No questions found
(a) On Fig. 1.1, add a label line and the correct letter for each of the three cell structures listed.
• nucleolus = N
• tonoplast = T
• chloroplast = C
[3]
(b) The drawing in Fig. 1.1 is 2000 times larger than the actual size of the cell.
Describe the steps you would follow to determine the actual diameter of the cell in micrometres (μm), at X—Y.
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(c) The drawing in Fig. 1.1 was made using the high power objective lens of a light microscope. Some of the structures in Fig. 1.1 confirm that the cell is eukaryotic.
An electron micrograph of the same cell would reveal additional cell structures that are found in eukaryotes and not in prokaryotes.
List two examples of these additional cell structures.
1 .................................................................................................................
2 .................................................................................................................[2]
(d) Some of the water that moves out of the xylem within the leaves takes an apoplastic pathway to the spongy mesophyll cells. There is a film of water on the external surfaces of these cells. This allows the intercellular air spaces to become saturated with water vapour.
(i) State, in terms of water movement from the xylem to the spongy mesophyll cells in the leaf, what is meant by the apoplastic pathway.
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(ii) Outline the properties of water that contribute to the apoplastic movement of water to the spongy mesophyll cells and to the movement of water into the intercellular air spaces.
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(iii) Describe what happens to the water vapour in the intercellular air spaces during the day and explain why this happens.
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536
550
596
(a) On Fig. 1.1, add a label line and the correct letter for each of the three cell structures listed.
• nucleolus = N
• tonoplast = T
• chloroplast = C
[3]
(b) The drawing in Fig. 1.1 is 2000 times larger than the actual size of the cell.
Describe the steps you would follow to determine the actual diameter of the cell in micrometres (μm), at X—Y.
....................................................................................................................
....................................................................................................................
....................................................................................................................
....................................................................................................................[2]
(c) The drawing in Fig. 1.1 was made using the high power objective lens of a light microscope. Some of the structures in Fig. 1.1 confirm that the cell is eukaryotic.
An electron micrograph of the same cell would reveal additional cell structures that are found in eukaryotes and not in prokaryotes.
List two examples of these additional cell structures.
1 .................................................................................................................
2 .................................................................................................................[2]
(d) Some of the water that moves out of the xylem within the leaves takes an apoplastic pathway to the spongy mesophyll cells. There is a film of water on the external surfaces of these cells. This allows the intercellular air spaces to become saturated with water vapour.
(i) State, in terms of water movement from the xylem to the spongy mesophyll cells in the leaf, what is meant by the apoplastic pathway.
....................................................................................................................
....................................................................................................................
....................................................................................................................
....................................................................................................................[2]
(ii) Outline the properties of water that contribute to the apoplastic movement of water to the spongy mesophyll cells and to the movement of water into the intercellular air spaces.
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....................................................................................................................[4]
(iii) Describe what happens to the water vapour in the intercellular air spaces during the day and explain why this happens.
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518
559
510
(a) Watson and Crick used results from work carried out by Erwin Chargaff. He found that the proportions of the bases A, T, C and G were different in different species, but within each species:
• the proportion of A was equal to the proportion of T
• the proportion of G was equal to the proportion of C.
(i) Name the bases A, T, G and C.
A ........................................................................................................................................
T ........................................................................................................................................
G ........................................................................................................................................
C ................................................................................................................................... [2]
(ii) Suggest and explain how Chargaff's findings helped Watson and Crick work out the structure of DNA.
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(b) Phoebus Levene isolated the nucleotides of DNA and identified the carbohydrate component of each nucleotide.
State the name of this carbohydrate component.
..............................................................................................................................................[1]
(c) Before the discovery of the structure of DNA as the molecule of inheritance, scientists thought that proteins were most likely to be the molecules that carried information.
Suggest how the structure of proteins made scientists think that these were the molecules that carried information.
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563
556
582
(a) Watson and Crick used results from work carried out by Erwin Chargaff. He found that the proportions of the bases A, T, C and G were different in different species, but within each species:
• the proportion of A was equal to the proportion of T
• the proportion of G was equal to the proportion of C.
(i) Name the bases A, T, G and C.
A ........................................................................................................................................
T ........................................................................................................................................
G ........................................................................................................................................
C ................................................................................................................................... [2]
(ii) Suggest and explain how Chargaff's findings helped Watson and Crick work out the structure of DNA.
