Syllabus Edition
First teaching 2020
Last exams 2024
2 marksFig. 1 shows a diagram of part of a cell surface membrane.
Fig. 1
Identify molecules A and B.
2 marksDescribe the role of molecule C in Fig. 1.
2 marksState two functions of molecule D in Fig. 1.
2 marksExplain the importance of molecule E in Fig. 1 when the cell is exposed to high temperatures.
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4 marksFig. 1 shows a cell surface membrane and some molecules of a small, nonpolar substance shown as substance X.
Fig. 1
Predict and explain what will happen to substance X in Fig. 1.
1 markGive a possible name for substance X.
2 marksSubstance Y is a large molecule and is not lipid-soluble.
Describe how substance Y would travel across a cell membrane from an area of high to low concentration.
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2 marksState and explain how an increase in temperature would affect the rate of movement of substance Y across a cell membrane.
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3 marksState the two types of molecules that most often act as receptors on the surfaces of cell membranes.
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State the generic name of the signalling molecules that are secreted from certain cells.
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2 marksDescribe the step that occurs between the secretion of the signalling compound stated in part (a)(ii) and its arrival at the membrane compound stated in part (a)(i).
4 marksFig. 1 shows some keywords from the cell signalling pathway involved in the regulation of blood glucose levels.
Fig. 1
Link each box on the left with the most appropriate one on the right using a straight line.
1 markHormones, like insulin mentioned in part (c), act as messengers in cell signalling in the endocrine system.
Name the group of chemical messengers that play a role in the transmission of nervous impulses.
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Glucagon is a hormone that affects the activity of liver cells, leading to an increase in blood glucose levels. Glucagon acts as a ligand.
Suggest the features of glucagon that make it an example of a ligand.
2 marksUsing your knowledge of the cell surface membrane:
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4 marksGlycoproteins play an important role in cell signalling.
Explain the role of glycoproteins in initiating a response inside a cell.
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2 marksLinoleic acid is an unsaturated fatty acid that is found in some triglycerides and some phospholipids.
Phospholipids are components of cell membranes.
Fig. 1 shows a molecule of linoleic acid.
Fig. 1
The composition of cell membranes of plants changes in response to changes in temperature.
At the start of the cold season, there is an increase in the proportion of phospholipids with unsaturated fatty acids in the chickpea, Cicer arietinum. Chickpea plants that do not make this change do not survive.
Suggest how the increase in the proportion of phospholipids with unsaturated fatty acids helps plants, such as chickpea, survive decreases in temperature.
3 marksState why triglycerides and phospholipids cannot be described as polymers.
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State two differences in the structure of triglycerides and phospholipids.
4 marksPlatelets metabolise linoleic acid to produce a molecule known as thromboxane.
Thromboxane is released by platelets when blood loss occurs. Thromboxane acts on smooth muscle cells in the walls of arteries. This causes arteries to constrict, which reduces blood flow.
Explain why the constriction of arteries following blood loss is an example of cell signalling.
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1 markFig. 1 shows the molecular diagram of part of the fluid mosaic structure of the plasma membrane. These molecules play an important role in maintaining the stability of the plasma membrane.
Fig. 1
Identify the part of the fluid mosaic structure of the plasma membrane represented by the molecular diagram in Fig.1.
3 marksScientists have found that wheat crops adapted to grow in winter have increased unsaturated phospholipid content.
Suggest why the presence of unsaturated phospholipids would be advantageous.
2 marksPieces of phospholipid bilayer were analysed from two different mammalian cell surface membranes. Sample X contained phospholipid molecules at a density of 4.2 x 106 molecules µm-2, whereas sample Y contained phospholipid molecules at a density of 5.5 x 106 molecules µm-2. One sample was from an exocrine pancreatic cell and the other was from a skin cell. Identify, with reasons, which cell type corresponds to samples X and Y.
2 marksResearchers have discovered that an individual phospholipid molecule can exchange places with its neighbouring phospholipid molecule in a monolayer as frequently as 107 times per second.
By contrast, phospholipid molecules almost never exchange places with each other from one monolayer to the other within a bilayer, referred to as a ‘flip-flop’ exchange. The ‘flip-flop’ takes place around once a month for a typical phospholipid molecule.
Suggest why there is this difference in molecular behaviour.
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In 1935 a model describing the structure of the cell surface membrane was proposed by the biologists Davson and Danielli. Fig. 1 shows a representation of their proposal.
Fig. 1
The model shown in Fig. 1 was replaced in 1972 when two other scientists, Singer and Nicolson, proposed the fluid mosaic model to describe the structure of the cell surface membrane.
Describe what is meant by the term 'fluid mosaic'.
Compare the model of membrane structure shown in Fig. 1 with the fluid mosaic model that replaced it.
Explain how the features of a phospholipid contribute to the structure of a cell surface membrane.
State two features of cell membranes other than the structure that can be explained by the fluid mosaic model.
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Some components of the cell surface membrane include:
Draw a labelled diagram of a section through a cell surface membrane to show how the components mentioned above are organised within the membrane. Include other named components and label the inner and outer surfaces of the membrane.
The cell surface membrane is said to be partially permeable.
Explain how the structure of a phospholipid prevents some substances from diffusing directly between the phospholipids that make up the cell surface membrane.
High temperatures can denature membrane proteins.
Suggest the effect this would have on a cell surface membrane.
State one role of phospholipid bilayers within the cell.
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1 markFig. 1 is an electron micrograph of part of a eukaryotic cell.
A ruler is shown in the image for scale.
Fig. 1
State how it is possible to deduce that Fig. 1 is a transmission electron micrograph and not a scanning electron micrograph.
2 marksBoth the Golgi body and the rough endoplasmic reticulum are part of the network of membranes inside cells.
Outline structural features shown in Fig. 1 that identify G as the Golgi body and not the rough endoplasmic reticulum.
2 marksCalculate the actual diameter, X–Y, of the mitochondrion labelled in Fig. 1
Write down the formula that you will use to make your calculation. Give your answer to the nearest whole nanometre (nm).
4 marksMany of the cell structures in Fig. 1 are surrounded by membranes.
Membranes are approximately 6 nm to 7 nm wide.
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ii)
The inner membrane of the mitochondrial envelope is much less permeable than the outer membrane.
Suggest one way in which the structure of the inner membrane of the mitochondrion may differ from that of the outer membrane to produce a less permeable inner membrane.
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