Space for calculation
(1)
PageS of9

Standard Grade Biology Sub-topic 2 Osmosis Greenfaulds High School KU PS
(ii) Why was it necessary to present the results ofthe investigation as a percentage?
-----------------------(1)
(iii) Describe the relationship between the concentration ofsucrose solution and the
percentage ofcells plasmolysed.
______________________(1)
(iv) Which solution has the highest water concentration?
----------------------(1)
(v) Explain why the cells were left for I 5 minutes before examining them.
(1)
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