8.2 Bellringer.. (1)In your own words, define passive, active, and

transport

Now, imagine sitting in a boat that is moving downstream with the current. Then, imagine a small motor to move the same boat upstream against the current.

(2)Determine which action shows passive transport and which shows active transport

(3)Which requires an input of energy?

8.2 Cell Transport

**The cell must move different substances into and out of the cell

This happens in a variety of ways….

Sometimes the cell has to use energy, sometimes they do not

**8.2 discusses the different methods of cell transport

Passive Transport Diffusion – passive transport of substances DOWN a

concentration gradient (from high to low concentration)

Concentration gradient – one area has a higher concentration than another area

Equilibrium – when a space is filled evenly

Diffusion is simplest type of passive transport

Some substance diffuse through lipid bilayer

Others though transport proteins

Diffusion Cell membrane is selectively permeable

Nonpolar interior of lipid bilayer repels ions and most polar molecules

These substances are prevented from diffusing across membrane

Very small or nonpolar molecules can diffuse across the membrane down their concentration gradient

Simple Diffusion Moves small, nonpolar molecules directly through

lipid bilayer

Ex-

O2

CO2

Diffusion

Model of Diffusion

Facilitated Diffusion Moves ions and polar molecules that simple diffusion

cannot

Transport proteins help these substances diffuse through the cell membrane

Two types:

Channel protein

Carrier protein

Channel Proteins Ions, sugars, and amino acids can diffuse with help of

channel proteins

Proteins, sometimes called pores, serve as tunnels through the lipid bilayer

Each channel allows the diffusion of a specific substance

Ex – only sodium ions can pass through sodium ion channels

Carrier Protein Transport substances that fit within their binding site

(1)Carrier protein binds to specific substances on one side of cell membrane

(2)Binding causes protein to change shape

(3)As shape changes, the substance is moved across the cell membrane and released on other side

Facilitated Diffusion

Osmosis Definition – diffusion of water across selectively

permeable membrane

Type of facilitated diffusion (passive transport)

From high to low concentration

Allows cells to maintain water balance as environment changes

Pass through water channels

Protein channels specific to water..

Osmosis

Osmosis There are three possibilities for the direction of

water movement:

Water moves out – (hypertonic solution)

Causes cell to shrink

Water moves in – (hypotonic solution)

Causes cell to swell

Cell could burst if it swells too much

Plant cells have rigid cell wall to prevent this

No net water movement – (isotonic solution)

No change in cell volume

Hypertonic, Hypotonic, and Isotonic Solutions

Effects of Osmosis **Plants and fungi have cell walls to help regulate

Most plants are healthiest in a hypotonic environment

Some unicellular eukaryotes have contractile vacuoles

Force excess water in cell out

Animals cells do not have cell walls or contractile vacuoles

They actively remove solutes from cytoplasm

Active Transport Transports of substance against concentration

gradient

Low to high concentration

Active Transport – requires energy

Most energy supplied directly or indirectly in the form of ATP (adenosine triphosphate)

Pumps Substances bind to carrier proteins in low

concentrations, released in higher concentration

Carrier proteins function as “pumps” – move substances against their concentration gradient called membrane pumps

Sodium-Potassium Pump One of the most important membrane pumps in

animal cells

In a complete cycle, the sodium-potassium pump transports three sodium ions, Na+, out of a cell and two potassium ions, K+, into the cell. Pump actively transports against their concentration

gradients Energy supplied by ATP

Sodium-Potassium Pump **The sodium-potassium pump has four steps:

1. Three sodium ions inside the cell bind to the sodium-potassium pump.

2. The pump changes shape, transporting the three sodium ions across the cell membrane and releasing them outside the cell.

3. Two potassium ions outside the cell bind to the pump.

4. The two potassium ions are transported across the cell membrane and are released inside the cell.

Sodium-Potassium Pump Important:

Pump prevents sodium from accumulating in the cell

Pump helps maintain the concentration gradient of sodium ions and potassium ions across cell membrane

Many cells use this pump to help transport other substances (glucose) across the cell membrane

Movement in Vesicles Many substances, like proteins and polysaccharides,

are too large to be transported by carrier proteins So, they are moved across the cell membrane by vesicles

The movement of a substance into a cell by a vesicle is

called endocytosis

The movement of a substance by a vesicle to the outside of a cell is called exocytosis

ENDOCYTOSIS

EXOCYTOSIS