Practical C4.
RATE OF OSMOSIS
BACKGROUND
All living organisms consist of cells and all cells are surrounded by a membrane. One of the
major functions of the membrane is to regulate the passage of materials into and out of the
cell. These materials include dissolved gases, sugars, salts and water. Cell membranes are
‘partially-permeable’ or ‘semi-permeable’ which means that some substances can easily pass
through them, whereas others cannot. Most materials move by simple diffusion from high
concentration on one side of the membrane to a lower concentration on the other. Some
substances may be actively transported, which requires the provision of energy.
Water is the most abundant and one of the most important substances in cells. The diffusion
of water across a partially-permeable membrane is called osmosis.
Vegetables are storage organs of plants which consist of cells and the products of cells. The
cells are surrounded by a cell wall and, inside that, a plasma membrane. Vegetable tissue
provides an excellent model to assist the understanding of the structure and function of
membranes.
Part A Validating the technique
MATERIALS REQUIRED (per group)
1 large fresh potato
knife
spoon
paper towelling
ruler
100 mL 10% NaCl soln
100mL distilled water
2 x 250 mL beakers
accurate triple arm or electronic balance
METHOD
1. Read right through this method and prepare a suitable data table in
the space provided on the next page to record the masses.
2. Obtain a large fresh potato, peel it and use a ruler to measure and a
knife to cut four 2cm x 2cm cubes, split them into 2 pairs and use a
balance to determine the mass of the pairs as accurately as possible.
3. Place one pair of the cubes in one of the beakers and add the 10% salt
solution so that the cubes are fully covered and leave it for 20
minutes, remove excess water and weigh and record the mass again.
Calculate the change in mass and calculate % loss or gain and also
enter this in the table. Also record any other observations.
4. Place the other two cubes in the other beaker and cover them with distilled water and leave
it for 20 minutes, remove excess water and weigh and record the mass again. Calculate
the change in mass and calculate % loss or gain and also enter this in the table. Also
record any other observations.
5. When you have finished with your potato cubes please dispose of them as instructed.
RESULTS
In this space construct a table to record your measurements, possibly draw a graph and note
any difficulties you encountered with the materials or techniques and how you will resolve
them in Part B.
Part B
‘Design your own’ Practical
At the discretion of your teacher you may now be required to use the technique and
knowledge from Part A to Design, Conduct and Report on your own practical investigation of
this or another factor that may affect diffusion in agar or osmosis in potatoes.
You will need to:
 prepare an Abstract after you have finished your experiment
 write an Introduction
 List the Materials you will need and explain the Method you will use
 Record your Results in whatever form(s) you think appropriate
 Write a Discussion of your method and results
 State a Conclusion about the validity or otherwise of your hypothesis
You may refer to the Assessment Table on the last page for more detail about the relevant
Intended Student Learnings and suggested marks for each of these headings.
C4 - Student Performance against the Assessment Design Criteria
and Performance Standards
Name of student
Class
Knowledge &
Understanding
Application
Analysis and
Evaluation
Investigation
Specific features
I1
Design of biological investigations.
I3
Manipulation of apparatus and technological
tools to implement safe and ethical investigation
procedures.
I4
The obtaining, recording, and display of
findings of investigations using appropriate
conventions and formats.
AE1
Analysis of data and concepts and their
connections, to formulate conclusions and make
relevant predictions.
AE2
Evaluation of procedures, with suggestions for
improvement.
A2
Use of appropriate biological terms,
conventions, formulae, and equations.
A3
Demonstration of skills in individual and
collaborative work.
KU1
Demonstration of knowledge and
understanding of biological concepts.
KU3
Communication of knowledge and
understanding of biology in different formats
Comment/evidence with
regard to meeting
Performance Standards
Grade
© S.T.A.R. 2014. Unauthorized copying prohibited.
Other comments:
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C4 - Student achievement against specific Report headings
Report headings and Intended Student Learnings
A.
In their laboratory work and their written report, students should provide evidence of how well they have
achieved the following student learnings:
D.
C.
Abstract
KU3

Write a (concise) report of an investigation that includes a description of its purpose and procedure, results,
analysis, interpretation, and conclusions.
Introduction
I1




State the purpose of the investigation or experiment.
State the key ideas or background biology
State a testable hypothesis
Formulate a question for an investigation
 Suggest possible investigations to test the question
Materials and Methods
I1
I3,4







Identify and classify variables (independent and dependent)
Identify any factors that are deliberately held constant
Design and carry out investigations or experiments
Describe the steps of an investigation or procedure
Draw or interpret diagrams of the apparatus
Collect data using measurements that can be reproduced consistently.
Select an instrument of appropriate resolution
Results
I4







Record and analyse observations
Use measurements to an appropriate number of significant figures
Distinguish between quantitative and qualitative evidence.
record careful and honest observations
use a table to present data
Plot a graph of dependent variable versus independent variable
Draw a line of best fit through a series of points on a graph
Discussion
AE1
AE2










AE1
Identify sources of errors and uncertainty
Distinguish between random and systematic errors
Explain the importance of increasing the number of samples
Explain the importance of repeating a practical investigation
Determine which of two or more sets of measurements is most reliable
Use averages or graphing as a means of detecting or minimising random errors.
State which result of two or more experiments is most accurate
Describe a pattern observed in the results
Using the scatter in the graphs to compare the random errors.
Analyse and evaluate information, interpret results and suggest improvements
Conclusion

Write a conclusion that is based on the results of an investigation
Application skills
A2


