Chapter 4 Cells & Their Environment

DO NOW 1) Grab a Chapter 4 packet 2) Try to answer questions 1 & 2 on page one 3) Wait quietly to begin

Learning Targets 1) I can – predict the direction of substance movement into and out of the cells in terms of diffusion 2) I can – describe the importance and role of ion channels and facilitated diffusion in passive transport

Remember – Homeostasis? Passive Transport Homeostasis Cells do this by controlling the movement of substances across their cell membrane Diffusion: Movement across the cell membrane Passive Transport = No cellular energy required Try This: Write a sentence using the word “diffuse”

Diffusion: Movement of a substance from an area of higher concentration to an area of lower concentration Don’t have to use energy

Diffusion Concentration Gradient A difference in concentration of a substance across a space – moving from high to low concentration down concentration gradient Equilibrium- When the substances are equally divided among all areas then they have reached equilibrium When concentration of a substance is equal throughout a space

Diffusion Across the Cell Membrane Diffusion *Remember – Does the cell membrane just let anything through? (what do we call this) Many molecules and ions enter or exit the cell by diffusing across the membrane They move DOWN concentration gradient (high to low) Cell membrane is selectively permeable

STAND UP! Let’s try to model DIFFUSION down a concentration gradient and EQUILIBRIUM

Back to Learning Target ✔ I can – predict the direction of substance movement into and out of the cells in terms of diffusion 1) Grab an index card. 2) Write a description of your movement. Use the new terms you just learned such as – diffusion, high to low concentration, concentration gradient, and equilibrium 3) Stand up and share with others

Crossing the Cell Membrane What crosses the cell membrane? Usually only nonpolar or very small molecules diffuse well through nonpolar lipid bilayer But most polar molecules and ions cannot pass through the lipid bilayer Thanks to transport proteins called – channels – passageways are made so polar molecules & ions can move across the cell

Crossing the Cell Membrane Ion Channels Each channel allows only a specific substance to pass through This is how the cell controls what enters and leaves! Allows important ionic substances to flow into cell without contacting nonpolar membrane parts

Crossing the Cell Membrane Ion Channels Some channels remain open, others are gated Ion channels include : Sodium (Na), potassium (K), & Calcium (Ca) that are important to cell functions No energy needed (passive transport)

Crossing the Cell Membrane Electrical charge and ion transport 1. Ion charge can determine how it moves across cell membrane 2. Inside of cell is usually negative 3. Positive ions tend to move into cell more readily (opposites attract) 4. Negative ions move out of cell (like charges repel) Ex: Na+, Cl-, K+, Ca 2+

Crossing the Cell Membrane Facilitated Diffusion 1. Carrier proteins are used to bind to & carry amino acids and sugars into the cell 2. Called “Facilitated” because the carrier proteins “help” the amino acids and sugars 3. Still no energy required, passive 4. Carrier proteins shield substances from nonpolar interior of membrane

Back to Learning Target ✔ I can – describe the importance and role of ion channels and facilitated diffusion in passive transport Numbers 1 & 2: Imagine you are a Na+ ion, describe how an ion channel works for you Numbers 3 & 4: Imagine you are an amino acid, describe how facilitated diffusion works for you

Demonstration 1) Each group will need: Beaker with water Iodine solution A baggie with water and cornstarch Iodine is a “starch indicator” - when it comes into contact with starch it turns dark purple Starch is a large, complex sugar Iodine is a small, I - ion

DO NOW 1) Take out your Chapter 4 packet and grab your textbook 2) Answer DO Now #1 questions on page 3) Wait quietly to begin

Learning Targets 1) I can – describe the movement of water in and out of the cell in terms of osmosis 2) I can – differentiate between a hypertonic, hypotonic, and isotonic solution

Demonstration 1) Each group will need: A cup of distilled water A cup of salt water (place two spoonfuls of salt in the other cup of water to make) Two small potato slices 2) Find a safe place in the room for your cups, we will come back to them at the end

Osmosis Water molecules are small and can diffuse through the cell membrane 1. Diffusion of water through a selectively permeable membrane 2. Passive transport (no cellular energy) 3. Water moves from high to low concentration

Osmosis 4. Water flows toward area with high concentration of dissolved particles

Osmosis – Three Types of Solutions Osmosis – Three types of Solutions The direction of water movement depends on the concentration of “free” water molecules inside and outside the cell There are three solutions that describe the movement of water Hypertonic Hypotonic (Think HIPPO) Isotonic

