d. Movement of Substances in and out of cells23/09/2010 03:01:00
Objectives:
d) Movement of Substances into and out of cells.
2.12
understand definitions of diffusion, osmosis and active transport.
2.13 Understand that movement of substances into and out of cells can be by
diffusion, osmosis and active transport.
2.14 Understand the importance in plants of turgid cells as a means of
support.
2.15 Understand the factors that affect the rate of movement of substances
into and out of cells to include the effects of surface area to volume ratio,
temperature and concentration gradient.
2.16 Describe experiments on diffusion and osmosis using living and non-living
systems.
2.12 Simple Definitions
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2.12 understand definitions of diffusion, osmosis and active transport.
Reference:
EDEXCEL BOOK: Pg. 9&10
OLD CAMBRIDGE BOOK Ref:
Pg. 6
2.1 “Diffusion results from random movement”
2.2 “Diffusion is important to organisms”
Pg. 7
2.3 “In osmosis, water diffuses through a partially permeable
membrane”
Pg. 10
2.9 “Cells take in substances by active transport”
 Read each of the references above.
 Discuss the meaning of the words ‘Diffusion’, ‘Osmosis’ and ‘Active Transport’
Write down a concise definition for each of the words: ‘Diffusion’, ‘Osmosis’
and ‘Active Transport’.
Diffusion
Definition:
 Check out the following website for a quick animation on diffusion:
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusio
n_works.html
 Watch the Brainpop animations: “Diffusion: Matter Likes to Mix” and
“Passive Transport: Getting Stuff in and out of Cells, the easy way”.
 Copy down the summary notes on diffusion
Osmosis
Definition:
 Check out the following website for a quick animation on osmosis:
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis
_works.html
Active Transport
Definitions:
 Check out the following website for a quick animation of Active Transport
http://www.coolschool.ca/lor/BI12/unit4/U04L03/active%20transport_jeffedi
t.swf
 Watch the Brainpop animation: “Active Transport: Getting stuff in and out
of a cell, the hard way”.
 Copy down the summary notes on active transport
Answer pg. 7 questions 1-3 in the yellow box at the top of the page.
Observing Diffusion
Make notes to describe what you observed for the following two
demonstrations:
Showing Diffusion in Solution
Showing Diffusion in Gases
Questions
1. Which shows the changes in appearance of a plant cell as it remains in a
concentrated sugar solution for thirty minutes? (1)
2. By which process does oxygen move into the cytoplasm of a root hair cell? (1)
A diffusion
B osmosis
C photosynthesis
D transpiration
3. In an osmosis experiment, four potato strips, each 5 cm in length, were left
in salt solutions of different concentrations.
The table shows the lengths of the strips after 30 minutes.
Which salt solution was the most concentrated? (1)
4. The diagram shows a section through a leaf.
By which process does carbon dioxide pass
from X to Y? (1)
A diffusion
B osmosis
C translocation
D transpiration
5. The diagram shows two solutions that are separated by a partially permeable
membrane.
In which direction will most water molecules move? (1)
A from X to Y, against their concentration gradient
B from X to Y, down their concentration gradient
C from Y to X, against their concentration gradient
D from Y to X, down their concentration gradient
6. Some red blood cells were placed in distilled water and others were placed in
three salt solutions of different concentrations.
Which diagram shows the appearance of a cell has changed after being in the
distilled water for a short time? (1)
7. A strong solution of salt accidentally flooded a field of young rice plants.
The graph shows the effect on two varieties of rice in the field.
What causes the effect shown by the graph? (1)
A Water enters the root cells of X.
B Water enters the root cells of Y.
C Water leaves the root cells of X.
D Water leaves the root cells of Y.
8. Materials can enter the cells by diffusion and osmosis.
Define diffusion. (2)
9. Describe how osmosis differs from diffusion. (2)
10. Complete the sentences by choosing the correct words from the box.
Oxygen enters cells by the process of .......................................... .
This is the movement of molecules from where they are at a
.......................................... concentration to where they are at a
.......................................... concentration. Water molecules pass
from a dilute solution into a concentrated solution through the partially
permeable cell .......................................... . This process is called
.......................................... . A plant
.......................................... if the cells are short of water. (6)
11. Complete the table by writing the correct process next to its description.
Description
Moving air in and out of the lungs
The movement of particles of a
substance from high to low
concentration
The release of energy from glucose
Process
2.12 Animal Cells
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2.12 Understand that movement of substances into and out of cells can be by
diffusion, osmosis and active transport.
Reference:
EDEXCEL BOOK:Pg. 9&10
OLD CAMBRIDGE BOOK Ref:
pg. 8
2.4 “Cell Membranes are Partially Permeable”
2.5 “Animal Cells Burst in Pure Water”
2.6 “Animal Cells Shrink in Concentrated Solutions”
Notes
What is meant by the term ‘Partially Permeable’?
Name some substances which will move INTO a cell by diffusion.
Name some substances which will move OUT of a cell by diffusion.
What is the only substance to move by OSMOSIS?
Using the example of plant absorbing ions from the soil, explain how ions enter
the root hair cell.
Animal Cells
Use the diagram below and references above to explain what happens to Red
Blood Cells in each of the following solutions:
Hypertonic (i.e. concentrated salt solution)
Isotonic (i.e. same concentration as Red Blood Cell)
Hypotonic (i.e. dilute salt solution)
Questions
Answer questions 1-6 in the yellow box on pg. 8
Question
Red blood cells are affected by the amount of water in the solutions that
surround them.
Describe what has happened to cells A and C.
Explain the changes in cell C.
(2)
(3)
2.14 Plant Cells
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2.14 Understand the importance in plants of turgid cells as a means of support.
