Cell Movement: PassiveTransport Honors Biology Ms. Kim

Membrane structure LEADS TO selective permeability A cell must exchange materials with its surroundings selectively permeable – a process controlled by the selectively permeable plasma membrane

Cell Transport Means moving things INTO and OUT of the cell Cells need to take in – Food – Get rid of waste products (excretion) – Give out such useful substances as hormones and enzymes (secretion ).

Permeability and Cell Transport Hydrophobic (non polar) molecules – Are lipid soluble (can dissolve) – can pass through membrane easily Ex: Hydrocarbons, CO 2, O 2 Hydrophilic (Polar) molecules – Are NOT lipid soluble (can’t dissolve) Lipid INsoluble – Do not cross membrane easily Ex: Na +, Cl -, Glucose/ other sugars – NOTE: CHARGED molecules need “help” to cross membrane – NOTE: LARGE molecules, POLAR molecules need “help”

Types of Cellular Transport Passive Transport cells do NOT use energy 1.Diffusion 2.Facilitated Diffusion 3.Osmosis Active Transport cells DO use energy 1. Protein Pumps 2. Endocytosis 3. Exocytosis high low This is going to be hard! high low Weee!

1) Diffusion Diffusion: Movement of molecules from a high concentration to a lower concentration – Does not use energy – Can occur in non-living systems (ex: dye) Concentration: – Number of molecules of a substance in a given volume Concentration gradient: – Difference in concentration of a substance from one location to another 7

Types of Passive Transport Diffusion population ANY Diffusion is the tendency for a population of molecules (of ANY substance) to spread out evenly into available space – A “net” movement Ex: Perfume, a fart, tea, food coloring in water (see demo)

DIFFUSION In absence of other forces… – Molecules move (diffuse) from area of HIGH [ ] to an area of lower [ ] OWN – A.k.a.  Molecules move DOWN its OWN concentration gradient No chemical work (ATP energy) is used  diffusion is spontaneous!

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Substances diffuse down their OWN concentration gradient Figure 7.11 B (b) Net diffusion Equilibrium

12 Diffusion of Liquids copyright cmassengale

Factors Affecting Diffusion 1. Temperature Higher temperature  more kinetic energy  molecules move faster 2. Pressure Higher pressure  molecules move faster Example  Tea: Higher temperature and more pressure (twirling/stirring) it around) makes diffusion happen faster.

2) Facilitated Diffusion Molecules move down (not against) a concentration gradient with the aid of special proteins (channel or carrier proteins) – Speeds up the process – Proteins CAN change SHAPE Does NOT use energy (NO ATP NEEDED) = type of passive transport Moves things from high to low concentrations – Moves POLAR molecules  can NOT easily pass through the membrane on it’s own. Example: ions, smaller polar molecules (ex: sugar) Example: ions, smaller polar molecules (ex: sugar) 14

Cha nnel proteins -Provide “tu nnel s” Figure 7.15 EXTRACELLULAR FLUID Channel protein Solute CYTOPLASM A channel protein (purple) has a channel through which water molecules or a specific solute can pass. (a) Channel Proteins animationsChannel Proteins

Carrier proteins -Undergo a subtle change in shape “carry” solute across the membrane Carrier protein Solute

3. Osmosis Osmosis: – diffusion of water across a membrane Water moves across a semipermeable membrane from an area of high water concentration to an area of low water concentration If water can cross a membrane, but the solute cannot, then… – The water moves towards the side with MORE solute to balance the concentrations 17

Effects of Osmosis on Water Balance Osmosis water (water diffusion) semipermeable membrane The movement of water (water diffusion) across a semipermeable membrane – Involves the movement of FREE water molecules down a water [ ] gradient High solute  low “free” water [ ] or…. High solute  low “free” water [ ] or…. Low solute  high free water [ ] Low solute  high free water [ ]

Osmosis is affected by the concentration gradient of dissolved substances ( solutes ) OsmosisOsmosis animation

21 OSMOSISOSMOSIS

22 Diffusion of H 2 O Across A Membrane High H 2 O potential Low solute concentration Low H 2 O potential High solute concentration copyright cmassengale

