HOMEOSTASIS and TRANSPORT

A4. Homeostasis and Transport Describe how the structure of the plasma membrane allows it to function as a regulatory structure and/or protective barrier for a cell. Compare the mechanisms that transport materials across the plasma membrane. Explain how organisms maintain homeostasis. Describe how membrane-bound organelles facilitate the transport of materials within a cell.

A4. Vocabulary plasma membrane lipid bilayer phospholipid impermeable selectively permeable protein channel protein pump osmosis diffusion facilitated diffusion active transport passive transport endocytosis exocytosis isotonic equilibrium hypertonic concentration gradient hypotonic homeostasis

Cell Membrane Structure and function A phospholipid bilayer Cell membranes are composed of phospholipids Phospholipids are arranged in two layers (bilayer) Each phospholipid has a “head” and two “tails” The head loves water (hydrophilic) The tails hate water (hydrophobic The lipid bilayer is flexible but strong

Cell Membrane Structure and Function DRAW THIS in your NOTES!!

Cell Membrane Structure and Function Fluid Mosaic Model The cell membrane acts as a fluid… It is not rigid Proteins and phospholipids can move around The cell membrane is a mosaic… Many different parts make up the cell membrane

Cell Membrane Structure and Function Functions of the Cell Membrane Barrier between the cytoplasm and the environment Protects and supports the cell Controls everything that enters and leaves the cell

Cell Membrane Structure and Function Permeability Membranes are selectively permeable Some things can cross the membrane (permeable) Gases, water, small particles Some things can cross the membrane with the help of a protein channel or pump Ions, proteins, large particles Some things can’t cross the membrane (impermeable)

Let’s Build a Model of a cell membrane! Cotton swabs represent phospholipids Other components are embedded within the phospholipid bilayer Can you move the components back and forth?

Can you do it? Give as many names for the boundary of the cell as you can…

Mechanisms of Passive Transport Passive Transport Defined requires NO energy Depends on a concentration gradient (difference) Concentration = relative amount of substance SUBSTANCE moves from HIGH concentration (of substance) to LOW concentration (of substance) Some materials can pass freely, other materials need a protein channel

Mechanisms of Passive Transport Passive Transport is like… Create an analogy… The hill is like the concentration gradient The ball is like a molecule moving down its gradient In a cell this gradient has to do with concentration of materials on either side of the membrane A ball rolling down a hill

Mechanisms of Passive Transport 1. Diffusion (a.k.a. simple diffusion) Passive transport Depends on a concentration gradient Concentration = relative amount of substance Gradient = difference MOVEMENT from HIGH concentration to LOW concentration Down the concentration gradient

Mechanisms of Passive Transport 2. Facilitated Diffusion Passive – requires NO energy Depends on a concentration gradient (difference) Concentration = relative amount of water MOVEMENT from HIGH concentration to LOW concentration just like simple diffusion EXCEPT needs a protein channel

Mechanisms of Passive Transport 3. Osmosis Diffusion of water WATER moves from HIGH concentration (of water) to LOW concentration (of water) Aquaporins = protein channels for water to pass Plays a role in maintaining homeostasis (water balance)

Which way will the water molecules move? Osmosis Which way will the water molecules move? Why wouldn’t the green or purple molecules move?

Mechanisms of Active Transport Defined Requires energy Material flows AGAINST the concentration gradient From LOW concentration to HIGH concentration Requires protein pumps (need energy to work)

1. Protein Pumps Movement within a cell Use ATP energy to move or “pump” material into an area that already has a high concentration It’s like pumping air into a basketball

Movement within a cell 1. Protein Pumps

2. Bulk Transport Movement within a cell Used to transport very large molecules or food Endocytosis = bringing materials into the cell Exocytosis = taking materials out of the cell Cell membrane/vesicles play a role

Movement within a cell 2. Bulk Transport

Defined Homeostasis Maintaining stability in the cell or body Variables within the body can fluctuate Temperature, pH, water balance Important to maintain homeostasis near set point Cell membrane aids in maintaining homeostasis

Osmosis and water balance Homeostasis Osmosis and water balance Diffusion of water Passive (no energy required) Water will move across the membrane down its concentration gradient Cell membrane regulates the amount of water inside a cell

ISOTONIC Conditions Homeostasis Amount of water inside = amount of water outside Water moves back and forth across the membrane equally in both directions Equilibrium = equal concentrations of water on both sides of the membrane

HYPERTONIC Conditions Homeostasis HYPERTONIC Conditions Amount of solute surrounding cell is high (high solute = low water) Water moves out of the cell to balance concentrations of water on both sides of membrane Cell shrinks (dehydrates) EX: saltwater

Hypotonic conditions Homeostasis Amount of solute surrounding cell is low (low solute = high water) Water moves INTO the cell to balance concentrations of water on both sides of membrane Cell swells (animal cells could burst) EX: pure water

Homeostasis Osmosis

Why would plant cells be better off than animal cells Why would plant cells be better off than animal cells? What would happen to the cells of a freshwater fish if it was put into a saltwater tank?

Cell Transport Review Divide your poster into six sections In each section, diagram one of the following modes of transport Simple diffusion Facilitated diffusion Osmosis Active transport via protein pumps Exocytosis endocytosis

Keystone Questions Carbon dioxide and oxygen are molecules that can move freely across a plasma membrane. What determines the direction that carbon dioxide and oxygen move? Orientation of cholesterol in the plasma membrane Concentration gradient across the plasma membrane Configuration of phospholipids in the plasma membrane Location of receptors on the surface of the plasma membrane

Keystone Questions A sodium-potassium pump within a cell membrane requires energy to move sodium and potassium ions out of a cell. The movement of glucose into or out of a cell does not require energy. Which statement best describes the movement of these materials across a ac cell membrane? Sodium and potassium ions move by active transport, and glucose moves by osmosis Sodium and potassium ions move by active transport and glucose moves by facilitated diffusion. Sodium and potassium ions move by facilitated diffusion and glucose moves by osmosis Sodium and potassium ions move by facilitated diffusion and glucose moves by active transport

Keystone Questions Which example is an activity that a fish most uses to maintain homeostasis within its body? Using camouflage to avoid predators Feeding at night to regulate body temperature Moving to deeper water to regulate metabolic wastes Exchanging gases through its gills to regulate oxygen levels.

Keystone Questions 4. Diffusion occurs because Molecules are attracted to one another Molecules constantly move and collide with one another Cellular energy forces molecules to collide with one another Cellular energy pumps molecules across the cell membrane

Keystone Questions During diffusion, when the concentration of molecules on both sides of the membrane are equal, molecules will Move across the membrane to the outside of the cell Stop moving across the membrane Continue to move across the membrane in both directions Move across the membrane to the inside of the cell