Unit 4: The Cell & Its Environment Ch. 2:1 (pg. 31) Cell Theory Ch. 2:3 (pgs. 38-40) Special Cell Processes (Diffusion & Osmosis)

Cells Who first observed cells? What was he looking at? cork Who first observed cells? What was he looking at? Did he see live cells? No, just cell walls. Robert Hooke Who first observed cells? by Robert Hooke in 1665 What was he looking at? viewing cork w/ microscope Did he see live cells? Saw many compartments named them “cells” Actually only saw cell walls b/c cells already dead

Further Discoveries Lead to the Cell Theory All organisms are made of one or more cells. (Schleiden & Schwann) The cell is the basic unit of structure and function in organisms. (Schleiden & Schwann) Cells are produced from other cells (Virchow) Cell Theory Rap Schleiden… all plants are composed of cells & are the basis of a plant’s functions Schwann… all animals are composed of cells & are the basis of an animal’s functions Virchow… all cells come from cells Cell theory is a cornerstone of modern biology 3

Properties of the Plasma Membrane What are the functions (jobs) of the cell membrane? Boundary between cell & its environment “Gatekeeper” Lets certain materials in/out (“selectively permeable”) What are the functions (jobs) of the cell membrane? Surrounds each cell creates boundary between cell contents & outside environment (including other cells) Acts as a gatekeeper & is selectively permeable (only lets certain materials in & out) 4

A Model of the Plasma Membrane In general, what does the plasma (cell) membrane look like? phospholipid bilayer Two layers of phospholipids Heads like water (hydrophilic) & point to outside & inside of cell towards water Tails fear water (hydrophobic) & point away from outside & inside of cell away from water (towards each other to middle of membrane) 5

A Model of the Plasma Membrane What does the plasma (cell) membrane look like in more detail? “Fluid Mosaic Model” Molecules (like proteins) embedded in phospholipid bilayer & in constant motion What does the plasma (cell) membrane look like in more detail? “Fluid Mosaic Model” Proteins & cholesterol embedded in phospholipid bilayer (in constant motion) Structure and chemical composition determines what can pass through B/c components of the membrane are constantly moving, like a fluid, & b/c the membrane has a pattern of proteins embedded in it, the current model of membrane structure is called the “fluid mosaic model” (form is closely related to function) Membrane Movement Animation 6

Movement of Materials Across the Cell Membrane: Passive Transport What is passive transport? Does passive transport require energy? Why/why not? Ex. of passive transport? Concentration gradient = differences in concentration What is passive transport? Movement of molecules from an area of high concentration to low concentration (with the gradient) Does passive transport require energy? energy is NOT needed Why/why not? b/c w/ gradient Ex. of passive transport? Ex. diffusion, osmosis, & facilitated diffusion Can be compared to a child sliding down slide/rolling down a hill

Movement of Materials Across the Cell Membrane: Passive Transport Ex. Diffusion How do molecules of solute move? Do they ever completely stop? Ex. Diffusion How do molecules of solute move? molecules of solute (dissolved substance) move from an area of higher concentration to an area of lower concentration due to kinetic energy (High to Low) Do they ever completely stop? No, a “dynamic equilibrium” is reached (movement continues in & out with no net change (evens out) • Note: molecules will still move around but stay spread out essentially equally.) http://www.phschool.com/science/biology_place/labbench/lab1/concepts.html 8

End up with equal numbers of solute on both sides…

Movement of Materials Across the Cell Membrane: Passive Transport What is the special name for the diffusion of water? osmosis Diffusion of water through selectively permeable membrane……. So common it’s given a special name…. Osmosis Passive Transport: Osmosis: diffusion of water through a selectively permeable membrane •Cells need to be in osmotic balance w/ watery environment (dynamic equilibrium) Water moves from high to low concentrations (Water moves toward higher concentration of solutes/ lower concentration of water until concentration evens out) •Water moves freely through pores. •Solute (green) is too large to diffuse across. 11

Effects of Water Concentrations on Cells What is an isotonic solution? concentration of solutes (& water) same on both sides of the membrane Which way would water move? What is an isotonic solution? concentration (amount) of solutes (& water) same on both sides of the membrane Which way would water move? no net water movement (dynamic equilibrium), water moves in & out equally (even though in constant motion) http://www.phschool.com/science/biology_place/labbench/lab1/types.html How osmosis works animation

Effects of Water Concentrations on Cells What is a hypotonic solution? lower concentration of solutes outside cell higher concentration of water outside cell Which way would water move? What is a hypotonic solution? lower concentration of solutes outside cell/higher concentration of water outside cell Which way would water move? net water movement into cell A trick to remember: “Hi hippo, come on in the water.” http://www.phschool.com/science/biology_place/labbench/lab1/types.html How osmosis works animation

Effects of Water Concentrations on Cells What is a hypertonic solution? higher concentration of solutes outside cell lower concentration of water outside cell Which way would water move? What is a hypertonic solution? higher concentration of solutes outside cell/lower concentration of water outside cell Which way would water move? net water movement out of cell “Hyper… go outside & take some water with you.” http://www.phschool.com/science/biology_place/labbench/lab1/types.html How osmosis works animation

Effects of Water Concentrations on Cells: Cytolysis & Plasmolysis Animal cell (cell & surrounding liquid both contain dissolved particles in equal concentrations) Hypotonic solution - Cell swells and may burst (lyse) =cytolysis Isotonic solution - Normal (Usual environment) Hypertonic solution - Cell shrinks (plasmolysis) Plant cell (cell contains dissolved particles & surrounding liquid is fresh & does not contain dissolved particles) Hypotonic solution - Turgid cell (Usual environment)… cell does not burst b/c of cell wall pressing inward to counterbalance the outward pressure of the water Isotonic solution – Non-turgid or wilted cell Hypertonic solution - Plasmolyzed (shrunken) cell What adaptation prevents the plant cell from bursting? What happens to cells in different types of solutions?

