Agenda 10/27Cell Membrane and Homeostasis

2.1 Relate cell parts/organelles (plasma membrane) to their functions. Explain the role of cell membranes as a highly selective barrier (diffusion, osmosis, facilitated diffusion, active transport).

Homeostasis– Maintaining a relatively constant internal environment

Cells need the proper concentration of nutrients and water, and to eliminate wastes.

The cell membrane is selectively permeable – it allows some things to pass through,

while blocking other things.

Structure of the Cell Membrane

Phospholipid bilayer – two sheets of phospholipids.

Embedded with proteins and strengthened with cholesterol molecules.

What’s a Phospholipid? 2 fatty acid chains, a phosphate group,

and a glycerol.– Hydrophilic heads face out

– hydrophobic fatty acids hang inside.

Fluid Mosaic Model The parts of the cell membrane form a

fluid that can move more or less freely. The cell membrane is a “mosaic” in that

it is composed of several different parts

Cell Membrane

Cellular Transport Diffusion – movement of particles from

an area of high concentration to an area of low concentration.– Continues until an equilibrium is reached

Osmosis

Diffusion of water across a selectively permeable membrane.

Occurs until water is balanced on both sides of the membrane.

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AquaporinsAquaporins Water Channels Protein pores used during

OSMOSIS WATERMOLECULES

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Cellular Transport [1] Passive transport – no energy is

needed to move particles (from high to low concentration).

– Facilitated diffusion –proteins act as tunnels allowing particles to cross the cell membrane

Cellular Transport [2] Active transport – energy is

needed to move particles across the membrane (from low to high concentration).

1. Transport (or carrier) proteins

2. Endocytosis (endo- = into; cyto- = cell)

3. Exocytosis (exo- = out)

Active Transport: Transport Proteins

Allow movement of particles against the concentration gradient (from low to high)

Carrier proteins –protein changes shape to open and close passages across membrane.

Carrier Protein

Active Transport: Endocytosis

Movement of larger

particles INTO the cell

ExocytosisMovement of larger

particles OUT of the cell

Osmosis

Diffusion of water across a selectively permeable membrane.

Occurs until water is balanced on both sides of the membrane.

Solutions

Solute: substance that is dissolved into something else

Solvent: the substance the solute is dissolved into

Cell Concentrations

Hypertonic solutions – more dissolved solute.

Hypotonic solutions – less dissolved solute.

Isotonic solutions – the same dissolved solute.

Osmosis

Osmosis in Cells

Animal Cells- – Crenation- cell shrivels as water leaves– Lysis- cell bursts when too much water

enters Plant Cells-

– Turgor Pressure- pressure of full central vacuole pressing out on cell wall- when low, plant wilts

Osmosis in Cells

Contractile vacuoles – expel excess water from bacterial cells that live in water to keep cells from bursting.

Turgor pressure – water pressure in a plant cell (central vacuole). Loss of turgor pressure causes wilting.

Membrane Proteins

1. Determine what particles can pass through the membrane.

2. Serve as enzymes.3. Act as markers inside and outside of

the cell (communication).

Can you identify the cell parts?

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