2.1.5 A) Role of Membranes

Question 1

What are the roles of membranes within cells and at the surface of cells?

Answer 1

• regulates transport of substances in and out of the cell
• sites of cell communications (cell signalling)
  
  • may release chemicals that signal to other cells
  • contains receptors for such chemical signals and so is a site for cell signalling - hormones and drugs may bind to receptors in the membranes
• may be sites of chemical reactions
• partially permeable barriers between the cell and its environment, between organelles ad the cytoplasm and within organelles
• may contain enzymes involved in specific metabolic pathways
• has antigens so the organism’s immune system can recognise the cell as being ‘self’ and not attack it
• compartmentalisation - separate cell’s components from its external environment (external surroundings in single celled, tissue fluid or cells surrounding in multicellular)

Question 2

Compartmentalisation:

Answer 2

• the formation of membrane-bound areas in a cell
• vital for cells as metabolic reactions inc. many different and often incompatible reactions

Question 3

Permeability:

Answer 3

the ability to let substances pass through

Question 4

How do substances pass through membranes?

Answer 4

• some very small molecules simply diffused through the cell membrane in between its structural molecules
• some substances dissolve in the lipid layer and pass through
• other substances pass through special proteins or are carried by carrier proteins
• as these membranes don’t let all types of molecule pass through them they are described as partially permeable