Cells: Membrane Structure & Transport (DP IB Biology: SL)

The sentence below describes a cellular process and an associated eukaryotic cellular structure.

 Cells which have a high rate of …I… will have many ...II… .

 Select the terms that best fit the gaps in this sentence.

	I	II
A	Facilitated diffusion	Mitochondria
B	DNA replication	Lysosomes
C	Exocytosis	Vesicles
D	Phospholipid production	Ribosomes

The diagram below shows red blood cells that have been bathed in solutions of different solute concentration.

Which row of the table correctly describes the three solutions that these red blood cells have been bathed in?

	I	II	III
A	Same osmolarity (isotonic)	Higher osmolarity (hypotonic)	Lower osmolarity (hypertonic)
B	Same osmolarity (isotonic)	Higher osmolarity (hypertonic)	Lower osmolarity (hypotonic)
C	Same osmolarity (isotonic)	Lower osmolarity (hypotonic)	Higher osmolarity (hypertonic)
D	Higher osmolarity (hypertonic)	Lower osmolarity (hypotonic)	Same osmolarity (isotonic)

Which row correctly matches the molecules found in the cell surface membrane with their function?

	Influences membrane fluidity	Act as receptor sites for hormones	Bind to antibodies
A	Glycolipids and glycoproteins	Cholesterol	Proteins and glycolipids
B	Glycoproteins	Glycolipids and glycoproteins	Cholesterol
C	Cholesterol	Proteins and glycoproteins	Glycoproteins
D	Phospholipids and cholesterol	Proteins and glycolipids	Phospholipids and cholesterol

Cystic fibrosis causes a defect in the cell surface membrane of epithelial cells, disrupting the transport of chloride ions out of affected cells.

Which membrane component is affected?

A student sketches a section of a cell surface membrane to show the fluid mosaic model.

How would they correctly label their sketch?

	W	X	Y	Z
A	Integral protein	Peripheral protein	Phospholipid	Glycoprotein
B	Peripheral protein	Integral protein	Glycoprotein	Phospholipid
C	Glycoprotein	Peripheral protein	Integral protein	Phospholipid
D	Integral protein	Integral protein	Glycoprotein	Phospholipid

Select the table row that correctly completes the following sentence:

Cholesterol is a component of animal cell membranes. Most of a cholesterol molecule is ...I… . This means that cholesterol ...II… 

	I	II
A	...hydrophobic, so it is attracted to the hydrocarbon tails at the centre of the membrane.	...reduces the fluidity of the membrane and reduces its permeability to particles such as sodium ions and hydrogen ions.
B	...hydrophilic, so it is attracted to the hydrocarbon tails at the centre of the membrane.	...increases the fluidity of the membrane and reduces its permeability to particles such as sodium ions and hydrogen ions.
C	...hydrophobic, so it is attracted to the hydrocarbon tails at the centre of the membrane.	...reduces the fluidity of the membrane and increases its permeability to particles such as sodium ions and hydrogen ions
D	...hydrophilic, so it is attracted to the phosphate heads on the periphery of the membrane.	...increases the fluidity of the membrane and increases its permeability to particles such as sodium ions and hydrogen ions.

A student places an animal cell and a plant cell into distilled water and notes down the following observations.

       Animal cell: swells and then bursts.

      Plant cell: swells.

What is the reason for this difference?

Halophytes are plants that are able to survive in regions where they are regularly covered by salty seawater. 

Which adaptation would you expect halophytes to have to enable them to live in this environment?

The Davson-Danielli model of cell membrane structure stated that cell membranes consisted of a phospholipid bilayer sandwiched between two layers of protein.

Which piece of evidence contributed to the falsification of the Davson-Danielli model and the acceptance of the Singer-Nicolson fluid mosaic model?

What is the difference between simple diffusion and facilitated diffusion?

	Simple diffusion	Facilitated diffusion
A	Diffusion rate inversely proportional to concentration gradient	Diffusion rate proportional to concentration gradient
B	Never involves a membrane	Always involves a membrane
C	Occurs across any part of the membrane	Occurs via channels in the membrane
D	A passive process that does not require energy from ATP	An active process that requires energy from ATP

Signalling molecules are used to transfer information around the body. Once at the target cell, there are different ways in which different types of signalling molecule cause a response.

Which of the following is able to enter a cell directly through the phospholipid bilayer to cause a response without the requirement for a membrane protein?

Proteins in the cell surface membranes of mouse cells and human cells were labelled with coloured dyes, with a different colour for human and mouse proteins.

When a cell from each species is fused together, the different-coloured labels are first found in different regions of the hybrid cell’s cell surface membrane. After 40 minutes, the labels are evenly distributed around the entire cell surface membrane. This is shown in the diagram below; the viewpoint is looking down onto the surface of the membrane.

 What explains this observation?

Membranes in cells include the following components.

1. cholesterol
2. glycoproteins
3. phospholipids
4. proteins

Which row of the table shows the correct function of each component? 

	Stabilising the hydrophobic layer	Recognising self / non self	Being not fully permeable to water	Transporting ions through membranes
A.	1	2	3	4
B.	3	1	2	4
C.	1	3	1	2
D.	4	3	4	2

An experiment to calculate the osmolarity of potato was performed using the following protocol:

1. Dice potato into 1cm³ cubes.
2. Add potato cubes to 6 test tubes, each containing solution with a different sucrose concentration.
3. Wait 12 hours.
4. Weigh the cubes from each test tube and plot a graph. 

The mean mass of the potato cubes was 2.50g before being added to the solution and the graph shows the masses of potato cubes after the experiment.

What concentration of sucrose has the same osmolarity as the potato?

The graph shows how the concentration of a substance affects its rate of absorption into a cell.

Substance X enters by simple diffusion, substance Y by facilitated diffusion. 

Why does the curve for substance Y plateau above a certain concentration?