Cell Size and Membrane Transport Essential Questions: EQ: How do cells maintain homeostasis? EQ: How are materials transported into and out of the cell? Georgia Performance Standards: Analyze the nature of relationships between structures and functions in living cells. Explain the role of cell organelles for both prokaryotic and eukaryotic cells, including the cell membrane, in maintaining homeostasis and cell reproduction. Explain the impact of water on life processes (i.e. osmosis, diffusion)

Warm-up How is a window screen similar to a cell membrane? 1. What are some things that can pass through a window screen? 2. What are some things that cannot pass through a window screen? Why is it important to keep these things from moving through the screen? 3. The cell is surrounded by a cell membrane, which regulates what enters and leaves the cell. Why is it important to regulate what moves into and out of a cell?

Cell size and shape are related to its function Cells must be SMALL in order to function efficiently –Organelles near the cell membrane to transport nutrients in and wastes out. –VERY EFFICIENT A LARGE cell has a smaller surface area relative to its volume than smaller cells have. –Organelles far from cell membrane. Hard to transport nutrients in and wastes out –NOT EFFICIENT

Cell Size with “Cube”Demo: The ratio of surface area to volume imposes and upper limit on cell size. Math Example Larger cube has more volume and less surface area (not efficient). Smaller cube has less volume and more surface area (efficient)

The Cell Membrane Maintains Homeostasis Structure –Semi-permeable –Made of a phosphoLIPID bilayer –Contains proteins and carbohydrates –Has polar hydrophilic (water loving) and non-polar hydrophobic (water fearing) parts Function –Provides support and protection –Controls what enters and leaves the cell

Outside of cell Inside of cell (cytoplasm) Cell membrane Proteins Protein channel Lipid bilayer Carbohydrate chains The Structure of the Cell Membrane Go to Section:

Floating around in the cell membrane are different kinds of proteins. They are not held in any fixed pattern but instead float around in the phospholipid layer AKA Fluid Mosiac Model

This is a cross section of the cell membrane you should notice two different structures: The phospholipids are the round yellow structures with the blue tails. The proteins are the lumpy structures that are scattered around among the phospholipids.

This is a simple representation of a phospholipid. The yellow structure represents the hydrophillic or water loving section of the phospholipid. The blue tails that come off of the sphere represent the hydrophobic or water fearing end of the phospholipid.

If you mix phospholipids in water they will form these double layered structures. The hydrophillic ends will be in contact with water. The hydrophobic ends will face inwards touching each other.

Proteins Transport proteins: regulate what enters or leaves the cell (Carrier & Channel)

B.Channel Proteins: Channel proteins simply act as a passive pore. Molecules will randomly move through the opening in a process called diffusion. *

TYPES OF TRANSPORT PASSIVE= Requires NO Energy HIGH concentration  LOW concentration –Diffusion –Osmosis –Facilitated Diffusion ACTIVE= Requires Energy LOW concentration  HIGH concentration –Endocytosis –Exocytosis

Passage Through Cell Boundaries Types of Passive Transport: Diffusion –ANY substance moves from areas of HIGH concentration to areas of LOW concentration –Requires NO energy (ATP) –Equilibrium is reached when the concentration is equal on both sides of the membrane –Rate determined by temp. and size of molecule

Passage Through Cell Boundaries Osmosis –Diffusion of water through a selectively permeable membrane, until the concentration of substances are at an equilibrium. –Types of Solutions: Isotonic (Equal amounts of solute and solvent) Hypertonic (more solute than solvent) Hypotonic (more solvent than solute)

The Effects of Osmosis on Cells Cells placed in an isotonic solution neither gain nor lose water. (=) Cells in a hypotonic solution, animal cells swell and can burst. The vacuoles of plant cells swell, pushing the cell contents out against the cell wall. hypo= “hippo” think of Violet from Willy Wonka cytolysis= cell bursts In a hypertonic solution, animal cells shrink (plasmolysis), and plant cell vacuoles collapse.

Cell membrane Higher Concentration of Water Lower Concentration of Water Water molecules Sugar molecules Section 7-3 Osmosis Go to Section:

Facilitated Diffusion Large molecules like glucose can not pass through on their own Protein channels found within the lipid bilayer “facilitate” the passage of these substances HIGH  LOW Requires NO energy (ATP) High Concentration Low Concentration Cell Membrane Glucose molecules Protein channel

Active Transport Sometimes cells must move materials against concentration gradients (from low concentration to high to concentration) Requires energy (ATP needed)

Types of Active Transport 1. Channel proteins: –Proteins found in the lipid bilayer can “pump” small molecules in/out of the cell with energy 2. Endocytosis – cell can gather large substances and move them into the cell by folding its cell membrane (creating a vesicle) around the materials. 3. Exocytosis – Vacuoles from within the cell fuse with the cell membrane and force contents out of the cell

Molecule to be carried Low Concentration Cell Membrane High Concentration Molecule being carried Low Concentration Cell Membrane High Concentration Energy Section 7-3 Active Transport Go to Section:

ENDOCYTOSIS “endo”= into or inside “cyto”= cell MOVEMENT INTO CELL transport.htm

EXOCYTOSIS “Exo”= exit, out of “cyto”=cell MOVEMENT OUT OF CELL

Checkpoint 1.How is homeostasis maintained by the cell membrane? 2.A. What type of transport does NOT require energy? B. Explain the concentration flow. C. Give 3 examples 3.A. What type of transport requires energy? B. Explain concentration flow. C. Give 3 examples.