Topic 2: Membrane transport

Question 1

To survive, cells need to: (2 points)

Answer 1

1. take in substances like OXYGEN AND GLUCOSE which are used for metabolic cell reactions eg. respiration to release energy for cell processes
2. remove waste products eg. CARBON DIOXIDE

Question 2

For molecules to enter or leave the cell they must cross

the ____ _________ .

Answer 2

cell membrane

Question 3

What are the 6 ways that molecules can cross membranes?

Answer 3

1. Simple diffusion
2. Facilitated diffusion
3. Osmosis
4. Active transport
5. Exocytosis
6. Endocytosis

Question 4

Key Summary: Define simple diffusion (1 point)

Answer 4

1. The NET movement of molecules or ions from a region of THEIR HIGH concentration to a region of THEIR LOWER concentration, down a CONCENTRATION GRADIENT.

Question 5

Key Summary: What are the properties of simple diffusion (3 properties)

Answer 5

1. PASSIVE process (does not require energy)
2. DOWN A CONCENTRATION GRADIENT (high to low)
3. Can reach EQUILIBRIUM where there is NO NET CHANGE in the number of molecules on either side of a membrane
   (but molecules still cross the membrane in both directions).

Question 6

What kind of molecules diffuse through the bilayer between the phospholipids?
(3 types)

Answer 6

1. Small molecules (e.g. O2 & CO2)
2. Lipid based molecules (e.g. steroid hormones)
3. {non-polar/hydrophobic} molecules

Question 7

Key Summary: Define facilitated diffusion (2 points)

Answer 7

1. The NET movement of molecules or ions from a region of THEIR HIGH concentration to a region of THEIR LOWER concentration, DOWN A CONCENTRATION GRADIENT,
2. THROUGH CARRIER OR CHANNEL PROTEINS.

Question 8

Key Summary: Give the properties of facilitated diffusion (4 properties)

Answer 8

1. Molecules move DOWN A CONCENTRATION GRADIENT, from high concentration to low concentration
2. PASSIVE process (does not require energy)
3. Involves CHANNEL PROTEINS WHICH MAY OPEN AND CLOSE or CARRIER PROTEINS WHICH CAN CHANGE SHAPE
4. Allows {large / polar} molecules or charged molecules or ions eg. sodium ions, to pass through a membrane

Question 9

Key Summary: Define osmosis (2 points)

Answer 9

1. The movement of WATER from an area of high concentration of FREE water molecules (low solute concentration) to an area of low concentration of FREE water molecules (high solute concentration)
2. across a PARTIALLY PERMEABLE MEMBRANE.

Question 10

Key Summary: Give the properties of osmosis (5 properties)

Answer 10

1. PASSIVE process (does not require energy)
2. Movement of WATER ONLY
3. Through a PARTIALLY PERMEABLE MEMBRANE
4. Mostly through channel proteins called AQUAPORINS or through phospholipid bilayer, as they are small (but slower)
5. Molecules move DOWN A CONCENTRATION GRADIENT

Question 11

Explain carrier proteins carry out {facilitated diffusion / active transport} (depends on gradient)
(3 steps)

Answer 11

1. {Molecule/ion} BINDS to a binding site with a specific complementary shape, on the carrier protein
2. Carrier protein CHANGES SHAPE
3. Molecule/ion} can then PASS THROUGH THE PROTEIN to the other side of the membrane

Question 12

Describe the properties of channel proteins

5 properties

Answer 12

1. Aqueous (water filled) PORES in the membrane
2. Only involved in facilitated diffusion – high to low concentration
3. SPECIFIC for one type of molecule or one molecule eg. sodium ion channels
4. Faster transport than carrier proteins
5. SOME ARE ABLE TO OPEN AND CLOSE (are gated) – like the CFTR protein

Question 13

Key Summary: How are carrier and channel proteins involved in membrane transport?
(3 points)

Answer 13

1. Allow {large/charged/hydrophilic} molecules or ions to MOVE THROUGH THEM to cross the cell membrane
2. Carrier proteins are involved in ACTIVE TRANSPORT AND FACILITATED DIFFUSION
3. Channel proteins are involved in FACILITATED DIFFUSION

Question 14

Key Summary: Define active transport (2 points)

Answer 14

1. Active transport is the movement of molecules or ions across a membrane AGAINST A CONCENTRATION GRADIENT (low to high concentration),
2. using energy in the form of ATP to drive carrier protein pumps in the membrane.

Question 15

Key Summary: Give the properties of active transport (3 properties)

Answer 15

1. ACTIVE process – energy in the form of ATP is needed
2. AGAINST A CONCENTRATION GRADIENT (low to high)
3. Molecules bind to and pass through CARRIER PROTEINS WHICH CHANGE SHAPE, so it is a ONE WAY TRANSPORT

Question 16

Some cells need to move more than just one molecule at a time across a membrane.

Bulk transport is possible because membranes are ____, so are flexible enough to ___ or _____ ___

Answer 16

fluid

fuse

pinch off

Question 17

Key Summary: Describe the steps of exocytosis (Bulk transport of molecules OUT of a cell)
(3 steps)

Answer 17

1. Molecules to be transported out of the cell are enclosed in a vesicle
2. Vesicle MOVES to the cell membrane and FUSES with the membrane
3. Contents of the vesicle are released outside the cell

Examples of molecules moved: Large molecules, enzymes, protein hormones (eg. insulin), neurotransmitters

Question 18

Exocytosis is an active process, so it needs _______ in the form of ____ for ___________ ___ _________.

Answer 18

energy

ATP

movement of vescicles

Question 19

Key Summary: Describe the steps of endocytosis (Bulk transport of molecules INTO a cell)
(2 steps)

Answer 19

1. The membrane invaginates (bulges inwards) and wraps around the particle(s)
2. then pinches off to FORM a vesicle inside the cell

Examples of molecules moved: Large molecules e.g. cholesterol. Bacteria are also engulfed by white blood cells in this way (called phagocytosis)

Question 20

Oxygen is transported by __________ through {membrane/bilayer between phospholipids}, as it is ______.

Answer 20

diffusion

small

Question 21

Carbon dioxide is transported by __________ through {membrane/bilayer between phospholipids}, as it is ______.

Answer 21

diffusion

small

Question 22

Lipid soluble molecules are transported by __________ through {membrane/bilayer between phospholipids}, as it is not __________ by _______ _____ ______.

Answer 22

diffusion

repelled

fatty acid tails

Question 23

Water is transport by ________ through _________ (faster) OR between phospholipids as it is ______ enough even though it is _____ (slower).

Answer 23

osmosis

aquaporins

small

polar

Question 24

Glucose and amino acids (large, polar) are transported through __________ or __________ proteins by ___________ ___________ or ___________ ___________. Depending on the gradient, either _____________ or _____________ if in bulk.

Answer 24

carrier

channel

facilitated diffusion

active transport

endocytosis

exocytosis

Question 25

Ions (charged) are transported through __________ or __________ proteins by __________ __________ or __________ __________ (depending on the gradient).

Answer 25

carrier

channel

facilitated diffusion

active transport

Question 26

Molecules move out of a cell in bulk (e.g. hormones, neurotransmitters) by ____________.

Answer 26

exocytosis

Question 27

Any large substances moving into a cell (e.g. bacteria, fluids) are transported by ____________.

Answer 27

endocytosis