Transport across cell membranes

Question 1

Simple vs facilitated diffusion

Answer 1

• simple = molecules move directly though the phospholipid bilayer
• facilitated = molecules pass through transport proteins (large use carrier, charged use channel)

Question 2

Factors that affect rate of diffusion

Answer 2

• surface are (increase = increase rate of diffusion
• concentration gradient (increase = increase rate of diffusion)
• thickness (decrease = decrease diffusion distance = increase rate of diffusion)
• temperature (increase = kinetic energy = molecules move faster = increase rate of diffusion)
• size of molecules (smaller molecules = increase rate of diffusion)

Question 3

What is Fick’s Law?

Answer 3

(surface are x concentration gradient) / Thickness

Question 4

Osmosis definition

Answer 4

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

Question 5

Which liquid has the highest water potential?

Answer 5

• distilled/pure water
• has a value of 0kPa
• lower water potential by adding solutes (makes water potential negative)
• water moves from less negative water potential to more negative water potential

Question 6

Surround animal cell with pure water?

Answer 6

Swells and burst (water enters by osmosis)

Question 7

Surround animal cell with pure water?

Answer 7

Swells and burst (water enters by osmosis)

Question 8

Surround plant cell with pure water

Answer 8

• Swells but does not burst
• cell wall prevents it from bursting
• made of cellulose - strong material
• the cell is turgid

Question 9

Surround animal cell with concentrated sugar/salt solution?

Answer 9

Shrinks (water leaves by osmosis)

Question 10

Surround plant cell with concentrated sugar/salt solution

Answer 10

• water moves by osmosis
• cell wall prevents cell from shrinking, keeps it rigid
• the protoplast (cell membrane plus contents) shrink
• the cell is plasmolysed

Question 11

Define active transport

Answer 11

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

Question 12

Describe the process of active transport

Answer 12

molecules (in area of low concentration) bind to carrier protein

• ATP breakdown to ADP, Pi and Energy
• the Pi and energy cause the carrier protein to change shape
• carrier protein release molecules on opposite side (in area of high concentration
• the carrier proteins release the attached Pi to return to its original shape

Question 13

Adaptations of small intestine

Answer 13

• folding to form Villus (large SA)
• cells lining small intestine have microvilli (large SA)
• walls of small intestine is thin (short diffusion distance)
• rich blood supply (maintains concentration gradient)
• cells lining small intestine have transport proteins and mitochondria

Question 14

Active transport of glucose in small intestine

Answer 14

• sodium ions are actively transported from the cells lining the small intestine into the blood
• lowers the sodium ion concentration in the cell
• therefore sodium ions move from the lumen of the small intestine into the cell
• this pulls in glucose via a cotransport protein
• therefore glucose builds up in the cell and moves into the blood by diffusion