What determines the number of spines
on a holly leaf?
Technical & Teaching Notes
Type and purpose of activity
This experiment can be used to:
- develop knowledge and understanding of structural defence mechanisms in plants
- develop problem solving skills and in particular Outcome 2 PC:
- (b) Information is accurately processed, using calculations where appropriate.
Introduction and context
This experiment involves minimal laboratory work but provides a good opportunity to collect data and process it appropriately.
A tall unpruned holly tree is required to obtain the initial specimens. Small branches could be cut at various heights and labelled appropriately. Alternatively leaves could be dried and put in sealed, labelled polythene bags. Either way, the leaves should last for several years. The Royal Botanic Garden in Edinburgh (Tel. 0131 552 7171) is a possible source of holly leaves.
Although it is generally accepted that the higher up the leaves the less spines they will have, the relationship is not always straightforward. The number of spines produced varies from one variety to another. Also, constant pruning e.g. to produce a hedge, appears to increase spine production.
References
Peterkin G.F. & Lloyd P.S. (1967) Ilex aquifolium, Biological Flora of the British Isles, 108, 841-858.
Dormer K.J. & Hucker J. (1957) New Series Annual of Botany, 21 (83), 385-398.
Classroom management
If enough leaves are obtained, students could work individually.
The leaves from different heights must, of course, be clearly labelled in such a way that they can be easily examined for spines but not easily mixed up with leaves from other heights.
Supply of materials
In order to satisfy the core skill in problem solving, students will be required to 'identify and obtain resources' required for themselves. It is therefore not appropriate to provide all equipment and materials in e.g. a tray system for each student/group. Normal laboratory apparatus should not be made available in kits but should generally be available in the laboratory. Trays could be provided containing one type of specialist equipment or materials.
Extension work
- Do unshaded leaves produce the same number of spines as shaded ones?
- Are the number of spines dependent on the time of year the leaf was formed?
- Do longer leaves have more spines?
- Are the number of spines on each side of a leaf the same on average?
- Are the length of spines related to the amount of browsing or pruning a stem receives?
- Is the number of spines related to the sex of the tree? (Holly is either male or female)
TECHNICAL GUIDE
Materials required
Materials required by each student/group:
- A minimum of 10 holly leaves of about the same size, cut from a range of heights above the ground (e.g. 0.5m, 1.5m, 2.5m, 3.5m and 4.5m). The leaves may still be attached to the branch which is clearly labelled.
- Alternatively, the leaves can be detached, dried and put in sealed, labelled polythene bags.
- If large numbers of leaves are involved then a counter will prove useful.
- No other preparation is required.
Supply of materials
It is not appropriate to provide all equipment and materials in e.g. a tray system for each student/group. Equipment and materials should be supplied in a way that students have to identify and obtain resources. Normal laboratory apparatus should not be made available in kits but should generally be available in the laboratory. Trays could be provided containing one type of specialist equipment or materials.
PREPARING FOR THE ACTIVITY
Read through the Student Activity Guide and consider the following questions.
Analysis of activity
- What is the aim of the activity?
- What is being varied in the activity?
- What work was previously carried out to obtain the leaves?
- What measurements are you going to make?
- Getting organised for experimental work
- Your teacher/lecturer may ask you to do this activity individually. If you are part of a group, decide how the activity will be managed by allocating tasks to each member. It is important that you play an active part in collecting results.
Recording of Data
Prepare a table to record your results. You should use a ruler, correct headings and appropriate units.
Evaluation
Consider the following:
- Why the number of spines on a number of leaves were counted at each chosen height?
- Were the heights chosen appropriate to reach an accurate conclusion?
- Were the leaves used chosen at random? Why might this be important?
- Which possible variables were controlled? Why was it important to control them?
- Which variables in the leaves has it not been possible to control? How important do you think these variables are?
STUDENT ACTIVITY GUIDE
Background Information
- Holly leaves are capable of producing spines. This investigation is being carried out to see if there is a relationship between the number of spines on a leaf and its height above the ground.
- To do this, small branches of holly have been cut at different heights from a large unpruned holly tree. You will randomly choose a number of leaves from each height and calculate the average number of spines that leaves from each chosen height will have.
Equipment and materials
Materials required by each student/group
Holly leaves from a range of heights. The height at which each branch/batch of leaves was obtained should be clearly noted.
Instructions
- Collect branches/batches of holly leaves. The height above ground at which each branch/batch of leaves was obtained should be clearly noted.
- Select, say, 10 leaves at random from one branch/batch, count the number of spines on each leaf and calculate the average number of spines per leaf in each batch.
- Note your results in a suitable table.
- Repeat this procedure with each available branch/batch of leaves.
- Present your results as a graph with suitable scales and axes with quantities and units
Science & Plants for Schools:
The number of spines on a holly leaf: p. 1
This document may be photocopied for educational use in any institution taking part in the SAPS programme.
It may not be photocopied for any other purpose. Revised 2012.