1.3 – Membrane structure – Sciences for IGCSE & IB

1.A diagram of a membrane

[Source: © International Baccalaureate Organization 2017] In the diagram, which structure is an intrinsic or integral protein?

A
B
C
D

2. In the diagram, which part of the membrane structure does the molecule below form?

A
B
C
D

3. Cladograms can be created by comparing DNA or protein sequences. The cladogram on the left is based on DNA sequences and the cladogram on the right is based on comparing protein sequences.

What is the reason that cladograms based on DNA sequences are more reliable predictors of the phylogenetic relationship of species than cladograms based on protein sequences?

Amino acids are not as chemically stable as DNA nucleotides
DNA mutates but amino acids do not
Several different triplets of bases can code for the same amino acid
There are 20 different amino acids but only 4 nucleotides

4. The bacterium Neisseria gonorrhoeae causes infections related to the human reproductive system. The graph shows the percentage of samples in which this bacterium showed resistance to six antibiotics over a period of ten years.

What is a possible explanation for the total percentage resistance being larger than 100% in 2010?

People do not take the antibiotics as prescribed
More people have been sampled in that year
There was an epidemic of Neisseria gonorrhoeae in that year
Some bacteria are resistant to more than one antibiotic

5. What is a role of cholesterol in animal cells?

It increases body fat
It controls membrane fluidity
It lines the inner wall of capillaries
It is a constituent of bile

6. Which evidence falsifies the Davson–Danielli model? I.The presence of globular proteins within the phospholipid bilayer. II.Non-polar amino acids cause proteins to remain embedded in membranes III. Membrane proteins remain in a fixed position inside a membrane

I only
I and II only
II and III only
I, II and III

7. The cell membrane model proposed by Davson–Danielli was a phospholipid bilayer sandwiched between two layers of globular protein. Which evidence led to the acceptance of the Singer–Nicolson model?

The orientation of the hydrophilic phospholipid heads towards the proteins
The formation of a hydrophobic region on the surface of the membrane
The placement of integral and peripheral proteins in the membrane
The interactions due to amphipathic properties of phospholipids

8. The diagram shows a plasma membrane.

Which molecule is labelled X?

Cholesterol
Glycoprotein
Phospholipid
Amylase

9. Which are functions of membrane proteins?

Hormone binding sites and DNA replication
Cell adhesion and translation
Cell to cell communication and protein pumps
Passive transport and glycosis

10. What are the parts of the cell membrane indicated in the diagram?

A
B
C
D

11. What feature of cell membranes allows endocytosis to occur?

Fluidity of phospholipid bilayer
Presence of protein pumps
Presence of carrier proteins
Glycoprotein binding sites

12. Which process is possible due to the fluidity of cell membranes?

Endocytosis
Osmosis
ATP production
Cell recognition

13. What is the approximate thickness of the plasma membrane of a cell?

10 nm
50 nm
10 µm
50 µm

14. Which process is possible due to the fluidity of cell membranes?

Endocytosis
Osmosis
ATP production
Cell recognition

15.What is the approximate thickness of the plasma membrane of a cell?

10 nm
50 nm
10 µm
50 µm

16. A number of different proteins are involved in nerve function. Which of the following does not require a membrane protein?

Active transport of sodium
Diffusion of K+ into the cell
Diffusion of the neurotransmitter across the synapse
Binding of the neurotransmitter to the post-synaptic membrane

17. The diagram below shows a plasma membrane. What is molecule X?

Cholesterol
Peripheral protein
Glycoprotein
Polar amino acid

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