2.3 Transport across membranes

Question 1

what is the membrane called

Answer 1

fluid mosaic model

Question 2

why is the membrane called the fluid mosaic model

Answer 2

• fluidity of membrane and the mosaic arrangement of proteins

Question 3

what does the phospholipid bilayer allow

Answer 3

• lipid soluble molecules to pass through but not water soluble
• makes membrane self sealing and flexible

Question 4

components of the membrane

Answer 4

proteins, phospholipids, cholesterol, glycolipids and glycoproteins

Question 5

why are proteins present in the cell membrane

Answer 5

• aid movement across membrane
• provide mechanical support
• act in conjunction with glycoproteins as receptors

Question 6

why is cholesterol present in the cell membrane

Answer 6

• make the membrane more rigid
• reduces movement of phospholipids
• prevents leakage of water and ions form cell as its hydrophobic

Question 7

why are glycolipids present on the cell surface membrane

Answer 7

• act as cell surface receptors for certain molecules
• allow cells to adhere to one another to form tissues

Question 8

why are glycoproteins present on cell membranes

Answer 8

• act as cell surface receptors and neurotransmitters
• allow cells to recognise eachother and attach to form tissues

Question 9

what is diffusion

Answer 9

• movement of (small) molecules from an area of higher concentration to an area of lower concentration down a concentration gradient
• occurs directly through phospholipid bilayer

Question 10

what is facilitated diffusion

Answer 10

• requires channel protein to transport polar molecules, charged and water soluble molecules across a membrane

Question 11

what is osmosis

Answer 11

movement of water molecules from an area of high water potential to an area of low water potential down a concentration gradient through a partially permeable membrane

Question 12

what is active transport

Answer 12

movement of molecules using a carrier protein from an area of low concentration to an area of high concentration against a concentration gradient
- requires ATP

Question 13

what is exocytosis

Answer 13

vesicles containing large particles are fused to the cell surface membrane and released from the cell

Question 14

what is endocytosis

Answer 14

particles are enclosed in vesicles made from cell surface membrane and transported into the cell

Question 15

what is co transport

Answer 15

• uses ions to move substances into and out of cells
• sodium potassium pump

Question 16

what is an example of a co transporter

Answer 16

can be found on cell surface membrane of epithelial cells in ileum
- absorption of sodium and glucose

Question 17

what affects (increases) the rate of diffusion

Answer 17

surface area increases
diffusion gradient becomes more steep
temperature increase
diffusion distance distances

Question 18

what is a channel protein

Answer 18

a protein that allows the transport of a specific substance across a membrane

Question 19

what is a carrier protein

Answer 19

type of protein that transports a specific type of molecule across a membrane

Question 20

how is sodium and glucose absorbed in the ileum

Answer 20

• active transport of sodium (into blood from epithelial cell) lowers sodium ion concentration inside cell
• this creates a sodium ion concentration gradient between ileum and epithelial cell
• sodium ions then move into the cell from the ileum by facilitated diffusion
• they carry glucose molecules along with them via a co transporter
• glucose concentration inside cell increases and moves into the blood via facilitated diffusion

Question 21

what kind of transport is the sodium potassium pump

Answer 21

active transport