A3






Use biological terminology, conventions, and symbols
Use concise language and graphics to present information.
Work ethically with animals
Report accurately and honestly
Recognise hazards and work safely
Demonstrate initiative and focused work skills
Negotiate procedures with the other members of the team
Perform the role of a team member.
Communication
KU1
KU3


Demonstrate knowledge and understanding of biological concepts
Communication of knowledge and understanding of biology
© S.T.A.R. 2014. Unauthorized copying prohibited.
Name of student
A
Class
Practical
Analysis and Evaluation
Application
Knowledge and Understanding
Designs a logical, coherent, and detailed biological investigation.
Critically and systematically analyses data and
their connections with concepts, to formulate
logical and perceptive conclusions and make
relevant predictions.
Applies biological concepts and evidence from
investigations to suggest solutions to complex
problems in new and familiar contexts.
Consistently demonstrates a deep and broad knowledge and
understanding of a range of biological concepts.
Critically and logically selects and consistently and appropriately acknowledges information
about biology and issues in biology from a range of sources.
Manipulates apparatus and technological tools carefully and highly effectively to implement
well-organised safe and ethical investigation procedures.
Critically and logically evaluates procedures and
suggests a range of appropriate improvements.
Designs a well-considered and clear biological investigation.
Uses clear and well-organised analytical skills to
examine connections between data, concepts,
and issues in biology.
Applies biological concepts and evidence from
investigations to suggest solutions to problems
in new and familiar contexts.
Evaluates procedures and suggests some
appropriate improvements.
Uses appropriate biological terms, conventions,
formulae, and equations effectively.
Uses mostly logical analysis and evaluation of
data and other evidence to formulate consistent
and relevant conclusions.
Applies mostly constructive and focused
individual and collaborative work skills.
Uses generally organised analytical skills to
examine connections between data, concepts,
and issues in biology.
Applies biological concepts and evidence from
investigations to suggest some solutions to
basic problems in new or familiar contexts.
Evaluates some procedures in biology and
suggests some improvements that are generally
appropriate.
Uses generally appropriate biological terms,
conventions, formulae, and equations with
some general effectiveness.
Obtains, records, and displays findings of investigations using generally appropriate
conventions and formats with some errors but generally accurately and effectively.
Analyses and evaluates data and other evidence
to formulate simple and generally relevant
conclusions.
Applies generally constructive individual and
collaborative work skills.
Prepares the outline of a biological investigation.
Describes basic connections between some data,
concepts, and issues in biology.
Applies some evidence to describe some basic
problems and identify one or more simple
solutions, in familiar contexts.
Logically selects and appropriately acknowledges information about biology and issues in
biology from different sources.
Manipulates apparatus and technological tools carefully and mostly effectively to implement
organised safe and ethical investigation procedures.
Obtains, records, and displays findings of investigations using appropriate conventions and
formats mostly accurately and effectively.
C
Designs a considered and generally clear biological investigation.
Selects with some focus, and mostly appropriately acknowledges, information about biology
and issues in biology from different sources.
Manipulates apparatus and technological tools generally carefully and effectively to
implement safe and ethical investigation procedures.
D
Selects and may partly acknowledge one or more sources of information about biology or an
issue in biology.
Uses apparatus and technological tools with inconsistent care and effectiveness and
attempts to implement safe and ethical investigation procedures.
Obtains, records, and displays findings of investigations using conventions and formats
inconsistently, with occasional accuracy and effectiveness.
E
Uses appropriate biological terms, conventions,
formulae, and equations highly effectively.
Demonstrates initiative in applying constructive
and focused individual and collaborative work
skills.
Obtains, records, and displays findings of investigations using appropriate conventions and
formats accurately and highly effectively.
B
Date
Investigation
Identifies a simple procedure for a biological investigation.
For some procedures, identifies improvements
that may be made.
Attempts to extract meaning from data and other
observations and to formulate a simple conclusion
that may be relevant.
Attempts to use some biological terms,
conventions, formulae, and equations that may
be appropriate.
Uses knowledge of biology perceptively and logically to
understand and explain social or environmental issues.
Uses a variety of formats to communicate knowledge and
understanding of biology coherently and highly effectively.
Demonstrates some depth and breadth of knowledge and
understanding of a range of biological concepts.
Uses knowledge of biology logically to understand and explain
social or environmental issues.
Uses a variety of formats to communicate knowledge and
understanding of biology coherently and effectively.
Demonstrates knowledge and understanding of a general range of
biological concepts.
Uses knowledge of biology with some logic to understand and
explain one or more social or environmental issues.
Uses different formats to communicate knowledge and
understanding of biology with some general effectiveness.
Demonstrates some basic knowledge and partial understanding of
biological concepts.
Identifies and explains some biological information that is relevant
to one or more social or environmental issues.
Communicates basic information to others using one or more
formats.
Attempts individual work inconsistently, and
contributes superficially to aspects of
collaborative work.
Acknowledges that connections exist between
data, concepts, and/or issues in biology.
Identifies a basic problem and attempts to
identify a solution in a familiar context.
Demonstrates some limited recognition and awareness of
biological concepts.
Acknowledges the need for improvements in one
or more procedures.
Uses some biological terms or formulae.
Shows an emerging understanding that some biological
information is relevant to social or environmental issues.
Identifies a source of information about biology or an issue in biology.
Attempts to use apparatus and technological tools with limited effectiveness or attention to
safe or ethical investigation procedures.
Attempts to record and display some descriptive information about an investigation, with
limited accuracy or effectiveness.
Attempts to organise some limited data or
observations.
Shows emerging skills in individual and
collaborative work.
Attempts to communicate information about biology.
Performance standards (© SACE Board 2011)