Key Stage 5 – Fixation with
intimacy
Notes for teachers
At a glance
In this activity students use a variety of sources to carry out research into nitrogen-fixing bacteria
and their symbiotic relationship with certain plants such as peas.
They practise their science literacy skills by working together to interpret an excerpt from a
scientific article and then work individually to interpret further sources in order to answer a series
of questions.
In doing so they will apply their knowledge of biochemical pathways to explain the exchange of
substances within an infected plant cell and explain how research taking place at the University of
Oxford could help to reduce our reliance on artificial fertilisers.
Learning Outcomes


Students analyse a metabolic pathway diagram and excerpt from a scientific article.
Students apply knowledge to explain the processes involved in the symbiotic relationship
between rhizobia bacteria and pea plants.
www.oxfordsparks.net/video/give-peas-chance
Each student will need


1 copy of the pupil worksheet
1 copy of the sheet 'Fixation with intimacy article'
Possible Lesson Activities
1. Starter activity
 Show the video ‘Give peas a chance’ to the class.
2. Main activity: Group literacy task
 Introduce the work of Professor Philip Poole by asking students to read through

Feeding the world on the pupil worksheet.
Students should then study further details of his work by reading the extract from
Microbiology Today on the sheet 'Fixation with intimacy article'. Ask students to
highlight any words in the article that they do not understand. Students should then
work as pairs or small groups to compare their words and help each other to
understand their meaning. Ask each group to compile a list of a maximum of three
words that they are still unsure about and write them on the board. Take time to go
through these words as a class and decipher their meaning in relation to the article.
3. Main activity: Students work alone to answer questions
 Ask students to work as individuals to complete the task on the pupil worksheet. They
use the sources to answer questions. They can use the information on the sheet:
Information on the infection process and the image showing metabolic interactions of
an infected plant cell as well as the article extract.
 Answers:
1. It is a long-term interaction between two organisms: the rhizobia bacteria and the
plant. As both organisms benefit from the relationship it is mutualistic.
2. The signalling using flavonoids induces the production of nod factors by the
bacteria. Nod factors identify the bacteria as rhizobia and allow the bacteria to
infect the plant root cells. Without this process the plants would be open to other,
potentially pathogenic, bacteria infecting them.
3. Sucrose enters the infected plant cell from the phloem and is converted to malate
which is fed into the TCA cycle of the bacteroid. Electrons and ATP produced by
the cycle are used to reduce nitrogen into ammonia using the enzyme
nitrogenase. Ammonia is exported out of the bacteroid and, in the presence of the
plant enzyme glutamate synthetase, ammonium ions and glutamate are
assimilated into glutamine which is exported into the phloem for transportation.
4. Otherwise glutamine would be produced and used by the bacteria and not the
plant. The plant would not gain anything from the symbiosis.
www.oxfordsparks.net/video/give-peas-chance
5.
6.
Fertilisers are added to soil to supply plants with a source of nitrogen which they
can absorb through their roots and use to build proteins. If we can develop other
crop plants such as wheat and corn which have this relationship with rhizobia then
they could also fix nitrogen. This would reduce the amount of fertilisers we need
to put onto the soil, which would have a positive impact on the environment. The
manufacture of artificial fertilisers uses up valuable resources and energy and
their use is linked to pollution e.g. eutrophication.
Manipulate the genome of other crop plants so they have the nod factor receptors
on the surface of their root cell membranes. This would mean that rhizobia could
infect them.
4. Plenary
 Go through the answers to the questions to check student understanding.
www.oxfordsparks.net/video/give-peas-chance