Triple Science case study
Biology
Name of centre
Bodmin College: a Specialist Science College
Name of teacher
Katie Block
Subject
Biology
Specification
Edexcel
Brief description of case study
Students use practical and enquiry skills to collect data in order to find out whether
starch is always found in leaves.
Disclaimer
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Signed: K Block
Date: 26 September 2008
Page 1 of 9
Topic
Range and content
Storage of starch in plants and the use of starch Æ glucose in respiration
How Science Works
1.2 Practical and enquiry skills
Pupils should be taught to:
a plan to test a scientific idea, answer a scientific question, or solve a scientific problem
b collect data from primary or secondary sources, including using ICT sources and tools
c work accurately and safely, individually and with others, when collecting
first-hand data
Extract from Key stage 4 programme of study: http://curriculum.qca.org.uk/key-stages-3-and4/subjects/science/keystage4/index.aspx
Context of the lesson within scheme of learning
In previous lessons students investigated plant cells and photosynthesis to make
predictions about where starch may be found in a plant. They drew and labelled
diagrams and considered the function of all of the parts. In this lesson students use their
knowledge to make a prediction about starch and where it might be found in plants, and
then carry out an investigation to answer their question.
Learning objectives
•
Apply knowledge about plant cells and photosynthesis to predict where starch may
be found in a plant.
•
Work safely and accurately to obtain reliable results to answer the question ‘Where
will starch be found in plants?’
Learning outcomes
Students will be able to:
•
reflect on their knowledge of plant cells, photosynthesis and respiration to predict
where starch will be found in a plant
•
work safely to gain accurate results about where starch is present
•
discuss and develop an explanation for their results.
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Key concepts/knowledge/skills/understanding addressed by this lesson
Plants photosynthesise to produce glucose, which is converted into starch.
Plants kept in the dark de-starch, in order to use glucose for respiration.
Plants kept in the light should have starch present in their leaves.
Safe use of practical equipment.
Curriculum opportunities
X
a Research, experiment, discuss and develop arguments.
b Pursue an independent enquiry into an aspect of science of personal interest.
c Use real-life examples as a basis for finding out about science.
d Study science in local, national and global contexts, and appreciate the
connections between these.
e Experience science outside the school environment, including in the workplace,
where possible.
f Use creativity and innovation in science, and appreciate their importance in
enterprise.
g Recognise the importance of sustainability in scientific and technological
developments.
h Explore contemporary and historical scientific developments and how they
have been communicated.
Other curriculum opportunity from specification (give details):
Extract from Key stage 3 programme of study: http://curriculum.qca.org.uk/key-stages-3-and4/subjects/science/keystage3/index.aspx?return=/key-stages-3-and-4/subjects/science/index.aspx
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How Science Works progression in this lesson
The aspect of How Science Works being developed is:
• Enquiry skills: collecting first-hand data to answer a scientific question
•
Using investigative approaches: assessing risk and working safely
How are students making progress?
• This practical includes the use of ethanol and naked flames, and is potentially
dangerous.
• Students are asked to use and apply risk assessments in carrying out this practical.
They will include an explanation about how the risks have been identified and
controlled in their recording of the practical.
Assessment opportunities in this lesson
An understanding of photosynthesis and respiration will be assessed via questioning,
particularly when students discover no starch in the leaves of the plant that has been
kept in the dark.
Practical skills in risk assessment, working safely and accuracy of working can be
assessed throughout the investigation.
How ICT is used to support learning
A data projector is used to display information during the practical to support students.
Overview of lesson
Lesson title: Kept in the dark
Approximate length of lesson: 80–85 minutes
Starter
Individual activity: Choose 10 foods, link food back to the plant from which it
originated, identify the main nutrient and state the place of origin
Main
1 In small groups students create a concept map of the uses of plants
and discuss
2 Introduce the question ‘Do you expect plant leaves to contain starch?’
Discuss. Students predict where they will find starch present
3 Introduce the practical. Students carry out a risk assessment
4 Students complete the practical
Plenary
Page 4 of 9
Discuss findings and answer the original question. Students suggest
reasons for their results
Lesson in detail
Lesson title
Kept in the dark
Lesson structure
Learning
episode and
timing
Detail
Starter
(10 minutes)
Project partially filled simple table on to the whiteboard.
For example:
Food
Plant
Nutrient
(mainly)
Place of
origin
Peanut butter Peanut
Fat/protein
Brazil
Chips
Starch
UK
Potato
Students should complete the table for 10 foods, identifying the plant
the food is linked to, what the main nutrient is that it contains, and
where the plant comes from.
Main 1
(10 minutes)
Students should work as small groups to categorise the ways in
which plants are used and construct a concept map. The ideas are
discussed and shared as a class.
Main 2
(10–15
minutes)
Introduce the make-up of plants by a series of questions.
• What is made in photosynthesis and how do we know?
•
What do plants use for energy and how do we know?
•
Which parts of the plant are most likely to have starch present?
Introduce the key question: ‘Do you expect plant leaves to contain
starch?’
Discuss in pairs and then in groups of four. Feed back to class.
Ask the students to make a justified prediction about what they will
find, referring to ideas about respiration and photosynthesis.
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Main 3
(10 minutes)
Introduce the practical work.