..............................................................................................................................................
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..............................................................................................................................................[3]
(b) Phoebus Levene isolated the nucleotides of DNA and identified the carbohydrate component of each nucleotide.
State the name of this carbohydrate component.
..............................................................................................................................................[1]
(c) Before the discovery of the structure of DNA as the molecule of inheritance, scientists thought that proteins were most likely to be the molecules that carried information.
Suggest how the structure of proteins made scientists think that these were the molecules that carried information.
..............................................................................................................................................
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..............................................................................................................................................[2]
541
549
527
(a) The antibiotic penicillin kills bacteria by causing them to lyse (burst). It is more effective in treating diseases caused by Gram-positive bacteria than diseases caused by Gram-negative bacteria. Outline how penicillin acts on bacteria and use Fig. 3.1 to suggest why penicillin has little or no effect at treating diseases caused by Gram-negative bacteria, such as some strains of
E. coli.
[3]
(b) The outer membrane contains transport proteins called OmpF porins. These porins allow the passive movement of water, ions and small, polar molecules across the outer membrane. Each OmpF porin is formed from three identical polypeptides.
(i) Explain what is meant by the term passive.
[1]
(ii) Suggest and explain the features of an OmpF porin as a membrane transport protein.
[4]
(iii)
E. coli can regulate the number of OmpF porins in the outer membrane to adapt to changing conditions. One control mechanism used by
E. coli involves the production of a small mRNA molecule known as micF. MicF binds to the part of the mRNA molecule containing the START codon for the OmpF polypeptide. Suggest and explain how the presence of micF prevents production of OmpF porins.
[2]
(c) Fig. 3.1 shows that the outer membrane of the cell wall of
E. coli contains lipopolysaccharides. These are not present in the cell surface membrane. Each lipopolysaccharide (LPS) consists of a lipid and a polysaccharide portion. The O antigen is the outer part of the polysaccharide portion of the LPS. It faces the aqueous external environment.
(i) Define the term polysaccharide.
[2]
(ii) Some strains of
E. coli are pathogenic. Different pathogenic strains have different O antigens. Suggest and explain why infection with one pathogenic strain of
E. coli does not provide immunity to a different pathogenic strain.
[3]
537
596
543
(a) The antibiotic penicillin kills bacteria by causing them to lyse (burst). It is more effective in treating diseases caused by Gram-positive bacteria than diseases caused by Gram-negative bacteria. Outline how penicillin acts on bacteria and use Fig. 3.1 to suggest why penicillin has little or no effect at treating diseases caused by Gram-negative bacteria, such as some strains of
E. coli.
[3]
(b) The outer membrane contains transport proteins called OmpF porins. These porins allow the passive movement of water, ions and small, polar molecules across the outer membrane. Each OmpF porin is formed from three identical polypeptides.
(i) Explain what is meant by the term passive.
[1]
(ii) Suggest and explain the features of an OmpF porin as a membrane transport protein.
[4]
(iii)
E. coli can regulate the number of OmpF porins in the outer membrane to adapt to changing conditions. One control mechanism used by
E. coli involves the production of a small mRNA molecule known as micF. MicF binds to the part of the mRNA molecule containing the START codon for the OmpF polypeptide. Suggest and explain how the presence of micF prevents production of OmpF porins.
[2]
(c) Fig. 3.1 shows that the outer membrane of the cell wall of
E. coli contains lipopolysaccharides. These are not present in the cell surface membrane. Each lipopolysaccharide (LPS) consists of a lipid and a polysaccharide portion. The O antigen is the outer part of the polysaccharide portion of the LPS. It faces the aqueous external environment.
(i) Define the term polysaccharide.
[2]
(ii) Some strains of
E. coli are pathogenic. Different pathogenic strains have different O antigens. Suggest and explain why infection with one pathogenic strain of
E. coli does not provide immunity to a different pathogenic strain.
[3]
520
503
500
Fig. 4.1 is a photomicrograph showing some cells in interphase and some cells in stages of mitosis.
(a) Choose from the cells labelled 1 to 5 in Fig. 4.1 to identify the cell in which:
• the nuclear envelope is reassembling ..............................
• the spindle begins to form ..............................
• there is a high rate of transcription and translation ..............................
[3]
(b) Cell 2 is in a stage of mitosis that occurs before the stage of mitosis shown in cell 1.
