Cellular Transport

Section 7.4

Cellular Transport

How do substances move throughout the cell? Ever smelled cookies baking while you were

in your bedroom?

Two ways to transport substances:Without energy= Passive TransportWith energy = Active Transport

Diffusion is Passive

Diffusion (AKA Passive Transport)- net mvmt of particles from an area where there are many to an area where there are fewer Animation

The amount of substances in a given area is called concentration

Substances diffuse from high to low concentrationsTherefore, it doesn’t require energy!Fig. 7.20What if the concentrations are the same?

When there is continuous movement of the particles, but no overall change in concentration it is called Dynamic Equilibrium

Three Main Factors of Diffusion

1. Concentration- high concentration, fast diffusion

2. Temperature- high temp, faster movement

3. Pressure- high pressure, particles are closer together and bounce into each other more often, faster diffusion

CHEMISTRY!!!

Diffusion Across the Plasma Membrane

Besides diffusing water across the cell, other ions and small molecules get diffused, too

Facilitated Diffusion- uses transport proteins to move other ions and small molecules across the plasma membrane

Types of Transport Proteins Used in Diffusion

1. Channel proteins open and close the P.M. to allow the substance to diffuse that are polar

2. Carrier Proteins change shape as they diffuse to help move substances through the membrane

Fig. 7.21 Passive Transport Reading Check- How do Na ions get into a

cell?

Applications of Diffusion

Kidney dialysisQuestion:

Do substances need a stimulus to diffuse across a membrane?

Osmosis- Water’ You Doing?Diffusion of Water

Water passes freely through the P.M. and doesn’t need transport proteins

The diffusion of water is called osmosisRegulating water in the cell helps maintain homeostasisHow it works:

Solute/solvent – which is which?Solute is the thing being dissolved, solvent does the dissolving

Water is the solvent If there is a lot of water, the concentration of the cell is low –

it’s dilute Fig. 7.22

Reading Check- Compare and contrast osmosis and diffusion

Types of Solutions- Egg Demo

1. Isotonic: Same concentration of water and solutes as its cytoplasm -Cells maintain normal shape Fig. 7.23

2. Hypotonic: if cell is in a solution that has a lower concentration of solute More water outside of cell than inside, so the water flows in

because of osmosis and the cell swells Too much swelling can lead to a burst! Because plants of rigid cell walls, they don’t burst in hypotonic

solutions Grocers use this idea to keep veggies fresh by misting them That’s how pickles are made

Fig. 7.24

3. Hypertonic: the concentration of the solute outside of the cell is higher than inside

Cells shrivel because the water is leaving the cell (less pressure)

In plants, it causes wilting Fig. 7.25 Evaluate the benefits of sports drinks that contain

electrolytes that athletes drink instead of water Is there any danger in consuming these drinks?

Osmosis

Active TransportWhat if a substance has to move from an area

of lower concentration to an area of higher? It requires energy and is called active transport

Occurs in pumps- carrier proteins that help in transport

Carrier ProteinsActive TransportFig. 7.26 Why does active transport require

energy?

Na+/K+ ATPase Pump- A type of Carrier ProteinFound in PM of animal cellsMaintains the level of sodium ions (Na+) and

potassium ions (K+) inside and outside of the cellWhat is it used for?

This protein pump is an enzyme to help with energy storing molecules

What’s it transport?Three Na+ out of the cell, 2 K+ into the cell

Why? The cell needs to get rid of Na+ and needs more K+But, since there’s lots of Na+ already on the outside of

the cell and lots of K+ already on the inside of the cell, active transport has to be used

Na+/K+ ATPase Pump

Three Na+ bind to the transport protein to move out of the cell

The transport protein requires ATP to change the shape of the protein

After the protein changes shape, it releases the Na+ to the outside of cell

In turn, the K+ on the outside of the cell bind to the protein

The protein changes shape and releases the K+ on the inside of the cell

Transporting Large Particles

Sometimes diffusion or transport proteins don’t get the job done because the particles are too large

Endocytosis is the process in which a cell surrounds the substance outside of the cell and engulfs it in the plasma membrane

The membrane then pinches off and leaves the substance inside the cell

EndocytosisMovie

Transporting Large Particles

Exocytosis is the opposite of endocytosisCells use it to expel wastes and secrete

cell products, like hormones, that were manufactured inside the cell

Both Endo and Exo require energy to maintain homeostasis in the cell

Movie

Visualize It!

Look at figure 7.29Make a Venn Diagram to compare and

contrast the processes of endocytosis and exocytosis.

Questions to Ponder

In what ways can materials move across a cell membrane?

What is the difference between osmosis, diffusion and facilitated diffusion?

Why are channel proteins needed?How do materials move against the

concentration gradient?Pg. 208- Cutting Edge Biology