Grade 7: Life science Soil UNIT 7L.5 6 hours About this unit This unit is the fifth of six units on life science for Grade 7. This unit is designed to guide your planning and teaching of lessons on life science. It provides a link between the standards for science and your lesson plans. The teaching and learning activities should help you to plan the content and pace of lessons. Adapt the ideas to meet your students needs. For extension or consolidation activities, look at the scheme of work for Grade 8 and Grade 6. You can also supplement the activities with appropriate tasks and exercises from your school s textbooks and other resources. Introduce the unit to students by summarising what they will learn and how this builds on earlier work. Review the unit at the end, drawing out the main learning points, links to other work and real life applications. Previous learning To meet the expectations of this unit, students should already know that individual micro-organisms are too small to see with the unaided eye. They should know that micro-organisms can be harmful and cause illness or food poisoning. Expectations By the end of the unit, students understand the importance of microorganisms in nitrogen fixation, decomposition and nutrient recycling. They use a microscope, prepare a slide and examine objects such as roots. Students who progress further can give examples of the use of microorganisms in food production. Resources The main resources needed for this unit are: samples of alfalfa with roots and root nodules, hand lenses, microscopes legume seeds, inert growth medium (e.g. perlite or vermiculite), distilled water, nitrogen-free nutrients, Rhizobium (sometimes known as Inoculum ) mixture of leaves and vegetable peelings, clear sealed container video clips of time-lapse photography showing organic matter decomposing Internet access Key vocabulary and technical terms Students should understand, use and spell correctly: fertiliser, alfalfa, Rhizobium, root nodules, legume decay, decomposition, compost, sewage treatment 69 Qatar science scheme of work Grade 7 Unit 7L.5 Life science 5 Education Institute 2005
Standards for the unit Unit 7L.5 6 hours SUPPORTING STANDARDS CORE STANDARDS Grade 7 standards EXTENSION STANDARDS Specialised bacteria in soil and root nodules fix atmospheric nitrogen Microorganisms in soil decompose organic matter and recycle nutrients 6.10.1 Know that if left unprotected, most foods will be contaminated by microorganisms in the air and become unfit to eat. 7.10.1 Know that specialised bacteria in the soil and in the roots of some plants fix atmospheric nitrogen. 7.10.2 Know that micro-organisms in soil decompose organic matter and dead organisms and help to recycle nutrients. 6.3.4 Use a simple microscope. 7.4.5 Prepare a microscope slide correctly; use a microscope to examine objects such as leaf surfaces and root hairs. 8.11.1 Know that micro-organisms are used in making foods such as bread, cheese and yoghurt. 70 Qatar science scheme of work Grade 7 Unit 7L.5 Life science 5 Education Institute 2005
Activities Unit 7L.5 Objectives Possible teaching activities Notes School resources Specialised bacteria in soil and root nodules fix atmospheric nitrogen Know that specialised bacteria in the soil and in the roots of some plants fix atmospheric nitrogen. Prepare a microscope slide correctly; use a microscope to examine objects such as leaf surfaces and root hairs. Ask students what helps plants to grow well and discuss the factors they suggest. Remind them of the investigations they carried out on the effect of adding fertiliser in Unit 7L.4 and that fertilisers contain nitrogen. Provide the following information from a soil and water quality specialist: Applying nitrogen fertiliser to good alfalfa stands is not recommended. Tell students that alfalfa is the oldest and most important forage crop in Qatar and worldwide. It is grown to feed livestock and originated in Asia around 2700 years ago. Challenge students to find out why alfalfa does not need fertiliser. Provide some samples of alfalfa, including their roots. Ask students to make careful observations of alfalfa roots using a hand lens and microscope. Encourage students to prepare their own slides of root nodules or to look at images or prepared slides on high-power magnification. Alfalfa roots have root nodules containing Rhizobium bacteria; ask students what they think Rhizobium may be doing so that alfalfa does not need nitrogen fertiliser. Ask students what percentage of the air is nitrogen. Explain that plants cannot access this nitrogen directly through their leaves and that