Download KS5_Nodule_experiment_Pupil_Sheets

Key Stage 5 Nodule experiment
Your task
Carry out an investigation to find out how the concentration of nitrate in the soil
affects the growth of root nodules on peas.
Pupil worksheet
Your write-up should include:
Nitrogen fixation
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Plants require nitrogen to build amino
acids and other molecules such as
DNA and chlorophyll. However, they
are unable to use atmospheric
nitrogen (N2) directly. They rely on soil
bacteria to fix the nitrogen into
nitrates. These then dissolve into
water, which the plants can absorb
through their roots.
A results table.
An analysis of the results.
A conclusion explaining what you discovered and scientific reasons why.
Method
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Some plants, like peas, have a
symbiotic relationship with nitrogenfixing bacteria called rhizobia, which
live inside structures called root
nodules. They fix atmospheric
nitrogen into ammonia, which the
plant can use. In return the plant
supplies the bacteria with carboncontaining compounds, which they
can metabolise.
Signalling between the rhizobia in the soil and the plant root cells starts pathways
which promote the growth of root nodules and the development of infection
threads which allow the bacteria to enter them. Once inside the cells the bacteria
are known as bacteroids and will start nitrogen fixation.
www.oxfordsparks.net/video/give-peas-chance
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Take three 200 cm3 polystyrene or plastic cups.
Make up enough soil/vermiculate mix to fill the three cups. Use one part soil
to two parts vermiculate.
Into each cup place one pea seed about 4 cm below the surface of the soil
mix.
Make up 1 dm3 of potassium nitrate (KNO3) solution. Your teachers will assign
you a concentration (1 mM, 5 mM, 10 mM , 20 mM or 30 mM).
Use the solution to water the soil mix. Add small amounts a bit at a time so to
completely wet the soil but not waterlog it.
Leave the peas to grow in a warm place. Water them using the potassium
nitrate solution when the soil is dry. Be careful not to overwater.
After 3 weeks of growth carefully remove the plants from the cups and rinse
the roots under running tap water to remove any soil.
Count the root nodules on each plant and calculate the mean number for one
plant.
Collaborate with the rest of the class to obtain a full set of results.