3.5 Cells and Their Environment Diffusion Osmosis Active transport Bulk movement

Cell Membrane Cells must take in nutrients And eliminate wastes Both must cross the cell membrane

Inside vs. Outside

Inside vs. Outside We will talk in terms of substances outside the cell membrane vs. inside the cell membrane We will look at the concentration of materials

Semi permeable Membrane Lets certain molecules pass through the pores Prevents other molecules from crossing

Semipermeable Membrane Small molecules: water and sugars enter and leave freely Large molecules: lipids, proteins, carbs, and ions can not pass through

Transport of Substance Passive Transport Active Transport

Passive Transport Movement of substances across a membrane without using any energy Goes “with” the concentration gradient Substances move from high concentration of substances to low concentration of substances

Substance do not need energy, like climbing No Energy Required Substance do not need energy, like climbing DOWN hill

Types of Passive Transport Diffusion facilitated diffusion filtration osmosis

Active Transport Uses energy to move substances across a membrane Goes “against” the concentration gradient From low concentration to high concentration

Substance need energy, like climbing Active Transport Area of High Concentration Area of Low Concentration Substance need energy, like climbing UP hill

Diffusion Passive Transport Substances enter or exit a cell Move “Down a concentration gradient” From High to Low

No Energy Required

Substance do not need energy, like climbing No Energy Required Substance do not need energy, like climbing DOWN hill

Water and Sugar Molecules

Facilitated Diffusion PT Molecules need help of transport proteins Water-soluble molecules and ions are helped across by transport proteins, due to the hydrophobic nature of the lipids that make up cell membranes.

Transport Proteins Proteins embedded in the lipid bilayer of the cell membrane Open up channels to let ions pass

Osmosis Passive Transport, like diffusion The seeping of a water through a cell wall or cell membrane When the concentration of the fluid is the same on both sides of the barrier, osmosis stops

Osmosis A solution consists of solvents and solutes Cytoplasm is a solution of water and dissolved solutes External cellular environment is also a water solution with solutes

Osmosis Look at solvent (water) And solute (compound or ion or element) Solvent and solutes move in OPPOSITE directions

Osmotic Effects of Solution Concentrations Hypertonic solutions Isotonic solutions Hypotonic solutions

Hypertonic Solution Concentration of solutes outside the cell is higher than inside the cell Solutes move inside Water moves outside Cell Shrink

Isotonic Solution Concentration of solutes outside the cell = the concentration inside the cell NO OSMOSIS occurs

Hypotonic Solution Concentration of solutes outside the cell is lower than it is inside the cell Water moves into the cell Salt moves out of the cell Cells can explode

Osmosis Example If blood cells (or other cells) are placed in contact with an isotonic solution, they will neither shrink nor swell. If the solution is hypertonic, the cells will lose water and shrink (plasmolyze). If the solution is hypotonic (or if pure solvent is used) the cells will swell; the osmotic pressure that is developed may even be great enough to rupture the cell membrane.

Osmosis Examples Saltwater from the ocean is hypertonic to the cells of the human body; the drinking of ocean water dehydrates body tissues instead of quenching thirst.

Osmosis Examples In plants osmosis is at least partially responsible for the absorption of soil water by root hairs and for the elevation of the liquid to the leaves of the plant. However, plants wilt when watered with saltwater or treated with too much fertilizer, since the soil around their roots then becomes hypertonic.

Active Transport Involves a carrier protein to pump ions and molecules across a cell membrane They use ATP for energy

Sodium-potassium pump The protein pump that moves potassium ions into and sodium ions out of a cell. In order for diffusion to occur….. Cells need to keep a low concentration of Na ions, and high levels of K ions inside the cell Outside cells , there are high concentrations of Na and low K To keep the appropriate concentrations, the sodium-potassium pump, pumps sodium out and potassium in

Bulk Movement Large molecules are “packaged” in vesicles and moved across the membrane Exocytosis Endocytosis

Exocytosis cellular secretion or excretion Substances, in vesicles, are discharged from the cell by fusion of the vesicle to the outer cell membrane

Endocytosis Cells absorb material from outside their cell membranes Materials enter the cell Endocytosis can be of three forms: Phagocytosis Pinocytosis

Phagocytosis The engulfing and ingestion of bacteria or other foreign bodies by phagocytes.

Pinocytosis Introduction of fluids into a cell