Lesson 11: Cell Transport Mechanisms PDF

STEM_BIO11/12-Ig-h- Lesson 11: Explain the transport mechanism in cells (diffusion, osmosis, facilitated transport, active 13; STEM_BIO11/12-Ig- tra...

STEM_BIO11/12-Ig-h- Lesson 11: Explain the transport mechanism in cells (diffusion, osmosis, facilitated transport, active 13; STEM_BIO11/12-Ig- transport); Differentiate exocytosis from endocytosis h-14 QUARTER 1 | S.Y. 2024-2025 | Sir L.A. Batomalaque PERMEABILITY OF THE PLASMA MEMBRANE Types of membrane and transport Lipid soluble molecules (e.g. alcohol) diffuse easily because lipids are membranes main 1. The plasma membrane is differentially- structural components permeable: only certain molecules can pass Gases readily diffuse through lipid bilayer. through freely. A permeable membrane allows all Movement of oxygen from air sacs (alveoli) to molecules to pass through; an impermeable blood in lung capillaries depends on membrane allows no molecule to pass through concentration of oxygen in the alveoli and a semi-permeable membrane allows some Whether we are talking about simple molecules to pass through. diffusion, facilitated diffusion or osmosis, the a. Small non-charged nonpolar molecules (e.g. movement of particles is due to collisions alcohol, oxygen) pass through the membrane between particles. Three factors influence / freely affect the rate of movement of these b. Small polar molecules (e.g. water, carbon particles. dioxide) easily pass through along their a. Temperature – rate of diffusion increases concentration gradient, i.e. direction of as temperature increases movement is from higher to lower b. Concentration – rate of diffusion increases concentration. as concentration increases c. Macromolecules (e.g. nucleic acids, starch / c. Size – rate of diffusion decreases as glycogen, triglycerides, proteins) cannot molecule size increases freely cross the plasma membrane. Similarly, large polar molecules like glucose cannot pass freely d. Ions and charged molecules (salts) have difficulty crossing the hydrophobic phase (hydrocarbon or fatty acid tail portion) of the bilayer. 2. Both passive (doesn’t require ATP) and active (requires ATP) mechanisms move molecules across membranes. a. Passive transport include: (a) simple diffusion, (b) facilitated diffusion and (c) osmosis b. Active transport include: (a) exocytosis, (b) endocytosis and (c) pinocytosis PASSIVE TRANSPORT: Diffusion Generally, in diffusion, molecules move from higher to lower concentration (i.e. down their concentration gradient) A solution contains a solute, usually a solid, and a solvent, usually a liquid In the case of dye diffusing in water, dye is a solute and the water is the solvent Membrane chemical and properties allow only a few types of molecules to cross by diffusion A. Simple diffusion GENERAL BIOLOGY 1 Lesson 11: Explain the transport mechanism in cells (diffusion, osmosis, facilitated 1 transport, active transport); Differentiate exocytosis from endocytosis  STEM_BIO11/12-Ig-h- Lesson 11: Explain the transport mechanism in cells (diffusion, osmosis, facilitated transport, active 13; STEM_BIO11/12-Ig- transport); Differentiate exocytosis from endocytosis h-14 QUARTER 1 | S.Y. 2024-2025 | Sir L.A. Batomalaque Heat energy causes molecules to move few solutes) and a concentrated solution randomly. This motion is called Brownian (call it B) as having a lower water motion. concentration (because it has lots of Brownian motion causes all molecules to solutes). If these two solutions were move continuously by random, simple separated by a selectively-permeable diffusion. This movement is spontaneous and membrane, water would flow from high does not require energy. Diffusion is the water to low water concentration, i.e. from movement of particles from an area of higher A to B. concentration to an area of lower concentration. If the concentration of two molecules in 2 areas is different, diffusion will cause molecules to move from the area with the higher concentration to the area with lower concentration. The greater the concentration difference, the more rapid the net diffusion. Diffusion evens out the concentration so they are equal everywhere. This condition of uniform concentration is called equilibrium. B. Facilitated diffusion Some important molecules