Biology - Chapter 4 : Transport Across Cell Membranes

Explain why phospholipids can form a bilayer but triglycerides cannot. (3)

• Phospholipids can hydrophobic tails and hydrophilic heads 

• Triglycerides are only hydrophobic 

• Charged/hydrophilic end of phospholipids attracts to water/either side of the bilaye

Describe the fluid mosaic model. (3)

• Phospholipid bilayer 

• Carrier or channel proteins embedded 

• Cholesterol present 

• Components can move in the fluid mosaic model 

Describe simple diffusion. (2)

• Movement of small, non-polar molecules 

• Down a concentration gradient 

Describe the factors affecting rate of simple diffusion into cells. (2)

• Surface area of cell membrane 

• Concentration gradient 

Describe facilitated diffusion . (2)

• Movement of charged molecules 

• Down concentration gradient via a carrier or channel protein 

Describe the factors affecting the rate of facilitated diffusion. (2)

• Concentration gradient

• Density or number of channel/carrier proteins

Describe how osmosis occurs. (2)

• Water moves from an area of higher water potential (Ψ) to an area of lower water potential

• Across a partially permeable membrane

Explain why a tissue gains mass in distilled water. (2)

• Tissues have more negative water potential (than distilled water)

• Water potential of distilled water is 0

• Water moves into tissue by osmosis

Describe a method to investigate the water qpotential of tissue. (4)

• Record mass before and after and calculate percentage change

• Place tissue in solutions with a range of concentrations

• Blot surface solution off

• The concentration causing 0% change in mass is equal to concentration of the tissue

• Plot a graph – the x-intercept represents the concentration of the tissues

State the equation to calculate the volume of stock needed to dilute it to a required concentration. (1)

C1V1=C2V2 OR

• Target concentration/Stock concentration = Volume of stock/Volume of solution so

• Volume of stock = Target concentration/Stock concentration × Volume of solution

State a method used to produce a range of solutions with different concentrations. (1)

• Dilution series

Describe active transport. (2)

• Movement against concentration gradient

• Via carrier protein using ATP

Describe the mechanism for absorption of glucose or amino acids in the ileum. (4)

• Co-transport

• Sodium ions actively transported out of cell into blood or tissue fluid

• Creating sodium ion concentration gradient

• Facilitated diffusion of amino acid or glucose with sodium ion via cotransporter/carrier protein

Describe and explain features of a cell adapted for absorption. (2)

• Folded membrane so large surface area

• Large number of channel/carrier proteins for active transport or facilitated diffusion

• Large number of mitochondria for aerobic respiration

• Membrane-bound digestive enzymes so maintain concentration gradient

Describe how the movement of substances across cell membranes is affected by membrane structure. (5)

• Phospholipid bilayer allows diffusion of nonpolar molecules

• Phospholipid bilayer prevents movement of charged molecules

• Membrane surface area determines rate of diffusion

• Carrier proteins allow active transport

• Channel and carrier proteins allow facilitated diffusion or cotransport

• Shape/charge of carrier/channel protein determines which substances can move through them

• Number of proteins determines how much movement

• Cholesterol affects fluidity/permeability

State and explain causes of increased membrane permeability. (3)

• Ethanol because it is a solvent for phospholipid bilayer

• Temperature because it makes bilayer more fluid and denatures intrinsic proteins

• pH as it denatures intrinsic proteins

Explain how increased temperature caused more pigment to leave the cell. (2)

• Damage to cell membran

• Proteins denature

• Increased fluidity to phospholipid bilayer

Describe and explain the colorimeter results as permeability of cell membrane to pigment increases. (2)

• Absorbance increases

• As more pigment present in the test solution

Describe a method to control water temperature of an experiment. (1)

• Water bath and thermometer