Energy transfer in ecosystems
Most of the sugars synthesised by plants through photosynthesis are used by the plant as respiratory substrates. The rest are used to make other groups of biological molecules. These biological molecules form the biomass of the plants.
In any ecosystem the biomass transfers between trophic levels can be measured and the efficiency of biomass transfers between trophic levels can be measured.
Biomass can be measured in terms of mass of carbon or dry mass of tissue per given area per given time. The chemical energy store in dry biomass can be estimated using calorimetry.
Human activities, such as agriculture, can manipulate the transfer of biomass through ecosystems.
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Science in the Environment Pack 2: Living Systems *suitable for home teaching*
In this comprehensive resource, from the University of York Science Education Group, there is a specific section of the pack on Ecosystems and energy- section 2A2.1.
The pack was originally intended as self study/independent learning material. It would be suitable for A level students to be asked to work through the ten pages of section 2A2.1. They could read through the material, making notes, and answering the questions throughout the text and at the end of the text. The level of detail is high end GCSE and the numerical requirements will challenge some A level students and support development of mathematical skills, even if the energy production equation is not a requirement of A level specifications.
Section 2A2.2 goes into detail about thermodynamics and is a step too far in terms of the requirements for A level biology.
Energy Transfer *suitable for home teaching*
This article from the Catalyst magazine focuses on food chains. It looks at photosynthesis and the loss of energy from plants to animals throughout the food chain. How this limits the number of animals that can survive on the energy fixed by a patch of vegetation is explained.
Although originally written for GCSE level students, the article does contain a good amount of detail on the measurement of energy transfer, and would make good pre-topic reading for A level biologists.
The questions embedded within the text of the article, such as estimate the area of territory a cat would need if it had to fend for itself, would make for a good starter activity.
Ecological Energetics
This is a old publication, but its importance should not be under estimated! This booklet provides a comprehensive study of the topic of energy transfer in ecosystems, and would make excellent reading for any teacher who needs to refresh their subject knowledge on this topic before delivering it to students.
This booklet contains sections that look at topics on:
• energy, energy conversion, conservation and utilization
• food webs and trophic levels
• grazers and detritus feeders in the ecosystem
• energy flow at the population level
• humans and balanced ecosystems
There are some very useful illustrations and data within the booklet which could be used with students. On page six, for example, fig1.1 illustrating the fate of solar energy would be an interesting study. Students could be given the following questions to consider: what units are used? Are these the units we use today? How were these measurements made? These questions could provide for the start of a discussion on this topic.
Practical Guide 7: Ecology
Published by the Nuffield Foundation this Revised Nuffield Advanced Biology Practical Guide is a lengthy and comprehensive guide to a range of possible practical activities related to ecology.
For energy transfer in ecosystems, the most useful chapter is chapter 29, which can be found from page 51 onwards.
There are two practical activities described to investigate energy transfer in ecosystems. One of these requires an aquarium, which may be something worth considering at the start of term as there are a number of other ways this can be used to support A level (for example, classification, microscope work etc).
A level students could complete the practical activity using an aquarium or could be given prepared slides and figures. There are a range of questions that can then be answered linked to this practical activity which provide a good level of challenge.
Similarly the practical activity on energy requirements of a stick insect could also be completed and the questions answered, again developing student’s practical competency, but also their ability to answer questions related to a practical activity.
