3. Enzymes
A section of Biology, 9700
Listing 10 of 276 questions
A student investigated the initial rate of reaction of catalase in breaking down hydrogen peroxide into oxygen and water: 2H2O2 O2 + 2H2O catalase The volume of oxygen collected was recorded over a period of 140 seconds. The results are shown in . time / s volume of oxygen / cm3 Use the information in to calculate the initial rate of reaction in cm3 s–1. Show your working. answer cm3 s–1 Explain the change in volume of oxygen collected as shown in . The student continued the investigation by determining the initial rates of reaction for five different concentrations of hydrogen peroxide. The line marked W in shows the results. The whole procedure was repeated after adding copper ions to the different concentrations of hydrogen peroxide. The line marked V on shows the results. 0.0 concentration of hydrogen peroxide / arbitrary units 0.5 1.0 1.5 2.0 2.5 3.0 3.5 initial rate of reaction / cm3 s–1 W V W V Use the information in to explain the effect of copper ions on the action of an enzyme, such as catalase. Enzyme molecules in cells eventually stop working and are broken down. Outline how cells replace the enzymes that are broken down.
9700_w11_qp_21
THEORY
2011
Paper 2, Variant 1
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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 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.
9700_w11_qp_22
THEORY
2011
Paper 2, Variant 2
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In the small intestine, the enzyme lactase hydrolyses the disaccharide lactose into the monosaccharides glucose and galactose. A deficiency of lactase can lead to a condition known as lactose intolerance. The lactose passes undigested into the large intestine resulting in diarrhoea. Some babies are born with congenital lactase deficiency, which is an inherited condition, and require lactose-free milk from birth. Suggest how two parents, who can digest lactose, can have a child with congenital lactase deficiency. The enzyme lactase can be produced by biotechnology and then used to produce lactose-free dairy products. Lactase is frequently used immobilised in alginate beads. shows a comparison between the activity of lactase free in solution and lactase immobilised in alginate beads, over a range of temperatures. Equal concentrations of free lactase and immobilised lactase were used. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 temperature / ° C enzyme activity / arbitrary units Key free lactase immobilised lactase With reference to : describe the effect of immobilisation on the activity of lactase suggest explanations for the differences between the activity of immobilised lactase and free lactase up to 40 °C. State the advantages of using immobilised enzymes instead of free enzymes.
9700_w11_qp_43
THEORY
2011
Paper 4, Variant 3
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