Question 1 Standards 1998

 

Cells transport substances across their membranes. Choose THREE of the following four types of cellular transport.

Osmosis

Active transport

Facilitated diffusion

Endocytosis/exocytosis

For each of the three transport types you choose,

a) describe the transport process and explain how the organization of cell membranes functions in the movement of

specific molecules across the membrane; and

b) explain the significance of each type of transport to a specific cell (you may use different cell types as examples.)

 

Osmosis (Max 4)

 

Description (part a)

 

Organization (part a)

 

Significance (part b)

 

structure linked to function

 

 

"how or why"

 

 

· movement of water from: high to low water concentration high to low water potential

· phospholipid bilayer allows

passage of small/ uncharged/

polar molecules

· Any legitimate link of water

passage to cell function

Animal cell examples:

high to low osmotic potential

· fluidity of membrane allows gaps

· can cause lysis

low to high solute concentration

low to high osmotic pressure

· protein-lined pores (renal tubule]

allow water movement

· can cause shriveling

diffusion of water

 

· in kidney (nephron) cells:

 

 

allows for osmoregulation

· passive and/or

does not require cellular energy

 

Plant cell examples:

· provides water for photosynthesis

 

 

· can create turgor

 

 

· can cause plasmolysis

 

 

· in guard cells: allows control of stomatal opening
 

 

· in root hairs: allows water uptake
 

 

 

 

 

 

 

Active Transport (Max 4)

· movement of molecules/ions

against their gradient

· cellular energy required

i.e. ATP; NADH; NADPH

· proteins act as carriers and/or

pumps

· protein conformation changes

· Any legitimate link of

passage to cell function

 

Animal cell examples:

· Na+/K+ pumps:

 

 

establish polarity

 

 

assist in repolarization

 

 

assist in glucose transport

 

 

Ca++ pumps

 

 

allow uptake for muscle contraction

 

  

allow uptake for neurotransmitter release

 

 

Plant cell examples:

 

 

· K+ pumps

 

 

regulate turgor

 

 

establish polarity

 

 

· H+ pumps permit

 

 

sucrose loading in phloem

 

 

 

Any specific cell example:

 

 

· H+ pumps

help generate H+ gradient

 

 

 

 

 

Facilitated Diffusion (Max 4)

 

 

 

 

· mediated movement of molecules/ solutes/ ions/ substances along their gradient

· proteins act as carriers of large and/or charged molecules

· ion channels transport ions

· Any legitimate link of passage to cell function

 

Animal cell examples:

· passive transport/ does not require cellular energy

· protein conformation changes

· Cl- ion channels:

assist cardiac repolarization

 

 

· Ca++ ion channels:

 

 

assist neurotransmitter release

 

 

assist muscle fiber contraction

 

 

 

Bacterial cells/ mitochondria/ chloroplasts:
 

 

· porins create permeability to small molecules

 

 

Any specific cell examples:

 

 

· Na+; K+; (ion) channels help establish polarity

 

 

· carrier proteins assist amino acid transport assist sugar transport

Endocytosis/Exocytosis (Max 4)

 

Endocytosis (including

phagocytosis and pinocytosis)

· transport of substance into cell via vesicle formation and/or membrane folding e.g.: engulf/ invaginate/ envelope/ pinch in

· transport of substance into cell via vesicle formation may be receptor-mediated

 

Exocytosis

· transport of substance out of cell via vesicle fusion

Both

· require energy

· Membrane fluidity/ solubility/fusion allows vesicles to join membrane

· clathrin and non-clathrin

coated pits allow specificity

· external/internal monolayers ("sidedness") allow fusion

· cytoskeleton is involved

· Golgi & ER form vesicles for secretion

· Any legitimate link of passage to cell function

Examples:

· protists: for nutrition

· mast cells: for secretion of histamines

· liver cells: for LDL/cholesterol uptake

 

Any specific cell example:

· export of cell products

· uptake of specific substances

· growth [addition of cell membrane]

  Scoring:

 · Bulleted items earn points

· Each mode of transport earns a maximum of 4 points. There is an internal maximum of one point per category (a1, a2,b).

· One additional point may be earned from any one category for discussion of a second bulleted item or an elegant elaboration.