COAS Biology 2 Teacher Resources Original material © Cambridge University Press 2009 2
12 Practical guidance
These practicals are included to give ideas for activities to support OCR A-level Biology
Units F215 [5.3.1: Ecosystems] and F216: Practical skills in Biology 2.
The practicals chosen relate closely to the learning outcomes, and may be used to develop
students’ practical skills in preparation for practical assessment.
However, they are not intended to form a complete practical course.
Safety
Although great care has been taken in checking the accuracy of the information provided, Cambridge University Press shall not be responsible for any errors, omissions or inaccuracies.
Teachers and technicians should always follow their school and departmental safety policies. You must ensure that you consult your employer’s model risk assessments and modify them as appropriate to meet local circumstances before starting any practical work. Risk assessments will depend on your own skills and experience, and the facilities available to you. Everyone is responsible for his or her own safety and for the safety of others.
The practicals should be carried out by teachers themselves before they are presented to students. Additional notes relating to each activity in this chapter are given below. These include, where appropriate, references to Hazcards and the CLEAPSS Laboratory Handbook, both of which provide model risk assessments and are available to CLEAPSS members.
The notes given below also contain some background information and advice, but in no way should they be regarded as risk assessments. Teachers and technicians are advised to read the relevant sections of the CLEAPSS Laboratory Handbook for further advice and guidance. The Handbook includes a great deal of useful background information and is an excellent source of references.
Practical 1: Investigating the distribution of plants along an environmental gradient, using a transect
The nature of the area to be sampled should be considered in the risk assessment for this investigation. Teachers should identify a suitable field site, such as a trampled path though the school field, or a gradient from dry to marshy ground. Keys or identification sheets should be prepared that show all the common plant species found in the area. A simple identification sheet can be made by photocopying leaves of the common species. The names can then be written onto the photocopy paper, and the sheets laminated. The Field Studies Council also publishes identification charts. See
www.field-studies-council.org/publications/foldout.aspx
Students could extend the investigation by measuring factors which might affect the plant distribution, such as the degree of soil compaction, or the soil water content. Compaction can be measured using a penetrometer – a simple instrument that measures the depth a spike is driven into the ground by a standard force. The percentage water content can be measured by heating a known mass of soil in an oven at 100 °C until the weight remains constant.
A point quadrat is easier to use than a frame (area) quadrat, avoiding subjective estimations of percentage cover, or difficulties in counting numbers of plants in a field. However, the exercise could be carried out with a frame quadrat if required. (See Biology 1 Teacher Resources CD ROM, Chapter 12, Practicals 1 and 2 for instructions on use of frame quadrats.)
The distribution of each species across the transect can be plotted as a histogram (Figure 12.2).
Figure 12.2 Histogram showing the distribution of a species across a transect.
The histograms should be arranged vertically down the page, one above the other, for comparison between species.
Alternatively, the distributions can be plotted as kite diagrams. These are normally used for rocky shore transects, although there is no reason why they can’t be used for other habitats. The counts of ‘hits’ on the y-axis should be an ordinal variable, for example, an abundance scale of ranks, such as an ‘ACFOR’ scale (Abundant, Common, Frequent, Occasional, Rare).
The ‘rules’ for plotting a kite diagram are shown in Figure 12.3.
Figure 12.3 Kite diagram showing the distribution of a species across a transect.
Practical 2: Investigating the effect of water velocity on the distribution of swimming mayfly nymphs in a stream
The nature of the area to be sampled should be considered in the risk assessment for this investigation. Students should be warned about diseases caused by waterborne pathogens, such as Weil’s disease.
This is a common investigation carried out on field trips and at Field Centres. Swimming mayfly nymphs are found in greater abundance in faster flowing parts of a stream, where their methods of locomotion, gas exchange and nutrition are all well adapted to the faster flow rate. However, if a clean, fast flowing stream is available near the school or college, the sampling can be carried out there. A full risk assessment should be undertaken.
Oxygen meters are notoriously unreliable unless carefully calibrated, and unlikely to show a great deal of difference in the oxygen concentration of different parts of the stream, but they are worth trying out if available.
Identification sheets and keys can be purchased from the Field Studies Council.
COAS Biology 2 Teacher Resources Original material © Cambridge University Press 2009 2