like glucose, cannot easily cross the membrane so their movement must be helped (or facilitated) Special protein channels help move these substances across the membrane. Each protein channel is specific for the molecule it is transporting. Like simple diffusion, this process is spontaneous and does not require energy. C. Osmosis is the diffusion of water across a differentially-permeable membrane. It occurs when a solute cannot pass through a Osmotic pressure is hydrostatic pressure, on membrane but the solvent (water) can. side of membrane with higher solute Because osmosis is a special kind of diffusion, concentration, produced by water diffusing it occurs spontaneously and requires no to that side of membrane. energy. Example: thistle tube Water moves from an area where there is a. A differentially-permeable membrane more water to an area where there is less separates two solutions water. In general, water moves toward an b. Beaker has more water (lower percentage area with a high solute concentration of solute, hence dilute) and thistle tube because it has a lower water concentration. has less water (higher percentage of The amount of water in a solution is indirectly solute, hence concentrated) proportional to the amount of solute in the c. The membrane does not permit passage solution. of the solute Think of a dilute solution (call it A) as having a high water concentration (because it has GENERAL BIOLOGY 1 Lesson 11: Explain the transport mechanism in cells (diffusion, osmosis, facilitated 2 transport, active transport); Differentiate exocytosis from endocytosis  STEM_BIO11/12-Ig-h- Lesson 11: Explain the transport mechanism in cells (diffusion, osmosis, facilitated transport, active 13; STEM_BIO11/12-Ig- transport); Differentiate exocytosis from endocytosis h-14 QUARTER 1 | S.Y. 2024-2025 | Sir L.A. Batomalaque d. Membrane permits passage of water with the RBC (0.5M). Hence, the net movement of net movement of water from beaker to water is from the RBC’s cytoplasm towards inside of the thistle tube the solution where it floats, and the RBC loses e. Osmotic pressure allows liquid (i.e. water. The effect to the RBC is that it will water) increase on side of the membrane shrink (become shriveled, or plasmolysis with greater percentage of solute (thus occurred) eventually. water flows to the more concentrated solution, in the thistle tube) Water Balance in Cells with walls Osmotic pressure is a pressure that develops Cell walls help maintain water balance in a system due to osmosis. Osmosis is a a. If a plant cell is turgid, it is in a hypotonic constant process in life; for example, water environment. It is very firm and this is what is absorbed is the large intestine, retained in we consider healthy state of plant cells. Net the kidney and taken up by the bloodstream movement of water is form the surroundings towards the cell, but it will not burst like in TONICITY RBC because of the presence of cell wall. refers to the strength of the solution in o Swelling of plant cells in hypotonic relationship to osmosis; it determines the solution creates turgor pressure. Turgor movement of water into or out of cells. pressure pushes the plasma membrane It is also defined as “the ability of a solution to against the cell wall of plant, bacteria, cause a cell to gain or lose water” and it has a and fungi cells as well as those protist higher impact on cells without cell walls like in cells which have cell walls. This pressure, animal cells. Classic example is in human red turgidity, is caused by the osmotic flow of blood cell exposed to different concentration of water from area of low solute solution. concentration outside of the cell into the Tonicity is expressed in three (3) types: cell's vacuole, which has a higher solute a. Hypotonic is where a relative solute concentration. Healthy plant cells are concentration of one solution is less than the turgid and plants rely on turgidity to other solution. Example: The solute maintain rigidity. In contrast, this concentration of the solution where the RBC phenomenon is not observed in animal floats is less than (0.5M) than it is inside the cells which have no cell walls to prevent RBC (1.0 M). Hence, the net movement of them from being burst by the flow of water is towards the inside of