Cellular Transportation

Cellular Transportation

Passive transport is the transportation of

materials across a plasma membrane

without energy.

Active transport is the movement of particles

from an area of low concentration to an area

of high concentration that uses energy

provided by ATP or a difference in electrical

charges across a cell membrane.

Diffusion of Water

• The plasma membrane controls what can enter or leave a cell.

• The plasma membrane does not limit the

amount of water that passes or diffuses through.

• Remember… diffusion is the movement of particles from

an area of higher concentration to an area of lower concentration. It is a natural result of kinetic molecular energy.

Solution is a type of mixture in which all the

components are evenly distributed. Example

Kool- Aid Drink

Solute is a substance that is dissolved in a

solution Example Kool-Aid powder

Solvent is dissolving substance in a solution.

Example the water to make Kool- Aid.

Osmosis: Diffusion of Water • In cells, the water wants to have equal

concentrations of substances on both sides of the membrane.

• The diffusion of water across a selectively permeable membrane is called osmosis. In other words osmosis is the movement of water or another solvent through a permeable membrane from an higher concentration to an area of lower concentration

What controls osmosis? • Regulating water flow through the plasma

membrane is important to maintaining homeostasis.

• If a strong solution and a weak solution of the same things are put in direct contact, the water molecules will diffuse in one direction.

• The water will go toward the stronger side

until the concentration is the same everywhere.

The water wants to go to the area of higher

concentration (the stronger solution)

Concentration is the measure of the amount

or proportion of a given substance with

combined with another substance.

Concentration gradient is the graduated

differences in concentration of a solute per

unit distance through a solution.

Selective permeability =

like a screen

Some things can come in and some things are kept out

During osmosis, water diffuses across a selectively permeable membrane.

Notice that the number of sugar molecules did not change on each side of the membrane, but the number of water molecules on either side of the membrane did change.

6 sugar molecules

on this side

6 sugar molecules

on this side

24 sugar

molecules on

this side

24 sugar

molecules on

this side

Cells in an isotonic solution

• Same concentration on both sides

• Diffuses in and out at the same rate

• Cells retain their normal shape

In an isotonic solution, water molecules move into and out of the cell at the same rate, and the cells retain their normal shape as in (A).

Notice the concave (normal) disc shape of a red blood cell in (B).

A plant cell has its normal shape and pressure in an isotonic solution in (C).

Cells in an isotonic solution – neutral …same concentration on both sides

Put the fish in an isotonic solution

It would be like putting a freshwater fish in a freshwater fish tank…

Put the fish in an isotonic solution

The fish would stay the same size.

Cells in a hypotonic solution

• Concentration of dissolved substance is lower in the solution outside the cell

• There is more water outside the cell

• Cells in hypotonic solutions experience osmosis that FLOWS IN

• The cell swell and internal pressure increases

Cells in an hypotonic solution – concentration of dissolved molecule lower outside the cell

In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell (A).

Animal cells, like these red blood cells, may continue to swell until they burst. (B).

Plant cells swell beyond their normal size as pressure increases (C).

It would be like putting a saltwater fish in a freshwater fish tank…

Put the fish in an hypotonic solution

The fish would swell… it may even burst!

Put the fish in an hypotonic solution

Cells in a hypertonic solution

• The concentration of dissolved substances is higher outside the cell than inside the cell

• Cells in hypertonic solutions experience

osmosis that causes water to FLOW OUT • Animal cells shrink in hypertonic solutions

because of decreased pressure • Plants wilt under these conditions

Cells in an hypertonic solution – concentration of dissolved molecule higher outside the cell

In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink (A).

Animal cells like these red blood cells shrivel up as they lose water (B).

Plant cells lose pressure as the plasma membrane shrinks away from the cell wall (C).

It would be like putting a freshwater fish in a saltwater fish tank…

Put the fish in an hypertonic solution

The fish would shrivel like a raisin.

Put the fish in an hypertonic solution

Direction of Osmosis

Hypotonic Hypertonic Isotonic

Solute higher

inside cell than

outside

Solute

molecules

higher outside

cell than inside

Solute is equal

inside and

outside of the

cell

Water tends to flow from hypotonic to hypertonic solutions

Salt sucks… if you are a slug… is it a hyper or hypotonic environment for the slug?

Remember…Higher concentration on the outside = ?

Concentration gradient

• This diagram shows a “concentration gradient”.

• There is a higher concentrate of dissolved particles on one side.

Concentration gradient

• When we move from areas of higher concentration to lower concentration, we are moving with the gradient.

• When we move from areas of lower concentration to higher concentration, we are moving against the gradient.