Outline the changes that would occur from the stage of mitosis shown in cell 2 to the stage shown in cell 1.
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[2]
(c) Suggest why some cells in Fig. 4.1 appear empty, with no nucleus or chromosomes.
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[1]
580
505
504
Fig. 4.1 is a photomicrograph showing some cells in interphase and some cells in stages of mitosis.
(a) Choose from the cells labelled 1 to 5 in Fig. 4.1 to identify the cell in which:
• the nuclear envelope is reassembling ..............................
• the spindle begins to form ..............................
• there is a high rate of transcription and translation ..............................
[3]
(b) Cell 2 is in a stage of mitosis that occurs before the stage of mitosis shown in cell 1.
Outline the changes that would occur from the stage of mitosis shown in cell 2 to the stage shown in cell 1.
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[2]
(c) Suggest why some cells in Fig. 4.1 appear empty, with no nucleus or chromosomes.
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[1]
504
553
502
(a) Some of the structures in the human gas exchange system through which tobacco smoke passes are shown in Fig. 5.1. Describe the gross structure of the human gas exchange system. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ...............................................................................................................................[3]
(b) Soon after a person stops smoking, the short term effects of nicotine are reversed. State the changes that will occur in the cardiovascular system as a result of reduced nicotine levels. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... .......................................................................................................................[2]
(c) Fig. 5.2 shows oxygen dissociation curves for adult haemoglobin. Curve A shows measurements obtained from a person who is a heavy smoker. Curve B shows measurements obtained several weeks after the same person stopped smoking. With reference to Fig. 5.2, describe and explain how the results show some of the health benefits of stopping smoking. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ...........................................................................................................................[4]
(d) A person who gives up smoking decreases their risk of developing lung cancer, a non-infectious disease. Explain why lung cancer is described as a non-infectious disease. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... .......................................................................................................................[2]
514
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536
(a) Some of the structures in the human gas exchange system through which tobacco smoke passes are shown in Fig. 5.1. Describe the gross structure of the human gas exchange system. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ...............................................................................................................................[3]
(b) Soon after a person stops smoking, the short term effects of nicotine are reversed. State the changes that will occur in the cardiovascular system as a result of reduced nicotine levels. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... .......................................................................................................................[2]
(c) Fig. 5.2 shows oxygen dissociation curves for adult haemoglobin. Curve A shows measurements obtained from a person who is a heavy smoker. Curve B shows measurements obtained several weeks after the same person stopped smoking. With reference to Fig. 5.2, describe and explain how the results show some of the health benefits of stopping smoking. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ...........................................................................................................................[4]
(d) A person who gives up smoking decreases their risk of developing lung cancer, a non-infectious disease. Explain why lung cancer is described as a non-infectious disease. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... .......................................................................................................................[2]
529
549
521
Enzyme inhibitors and monoclonal antibodies can be used in the treatment of disease.
(a) Mevinolin is an enzyme inhibitor that can be prescribed as a drug to reduce the concentration of cholesterol in blood plasma.
High concentrations of cholesterol in the blood have been linked to an increased risk of cardiovascular disease.
Mevinolin acts as a competitive inhibitor of the enzyme HMG CoA reductase. This enzyme catalyses one of the first steps in the synthesis of cholesterol, as shown in Fig. 6.1.
[Image_1: HMG CoA reductase diagram]
Explain how mevinolin inhibits the enzyme HMG CoA reductase.............................................................
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(b) Outline the use of monoclonal antibodies in the treatment of disease...............................................
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576
544
551
Enzyme inhibitors and monoclonal antibodies can be used in the treatment of disease.
(a) Mevinolin is an enzyme inhibitor that can be prescribed as a drug to reduce the concentration of cholesterol in blood plasma.
High concentrations of cholesterol in the blood have been linked to an increased risk of cardiovascular disease.
Mevinolin acts as a competitive inhibitor of the enzyme HMG CoA reductase. This enzyme catalyses one of the first steps in the synthesis of cholesterol, as shown in Fig. 6.1.
[Image_1: HMG CoA reductase diagram]
Explain how mevinolin inhibits the enzyme HMG CoA reductase.............................................................
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..................................................................................................................................................[3]
(b) Outline the use of monoclonal antibodies in the treatment of disease...............................................
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..................................................................................................................................................[2]
504
510
507
