No questions found
Fig. 1.1 is a diagram of an antibody molecule.
(a) (i) Name the part labelled X.
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(ii) Name the bond labelled Y.
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(iii) The antibody molecule in Fig. 1.1 has quaternary structure.
Explain the meaning of the term quaternary structure as applied to proteins.
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(b) When a pathogen enters the body, a primary immune response occurs. This response includes the production of antibodies.
Describe the stages in the immune response that lead to antibody being produced against a specific antigen.
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(c) Vaccination was used in the eradication of smallpox.
Explain, in terms of antigens, why it has not been possible to do the same for malaria.
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589
507
525
(a) Bacteria in root nodules of leguminous plants carry out nitrogen fixation.
Describe how nitrogen that is available to these bacteria can eventually become part of animal protein.
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(b) Fig. 2.1 shows the base sequence of a DNA triplet code used to produce mRNA. Fill in the corresponding tRNA anticodon in the space provided.
Fig. 2.1
[1]
(c) More mRNA molecules than tRNA molecules are synthesised in cells.
Suggest a reason for this.
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(d) Describe the role of ribosomes in protein synthesis.
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541
546
578
Fig. 3.1 is a photomicrograph of two animal cells, A and B, at different stages of the mitotic cell cycle.
[Image_1: photomicrograph of two animal cells]
(a) (i) For each cell, state the name of the stage of the cell cycle shown in Fig. 3.1.
cell A ..........................................................
cell B .......................................................... [2]
(ii) Describe the events that occur during the stage of the cell cycle named for cell A in (a)(i).
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[4]
(b) The magnification of Fig. 3.1 is ×5000.
Calculate the diameter of the nucleus of cell B between lines P and Q.
Show your working and give your answer to the nearest micrometre (μm).
answer .......................................... μm [2]
(c) State the advantages of light microscopy, rather than electron microscopy, for studies of the cell cycle.
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[3]
593
507
520
Fig. 4.1 is a diagram of a section through a mammalian heart.
[Image_1: Fig_4.1_Heart_Diagram]
(a) Use a label line and the appropriate letter to label each of the following on Fig. 4.1:
W right atrium
X tricuspid valve
Y aorta. [3]
(b) Starting from the left ventricle, describe the route taken by the blood as it travels to the lungs.
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(c) Describe and explain how the structure of the human gas exchange surface is adapted for maximum efficiency.
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513
541
598
(a) Describe the structure of a cellulose molecule and explain how cellulose is a suitable material for the cell walls of plants.
description
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explanation
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[4]
(b) (i) With reference to Fig. 5.1, describe the results of this study.
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(ii) Explain, in terms of energy flow in ecosystems, the importance of the results in Fig. 5.1.
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(c) Digested material in animals is absorbed using both facilitated diffusion and active transport.
State two similarities and two differences between facilitated diffusion and active transport.
similarities:
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differences:
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[4]
533
523
525
Fig. 6.1 is a photomicrograph of phloem sieve tubes from a plant stem.
[Image_1: Fig. 6.1]
(a) State two features, visible in Fig. 6.1, which distinguish sieve tubes from xylem vessels.
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(b) Explain briefly how sucrose is moved, or translocated, through sieve tubes.
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(c) Some enzymes are found in phloem tissue. Describe how enzymes catalyse reactions.
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[3]
569
508
550
