4.1. Fluid mosaic membranes
A subsection of Biology, 9700, through 4. Cell membranes and transport
Listing 10 of 134 questions
A method called freeze-fracture can be used to study the structure of cell membranes. The membrane is frozen and then split down the middle, separating the two layers of phospholipids from each other. Any proteins contained within one layer remain in that layer. Proteins which span the membrane can be found in either layer after freeze-fracture, depending on the properties of the protein. Which statement about the results of freeze-fracture studies are correct?
9700_w16_qp_12
MCQ
2016
Paper 1, Variant 2
View
The diagram shows an experiment in which two different cell surface membranes were joined to form a single large membrane. The outer surface of one membrane contained molecules of protein P and the outer surface of the other membrane contained molecules of protein Q. The positions of the two proteins in each membrane were observed just before they were joined together and 1 hour after they were joined. + protein P joined membrane after 1 hour protein Q Which statements are correct?
9700_w17_qp_13
MCQ
2017
Paper 1, Variant 3
View
is a transmission electron micrograph of part of a cell. 2 μm X Name the organelle labelled X. Put a tick (3) in the box beside the type, or types, of cell that contain this organelle. animal cell plant cell bacterial cell Use the scale bar to calculate the magnification of . Write down the formula and use it to make your calculation. Show your working. formula magnification ◊ The organelle in is made from structures surrounded by a single membrane. Name two organelles that are surrounded by double membranes. The structure of the cell surface membrane is described as a fluid mosaic. Explain what is meant by the term fluid mosaic. Outline the roles of the cell surface membrane.
9700_w17_qp_21
THEORY
2017
Paper 2, Variant 1
View
shows the structure of an alveolus and surrounding structures in a mammalian lung. The lining of each alveolus is formed by two types of epithelial cell, alveolar type 1 and alveolar type 2. alveolar type 2 cell secretion of surfactant thin film of water with surfactant alveolar type 1 cell macrophage neutrophil not to scale Explain how the structure of an alveolar type 1 cell is adapted to its function. Alveolar type 2 cells secrete pulmonary surfactant into the watery fluid that lines the alveolus. The surfactant reduces the surface tension of the fluid so that the alveolus does not collapse. Pulmonary surfactant is a mixture of phospholipids and proteins. The phospholipids form a monolayer on the surface of the fluid. Explain how phospholipids interact with water to form a monolayer on the surface of the fluid. Macrophages and neutrophils are found in the lungs, as shown in . Describe the role of macrophages in the lungs. Neutrophils leave the blood and secrete the extracellular enzyme, elastase. Suggest why neutrophils secrete elastase. The protein alpha-1 antitrypsin is produced in cells in the liver and is transported to the lungs, where it inhibits the action of elastase. Some people produce a different form of this protein that remains within liver cells. These people are at an increased risk of developing emphysema, in which alveolar walls break down. Emphysema is one of the conditions associated with chronic obstructive pulmonary disease (COPD). Explain why these people are at increased risk of developing emphysema.
9700_w17_qp_23
THEORY
2017
Paper 2, Variant 3
View
Questions Discovered
134