Transport across membrane

Question 1

Describe fluid mosaic model of membranes

Answer 1

Fluid: phospholipid bilayer in which individual phospholipids can move = membrane has flexible shape

Mosaic = extrinsic & intrinsic proteins of different sizes & shapes are embedded

Question 2

Explain role of cholesterol & glycolipids in membranes

Answer 2

• Cholesterol: steroid molecule in some plasma membranes; connects phospholipids & reduces fluidity to make bilayer more stable
• Glycolipids: cell signalling & cell recognition

Question 3

Explain functions of extrinsic proteins in membranes

Answer 3

• binding sites/ receptors e.g. for hormones
• antigens (glycoproteins)
• bind cells together
• involved in cell signalling

Question 4

Explain functions of intrinsic proteins in membranes

Answer 4

• electron carriers (respiration/ photosynthesis)
• channel proteins (facilitated diffusion)
• carrier proteins (facilitated diffusion/ active transport)

Question 5

Explain functions of membranes within cells

Answer 5

• Provide internal transport system
• Selectivley permeable to regulate passage of molecules into/ out of organelles
• Provide reaction surface
• Isolate organelles from cytoplasm for specific metabolic reactions

Question 6

Explain functions of cell-surface membrane

Answer 6

• Isolates cytoplasm from extracellular environment
• Selecively permeable to regulate transport of substances
• Involved in cell signalling/ cell recognition

Question 7

Name & explain 3 factors that affect membrane permeability

Answer 7

• Temp: high temp. denatures membrane proteins/ phospholipid molecules have more kinetic energy & move further apart.
• pH: changes tertiary structure of membrane proteins
• Use of solvent: may dissolve membrane