transport across membranes

Question 1

structure of cell membrane

Answer 1

-fluid - phospholipids and proteins are able to move freely and laterally within the phospholipid bilayer
-mosaic - different proteins are randomly embedded and scattered among the phospholipids

Question 2

components of cell membrane

Answer 2

-phospholipids
-proteins
-glycoproteins and glycolipids

Question 3

structure of phospholipids

Answer 3

-consists of a hydrophilic phosphate (face aqueous cytoplasm and extracellular space) and 2 hydrophobic fatty acid chains (hydrophobic core)
-arranged as a bilayer in membrane structures

Question 4

function of phospholipids

Answer 4

-the bilayer arrangement of the phospholipids forms a barrier in an aqueous environment

Question 5

structure of extrinsic proteins

Answer 5

-loosely attached to membrane surface and are exposed to the aqueous medium of extracellular fluid and cytoplasm
-either side of the bilayer

Question 6

structure of intrinsic proteins

Answer 6

-embedded in hydrophobic core of phospholipid bilayer
-unilateral/ transmembrane

Question 7

function of transmembrane proteins

Answer 7

-channel proteins have hydrophilic channels which transport hydrophilic substances across membrane
-carrier proteins have binding sites which bind and transport specific substances across down concentration gradient/ against concentration gradient using energy released

Question 8

structure of glycoproteins and glycolipids

Answer 8

-glycoproteins - proteins with addition of short carbohydrate chains
-glycolipids - lipids/ phospholipids with addition of short carbohydrate chains
-found on the outer surface of the membrane

Question 9

function of glycoproteins and glycolipids

Answer 9

-cell-cell recognition where cells are able to recognise and bind to one another
-cell-cell adhesion where two adjacent cells may bind with each other, enabling cells to form a tissue
-receptor to bind to molecules for cell signalling

Question 10

primary functions of cell membrane

Answer 10

boundary
-the cell surface membrane forms a boundary that separates the cell contents from the external extracellular environment
-internal cytoplasm environment of the cell can be kept relatively constant in order to function optimally

compartmentalisation
-internal cell membranes of organelles enable compartmentalisation of cell contents and prevent mixing
-specialisation of cell function by concentrating specific substances needed for metabolic processes

selectively permeable membrane
-to prevent free interchange of substances
-hydrophobic and lipid-soluble substances are able to easily move through the hydrophobic core
-hydrophilic substances are repelled by hydrophobic fatty acid tails in the hydrophobic core
-close packing of phospholipids further prevents larger-sized substances from moving through

Question 11

passive transport

Answer 11

-the movement of substances down a concentration gradient without the use of energy
-simple diffusion, facilitated diffusion and osmosis

Question 12

simple diffusion

Answer 12

-refers to the net movement of substances down concentration gradient
-hydrophobic substances

factors affecting rate of simple diffusion
-molecular mass - lower molecular mass results in faster diffusion
-temperature
-concentration gradient
-distance
-surface area to volume ratio

Question 13

facilitated diffusion

Answer 13

-net movement of substances down a concentration gradient with the help of specific transport proteins
-hydrophilic substances

Question 14

osmosis

Answer 14

-the net movement of water molecules down a water potential gradient across a selectively permeable membrane

3 relative concentrations of solutions
-hypotonic solution - less negative water potential than cytoplasm
-isotonic solution - same water potential as cytoplasm
-hypertonic solution - more negative water potential than cytoplasm

Question 15

osmosis in animals cells

Answer 15

-when in less negative water potential, animal cell swells in volume and could burst/ lyse
-when in more negative water potential, animal cell shrinks in volume and crenates

Question 16

osmosis in plant cells

Answer 16

-when in less negative water potential, plant cell becomes turgid
-when in more negative water potential, plant cell becomes plasmolysed and cell surface membrane pulls away from the cellulose cell wall and has shrunk vacuole volume

Question 17

active transport

Answer 17

-movement of substances against a concentration gradient using energy across a selectively permeable membrane
-carrier proteins have binding sites which bind and transport specific substances across membrane against their concentration gradient using energy released

Question 18

contexts of active transport

Answer 18

-absorption of ions by root hair cells in plants
-absorption of glucose and amino acids by cells of the villi
-nerve impulse transmission in nerve cells

Question 19

bulk transport

Answer 19

-used to transport very large substances. energy released from mitochondria is required.
-endocytosis and exocytosis

Question 20

endocytosis

Answer 20

-involves an invagination of cell surface membrane to allow an intake of very large substance
-an endosome containing the substance is formed after pinching/ budding off from the cell surface membrane
-phagocytosis

Question 21

exocytosis

Answer 21

-involves transport of very large substances out of cell
-secretory vesicle fuses with the cell surface membrane, releasing the proteins into extracellular environment by exocytosis