Reference:
EDEXCEL BOOK: Pg. 123 & 124
OLD CAMBRIDGE BOOK Ref:
Pg.9
2.7 “Plant cells do not burst in pure water”
2.8 “Plant cells plasmolyse in concentrated solutions”
Diagram 2.6 “A Plant Cell in Pure Water”
Diagram 2.7 “A Plant Cell in Concentrated Solution”
Notes
 Read through the references given above.
 Make notes on each of the following terms.
Turgid
Flaccid
Plasmolysed
Questions
Answer questions 1-7 on page 9.
1. Five dried peas A, B, C, D and E were weighed, soaked in water for two hours
and weighed again. The peas were then soaked in a sugar solution for two hours
and reweighed.
Mass of pea/g
Pea
Dried
After soaking in
water for 2 hours
A
0.4
1.3
0.8
B
0.5
1.4
0.9
C
0.6
1.5
0.9
D
0.6
1.7
1.2
E
0.6
1.6
1.2
Mean mass
0.5
After soaking in
sugar for 2 hours
a. Complete the table by working out the mean masses. (1)
b. Suggest TWO reasons why peas A, B and D have different masses when
dried.(2)
c. Peas C and D had the same mass before soaking, but different masses after
soaking. Suggest a reason for these differences.(1)
d. Before reweighing the peas, suggest ONE precaution that could be taken to
increase the accuracy of the results.(1)
e. Explain the change in mass of the peas when they were removed from the
water and placed in the sugar solution. (3)
f. Name the process responsible for these changes in mass of the pea seeds. (1)
2. Two pieces of onion epidermis were obtained. One was placed in distilled
water and the other in a concentrated sugar solution. A single cell from each
piece is shown.
a. Which cell was placed in distilled water?(1)
b. What is found at X? (1)
c. List three visible differences between cell A and cell B, which are due to
osmosis. (3)
3. In an experiment , four potato chips were all cut so that they were the same
mass. They were then paced in separate test-tubes. Each test-tube contained
a different concentration of sugar solution.
The results given are the masses of the potato chips 24 hours later. (They had
been dried using a paper towel)
Test-tube
Amount of sugar (g/100 cm3
solution)
Increase (+) or
Decrease (–) in
mass in g
A
B
C
20
14
12
–0.7
0
+0.2
D
6
+0.6
a. Which test tube contains the most concentrated sugar solution? (1)
b. At what sugar concentration is there no change in mass? (1)
c. Explain why there is no change in mass at this concentration of sugar solution.
(1)
4. Strips of rhubarb epidermis were placed in three solutions A, B and C and the
results recorded in the table.
Solution
Appearance
A
Cell membrane pushed against
cell wall; large vacuole
B
Cell membrane pulled away from
cell wall; small vacuole
C
No change
a. Name the process under investigation. (1)
b. Explain what happened during the process to cause the cell membrane to push
against the cell wall in solution A. (1)
c. Why were there no changes in the rhubarb cells in solution C? (1)
2.15 Factors affecting rate of movement
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2.15 Understand the factors that affect the rate of movement of substances
into and out of cells to include the effects of surface area to volume ratio,
temperature and concentration gradient.
Reference:
EDEXCEL BOOK: Pg. 53 Fig 5.2, also Pg. 54 Fig 5.3
 Discuss the factors which influence the rate of movement of substances into
and out of cells.
Write down notes under each of the following headings.
Surface area : Volume
Temperature
Concentration Gradient
2.16 Investigating Osmosis
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2.16 Describe experiments on diffusion and osmosis using living and non-living
systems.
Reference:
EDEXCEL BOOK: Pg.10 Experiment 4
There are three sections to writing an Internal Assessment.
The format is the same for each assessment.
Design (D) = 6 marks
Data Collection and Processing (DCP) = 6 marks
Conclusion and Evaluation (CE) = 6 marks
You are going to complete an Internal Assessment which will count along with
Test scores towards your grade for reports.
You will be provided with guidelines on how to complete the Design, Data
Collection and Processing and Conclusion and Evaluation.
Before you begin, you will carry out two preliminary investigations to help you
better understand the process of osmosis.
Investigation 1: Osmosis in “A Model Cell”
Follow the instructions below to carry out a simple experiment to investigate
osmosis.
Record your results in the table below.
Answer questions 1-4 after the practical.
You have to wait for 30mins whilst the experiment is in progress. Use this time
to answer the questions at the end of the document.
Model Liquid
Cell
inside
Visking
Tubing
Liquid
in
Beaker
Weight of Model
Cell (g)
A
Glucose
Water
+
B
Water
Glucose
-
At
start
Change in Weight of Cell (g)
After
30 mins
Calculating % Change in mass
% change in mass = Final mass (g) – Initial mass (g) X 100
Initial mass (g)
Model Cell
A
B
% Change in mass
Investigation 2: Osmosis in Potato Cells
Follow the instructions below to carry out a simple experiment to investigate
osmosis.
Record your results in the table below.
TestTube
Liquid in testtube
Original
Length of
Final
Length of
Change in
length of
% change
in length
Chip (mm)
A
Distilled water
B
Weak sugar
solution
C
Strong sugar
solution
Chip (mm)
chip (mm)
Calculating % Change in Length
% change in length = Final length (mm) – Initial length (mm) X 100
Initial Length (mm)
TestTube
Liquid in testtube
A
Distilled water
B
Weak sugar
solution
C
Strong sugar
Original
mass of
Final mass
of Chip
Change in
mass of
Chip (mg)
(mg)
chip (mg)
% change
in mass
solution
Calculating % Mass in Length
% change in length = Final mass (mg) – Initial mass (mg) X 100
Initial mass (mg)
Answer questions 1-4 after the practical.
You have to wait for 30mins whilst the experiment is in progress. Use this time
to answer the questions at the end of the document.