Transport Across Cell Membrane

Question 1

Structure and Function of Cell Membranes

The fluid mosaic model describes the structure of the plasma membrane as a …

This gives the membrane a ___ character.

Answer 1

Structure and Function of Cell Membranes

The fluid mosaic model describes the structure of the plasma membrane as a mosaic of phospholipids, cholesterol, proteins, and carbohydrates.

This gives the membrane a fluid character.

Question 2

Function of the plasma membrane

The plasma membrane defines the borders of cells and most organelles.

The plasma membrane is ___ permeable.

This means that the membrane allows some materials to freely enter or leave the ___, while other materials cannot move freely.

Answer 2

Function of the plasma membrane

The plasma membrane defines the borders of cells and most organelles.

The plasma membrane is selectively permeable.

This means that the membrane allows some materials to freely enter or leave the cell/organelle, while other materials cannot move freely.

Question 3

Structure of phospholipids

A phospholipid is a molecule consisting of …

The molecules arrange themselves into a ___ which ranges from __ to ___ nm in thickness

The ___ phospholipid head faces ___ and the ___ fatty acids faces ____

Answer 3

Structure of phospholipids

A phospholipid is a molecule consisting of glycerol, two fatty acids, and a phosphate-linked head group.

The molecules arrange themselves into a bilayer which ranges from 5 to 10 nm in thickness.

The hydrophilic phospholipid head faces outwards and the hydrophobic fatty acids faces inwards.

Question 4

Structure of cholesterol

Cholesterol is a ___ that sits with ___ in the core of the ___

Cholesterol is not found in ___ cell membranes.

Cholesterol molecules make the membrane …

This explains why cholesterol helps to maintain the ____ of animal cells.

Answer 4

Structure of cholesterol

Cholesterol is a lipid that sits with phospholipids in the core of the membrane.

Cholesterol is not found in bacterial cell membranes.

Cholesterol molecules make the membrane more rigid.

This explains why cholesterol helps to maintain the shape of animal cells.

Question 5

The permeability of cell membranes can be influenced by several factors including:

___ affects the … in the cell membrane.
… can be used to control the ___

The more easily the phospholipid bilayer is dissolved, the …

Solvent concentration can be controlled by …

… increases the fluidity of the membrane, increasing its permeability

… can help keep temperature constant.

Answer 5

The permeability of cell membranes can be influenced by several factors including:

pH affects the protein structure in the cell membrane.

Buffer solutions can be used to control the pH.

The more easily the phospholipid bilayer is dissolved, the more permeable the membrane is.

Solvent concentration can be controlled by using the same solvent at the same concentration for each trial.

Higher temperatures increase the fluidity of the membrane, increasing its permeability.

Using a water bath can help keep temperature constant.

Question 6

Investigating Cell Membrane Permeability

1) Collect beetroot samples
Use a … to collect samples of uniform diameter.
Cut ___ of a uniform depth using a … on a white tile and rinse in cold water. This removes excess …

2) Add ethanol
Prepare at least five concentrations of ethanol (e.g. …) in beakers.
Place the discs into the ___ solution for __ minutes.
Make sure the samples are completely ___ by the ethanol solutions and ___ frequently throughout the ___ minutes.

3) Remove the discs
Remove the discs from the solutions to prevent … and allow a fair ___ between the experiments.

4) Calibrate the colorimeter
Calibrate a colorimeter by using a ___ of … at an absorbance of ____
The cuvettes must be ____ and the …. must not be touched to prevent potential ____ in the readings.

5) Measure absorbance
Measure the absorbance of each ___
Plot the results in a graph with ____ on the x-axis and ____ on the y-axis.
The darker the solution … This is reflected in a higher reading for ___

Answer 6

Investigating Cell Membrane Permeability

1) Collect beetroot samples
Use a cork borer to collect samples of uniform diameter.
Cut discs of a uniform depth using a sharp scalpel on a white tile and rinse in cold water. This removes excess pigment that has leaked through physically broken cell membranes.

2) Add ethanol
Prepare at least five concentrations of ethanol (e.g. 0%, 10%, 20%, 30%, 40%) in beakers.
Place the discs into the corresponding solution for 10 minutes.
Make sure the samples are completely covered by the ethanol solutions and mixed frequently throughout the 10 minutes.

3) Remove the discs
Remove the discs from the solutions to prevent further changes and allow a fair comparison between the experiments.

4) Calibrate the colorimeter
Calibrate a colorimeter by using a cuvette of distilled water at an absorbance of 520nm.
The cuvettes must be dry and the clear sides must not be touched to prevent potential errors in the readings.

5) Measure absorbance
Measure the absorbance of each solution.
Plot the results in a graph with concentration on the x-axis and absorbance on the y-axis.
The darker the solution, the more pigment has been released. This is reflected in a higher reading for absorbance.