Ask students to carry out a risk assessment of the practical before
they begin.*
•
Students should set up a water bath and then turn off the gas
once the water is boiling.
•
Place a leaf from the plant kept in the light into the boiling water
for 1 minute.
•
Remove the leaf and dry it using paper towel. Then place the leaf
in a boiling tube with ethanol. Leave the leaf in the boiling tube
with the ethanol in the water bath for 10 minutes.
•
Remove the leaf and rinse it in the warm water. Dry the leaf using
paper towel, place it on a tile and add a few drops of iodine
solution.
•
Repeat for a leaf from a plant that has been kept in the dark for
24–48 hours.
*It is essential that students do not use ethanol when there are
naked flames in the room. I suggest that the teacher keeps the
ethanol and does not distribute it until all flames are extinguished, as
different groups are likely to work at different rates.
Main 4
(30 minutes)
Students complete the practical investigation, considering safety as
they work. During the 10-minute wait for the leaves to soak, students
draw a diagram in their books and annotate it with details of what is
happening. For example, ‘The boiling water helps to break down the
plant cell walls; the ethanol causes the chlorophyll to be extracted
from the leaf.’
When the practical is complete, students draw diagrams of the leaf
from the plant that was kept in the light and the one from the
de-starched plant.
Plenary
(10 minutes)
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Discuss whether the students’ findings are consistent with their
prediction.
In the light of the evidence collected in this practical, students are
asked to write an explanation of their results, using key ideas about
photosynthesis and respiration.
Reflection and evaluation
Starter
Students enjoyed completing the table by choosing the foods they ate regularly and
linking them to plants. There was some discussion and reflection on where their food
comes from. Students seemed knowledgeable about what types of foods were produced
locally.
Main
Main 1: The concept mapping was a useful activity to find out what students knew
already and it generated further discussion about plants and why they are so important.
Students carried out discussions in small groups. There were many different ideas and
these were shared with the whole class.
Main 2: The introduction of the main concept of the lesson provided the students with
the opportunity to reflect on what they could remember about photosynthesis and
respiration. Questions about starch and leaves were generated by students and other
students tried to answer them. Students all thought that the leaves would contain starch,
and few predicted that the leaves in the dark would be different. We did not discuss this
very much; students tended to construct fairly ‘shallow’ explanations about why they
predicted that all the leaves would contain starch, and struggled to make the links
between photosynthesis and respiration that could affect the result.
Main 3: The practical investigation was introduced. Students were already familiar with
the apparatus. I chose to use an enquiry inductive approach through this practical work
to help to reinforce the point about how photosynthesis and respiration are inter-related.
I felt that this would help the students to remember it and really develop their thinking.
Main 4: The students dealt effectively with the practical and were clear about how to
minimise the risks. It was useful for them to have a task to complete during the ‘waiting
time’, and there were useful conversations during this time as some students began to
revise their thinking in the light of the results obtained.
Plenary
The discussion following the practical was the most valuable. It gave the students a
chance to reflect on their findings and try to come up with a conclusion that matched the
results they had obtained. We discussed why there was no starch found in the leaves
that had been in the dark, and all students could explain that there could have been no
photosynthesis in these leaves. Most students could go further and explain that
respiration was still occurring in the leaves of the plant stored in the dark and that the
starch would have been used up by this process.
Some students suggested investigations to explore this further. One example was to
investigate the amount of starch in leaves from plants that were stored in the dark for
differing amounts of time between 2 and 24 hours, and to find out where in the leaf the
starch was used from first.
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Risk assessment
Main hazards identified
Who would
be affected?
Control measures to reduce risk
Ethanol near naked
flames
Students and
staff
No naked flames while the ethanol is
being used
Ethanol or iodine in eye
Students
Wear eye protection
Broken glass
Students
Take care when using glassware
Report any breakages immediately
Burns from Bunsen
burner or hot water
Students
Take care and use a test tube holder
for test tubes
Use tweezers to remove the leaves
from the hot water
Opportunities to take this further
Students will go on to develop their understanding and skill at collecting and interpreting
primary evidence further by devising a series of experiments to investigate limiting
factors in photosynthesis.
Page 8 of 9
Resources
Data projector
Two plants (we used geraniums), one kept in the light and one kept in a cupboard for
24–48 hours. You may need more plants, depending on the size of the groups that will
work with a leaf
Ethanol
Glassware
Tweezers
Test tube holders
Stopclocks
Bunsen burners
Iodine
White tiles
Dropping pipettes
Paper towels
A further investigation into starch in variegated leaves can be found on the Science and
Plants for Schools website at
www-saps.plantsci.cam.ac.uk/worksheets/activ/prac5.htm
Bibliography
National Strategies Framework for Teaching Secondary Science: Overview and Learning
Objectives (2008) www.standards.dcsf.gov.uk/secondary/frameworks
Science Programme of Study for KS3 (Extract from National Curriculum) (QCA 2008)
http://curriculum.qca.org.uk/key-stages-3-and4/subjects/science/keystage3/index.aspx?return=/key-stages-3-and4/subjects/science/index.aspx
Science Programme of Study for KS4 (QCA 2008) http://curriculum.qca.org.uk/keystages-3-and-4/subjects/science/keystage4/index.aspx
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