Which cells were in salt water? How can you tell? Which cells were in salt water? cells on right How can you tell? b/c shriveled b/c lost water due to being in hypertonic solution Elodea in salt water

Membrane Function Passive Transport: Facilitated Diffusion Even though they’re going w/ the concentration gradient (high  low) some substances: can not dissolve in lipid bilayer are too large to squeeze through carrier Facilitated diffusion Transport proteins facilitate (help) substances move across membrane Channel proteins (pores) provide water-filled passages through which small dissolved substances such as ions can diffuse… different ions pass through different pores (depends on size of ion, charge of ion, & inside diameter of channel) = tunnel Carrier (transport) proteins substance fits into one side of protein like a puzzle, once joined, the protein changes shape so that the substance is released on the other side (& the protein goes back to original shape) = squeezing a ball through a hose Gate proteins signal molecule binds w/ protein, gate opens, substance passes through, signal molecule unbinds, gate closes = toll booth

Membrane Function Passive Transport: Facilitated Diffusion So how can these materials permeate the membrane??? Facilitated diffusion With the help of: Channel proteins (pores) Carrier proteins Gate proteins Does facilitated diffusion require energy? Why/why not? No, b/c going from high  low carrier Facilitated diffusion Transport proteins facilitate (help) substances move across membrane Channel proteins (pores) provide water-filled passages through which small dissolved substances such as ions can diffuse… different ions pass through different pores (depends on size of ion, charge of ion, & inside diameter of channel) = tunnel Carrier (transport) proteins substance fits into one side of protein like a puzzle, once joined, the protein changes shape so that the substance is released on the other side (& the protein goes back to original shape) = squeezing a ball through a hose Gate proteins signal molecule binds w/ protein, gate opens, substance passes through, signal molecule unbinds, gate closes = toll booth

carrier (transport) protein channel protein (pores) Gate opens & ions can pass through Signal molecule combines w/ gate Signal molecule not combined w/ gate (gate closed) Once ions pass through, signal molecules unbind & gate closes gat e protein Channel & Gate Protein Animations Facilitated diffusion Transport proteins facilitate (help) substances move across membrane Channel proteins (pores) provide water-filled passages through which small dissolved substances such as ions can diffuse… different ions pass through different pores (depends on size of ion, charge of ion, & inside diameter of channel) = tunnel Carrier (transport) proteins substance fits into one side of protein like a puzzle, once joined, the protein changes shape so that the substance is released on the other side (& the protein goes back to original shape) = squeezing a ball through a hose Gate proteins signal molecule binds w/ protein, gate opens, substance passes through, signal molecule unbinds, gate closes = toll booth

Movement of Materials Across the Cell Membrane: Active Transport What is active transport? Does active transport require energy? Why/why not? Ex. of active transport? What is active transport? Movement of molecules from an area of low concentration to high concentration (against the gradient) Does active transport require energy? energy IS needed Why/why not? b/c against gradient Ex. of active transport? Ex. many ions Can be compared to a child climbing up a slide/rolling up a hill Concentration gradient = differences in concentration

Movement of Materials Across the Cell Membrane: Active Transport How can materials be moved against the concentration gradient (low  high)? transport proteins (pumps) that use energy (ATP) Passive & Active Transport Animation Protein/Transport Pumps Animation Active Transport Animation Each pump can bind to a particular particle whose shape fits it. Chemical energy is then used to alter the shape of the pump so that the particle to be moved & released on the other side of the membrane. Once the particle is released, the pump’s original shape is restored.

Endocytosis & Exocytosis Active Transport: Endocytosis & Exocytosis Not all materials can pass through membrane… So, how do they get into/out of the cell? Membrane encloses the material  pinches off  releases the material on the other side endocytosis exocytosis Exocytosis & Endocytosis Animation 1 Endocytosis & Exocytosis Animations 2

Endocytosis & Exocytosis Exocytosis & Endocytosis Animation 1 Active Transport: Endocytosis & Exocytosis Endocytosis & Exocytosis Animations 2 Which way do substances move during endocytosis? What are 2 types of endocytosis? phagocytosis pinocytosis What types of materials are moved by phagocytosis & pinocytosis? Do they require energy? Which way do substances move during endocytosis? Enter the cell What are two types of endocytosis? Phagocytosis cell engulfs large solid/undissolved particles forming a vacuole (“cell eating”) ex. amoebas & white blood cells Pinocytosis liquids (“cell drinking”) Do they require energy? Yes (active transport) Liquid droplets

Endocytosis & Exocytosis Exocytosis & Endocytosis Animation 1 Active Transport: Endocytosis & Exocytosis Endocytosis & Exocytosis Animations 2 Which way do substances move during exocytosis? What types of materials are moved by exocytosis? Does exocytosis require energy? Which way do substances move during exocytosis? Exit the cell What types of materials are moved by exocytosis? Waste and hormones/other materials the cell needs to send to other cells Does exocytosis require energy? Yes (active transport)

The Cell Wall What is the cell wall? Where is it located in the cell? What is it made of? What type of organisms have cell walls? What does the cell wall do for the cell? Does it affect the cell’s permeability? What is the cell wall? In many organisms, the plasma membrane is not outermost boundary the CELL WALL IS Where is it located in the cell? Cell wall (outside membrane) What is it made of? Mostly cellulose (polysaccharide), arranged in rows of fibers stacked in layers What type of organisms have cell walls? Plants, most algae, fungi, bacteria What does the cell wall do for the cell? Provides protection & support Does it affect the cell’s permeability? NO, the spaces btwn fibers allow water, ions, & other particles to pass through