9700_w11_qp_22
A paper of Biology, 9700
Questions:
6
Year:
2011
Paper:
2
Variant:
2

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For Examiner’s Use Azotobacter vinelandii is a bacterium found in the soil that is able to fix atmospheric nitrogen. One feature of nitrogen-fixing bacteria is the ability to synthesise the enzyme nitrogenase, a molybdenum- and iron-containing, protein complex. Molybdenum is a mineral ion found in the soil solution. It enters the cell as molybdate ions, through membrane transport proteins. The proteins have the ability to bind to, and hydrolyse, ATP. Name and describe the mechanism of transport of molybdate ions into the cell. State the structures in the bacterial cell where the protein components of nitrogenase are synthesised. Part of the equation for the reaction that is catalysed by nitrogenase in A. vinelandii is shown below. Complete the equation by naming the product of the reaction. nitrogenase atmospheric nitrogen (N 2 ) ATP and hydrogen For Examiner’s Use Table 3.1 shows the various types of nitrogen fixation that occur throughout the world and gives estimates of the mass of atmospheric nitrogen fixed in a year. Table 3.1 type of nitrogen fixation mass of nitrogen fixed / ×109 kg yr–1 non-biological Haber process combustion lightning biological agricultural land non-agricultural land sea Using data from Table 3.1, calculate the percentage of nitrogen fixation carried out worldwide by nitrogen-fixing organisms, such as A. vinelandii, in agricultural land. Show your working and express your answer to the nearest whole number. answer % Explain why the proportion of nitrogen gas in the atmosphere remains stable at 78%, even though nitrogen fixation removes nitrogen gas from the atmosphere. Describe and explain the benefits to humans of the presence of nitrogen-fixing bacteria, such as A. vinelandii, in agricultural land.
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