9.1. The gas exchange system
A subsection of Biology, 9700, through 9. Gas exchange
Listing 10 of 240 questions
The airways of the gas exchange system are lined with epithelium. Gradual changes in the structural features of this epithelium occur as the airways branch and become increasingly narrow. Table 4.1 shows the changes that occur in the number of goblet cells in the epithelium of the different structures of the gas exchange system. Table 4.1 gas exchange structure number of goblet cells in epithelium trachea many bronchi many larger bronchioles very few smaller bronchioles none alveoli none Goblet cells produce mucus, which is important in maintaining the health of the airways. The smallest bronchioles closest to the alveoli are known as respiratory bronchioles. Suggest and explain why respiratory bronchioles do not have any goblet cells. is a photomicrograph of a section through a bronchiole, which is surrounded by alveoli. tissue X magnification ×40 There are structural differences between the epithelium of the bronchiole and the epithelium of an alveolus. Describe the differences between the epithelium of bronchioles and the epithelium of alveoli, other than differences in the number of goblet cells. Tissue X, shown in , is located in the wall of the bronchiole. Name tissue X and outline the function of tissue X in the bronchiole. tissue X =
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THEORY
2022
Paper 2, Variant 2
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is a photomicrograph of a transverse section of a bronchus in the lungs. smooth muscle T Identify the tissue labelled T in . Describe the function of smooth muscle in the bronchus. The walls of alveoli contain some specialised epithelial cells called type II epithelial cells. These cells secrete surfactant. Surfactant helps to prevent the alveoli collapsing during breathing. Surfactant contains phospholipid, cholesterol and protein. The components of surfactant are synthesised in the rough endoplasmic reticulum and smooth endoplasmic reticulum and then passed to the Golgi body. The surfactant that is produced is stored in secretory organelles called lamellar bodies. The surfactant in the lamellar bodies is released onto the surface of the alveolar epithelium by exocytosis, as shown in . type II epithelial cell smooth endoplasmic reticulum rough endoplasmic reticulum nucleus release of surfactant from the epithelial cell by exocytosis lamellar body transport vesicle Golgi body Each lamellar body is surrounded by a single membrane. Draw a diagram to show the arrangement of phospholipid molecules in the membrane surrounding the lamellar body. Scientists studying the production and secretion of lung surfactant have discovered that a reduction in cholesterol in the cell surface membrane of type II epithelial cells reduces the secretion of surfactant. Suggest why secretion of surfactant is affected by a reduction in cholesterol in the cell surface membranes of type II epithelial cells. Lung surfactant is engulfed by macrophages that are in close contact with the type II epithelial cells. Suggest why macrophages engulf surfactant.
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THEORY
2023
Paper 2, Variant 1
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The alveoli of the lungs are the main gas exchange surface in humans. Explain how blood flow through the alveolar capillaries helps to maintain steep diffusion gradients for gas exchange. Ventilation of the lungs is the process of inhalation and exhalation. Ventilation helps to maintain steep diffusion gradients. Explain the role of elastic fibres in the alveolar wall during ventilation. Some cells in the alveolar wall are specialised to secrete surfactant to prevent collapse of the alveoli at the end of exhalation. In these cells, surfactant is stored in membrane-bound organelles known as lamellar bodies. Surfactant is a mixture of lipids, mainly phospholipids, and some proteins. A protein known as ATP-binding cassette transporter A3 (ABCA3) is needed to move surfactant phospholipids into lamellar bodies from the surrounding cytosol (fluid part of cytoplasm). Suggest and explain the features of protein ABCA3 that make it suited to its function. The gene ABCA3 codes for protein ABCA3. The gene is 80 kb (80 000 base pairs) long and is composed of introns and exons. Protein ABCA3 is composed of 1704 amino acids. shows the flow of genetic information in the production of ABCA3. gene ABCA3 primary transcript RNA messenger RNA (mRNA) polypeptide ABCA3 protein ABCA3 X Y Complete to name the processes occurring at X and Y. A triplet of bases codes for one amino acid. This fact only partly explains how the activity of gene ABCA3, which is 80 kb long, can result in the protein ABCA3, which is only 1704 amino acids long. Suggest other reasons to explain the difference in the number of base pairs in gene ABCA3 compared with the number of amino acids in protein ABCA3.
9700_w23_qp_22
THEORY
2023
Paper 2, Variant 2
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Questions Discovered
240