Rhizobium bacteria convert nitrogen gas in the soil into a form of nitrogen that the plant can use. Add that there are other bacteria in the soil that fix nitrogen. Students have already learnt that farmers can use nitrogen fertilisers to add nutrients to soil, but these can be expensive. If a farmer ploughed up a field of alfalfa there would be enough nitrogen for a subsequent crop of corn. Explain that alfalfa is a legume and other legumes that are important crop plants also have root nodules (e.g. clover, soybean, pea, bean, chickpea, lentil). Discuss with students why legumes are such important crop plants, particularly in developing countries. Enquiry skill 7.4.5 Use this column to note your own school s resources, e.g. textbooks, worksheets. Extension activity Encourage students to use reference material or the Internet to find out more about alfalfa cultivation in Qatar and about crop rotation, a technique farmers used to use of growing a cycle of different crops each year so that nutrients in the soil were not depleted. ICT opportunity: Use of the Internet If possible, allow students to investigate the effect root nodules have on plant growth. Provide students with legume seeds, inert growth medium (e.g. perlite or vermiculite), distilled water, nitrogen-free nutrients and Rhizobium (also known as Inoculum ). Let them grow plants for 4 6 weeks and measure height or mass to see whether there is a significant difference between plants with Rhizobium root nodules and a control group. Safety: Be careful when perlite or vermiculite is dry as the dust is an irritant. Either moisten them before use or make sure students wear masks. Enquiry skill 7.1.1 71 Qatar science scheme of work Grade 7 Unit 7L.5 Life science 5 Education Institute 2005
Objectives Possible teaching activities Notes School resources Micro-organisms in soil decompose organic matter and recycle nutrients Know that micro-organisms in soil decompose organic matter and dead organisms and help to recycle nutrients. Remind students that plants need to take in nutrients from the soil in order to grow well; ask where these nutrients come from in a natural habitat, where there are no fertilisers. Students may suggest that decaying organic matter and waste release nitrogen compounds. Explain that the process of decay also involves micro-organisms bacteria and fungi. Demonstrate the effect soil micro-organisms have on decomposition. Collect a mixture of leaves and vegetable peelings. Put half this mixture into a clear sealed container. Bury both samples next to each other in the school grounds and leave for several weeks. Dig up the two samples and ask the students to compare them. Show students video clips of time-lapse photography showing organic matter decomposing and emphasise that this is how nutrients are returned to the soil. Ask students to design a compost bin this needs to be well insulated and covered, but should also allow water and air to circulate. Ask students to annotate their designs with explanations of each design feature. If possible, arrange a visit to a sewage works, or a visit from a scientist who works there, to discuss how micro-organisms play a vital role in sewage treatment. Alternatively, there are many websites that show diagrams and descriptions of sludge treatment and production of methane gas in sewage works. Ask students to summarise how legumes and soil micro-organisms are involved in the recycling of nutrients in a diagram. Visit opportunity: Visit a local sewage treatment plant. ICT opportunity: Use of the Internet. Enquiry skill 7.3.1 72 Qatar science scheme of work Grade 7 Unit 7L.5 Life science 5 Education Institute 2005
Assessment Unit 7L.4 Examples of assessment tasks and questions Notes School resources Assessment Set up activities that allow students to demonstrate what they have learned in this unit. The activities can be provided informally or formally during and at the end of the unit, or for homework. They can be selected from the teaching activities or can be new experiences. Choose tasks and questions from the examples to incorporate in the activities. Advice on building a compost bin lists four critical factors for decomposition to take place. The critical factors are: air; moisture; nitrogen materials; time. For each factor, explain why it is important. Refer to micro-organisms in your answer. Here is a diagram to show how nutrients are recycled. Describe what happens at A, B, C and D. 73 Qatar science scheme of work Grade 7 Unit 7L.5 Life science 5 Education Institute 2005
74 Qatar science scheme of work Grade 7 Unit 7L.5 Life science 5 Education Institute 2005