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Transcript
How Cells Maintain Homeostasis Objective 2.03: Importance of Water, How cells maintain homeostasis, Movement of materials into and out of cells ? Homeostasis ? • Maintaining a stable, BALANCED, internal environment • Example: Water Water Water Cell Water Water Water Water Water Homeostasis! • Maintaining a stable, BALANCED, internal environment • Example: Water Water Water Cell Water Water Water Water Water Water FYI • Universal solvent = ability to dissolve many things • Transports materials in organisms = blood is mostly water • Makes up 70-95% of most organisms Water is Polar Polar Molecule - Has a positive and negative end - Attracts other water molecules = surface tension - Allows water to move up through thin tubes inside of plants = capillary action Plasma Membrane: Structure & Function Plasma/Cell Membrane • In an Animal Cell, it is the boundary between the inside and outside of the cell. • In a Plant Cell, it is between the cell wall and the inside of the cell • It is crucial in maintaining the cell’s homeostasis!! • It is selectively permeable (or semi-permeable) • It is choosy about what enters and leaves the cell. • It keeps nutrients in, and harmful substances out • The Cell Membrane is referred to as the Fluid Mosaic Model • Fluid: because the parts inside the cell membrane are always moving around. • Mosaic: because it is made of many different parts and molecules (lipids, cholesterol, proteins, carbohydrates, etc.) Structure of the Plasma Membrane • The plasma membrane is a Phospholipid Bilayer Phosphate + Fat 2 Layers • Other Components: Proteins, Cholesterol, Carbohydrates Phospholipids • The “heads”: – Hydrophilic – Polar – Attracted to H2O inside and outside cell • The “tails”: – Hydrophobic – Non-polar – do NOT like water – Point to the middle of the plasma membrane. Can things move through the cell membrane? • Of course! • If they are small, they can go through without energy needed –Ex: Water, Oxygen • If they are large, they have to go through a protein and it uses energy –Ex: Sugar What do you think… • A cell in your body does not maintain homeostasis, and too much water is allowed in. • What might happen!? The Movement of Materials into and out of Cells Two Types of Cell Transport Passive Transport • No energy required • Movement of materials is from high to low • Materials move DOWN a concentration gradient • Examples are diffusion, osmosis, and facilitated diffusion Active Transport • Energy is required • Movement of materials is from low to high • Materials move UP a concentration gradient • Requires the use of proteins Concentration Gradient!? • When the concentrations of solutions are different Outside a Cell HIGH concentration of solute (ex: salt) Inside a Cell LOW concentration of solute (ex: salt) Diffusion • Movement of particles from an area of high concentration to an area of low concentration • Goal is to reach dynamic equilibrium = inside and outside the cell are at equal concentrations Facilitated Diffusion • Same as diffusion BUT uses a protein in cell membrane • Used when particles are too big to squeeze through cell membrane Transport Proteins for Facilitated Diffusion • Channel Protein = does not change shape (a) • Carrier Protein = can change shape (b) Osmosis • Osmosis: The diffusion of water across a semi permeable membrane. Hypertonic (Cell Shrinks) 90% H2O In cell 10% Water In beaker Isotonic ( Dynamic Equilibrium) 50% H2O In cell 50% Water In beaker Hypotonic (Cell Swells) 10% H2O In cell 90% Water In beaker Cells in Solutions Bursts Turgor Pressure – cell membrane “pushes” on cell wall Shrivels Plasmolysiscell membrane pulling away from cell wall Where will the water go? • 40% water outside cell, 60% water inside cell • 40% sugar outside cell, 60% sugar inside cell Passive Transport Active Transport • No energy required • Movement of materials is from high to low • Materials move DOWN a concentration gradient • Examples are diffusion, osmosis, and facilitated diffusion • Energy is required • Movement of materials is from low to high • Materials move UP a concentration gradient Active Transport • Requires ENERGY! • Movement is from LOW to HIGH • Uses transport proteins (carrier or channel) • Ex: muscle contractions + electrolytes Energy!!!