transport across the cell membrane

Question 1

what is the function of the cell surface membrane?

Answer 1

regulates the movement substances into and out of the cell

Question 2

what does partially permeable mean?

Answer 2

• lets some molecules through but not others

Question 3

what molecules CAN pass through the plasma membrane?

Answer 3

• lipid soluable substances e.g. some hormones
• very small molecules

Question 4

what molecules CANT pass through the membrane?

Answer 4

• water soluable (polar ) substances
• large molecules

Question 5

what is simple diffusion?

Answer 5

the net movement of molecules from an area of high concentration to an area of low concentration
- until equilibrium is reached
- does not require ATP

Question 6

how do molecules move in simple diffusion without ATP?

Answer 6

• due to kinetic energy that they posses
• to enable them to constantly move in fluid

Question 7

what is facilitated diffusion?

Answer 7

the net movement of molecules from an area of high concentration to an area of low concentration
- through protein channels or carrier proteins

Question 8

what sorts of molecules move through protein channels or carrier proteins?

Answer 8

ions and polar molecules

Question 9

how do channel proteins transport molecules?

Answer 9

• protein channels form tubes filled with water
• this enables water soluable ions to pass through membrane

this process id still selectie, as channel protiens only open in the presence of stimuli

Question 10

how do carrier proteins transport molecules?

Answer 10

• carrier protiens bind with molecule (e.g. glucose)
• cause protein to change in shape
• this shape change enables molecule to be released to other side of membrane

Question 11

what is osmosis?

Answer 11

the movement of water from an area of high water potential to a low water potential across a partially permeable membrane

Question 12

what does water potential actually mean?

Answer 12

• pressure created by water molecule
• pure water= water potential 0
• the more negative the wp the more solute dissolved

Question 13

define isotonic, hypotonic, and hypertonic

Answer 13

isotonic= water potential is same in solution AND cell within solution
hypotonic= water potential is more positive than cell (solution has more water than cell)
hypertonic= water potential is more negative than cell (cell has more water than soltution)

Question 14

what would happen to an animal cell if it was placed in a hypotonic solution e.g. water?

Answer 14

• alot of water will move into cell by osmosis
• because animal cells dont have a cell wall, the pressure will cause cell to burst

plant cells do not burst because of cell wall so instead become turgid

Question 14

what would happen if an animal cell was placed in a hypertonic solution?

Answer 14

• water would move out of cell by osmosis
• so cell would shrink + become shrivelled

Question 15

what is active transport?

Answer 15

• the net movement of molecules and ions from an area of low to high concentration (against concentration gradient)
• using ATP and carrier proteins

Question 16

why is active transport selective?

Answer 16

• only certain molecules can bind to receptor sites on carrier proteins

Question 17

how does ATP enable active transport?

Answer 17

ATP will bind to the protein on insdie of membrane
- atp hydrolysed into ADP + Pi
- cause protein to change shape and open towards inside of membrane
- causes molecule to be released to other side of membrane

pi molecule is released from protein so it returns to original shape :)

Question 18

what is co transport?

Answer 18

the coupled movement of substances across a cell membrane via a carrier protein

Question 19

outline the process of co transport with glucose?

Answer 19

• sodium ions are actively transported out of the epithelial cell into the blood
• this reduces sodium ion concentration in epithelium cell (compared to lumen of iluem)
• sodium ions can then diffuse down conc gradietn from lumen to epithelial cell
• sodium ions diffuse through co-transporter proteins into epithelial cell against concentration gradient

Question 20

what are the adaptations of the epithelial cells?

Answer 20

epithelial cells contain large number of mitchondria
- provides ATP needed for sodium potassium pump

membrane of epithelial cells folded into large number of microvilli
- increases surface area of membrane, providing more space for membrane protiens needed for facilitated diffusion + active transport

glucose molecules absorbed are rapidly carried away by bloodstream
-provides steep conc gradient between epithelial cells and blood
- so facilitated diffusion of glucose into bloodstream takes place rapidly