lecture 4

Question 1

why are cells small

Answer 1

• cells need to be imported and exported
• as cell gets larger, volume is disproportionate to surface area (more nutrients can be imported and wastes exported in a small cell)

Question 2

characteristics of lipid bilayers

Answer 2

• made out of phospholipids (chain of carbons and hydrogens (fatty acids))
• one end is charged, other isn’t
• hydrophilic (love water) and hydrophobic (hate water)
• e.g. sea foam

Question 3

characteristics of a cell’s plasma membrane

Answer 3

• phospholipid bilayer embedded with proteins
• carb chains attached to proteins and lipids protrude from cell
• cytoskeleton filaments are attached to inside of membrane

Question 4

characteristics of fluid mosaic nature of plasma membrane

Answer 4

• proteins are scattered throughout membrane, mosaic pattern
• membrane is fluid - components move around on membrane
• fluidity imparts flexibility to cells

Question 5

what do the embedded molecules on the plasma membrane do

Answer 5

• cell recognition
• membrane channels
• receptors
• enzymatic reactions
• carrier porteins
• join cells together

Question 6

what is the differential permeability of the plasma membrane

Answer 6

small uncharged molecules (h2o, oxygen etc) can freely pass through but charged molecules and macromolecules cannot

Question 7

what is diffusion and where does it occur

Answer 7

• process where molecules move from high concentration to a low concentration until equilibrium is reached
• oxygen diffuses into capillaries and co2 out of capillaries
• PASSIVE

Question 8

what is osmosis and where does it occur

Answer 8

• movement of water molecules from a high concentration to a low concentration of water through a semi-permeable membrane
• PASSIVE

Question 9

active transport

Answer 9

• requires energy (ATP)

- e.g. sodium-potassium pump: raised potassium content inside cells while pumping sodium molecules outside

Question 10

what is endocytosis and exocytosis

Answer 10

entry of large particles/molecules into or out of cells

Question 11

what happens during endocytosis

Answer 11

a pit forms in the plasma membrane enclosing the transported substance in a small vesicle e.g. phagocytosis

Question 12

what is receptor mediated endocytosis

Answer 12

receptors bind substances, endocytosis allows selective entry into cell