Biology / AS level
A phospholipid bilayer forms a hydrophobic barrier containing proteins with transport, receptor and catalytic roles.
A phospholipid bilayer forms a hydrophobic barrier containing proteins with transport, receptor and catalytic roles. Membrane components move laterally, while cholesterol helps regulate membrane properties in animal cells.
Simple diffusion and facilitated diffusion move substances down relevant gradients without direct ATP use. Active transport uses energy to move against gradients. Water moves from higher to lower water potential across a partially permeable membrane; pressure as well as solutes can affect that potential.
Two compartments have water potentials −100 kPa and −300 kPa. Which way is net water movement if only water can cross?
−100 kPa is the higher water potential, so water moves toward −300 kPa until the relevant potentials balance.
Using the worked example as supplied data, predict the effect of changing one condition. Draw a labelled model, record your reasoning and identify a variable that would need controlling. No human, animal or microbial experiment is required.
Related simplified PhET model. Explain what it represents and what the living system does differently.
Hydrophilic head
Polar heads interact with water while nonpolar tails gather within the bilayer.
From −100 to −300 kPa
−100 kPa is the higher water potential, so water moves toward −300 kPa until the relevant potentials balance.
No
A channel or carrier can support passive movement down a gradient without direct ATP hydrolysis.