Pieces 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.
Researchers 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.
Diffusion can be studied using visking tubing. Students set up an investigation in which equal volumes of each of the following solutions were placed into separate visking tubings:
0.7 mol dm-3 sodium chloride
0.7 mol dm-3 glucose
The visking tubings, each of the same size, were placed in distilled water and maintained at a constant temperature of 23°C. The volume and mass of the bags were measured at 5 minute intervals for 160 minutes.
The data recorded is shown below.
Calculate the rates of increase in mass and in volume for the visking tubing containing glucose solution during the first 30 minutes.
A biologist investigated the osmolarity of different parts of turnip tubers of different ages (as shown in the diagram below). The osmolarity was estimated using discs of turnip tissue and sucrose solutions of different concentrations. The diagram below shows:
The appearance of the tubers
The places where the tissues were removed
The results are shown in the graph below
Estimate the osmolarity of the near new shoot sample of the old tuber.
