2. Transport Across Cell Membranes

Question 1

What is passive transport?

Answer 1

No energy required (no ATP expenditure)

High to low concentration gradient

Question 2

What is active transport?

Answer 2

Against concentration gradient (low to high)
Requires energy in the form of ATP
Need carrier proteins found in plasma membrane

Question 3

How do large particles pass into a cell? What is formed?

Answer 3

Endocytosis - active (needs ATP).

Plasma membrane surrounds the particle, forming a membrane-bound vesicle that pinches off the membrane.

Question 4

How do large proteins pass out of a cell?

Answer 4

Exocytosis. Energy required.

Question 5

Diffusion

Answer 5

Net movement of molecules or ions from a region of high concentration to a region of low concentration

Question 6

3 features of simple diffusion

Answer 6

1. Relies on random movement
2. Continues until equilibrium
3. Passive

Question 7

What types of particles undergo simple diffusion?

Answer 7

Small, uncharged, hydrophobic & non-polar molecules (oxygen & CO2)

Question 8

What types of particles undergo facilitated diffusion?

Answer 8

Hydrophilic molecules
Ions larger than CO2
Polar/charged molecules

Question 9

Features of facilitated diffusion

Answer 9

1. Water-filled channel proteins
2. Carrier proteins that change shape
3. Passive
4. Ion/molecule specific

Question 10

Facilitated diffusion: either channel or carrier, or both?

Answer 10

Either channel or carrier!

Question 11

What is the rate of facilitated diffusion limited by?

Answer 11

Number of channel/carrier proteins

Question 12

3 features of channel proteins

Answer 12

1. Span the membrane
2. Some are gated (e.g. open/close when hormone is present/absent)
3. Voltage-gated channels open & close depending on potential difference - this occurs in nerve impulses!

Question 13

3 features of carrier proteins

Answer 13

1. Molecule or ion binds to specific site
2. Protein changes shape to allow molecule across the membrane - but the process is STILL PASSIVE!!
3. Movement in either direction but ALWAYS DOWN THE CONCENTRATION GRADIENT!!

Question 14

Osmosis

Answer 14

Diffusion of water from high to low water potential across a partially permeable membrane

Question 15

4 features of osmosis

Answer 15

1. Passive
2. Requires a partially permeable membrane
3. Continues until equilibrium
4. Only FREE water molecules can move - not those associated with solute molecules

Question 16

Hypertonic solutions

Answer 16

Solution has a lower water potential

Question 17

Isotonic solutions

Answer 17

Both have equal water potentials

Question 18

Hypotonic solutions

Answer 18

Solution has a higher water potential

Question 19

Active transport

Answer 19

Movement of substances against the concentration gradient

Question 20

3 features of active transport

Answer 20

1. ALWAYS involves a carrier protein (specific for molecules/ions)
2. Requires energy in the form of ATP
3. Rate-limited

Question 21

What is ATP used for in active transport?

Answer 21

To change the shape of the carrier proteins to move the molecule to the other side of the membrane

Question 22

Why is active transport rate-limited?

Answer 22

Depends on number of carrier proteins present in the membrane

Question 23

Where does active transport occur?

Answer 23

In ALL CELLS!!

Question 24

The two example of bulk transport are…

Answer 24

Exocytosis and endocytosis

Question 25

What is exocytosis?

Answer 25

Release of substances - usually proteins and polysaccharides

Question 26

Examples of exocytosis

Answer 26

Insulin & neurotransmitters

Question 27

What is endocytosis?

Answer 27

Substances taken into cells by the creation of a vesicle

Question 28

Examples of endocytosis

Answer 28

Phagocytosis

Question 29

Endocytosis special case

Answer 29

Substances may first attach to receptors on membrane (e.g. cholesterol)

Question 30

Difference between epithelial cell and cilia

Answer 30

Cilia have hairs; epithelial cells have folds

Question 31

How is ileum adapted to increase rate of absorption? (4 things to mention)

Answer 31

1. Villi - increases surface area
2. Microvilli - increases surface area
3. Length of small intestine - increases surface area
4. Large surface area (provided by the 3 things above) for the insertion of channel/carrier proteins for facilitated diffusion, and carrier proteins for active transport. High density of channel/carrier proteins.

Question 32

What are villi?

Answer 32

Folds of the wall of the small intestine

Question 33

What are microvilli?

Answer 33

Extensions of the cell membrane of individual epithelial cells

Question 34

Co-transport of glucose is a type of…

Answer 34

Active transport!

Question 35

4 steps of co-transport of glucose

Answer 35

1. Na ions are actively transported using ATP from the epithelial cells into the blood by a carrier protein (sodium-potassium pump)
2. This maintains a higher concentration of Na ions in the lumen of the ileum than inside the epithelial cell
3. Na ions diffuse down the conc. gradient through a carrier protein called a co-transport protein, carrying glucose with it.
4. Glucose moves via facilitated diffusion into the blood

Question 36

Why is the process called co-transport (in the case of glucose)?

Answer 36

It relies on Na ions being actively transported into the bloodstream!
The only place where active transport takes place is step 1!

Question 37

Co-transport of glucose diagram

Answer 37

See Notion

Question 38

Co-transport is what type of process?

Answer 38

Active!

Even though some individual steps (i.e. facilitated diffusion) are passive