2.3 - Transport across cell membranes Flashcards
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 protein carrier/channel
- Osmosis of water down a water potential gradient
- Active transport against a concentration gradient via protein carrier using ATP
- Co-transport of 2 different substances using a carrier protein
Explain the function of this ATP hydrolase. (2)
- (ATP to ADP + Pi ) Releases energy
- (energy) allows ions to be moved against a concentration gradient /(energy) allows active transport of ions
The movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum. (2)
- (Maintains/generates) a concentration/diffusion gradient
for Na+ (from ileum into cell) - Na+ moving (in) by facilitated diffusion, brings glucose with it /Na+ moving (in) by co-transport, brings 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-transport/ carrier/channel proteins so fast rate (of absorption)
/ Large number of co-transport/carrier proteins for active transport
/ Large number of co-transport/ carrier/channel proteins for facilitated diffusion - Large number of mitochondria so make (more) ATP (by respiration)
/Large number of mitochondria for aerobic respiration
/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. (2)
- Phospholipid (bilayer) allows movement/diffusion of nonpolar/lipid soluble substances
- Phospholipid (bilayer) prevents movement/diffusion of polar/
charged/lipid-insoluble substances/ (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 / carrier determines which substances move
- Number of channels/carriers determines how much movement
- Membrane surface area determines how much diffusion/movement
- Cholesterol affects fluidity/rigidity/ permeability
Give two similarities in the movement of substances by diffusion and by osmosis. (2)
- (Movement) down a gradient / from high concentration to low
concentration - Passive / not active processes / Do not use energy from respiration / from ATP / from metabolism
A student investigated the effect of surface area on osmosis in cubes of potato. Describe the method the student would have used to obtain the results. Start after all of the cubes of potato have been cut. Also consider variables he should have controlled. (4)
- Method to ensure all cut surfaces of the eight cubes are exposed to the sucrose solution
- Method of controlling temperature
- Method of drying cubes before measuring
- Measure mass of cubes at stated time intervals
The cells of beetroot contain a red pigment. A student investigated the effect of temperature on the loss of red pigment from beetroot. He put discs cut from beetroot into tubes containing water. He maintained each tube at a different
temperature. After 25 minutes, he measured the percentage of light passing through the water in each tube.
The student put the same volume of water in each tube. Explain why it was important that he controlled this experimental variable. (2)
- (If) too much water the concentration of pigment (in solution) will be lower / solution will appear lighter / more light passes through (than expected)
/ (If) too little water the concentration of pigment (in solution) will
be greater / solution will appear darker / less light passes
through (than expected) - So results (from different temperatures) are comparable
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 / large surface area / Membrane has increased / large surface area 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 (in membrane) for active
transport - Large number of protein (channels / carriers in membrane) 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)
- (Higher salt) results in lower water potential of tissue fluid
- (So) less water returns to capillary by osmosis (at venule end)
- (Higher salt) results in higher blood pressure / volume
- (So) more fluid pushed / forced out (at arteriole end) of capillary
Compare and contrast the processes by which water and inorganic ions enter cells. (3)
- Comparison: both move down concentration gradient
- Comparison: both move through (protein) channels in membrane
‘accept aquaporins (for water) and ion channels’ - Contrast: 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
