The Plasma Membrane The Plasma Membrane and Homeostasisand Homeostasis

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Functions of Plasma Functions of Plasma MembraneMembrane Protective barrierProtective barrier

Regulate transport in & out of Regulate transport in & out of cell cell (selectively permeable)(selectively permeable)

Allow cell recognitionAllow cell recognition

Provide anchoring sites for Provide anchoring sites for filaments filaments of cytoskeletonof cytoskeleton

Provide a binding site for Provide a binding site for enzymesenzymes

Interlocking surfaces bind cells Interlocking surfaces bind cells together (junctions)together (junctions)

Homeostasis – Maintaining a Homeostasis – Maintaining a BalanceBalance

Cells must keep the proper Cells must keep the proper concentration of nutrients and concentration of nutrients and water and eliminate wastes.water and eliminate wastes.

The plasma membrane is The plasma membrane is selectively permeable – it will selectively permeable – it will allow some things to pass allow some things to pass through, while blocking other through, while blocking other things.things.

Structure of the Plasma Structure of the Plasma MembraneMembrane

Lipid bilayer – two sheets of lipids Lipid bilayer – two sheets of lipids (phospholipids).(phospholipids).– Found around the cell, the nucleus, Found around the cell, the nucleus,

vacuoles, mitochondria, and vacuoles, mitochondria, and chloroplasts.chloroplasts.

– Embedded with proteins and Embedded with proteins and strengthened with cholesterol strengthened with cholesterol molecules.molecules.

What’s a Phospholipid?What’s a Phospholipid?

It’s a pair of fatty acid chains and a It’s a pair of fatty acid chains and a phosphate group attached to a phosphate group attached to a glycerol backbone.glycerol backbone.– Polar (water-soluble) heads face Polar (water-soluble) heads face

out and the nonpolar fatty acids out and the nonpolar fatty acids hang inside.hang inside.

Membrane ProteinsMembrane Proteins

1. Determine what particles can 1. Determine what particles can pass through the membrane.pass through the membrane.

2. Serve as enzymes (may speed 2. Serve as enzymes (may speed reactions).reactions).

3. Act as markers that are 3. Act as markers that are recognized by chemicals and recognized by chemicals and molecules from the inside and the molecules from the inside and the outside of the cell (the immune outside of the cell (the immune system).system).

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Simple DiffusionSimple Diffusion Molecules move Molecules move

from area of from area of HIGH HIGH to LOWto LOW concentrationconcentration

Requires Requires NONO energy to make the energy to make the molecules move.molecules move.• passive processpassive process

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Diffusion of LiquidsDiffusion of Liquids

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Diffusion through a MembraneDiffusion through a Membrane

Cell membrane

Solute moves DOWN concentration gradient (HIGH to LOW)

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OsmosisOsmosis Diffusion of waterDiffusion of water

across a across a membranemembrane

Moves fromMoves from HIGH HIGH water molecule water molecule concentrationconcentration (low solute) to(low solute) to LOW water LOW water molecule molecule concentrationconcentration (high solute)(high solute)

Diffusion across a membrane

Semipermeable

membrane

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Diffusion of HDiffusion of H22O Across A O Across A

MembraneMembrane

High H2O concentrationLow solute concentration

Low H2O concentrationHigh solute concentration

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Cell in Isotonic SolutionCell in Isotonic Solution

CELLCELL

10% NaCL90% H2O

10% NaCL

90% H2O

What is the direction of water movement?The cell is at _______________.equilibrium

ENVIRONMENTENVIRONMENT

NO NET NO NET MOVEMENMOVEMENTT

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Cell in Hypotonic SolutionCell in Hypotonic Solution

CELLCELL

10% NaCL90% H2O

40% NaCL

60% H2O

What is the direction of water movement?

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Cell in Hypertonic SolutionCell in Hypertonic Solution

CELLCELL

15% NaCL85% H2O

5% NaCL95% H2O

What is the direction of water movement?

ENVIRONMENTENVIRONMENT

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Cells in SolutionsCells in Solutions

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Which cell is at homeostasis?Which cell is at homeostasis?

Cytolysis Plasmolysis

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Osmosis in Red Blood CellsOsmosis in Red Blood Cells

IsotonicIsotonic Hypotonic

Hypertoniccopyright cmassengale

What Happens to Blood Cells?What Happens to Blood Cells?

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Cellular TransportCellular Transport

DiffusionDiffusion – movement of particles from – movement of particles from an area of high concentration to an area an area of high concentration to an area of low concentration.of low concentration.– Caused by Brownian motion Caused by Brownian motion

(movement of particles because of (movement of particles because of the movement of their atoms).the movement of their atoms).

– Continues until an equilibrium is Continues until an equilibrium is reached (no gradient).reached (no gradient).

– Dynamic equilibrium – particles move Dynamic equilibrium – particles move freely and are evenly distributed.freely and are evenly distributed.

Cellular Transport [1]Cellular Transport [1]

Passive transportPassive transport – no energy is – no energy is needed to move particles.needed to move particles.

– Facilitated diffusionFacilitated diffusion – embedded – embedded proteins act as tunnels allowing proteins act as tunnels allowing particles to “fall” through.particles to “fall” through.

Cellular Transport [2]Cellular Transport [2]

Active transport – energy is needed Active transport – energy is needed to move particles.to move particles.

– Carrier proteins – embedded proteins Carrier proteins – embedded proteins change shape to open and close change shape to open and close passages across the membrane.passages across the membrane.

– Endocytosis – taking something into Endocytosis – taking something into the cell.the cell.

– Exocytosis – expelling something from Exocytosis – expelling something from the cell.the cell.

OsmosisOsmosis

Diffusion of water across a Diffusion of water across a selectively permeable membrane.selectively permeable membrane.

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

Cell ConcentrationsCell Concentrations

Hypertonic solutions – more Hypertonic solutions – more dissolved solute.dissolved solute.

Hypotonic solutions – less dissolved Hypotonic solutions – less dissolved solute.solute.

Isotonic solutions – the same Isotonic solutions – the same dissolved solute.dissolved solute.

Overcoming OsmosisOvercoming Osmosis

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

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