7.3: CELL TRANSPORT (across the cell membrane!)

Vocabulary

• Osmosis• Diffusion• Facilitated Diffusion• Osmotic Pressure• Isotonic• Hypertonic• Hypotonic

• Active Transport• Endocytosis• Exocytosis• Protein Pumps

Background Info…• Every living cell contains a liquid interior

(cytoplasm) and is surrounded by a liquid.

• The cell (plasma) membrane separates what is inside the cell from what is outside of the cell

• What is the MAJOR function of cell membrane?– regulate the movement of molecules from one side of

the membrane to the other.• In other words—control what gets in and what gets out!

Selectively permeable: • property of biological membranes which

allows some substances to pass more easily than others

Transport proteins: • membrane proteins that transport

SPECIFIC molecules or ions across biological membranes

GLUCOSE

Binding

TransportRecovery

Dissociation

Movement across the cell membrane can

be: 1) PASSIVE cell does not have to spend

energy substance moves from where it

is MORE concentrated to where it is LESS concentrated.

2) ACTIVE cell “spends” energy to move a

substance from where it is LESS concentrated to where it is MORE concentrated (“UPHILL”)

Passive Transport: DIFFUSION

• movement of a substance from where it is conc. to where it is less conc. (“down a concentration gradient”)

Passive Transport: OSMOSIS

• diffusion of WATER

across a selectively

permeable membrane;

water moves DOWN its

concentration gradient

INSIDE THE CELL

OUTSIDE THE CELL

– the direction of water movement water can be described/predicted based on if the cell’s environment is:

• ISOTONIC: equal solute concentration compared to inside a cell

• HYPERTONIC: greater solute concentration than inside a cell

• HYPOTONIC: lower solute concentration compared to inside a cell

WATER MOVES FROM HYPO TO HYPERTONIC!!!

In animal cells: • in a HYPERTONIC environment,

water exits the cell;

cells shrivel and usually die

• in a HYPOTONIC environment,

water moves into cell,

causing it to swell and

possibly burst

In cells with cell walls (i.e. plant cells): • in a HYPERTONIC environment, water exits

the cell; cells shrivel and usually die

• in a HYPOTONIC environment, water moves into cell, causing it to swell; cells become more TURGID.

Passive Transport: FACILITATED DIFFUSION

• diffusion of solutes across a membrane, with the help of transport proteins

(passive transport because it is movement down a concentration gradient; cell does not need to spend any energy)

ACTIVE TRANSPORT: energy-requiring process; molecules are moved across the cell membrane AGAINST their concentration gradient (“uphill”)

ACTIVE TRANSPORT: ENDOCYTOSIS & EXOCYTOSIS

• transport of large molecules (e.g. proteins and polysaccharides) into or out of the cell

ENDOCYTOSIS EXOCYTOSIS

*importing large molecules by forming vesicles out of the cell membrane**vesicle forms in a small region of cell membrane***used by cells to bring in larger, extracellular substances (e.g. proteins)

ENDOCYTOSIS EXOCYTOSIS

*exporting large molecules by vesicles fusing w / the cell membrane**vesicle buds from ER or Golgi and migrates to cell membrane***used by cells to export products (e.g. cells in pancreas secreting insulin)

2 types of Endocytosis:

1) Phagocytosis: solid particles (“cell

eating”)

2) Pinocytosis: fluid droplets (“cell

drinking”)

Phagocytosis

Pinocytosis

What are the 3 types of passive What are the 3 types of passive transport across a membrane?transport across a membrane?

a)a) Diffusion, osmosis, and exocytosisDiffusion, osmosis, and exocytosis

b)b) Exocytosis, endocytosis, and Exocytosis, endocytosis, and phagocytosisphagocytosis

c)c) Diffusion, facilitated diffusion, and Diffusion, facilitated diffusion, and osmosisosmosis

d)d) Diffusion, osmosis, and endocytosisDiffusion, osmosis, and endocytosis