Author: Kim Edgell
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NAME: 							Teacher:
Membrane homework 1
Q1. (a)     Describe how you would test a piece of food for the presence of lipid.
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Scientists investigated the percentages of different types of lipid in plasma membranes from different types of cell. The table shows some of their results.
 
Type of lipid | Percentage of lipid in plasma membrane by mass
| Cell lining ileum of mammal | Red blood cell of mammal | The bacterium Escherichia coli
Cholesterol | 17 | 23 | 0
Glycolipid | 7 | 3 | 0
Phospholipid | 54 | 60 | 70
Others | 22 | 14 | 30
(b)     The scientists expressed their results as Percentage of lipid in plasma membrane by mass. Explain how they would find these values.
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Cholesterol increases the stability of plasma membranes. Cholesterol does this by making membranes less flexible.
(c)     Suggest one advantage of the different percentage of cholesterol in red blood cells compared with cells lining the ileum.
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(d)     E. coli has no cholesterol in its cell-surface membrane. Despite this, the cell maintains a constant shape. Explain why.
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Q2. The diagram shows part of a plasma membrane.
 
(a)     Describe two functions of the structure made from the parts labelled X.
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(b)     Give one function of the molecule labelled Y.
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(c)     The part labelled Z is involved in facilitated diffusion of substances across the membrane.
(i)      Give one similarity in the way in which active transport and facilitated diffusion transport substances across the membrane.
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(ii)     Give one way in which active transport differs from facilitated diffusion.
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(iii)     The graph shows the relationship between the concentration of a substance outside a cell and the rate of entry of this substance into the cell.
 
Explain the evidence from the graph that this substance is entering the cell by facilitated diffusion and not by simple diffusion.
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Q3. (a)     The structure of a plasma membrane is described as a fluid mosaic.
Explain why.
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(b)     Give two functions of proteins in plasma membranes.
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