Cell Membrane & Transport Cells maintain homeostasis (balance) by transporting substances across the membrane

CELL MEMBRANE STRUCTURE: CELL MEMBRANE FUNCTION:

Cell Membrane Structure – overview The cell membrane is a semi-permeable lipid bi-layer Semi-permeable means that some substances can pass through it Lipid bi-layer means two layers of lipids Sometimes called a plasma membrane, cell membrane, and lipid bilayer

Cell Membrane Functions – overview Acts as a protective barrier for the cell Regulates (controls) which substances enter and leave the cell Maintains homeostasis (balance) of the cell

Components of Membranes 1.Phospholipids Structure: – Hydrophilic heads (water-loving) – Hydrophobic tails (water-fearing) Function: create semi- permeable barrier

Components of Membranes 2. Proteins Structure: – Proteins found in the membrane Functions: – Transport materials across the membrane

Components of Membranes 3. Cholesterol – Structure: a steroid/lipid – Function: Maintain membrane fluidity in animal cells

Components of Membranes 4. Carbohydrates Structure: found on outside of cell only – Glycolipids – Glycoproteins Functions: cell recognition and communication

Fluid Mosaic Model A mosaic of proteins “float” in a sea of phospholipids

In Conclusion…. WRITE about the following Using your notes, explain how the structure of the cell membrane allows for its functions of: – Acts as a protective barrier for the cell – Regulates which substances enter and leave the cell – Maintains homeostasis of the cell

Solutions A solution is a homogeneous (all the same) mixture of two or more substances

Solutions The solute is the substance being dissolved (disappearing into) the liquid The solvent is the liquid that does the dissolving In living organisms, water is always the solvent

Examples of Solutions Salt water is a solution – What is the solute? – What is the solvent? Koolaid is a solution – What is the solute? – What is the solvent? What is another solution?

Examples of Solutions Salt water is a solution – What is the solute? salt – What is the solvent? water Koolaid is a solution – What is the solute? sugar powder – What is the solvent? water What is another solution?

Solutions Concentration is the amount of solute that is dissolved in the solvent (water) – 12% solution = 12% solute and 88% solvent Concentration is increased by adding more solute to the solution Concentration is decreased by adding more solvent to the solution

Osmosis and Tonicity Tonicity refers to the total solute concentration of the solution outside the cell.

What are the three types of tonicity? 1)Isotonic - equal 2)Hypotonic – lower; under 3)Hypertonic – higher, over

Isotonic concentration of water (solvent) outside the cell is the same as the concentration inside the cell.

What will happen to a cell placed in an Isotonic solution? The cell will have no net movement of water and will stay the same size. Ex. Blood plasma has high concentration of albumin molecules to make it isotonic to tissues.

Hypotonic concentration of water (solvent) outside the cell is higher than the concentration inside the cell.

What will happen to a cell placed in a Hypotonic solution? The cell will gain water and swell. If the cell bursts, then we call this lysis. (Red blood cells = hemolysis) In plant cells with rigid cell walls, this creates turgor pressure.

Hypertonic concentration of water (solvent) outside the cell is lower than the concentration inside the cell.

What will happen to a cell placed in a Hypertonic solution? The cell will lose water and shrink. In plant cells, the central vacuole will shrink and the plasma membrane will pull away from the cell wall causing the cytoplasm to shrink called plasmolysis.

Review Tonicity What will happen to a red blood cell in a hypertonic solution? What will happen to a red blood cell in an isotonic solution? What will happen to a red blood cell in a hypotonic solution?

Passive vs. Active Transport

Passive Transport Solute or water moves from an area of high concentration to an area of low concentration Does not require ATP energy

Types of Passive Transport 1. Diffusion – Small solutes that can easily move across the membrane move around until equilibrium (balance) is reached

Types of Passive Transport 2. Facilitated Diffusion – Membrane proteins help larger solutes cross the membrane (without using energy) Channel Protein (ex. aquaporin)Carrier Protein

Types of Passive Transport 3. Osmosis – Water moves across the cell membrane from high to low water concentration

Active Transport The cell uses energy (ATP) to move solutes from low to high solute concentration

Types of Active Transport 1.Ion pumps (require energy) – Sodium-potassium pump (animal cells) 3 Na + out for every 2 K + in – Proton (H+) pump (plant, fungi, bacteria cells) pumps H+ out of the cell

Types of Active Transport 2. Bulk Transport -Exocytosis : cell secretes large molecules -Endocytosis : cell takes in large molecules Phagocytosis – cell takes in food Pinocytosis – cell takes in a lot of water

Water Balance in Cells Osmoregulation is crucial to living organisms

Comparing the Cell to its Environment 1.Isotonic – environment is the same concentration as the cell – No net movement of water – Animal cells are at equilibrium – Plant cells are flaccid (limp)

Comparing the Cell to its Environment 2. Hypertonic – environment is a higher concentration than the cell – Net movement of water out of the cell – Animal cells shrivel, may die – Plant cells plasmolyze, and are likely to die

Comparing the Cell to its Environment 3. Hypotonic – environment is a lower concentration than the cell – Net movement of water into the cell – Animal swell and may lyse (burst) – Plant cells are turgid (happy) with pressure against the cell wall