Osmoregulation Osmoregulation – control of water balance Turgor pressure – pressure inside a cell Tonicity – tendency of a cell to lose or gain water based on the solution it is in 3 Types of solutions: – Isotonic – Hypotonic – Hypertonic 23

3 Different Types of Solutions Recall: SOLUTION = a uniform mixture of 2 or more substances ** compare solutions OUTSIDE cell to inside cell 1. ISOTONIC- Solution has same concentration of dissolved particles as the cell (same amount of solute outside and inside the cell) Water moves into and out of cell at equal rates and cell size remains constant Cell does not change shape NO – There will be NO net movement of water

ISOTONIC SOLUTION Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium)

hypertonic 2. If a solution is hypertonic Solution has a higher concentration of dissolved particles than the cell (more solute outside of the cell than it is inside the cell) – Water flows OUT of the cell – The cell shrivels up and turgor pressure decreases – “hyper” means more » (high [solute]) Ex: when salinity increases in lake, fish can die! The water will move out of the fish towards the area with MORE solutes (ocean) to balance the concentrations! Poor fish… NaCl

HYPERTONIC SOLUTION Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)!

3.hypotonic 3. If a solution is hypotonic Solution has a lower concentration of dissolved particles than the cell (less solute outside of the cell than it is inside the cell) – Water flows INTO the cell – The cell swells/gets big! – Ex. Happens with distilled water Animals: Cytolysis (when a cell BURSTS!) – “ hypo ” means “less” – (low [solute]) – Think: Hypo- sounds like hippo… hippos are big & round; cells in hypotonic solutions get big & round  Also, think “hypo” is “low” meaning “low” solutes SURROUNDING cell “Hypo” is LOW!!!

HYP0TONIC SOLUTION Result: Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)!

30 Cell in ___________ Solution CELL 10% NaCL 90% H 2 O 10% NaCL 90% H 2 O What is the direction of water movement? The cell is at _______________. Dynamic equilibrium ENVIRONMENT NO NET MOVEMENT

31 Cell in ____________ Solution CELL 10% NaCL 90% H 2 O 20% NaCL 80% H 2 O What is the direction of water movement? copyright cmassengale ENVIRONMENT

32 Cell in ___________ Solution CELL 15% NaCL 85% H 2 O 5% NaCL 95% H 2 O What is the direction of water movement? ENVIRONMENT copyright cmassengale

Osmosis Animations for isotonic, hypertonic, and hypotonic solutionsOsmosis

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True story A woman who competed in a radio station’s contest to see how much water she could drink without going to the bathroom died of water intoxication, the coroner’s office said Saturday. Jennifer Strange, 28, was found dead Friday in her suburban Rancho Cordova home hours after taking part in the “Hold Your Wee for a Wii” contest in which KDND promised a Nintendo Wii video game system for the winner.

Real life examples

Water Balance of Cells with Walls Cell walls Cell walls – Help maintain water balance Cell walls are in: – Plants – Prokaryotes – Fungi – Some protists

40 Plant Cells & Solutions Isotonic (Flaccid) Plant cells at isotonic solutions are flaccid (can also be in hypertonic solution) Cells are limp Hypotonic (Turgid) Plant cells prefer hypotonic solutions because the cell wall provides more support and plant cells are less likely to lyse (burst) Turgor pressure increases (vacuole fills with water) It is very firm A healthy state in most plants Hypertonic (Plasmolysis) Plants wilt, undergo plasmolysis The cytoplasm and plasma membrane begin to pull away from the cell wall Causes cell with walls to wilt & can be lethal.

Water balance in cells with walls Plant cell. Plant cells are turgid (firm) and generally healthiest in a hypotonic environ- ment, where the uptake of water is eventually balanced by the elastic wall pushing back on the cell. (b) H2OH2OH2OH2O H2OH2O H2OH2O Turgid (normal)Flaccid Plasmolyzed Figure 7.13

Types of Passive Transport #1 Passive Transport – DOES NOT require chemical energy (ATP)#2 Active Transport – DOES require chemical energy ( A TP)