3.2.3 - CELL MEMBRANE + TRANSPORT Flashcards
describe how phospholipids are arranged in a plasma membrane (2)
- in a bilayer
- hydrophobic fatty acid tails facing inward
- hydrophilic phosphate head facing outward
name and describe five ways substances can move across the cell-surface membrane into a cell (5)
- simple diffusion of small/non-polar molecules down a concentration gradient
- facilitated diffusion down a concentration gradient via a channel/carrier protein
- osmosis of water down a water potential gradient (high to low)
- active transport against a concentration gradient vi a protein carrier using ATP
- co transport of 2 different substances using a carrier protein
explain the function of ATP hydrolase (2)
- ATP –> ADP + Pi releases energy
- energy allows ions to be moved against a concentration gradient/allows active transport of ions
the movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum. explain how. (2)
- maintains/generates a concentration/diffusion gradient for Na+ (f4rom ileum into cell)
- Na+ moving in by facilitated diffusion brings glucose with it OR Na+ moving in by co transport bring glucose with it
describe and explain two features you would expect to find in a cell specialised for absorption (2)
- folded membrane/microvilli so large surface area for absorption
- large number of co transporters/channel proteins so fast rate of absorption
OR
large number of co transporters/channel proteins for active transport
OR
large number of co transporters/channel proteins/channel proteins for facilitated diffusion - large number of mitochondria so they make more ATP by respiration
OR
large number of mitochondria for aerobic respiration
OR
large number of mitochondria to release energy for active transport - membrane-bound (digestive) enzymes so maintains concentration gradient for fast absorption
the movement of substances across cell membranes is affected by membrane structure. describe how. (5)
- phospholipid bilayer allows movement/diffusion of non-polar/lipid-soluble substances
- phospholipid bilayer prevents movement/diffusion of polar charged/lipid soluble substances OR membrane proteins allow polar/charged substances to cross the membrane/bilayer
- carrier proteins allow active transport
- channel/carrier proteins allow facilitated diffusion/co-transport
- shape/charge of channel determines which substances move
- number of channels/carries determine how much movement
- membrane surface area determines how much movement/diffusion
- cholesterol affects fluidity/rigidity/permeability
give two similarities in the movement of substances by diffusion and by osmosis (2)
- movement down a concentration gradient/from high to low concentration
- passive processes/do not use energy from respiration/ATP/metabolism
in mammals, in the early stages of pregnancy, a developing embryo exchanges substances with its mother via cells lining the uterus. at this stage, there is a high concentration of glycogen in the cells lining the uterus.
suggest and explain two ways the cell-surface membranes of the cells lining the uterus may be adapted to allow rapid transport of nutrients. (2)
- membrane folded so increased surface area/ membrane has large SA for fast diffusion/facilitated diffusion/active transport/co-transport
- large number of protein channels/carriers (in membrane) for facilitated diffusion
- large number of protein carriers for active transport
- large number of protein carriers for co-transport
sodium ions from salt (sodium chloride) are absorbed by cells lining the gut. some of these cells have membranes with a carrier protein called NHE3.
NHE3 actively transports one sodium ion into the cell in exchange for one proton (hydrogen ion) out of the cell.
use your knowledge of transport across cell membranes to suggest how NHE3 does this. (3)
- co-transport
- uses (hydrolysis of) ATP
- sodium ion and proton bind to the protein
- protein changes shape (to move sodium ion and/or proton across the membrane)
high absorption of salt from the diet can result in a higher than normal concentration of salt in the blood plasma entering capillaries. this can lead to a build-up of tissue fluid.
explain how. (2)
ANY PAIR:
- (higher salt) results in lower water potential of tissue fluid
- so less water returns to capillary by osmosis (at venule end)
OR - (higher salt) results in higher blood pressure/volume
- so more fluid pushed/forced out (at arteriole end) of capillary
compare and contrasts the processes by which water and inorganic ions enter cells (3)
comparisons:
1. both move down concentration gradient
2. both move through (protein) channels in membrane
contrast:
3. ions can move against a concentration gradient by active transport
contrast the processes of facilitated diffusion and active transport (3)
- facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins
- facilitated diffusion does not use ATP/is passive whereas active transport uses ATP
- facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient
putting bee honey on a cut kills bacteria. honey contains a high concentration of sugar.
use your knowledge of water potential to suggest how putting honey on a cut kills bacteria (3)
- water potential in (bacteria) cells is higher (than in honey)/water potential in honey is lower than bacterial cells
- water leaves bacteria by osmosis
- loss of water stops metabolic reactions
E. coli has no cholesterol in its cell-surface membrane. despite this, the cell maintains a constant shape. explain why. (2)
- cell unable to change shape
- because the cell has a cell wall
- wall is rigid, because it is made of murein/peptidoglycan
