Transport across Cell Membranes ( Gas Exchange, Cell Recognition And Immune System, Mass Transport In Animals and Require Practical Questions )

Question 1

Describe how you would test a piece of food for the presence of lipid.

Answer 1

• Dissolve in alcohol, then add water

- White emulsion shows presence of lipids

Question 2

The part of the phospholipid labelled A is formed from a particular molecule. Name
this molecule.

( Image shows a whole molecular structure of a phospholipid )

Answer 2

• Glycerol

Question 3

Name the type of bond between A and fatty acid X.

Answer 3

• Ester

Question 4

Which of the fatty acids, X or Y, in the figure above is unsaturated?
Explain your answer.

Answer 4

• Y, contains a double bond between carbon atoms in hydrocarbon chain

Question 5

Scientists investigated the percentages of different types of lipid in plasma membranes from different types of cell.
The table shows some of their results.

( Graph shows type of lipids ( Cholesterol, Glycolipid, Phopholipid and others ), as well as the percentage of them in: Cell lining ileum of mammal, red blood cell of mammal and the bacterium Escherichia coli )

The scientists expressed their results as Percentage of lipid in plasma membrane by mass.
Explain how they would find these values.

Answer 5

• Divide mass of each lipid by total mass of all lipids

- Multiply by 100

Question 6

Cholesterol increases the stability of plasma membranes.
Cholesterol does this by making membranes less flexible.

Suggest one advantage of the different percentage of cholesterol in red blood cells
compared with cells lining the ileum.

Answer 6

• Red blood cells are free in the blood so cholesterol helps maintain its shape

Question 7

E. coli has no cholesterol in its cell-surface membrane.
Despite this, the cell maintains a constant shape.
Explain why.

Answer 7

• Cell us unable to change shape

- As it has a cell wall