Osmosis – Three Types of Solutions Osmosis – Three types of Solutions Use page 77 in your textbook to research each type When you finish, practice explaining the difference between each Hypertonic Hypotonic (Think HIPPO) Isotonic

Learning Targets ✔ I can – describe the movement of water in and out of the cell in terms of osmosis ✔ I can – differentiate between a hypertonic, hypotonic, and isotonic solution 1) Grab your cups from earlier and observe your potatoes. 2) In your notes on p. describe the solution your potato was in and the movement of water

Solutions Hypertonic Solution If the fluid outside the cell has: More dissolved particles than the cytoplasm (higher concentration) Water diffuses: Out of the cell Effect on Cell Cell Shrinks Ex: Ever have a sore throat? – Salt Water

Solutions Hypotonic Solution If the fluid outside the cell has: Less dissolved particles than the cytoplasm Water diffuses: Into the cell Effect on Cell Cell Swells Ex: Swollen doors on a humid day?

Solutions Isotonic Solution If the fluid outside the cell has: The same dissolved particles as the cytoplasm Water diffuses: Into and out of the cell at equal rates Effect on Cell Cell stays the same size

Solutions Cell bursting can be prevented by: 1. Rigid cell walls in plants and fungi 2. Contractile vacuoles in some unicellular eukaryotes 3. Animal cell mechanisms remove extra dissolved particles in cell

DO NOW 1) Take out your Chapter 4 packet 2) Answer DO Now #2 questions on page 3) Wait quietly to begin

Learning Targets 1) I can – describe the importance and role of the sodium – potassium pump and receptor proteins 2) I can – differentiate between endocytosis and exoytosis 3) I can – compare active transport with passive transport

Active Transport 1. Transport of substances across membrane against concentration gradients 2. Moves large sugars, amino acids in or out of cell from low to high concentration when necessary for cell

Active Transport 3. Requires energy (ATP) 4. Carrier proteins bind to and pump substances from one side of the cell to the other from low to high concentration

Active Transport Sodium- Potassium Pump 1. Keeps sodium, potassium levels in and out of cell balanced 2. Prevents sodium buildup in cell because it continuously diffuses in through ion channels 3. Excess sodium may cause the cell to burst 4. Requires energy (ATP)

Active Transport Movement in Vesicles Many proteins and polysaccharides are too large to be transported by carrier proteins 1. Endocytosis- movement of very large proteins and polysaccharides into the cell through vesicles Membrane forms a pouch around substance that pinches off

Active Transport Movement in Vesicles 2. Exocytosis- substance moved by vesicle, to outside cell, by binding to membrane

Active Transport Membrane receptor proteins Your body sends out “signal molecules” to communicate to all parts of the body ex: hormones Receptor proteins in cell membranes bind to specific signal molecules, so cell can respond to signal Allows distant cells to communicate through release of signal molecules

Active Transport Membrane receptor proteins When a signal molecule binds to a receptor protein, its signal can cause the cell to do 3 things: 1. Causes ion channels to open or close their gates so ions do or do not pass 2. Trigger second messengers that carry out the signal’s message within the cell 3. Activate enzymes to speed up cellular reactions

Active Transport Membrane receptor proteins 4. Many drugs act by blocking proper binding or signal molecules to receptor proteins Bad: Heroin Good: Heart monitoring drugs

Back to Learning Targets ✔ I can – describe the importance and role of the sodium – potassium pump and receptor proteins ✔ I can – differentiate between endocytosis and exoytosis Interview Questions: 1) What type of active transport are you? 2) How do you allow movement to occur in the cell? 3) Why is this good for the cell? (What does it prevent/allow?)

Back to Learning Targets ✔ ) I can – compare active transport with passive transport 1) Complete the t-chart comparing active and passive transport 2) Compare your charts with other students to see if you should add/remove and information

Practice Create a pictionary of the main types of passive transport and types of active transport mechanisms. Define each, state the method of movement, give examples and make drawings to illustrate each mechanism. Try to complete this activity without your notes- later you can go back and check your work against your notes and the textbook.

Real World Connection Drinking too much water can be just as bad as not drinking enough water. Can cause hyponatremia. This is because there’s not enough sodium (salt) in the cells. Drinking Gatorade can help.