the RBC, and water into the cell and must either the RBC gains more water. The effect to the continually pump out water or live in an RBC is that it will burst (lysed) eventually. isotonic solution where there is no Some single-celled organisms (e.g. Euglena osmotic pressure. spp, a protozoa) possess contractile vacuoles b. If a plant cell is flaccid, it is in an isotonic which stores excess water and squirt it out to environment. It is less firm than in a prevent from cell lysis (cytolysis). hypotonic environment and is considered in a b. Isotonic is where the relative solute “less healthy” condition. There is no net concentration of two solutions are equal. movement of water. Example: The solute concentration (sodium c. If a plant cell is plasmolyzed, it is in a ion, 1M) is similar inside and outside of the hypertonic solution. It is definitely similar to RBC. Hence, there will be no net movement wilting stage where a plant did not receive of water. water the past 24 hours. Net movement of c. Hypertonic is where a relative solute water is from the cell towards the concentration of one solution is greater than surroundings. Plasmolysis is a condition the other solution. Example: The solute where the plasma membrane pulls away from concentration of the solution where the RBC the cell wall as the cell shrinks. The cell wall floats is greater than (1.0 M) than it is inside is rigid and does not shrink. GENERAL BIOLOGY 1 Lesson 11: Explain the transport mechanism in cells (diffusion, osmosis, facilitated 3 transport, active transport); Differentiate exocytosis from endocytosis  STEM_BIO11/12-Ig-h- Lesson 11: Explain the transport mechanism in cells (diffusion, osmosis, facilitated transport, active 13; STEM_BIO11/12-Ig- transport); Differentiate exocytosis from endocytosis h-14 QUARTER 1 | S.Y. 2024-2025 | Sir L.A. Batomalaque - These processes are used for ACTIVE TRANSPORT macromolecules that are too big to pass through the cell membrane normally (e.g. Often, a cell requires substances that are at a lower proteins). concentration outside the cell than inside the cell. - Endocytocis is a cellular process in which These substances will not move by diffusion. substances are brought into the cell. Active transport allows a cell to concentrate ▪ The cell membrane bends inward, materials inside itself that are at a low forming a vesicle containing concentration in the environment. extracellular fluid and other In humans, active transport can account for 30% substances dissolved in it. of our resting energy use. ▪ the vesicle is then fused with a There are two (2) general types of active lysosome to become a digested transport macromolecules. o Special proteins in the membrane use energy ▪ Phagocytosis is bringing particles to transport these substances into the cell. into the cell (called “cell eating”) Note that this is much like facilitated while pinocytosis is bringing in diffusion in that it is specific for the molecule fluid (called “cell drinking”). it transports (uses protein channels, Example ▪ Exocytosis is the opposite of is sodium-potassium pump) but different in endocytosis. Materials are that it requires energy (ATP). excreted from a cell but the o Endocytosis and Exocytosis. mechanism is the still similar. GENERAL BIOLOGY 1 Lesson 11: Explain the transport mechanism in cells (diffusion, osmosis, facilitated 4 transport, active transport); Differentiate exocytosis from endocytosis  STEM_BIO11/12-Ig-h- Lesson 11: Explain the transport mechanism in cells (diffusion, osmosis, facilitated transport, active 13; STEM_BIO11/12-Ig- transport); Differentiate exocytosis from endocytosis h-14 QUARTER 1 | S.Y. 2024-2025 | Sir L.A. Batomalaque GENERAL BIOLOGY 1 Lesson 11: Explain the transport mechanism in cells (diffusion, osmosis, facilitated 5 transport, active transport); Differentiate exocytosis from endocytosis  STEM_BIO11/12-Ig-h- Lesson 11: Explain the transport mechanism in cells (diffusion, osmosis, facilitated transport, active 13; STEM_BIO11/12-Ig- transport); Differentiate exocytosis from endocytosis h-14 QUARTER 1 | S.Y. 2024-2025 | Sir L.A. Batomalaque GENERAL BIOLOGY 1 Lesson 11: Explain the transport mechanism in cells (diffusion, osmosis, facilitated 6 transport, active transport); Differentiate exocytosis from endocytosis