Cellular Transport

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 Transport • With 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 concentrations • Therefore, it doesn’t require energy! • Fig. 7.20 • What 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 • Concentration- high concentration, fast diffusion • Temperature- high temp, faster movement • 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 • Channel proteins open and close the P.M. to allow the substance to diffuse that are polar • 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 dialysis • Question: • 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 osmosis • Regulating water in the cell helps maintain homeostasis • How 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 • Isotonic: Same concentration of water and solutes as its cytoplasm -Cells maintain normal shape • Fig. 7.23 • 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

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 Transport • What 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 Proteins • Active Transport • Fig. 7.26 Why does active transport require energy?

Na+/K+ ATPase Pump- A type of Carrier Protein • Found in PM of animal cells • Maintains the level of sodium ions (Na+) and potassium ions (K+) inside and outside of the cell • What 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 • Endocytosis • Movie

Transporting Large Particles • Exocytosis is the opposite of endocytosis • Cells 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 7.29 • Make 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

Cellular Transport