Soils, farming and the activities of living things
Cartoon copyright belongs to Oregon State University/Forage Information System, Reference Materials: Pictures (no date) http://forages.oregonstate.edu/nfgc/images/cartoon.jpg
Discusses decomposition
- Full explanation (very difficult): explains the full cycle (role of decomposers in soil included + closes the cycle)
- Partial explanation (easy): has some parts of the decomposition cycle (doesn't include microbes)
Discusses photosynthesis
- Full explanation (very diffilcult): explains process, including energy from the sun is used to make food for the plant. Other elements of the process may also be included, e.g., role of carbon dioxide, chlorophyll, etc.
- Partial explanation (moderate): links photosynthesis to the sun.
Communicating in science
This task asks students to interpret the science messages in a cartoon and convert them to explanatory text. The words in the text box are intended to ensure students begin the task with an idea of the sort of focus they might be expected to take. Science ideas are often conveyed visually in mass media so "reading" the intended messages in these is an important skill to develop if science learning is going to be of use in the years beyond school.
Science understandings
The task asks students to draw together understandings from two different contextual strands – Living World and Planet Earth. This is an opportunity to show how science problems in the real world don't fit into clearly defined subject areas.
Communicating in science
The task requires students to explain a cycle – indicated as such by the arrows. While many students could convey relevant ideas about some parts of the cycle, just over 10% percent gave responses that indicated a full set of steps (i.e. the cycle was "closed" at its beginning point). As this example shows, we were not looking for elaborate explanations:
The sun produces heat and light. The grass photosynthesises light into nutrients necessary for survival. The cow gets its nutrients from the grass and then excretes it out onto the grass. The grass can get more nutrients. There are also bacteria that are invisible to the naked eye that decompose the cow dung. This dung is recycled to make the dirt rich in the necessary nutrients.
As in other ARB tasks, some students showed confusion about what the arrows were intended to symbolise (2 percent). Note the evidence of confusion about the nature of photosynthesis in both the following examples.
The invisible gravity also makes things decompose which are the vectors that are pointing to the poo. Then [there is] another vector under the ground and one curving and pointing to the top of the grass. Which means photosynthesis is called recycling.
The sun is shining down on the grass. The grass has water on it. The sun takes it up with its heat and the clouds take it in and uses it as rain. This is called photosynthesis.
Science understandings
Like another recent ARB task that asked students to interpret ideas conveyed visually (Illustrating the enhanced greenhouse effect), this task revealed several misconceptions.These are listed in the order of frequency, and an example given. (Note that some students may simply have expressed an idea in a way that was open to misinterpretation – that is, the problem was in the expression rather than the conception. Further questioning would establish the difference.)
- Conflating digestion with decomposition (11 percent of sample):
The cow absorbs the nutrients and decomposes the grass then poos it out as manure.
The cow decomposes the grass which is a good way of recycling.
- The sun is a direct source of nutrients for plants (8 percent of sample). Note that two of these examples also imply that the energy of the sun goes directly to the soil, rather than to the plants (2 percent thought this). Another 2 percent thought the sun drives decomposition.
- Photosynthesis is when the sun gives plants nutrients through heat and light.
- The sun and the cow dung give the soil nutrients to help the grass grow.
- First of all the sun is giving energy to the soil and the soil is giving nutrients to the grass.
The evidence from this task suggests that the "big ideas" of photosynthesis – its nature and purpose – are poorly understood.
Communicating in science
Possible teaching points:
Arrows are symbols that can easily be overlooked when we take their meaning for granted.
Students need lots of practice in asking questions such as:
- What does this arrow represent?
- Who decided this is what it should mean?
- What idea does it show by pointing this way?
- Do all the arrows have the same meaning?
When they show awareness of the need to check for meaning and conventions, and demonstrate the disposition to do so without being prompted, they will have developed one small but important aspect of the key competency Using Language, Symbols and Texts.
Explanations are not easy to write succinctly, even when prompt materials are provided. Sequencing ideas to clearly say what you intend to convey takes lots of practice. The patterns of responses suggest that most of the students who completed this ARB could benefit from such practice. When arrows are drawn in a way that symbolises a cycle, students need to join up their explanation to "close" the cycle back to its starting point.
Changes of state II models the text features of a scientific explanation.
Science understandings
Decomposition
The most important "big idea" that students need to understand about decomposition is that when things die they do not disappear, but are broken down into component substances by decomposers. It is the way nutrients are naturally recycled into the soil.
- Students are more likely to recognise that animals such as earthworms and slaters break down organic material, but many are less familiar with the role of invisible organisms such as fungi and bacteria. Investigate how these organisms feed.
- Compost is an accessible context for students to investigate both the decomposition of dead plant material and improvement of soils.
Photosynthesis
The most important "big idea" that students need to understand about photosynthesis is that plants make their own food, unlike animals which have to get their food from plants.
- Explore the function of leaves in green plants, where the light energy from the sun is used to convert water and carbon dioxide to carbohydrates (the plant's "food"). Students who have a clear idea at this level can begin to explore the chemical reactions that occur.
- Discuss the terms "food" and "nutrients", emphasising that nutrients are trace elements, etc., that plants get from the soil, and are necessary for good health, as opposed to food that the plants make.
Compare photosynthesis and decomposition
Once students have learnt about decomposition and photosynthesis, in small groups ask them to construct a concept map to show how these two processes contribute to the soil. Ask each group to compare and discuss their concept maps. This task would also provide useful information to inform further teaching and learning.
For a description of concept maps go to ESOL Online
This resource was developed as part of a set of related items that explore aspects of Communicating in science in the context of soils, soil microbes, and the recycling of nutrients.
- Farming and global warming is about reading and comparing written text and a flowchart.
- A soil food web shows a soil food web.
- Changes of state II models the text features of a scientific explanation.