CELLS Part 2 Processes https www youtube comwatch

CELLS Part 2: Processes https: //www. youtube. com/watch? v=LKN 5 sq 5 dt. W 4

Part 2: Molecule Movement & Cells • Passive Transport • Diffusion • Facilitated Diffusion • Osmosis • Active Transport • Endocytosis (phagocytosis & pinocytosis) • Exocytosis

Passive Transport • No energy required by the cell • Goes ‘with the gradient’ • differences in concentration, pressure, charge • Substances move to equalize the gradient (dynamic equilibrium) • High concentration moves to low concentration

Types of Passive Transport 1. Diffusion 2. Osmosis 3. Facilitated diffusion

Diffusion • Molecules move to equalize concentration https: //www. youtube. com/watch? v=_v 0 MRZx. U 2 bc https: //www. youtube. com/watch? v=f. N 7 b 1 a. Buno. M

Diffusion Across Cell Membrane • A few non-polar molecules move freely through the nonpolar lipid tails of bilayer • Carbon dioxide, Oxygen, small lipid molecules • Water, although polar, is small enough to pass through the bilayer (there actually numerous small protein channels water passes through called aquaporins…but just know that water can always get through!) • Channel & carrier proteins transport some larger polar molecules through it • Proteins embedded in lipid bilayer • Fluid mosaic model – describes fluid nature of a lipid bilayer with proteins

Osmosis • Diffusion of Water through a semipermeable membrane • Water moves from High concentration to Low (and requires NO cell energy) • Low solute concentration means there is high water concentration. High solute concentration means there is low water concentration

Osmosis: Hypotonic Solution • If a cell is in Hypotonic Solution: • Means there are less solutes in solution surrounding the cell than there are inside the cell. This means there is more water in solution. Water moves from high to low, so water (the solvent) will move INTO the cell. (Hyp. O means high H 2 O)

Osmosis: Hypertonic Solution • If a cell is in Hypertonic Solution: • Solutes are greater outside the cell, so there is less solvent (water) outside the cell. *That means there is more water inside the cell compared to outside. • Water will flow OUT of the cell, since water always goes high to low (osmosis)

Osmosis: Isotonic Solution • Means solutes are equal inside & out of cell. Water moves in and out at same rate- Dynamic Equilibrium (*No net difference in concentration; water is always moving back and forth at same rate)

https: //www. youtube. com/watch? v=Ia. Z 8 Mt. F 3 C 6 M https: //www. youtube. com/watch? v=Y_w 07 A 7 chnk

Effects of Tonicity on Cell Membranes *Examples shown here animal cells • Isotonic solution • water concentration is the same inside & outside of cell results in water moving in and out of the cell at the same rate • Hypotonic solution • higher concentration of water outside of cell results in lysis (bursting) in animal cells. In plant cells, it increases the pressure inside the cell (high turgor). Cell wall prevents them from lysing • Hypertonic solution • lower concentration of water outside of cell causes crenation (shrinking) in animal cells. Causes plasmolysis in plant cells

Plasmolysis in Plant Cells on left in isotonic solution Cells on right are in hypertonic sol’n

Facilitated Diffusion • Selectively permeable membrane • Channels (are specific) help molecule or ions enter or leave the cell • Channels usually are transport proteins (theses are like ‘open doors’) (aquaporins are channels that facilitate the movement of water) • No energy is used

Process of Facilitated Transport • Protein binds with molecule • Shape of protein changes • Molecule moves across membrane

Active Transport Requires energy (solutes move against gradient. LOW to HIGH concentration)

In Active Transport, Energy by the cell is REQUIRED because substances are moving AGAINST the gradient. The squares in the diagram represent a substance moving from LOW to HIGH.

Where do cells get energy for Active Transport? • 1 - Animals (eukaryotes) are heterotrophs and must ingest food (Ex- Carbohydrates) • 2 - After digestion (hydrolysis), glucose is transported to cells • 3 - Once glucose gets thru the cell membrane (usually by facilitated diffusion) the cell uses many enzymes to begin breaking the covalent bonds in glucose, which will provide energy the cell needs to do work. •

Active Transport-con’t • 4 - Most of these bond-breaking reactions occur in the Mitochondria and are part of a process called ‘Cellular Respiration’. • 5 - The energy released from glucose temporarily given to an energy “holding” molecule called ATP (Adenosine Triphosphate) • 6 - When cells need energy (ex- for Active Transport), ATP releases energy that was obtained from glucose. This allows the cell to do work, such as transporting other molecules AGAINST the gradient (Low to High)

Active Transport • Neurons (nerve cells) must send impulses to muscles, so they can contract. This requires a lot of cellular work, and a lot of active transport. The most well known example is the Sodium (Na)Potassium (K) pump. Both of these substances must move ‘against the gradient’ and this requires the ‘holding’ molecules, ATP, to release energy.

Other examples- Active Transport

Endocytosis- Active • Movement of large material • Particles • Organisms • Large molecules • Movement is into cells • Types of endocytosis • bulk-phase (nonspecific) • receptor-mediated (specific)