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Delivery guides are designed to represent a body of knowledge about teaching a particular topic and contain:
- Content: A clear outline of the content covered by the delivery guide
- Thinking Conceptually: Expert guidance on the key concepts involved, common difficulties students may have, approaches to teaching that can help students understand these concepts and how this topic links conceptually to other areas of the subject
- Thinking Contextually: A range of suggested teaching activities using a variety of themes so that different activities can be selected which best suit particular classes, learning styles or teaching approaches.
Content (from A-level)
|(a)||ecosystems, which range in size, are dynamic and are influenced by both biotic and abiotic factors||To include reference to a variety of ecosystems of different sizes (e.g. a rock pool, a playing field, a large tree) and named examples of biotic and abiotic factors.|
|(b)||biomass transfers through ecosystems||To include how biomass transfers between trophic levels can be measured
the efficiency of biomass transfers between trophic levels
how human activities can manipulate the transfer of biomass through ecosystems.
M0.1, M0.2, M0.3, M0.4, M1.1, M1.3, M1.6
|(c)||recycling within ecosystems||To include the role of decomposers and the roles of microorganisms in recycling nitrogen within ecosystems (including Nitrosomonas, Nitrobacter, Azotobacter and Rhizobium)
the importance of the carbon cycle to include the role of organisms (decomposition, respiration and photosynthesis) and physical and chemical effects in the cycling of carbon within ecosystems.
|(d)||the process of primary succession in the development of an ecosystem||To include succession from pioneer species to a climax community
|(e)||(i) how the distribution and abundance of organisms in an ecosystem can be measured
(ii) the use of sampling and recording methods to determine the distribution and abundance of organisms in a variety of ecosystems.
|M1.3, M1.4, M1.5, M1.7, M1.9, M1.10, M3.1, M3.2|
HSW7, HSW9, HSW12
An excellent collection of ecological essays: Why Big Fierce Animals Are Rare by Paul Colinvaux (originally published in 1978, Princeton University Press) includes a chapter on efficiency.
This introduces the concept of measuring efficiency quantitatively and could be expanded through use of comprehension questions into a homework task.
The original 1926 research paper by E. N. Transeau, cited in Colinvaux’s book, is available for anyone keen to engage with the primary data. Once you get into it the logic and accountancy-style approach to living processes is fascinating, but it is all words and numbers.
Approaches to teaching the content
Being the second ecological topic in the teaching sequence, it’s important to draw upon the understanding students gained from Biodiversity (as part of Module 4) and build upon this to explore the interactions and processes that make natural environments so dynamic.
Although the three ecology topics could be taught together, Ecosystems has a whole-organism focus that naturally encourages the ‘synoptic’ links which will be prevalent in the unified biology paper. Students have greater self-confidence with such material later on in the course, as they have better learnt to successfully integrate detail into a coherent argument.
With this in mind, it’s a good idea to start with sampling techniques; learning outcome 6.3.1(e) and then consider environmental factors (abiotic & biotic) that might explain patterns seen. Pond dipping and recording wet mass of invertebrates then allows practical experience of measuring efficiency, before examining succession and finally nutrient cycling.
Common misconceptions or difficulties students may have
Students’ main difficulty with sampling techniques arises because there are limited opportunities to collect data and develop greater confidence with important terms and ideas. Extracting the right figures (from exam questions) to calculate efficiency can be daunting, so determining biomass from Pond invertebrates provides hands-on experience to start the process. Ideas like succession that involve temporal change can be difficult, because transects are used to record such patterns, but with distance and so confusion sets in. The nitrogen cycle, with subtly different details to the role of each organism and the sheer number of component parts, often requires the concept to be approached in a number of ways to reinforce learning outcomes and better secure understanding.
Conceptual links to other areas of the specification – useful ways to approach this topic to set students up for topics later in the course
Sampling strategies can build upon the simple use of a quadrat in 4.2.1(b) to include interrupted belt transects which record plant succession. Identifying abiotic & biotic factors and the process of succession engenders greater confidence with 6.3.2(c & d) as change over time explains the need for active management with much conservation work.
Bucket sample of pond invertebrates brought into class. Fold out charts (from FSC) or other dichotomous keys used to identify and collect all individuals of same type into labelled petri dishes. Best if students work in small groups to do this, otherwise carnivores might start consuming each other.
When all organisms identified, wet biomass recorded by transferring each group of animals in turn to a tea strainer. Record mass of strainer + animals and then strainer on its own.
Two contrasting areas of nettles (in shade and brightly lit) chosen and students measure leaf length (from leaf apex to junction with petiole) of one plant from each area. Leaves are in opposite pairs on stem, so always choose left hand leaf of 3rd pair from stem apex. Discussion allows group to see why these details are important to standardise data collection but are they taking a representative sample of population?
In class, data can be entered into excel spreadsheet to calculate mean and SD. Bar chart (with error bars) can be plotted to visualise impact of light upon plant growth. Nettles chosen as one example of distinctive plant but others could be used e.g. Lesser Celandine or Dog’s Mercury.
Students (working in small groups) use the various headings on the printed sheet (Learner resource 2) to create a copy of the Nitrogen cycle on A3 paper.
This could then be checked for accuracy before each group set about annotating the cycle to demonstrate their knowledge of processes like nitrification and the environmental conditions required for each process to operate.
Finally each group could attempt to add extra labels that explain how agricultural fertiliser is produced and then how its application can lead to eutrophication.
6.3.1 Ecosystems is focused very clearly upon whole organisms and the diverse ways in which they interact with their environments. Understanding can only be secured if students are given an opportunity to experience some of these organisms and the practical considerations that often arise from the simplest ecological investigation as you try to collect representative data that can be reliably compared with other data sets. Such activities relate directly to PAG3, PAG11 and PAG12. Any opportunity to demonstrate the link between sampling strategy and the statistical analysis that is then possible will also help secure a better appreciation of the different characteristics of each test and improve student confidence in knowing when each test should be used.
Ecology is a naturally synoptic subject and it’s often useful to use card-based activities like Learner resource 2 ‘Building a Nitrogen cycle’ as ways of identifying such links and extending the learning experience through such a ‘holistic’ activity.
Fun elements can be introduced through parlour games like ’20 questions’ and ‘Pictionary’ whilst all the time revisiting key terms.
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