Concentration Gradient

The graduated difference in concentration of

a solute per unit distance through a solution.

Concentration

The measure of the amount or proportion of

a given substance when combined with

another substance.

A diffusion gradient

The molecules are more densely packed on

the left and so they tend to diffuse into the

space on the right. This is a diffusion gradient

Diffusion gradient 7

Passive transport

• With the concentration gradient – from higher concentration to lower concentration

• Requires no energy

Passive transport by proteins

• Transport proteins in plasma membrane help or “facilitate” movement of substances through the membrane

• This movement is with the concentration gradient

• It requires no energy

What is facilitated diffusion?

• Facilitated diffusion is a process in which

substances are transported across a

plasma membrane with the concentration

gradient with the aid of carrier (transport)

proteins. IT DOES NOT REQUIRE

ENERGY!

Passive Transport

Passive transport can occur by (A) simple diffusion,

(B) facilitated diffusion by channel proteins,

and (C) facilitated diffusion by carrier proteins.

What are carrier proteins?

Carrier proteins are proteins embedded in

the plasma membrane involved in the

movement of ions, small molecules, and

macromolecules into and out of cells. Carrier

proteins are also known as transport

proteins.

Humans obtain their oxygen by diffusion

But not through the skin

Although the skin is well supplied with blood

vessels, there are too many layers of cells for

diffusion to be fast enough

Humans have lungs and it is in these lungs

that diffusion occurs

18

CO2 diffuses

out O2 diffuses in

Section through

worm’s skin

the blood vessels

absorb the O2 and

carry it to the body

0.04mm

Earthworm diffusion takes place through

the thin skin of the worm

16

position of lungs

in thorax

windpipe

lung

diaphragm

heart

human lungs

Human lungs 19

the air passages in the lung

branch into finer and finer tubes

each tube ends up in

a cluster of tiny air

sacs.

Lung Structure 20

blood supply to air sac

air breathed

in and out

diffusion of

oxygen

diffusion of

carbon dioxide O2

CO2

A single air sac 21

0.03 mm

question 4

Fish

gill cover

gill cover cut away

gills

gill filaments

23

Leaf

O2 and CO2 diffuse

into the spaces between cells

the ‘veins’

bring water

O2 and CO2

diffuse through

pores in the

epidermis

In a thin leaf, the

diffusion distance

is short

26

In mammals, birds, reptiles and amphibia,

oxygen and carbon dioxide are exchanged by

diffusion in the lungs

In fish, this exchange of gases takes place by

diffusion through the gills

The oxygen dissolved in the water diffuses into

the blood vessels in the gills.

22

Plants have no special organs for breathing

They have to rely on diffusion for their supplies

of oxygen and carbon dioxide

There are pores in the leaves and stems through

which the gases diffuse

In daylight, CO2 (for photosynthesis) will be

diffusing in and O2 will be diffusing out

In darkness, O2 will diffuse in and CO2 will diffuse

out as a result of respiration

25 Plants

Active Transport

• Cells can move substances from areas of lower concentration to areas of higher concentration

• This is moving against the concentration

gradient • This will require extra help from carrier

proteins • Energy is needed!

How active transport occurs

• A particle binds with a carrier protein – usually pretty specific (like a lock and key)

• When the correct ones fit, chemical energy allows the cell to change the shape of the carrier protein like opening a door.

• Once the particle is on the other side, the carrier protein goes back to its normal shape.

Carrier proteins are used in active transport to pick up ions or molecules from near the cell membrane, carry them across the membrane, and release them on the other side.

Why does active transport require energy?

Molecules tend to move from higher to lower concentration. Active transport reverses the trend requiring energy input.

Type of

Transport

Transport

Protein

Used?

Direction of

Movement

Requires

Energy

Input from

Cell?

Classification

of

Transport

Simple

Diffusion

Osmosis

Facilitated

Diffusion

Active

Transport

Transport Through the Plasma Membrane

A Type of Active Transport is Bulk Transport:

Endocytosis and Exocytosis

Transport of large particles

• Endocytosis = cells surrounds and takes in materials from its environment.

Endocytosis A process in which a cell engulfs extracellular material through an inward folding of its plasma membrane. • Some single cell organisms like amoebas eat

this way. • This does require energy.

Transport of large particles

• Exocytosis- A process in which a cell releases substances to the extracellular environment by fusing a vesicular membrane with the plasma membrane, separating the membrane at the point of fusion and allowing the substance to be released.

• The expulsion of waste materials from the cell.

Some unicellular organisms ingest food by endocytosis and release waste or cell products from a vacuole by exocytosis.