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? How is a window screen similar to a cell membrane?

1. What are some things that can pass through a window 1. What are some things that can pass through a window screen?screen?

2. What are some things that cannot pass through a 2. What are some things that cannot pass through a window screen? Why is it important to keep these things window screen? Why is it important to keep these things from moving through the screen?from moving through the screen?

3. The cell is surrounded by a cell membrane, which 3. The cell is surrounded by a cell membrane, which regulates what enters and leaves the cell. Why is it regulates what enters and leaves the cell. Why is it important to regulate what moves into and out of a cell?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

Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel

Lipid bilayer

Carbohydratechains

The Structure of the Cell Membrane

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•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 EnergyHIGH concentration LOW concentration

– Diffusion– Osmosis– Facilitated Diffusion

• ACTIVE= Requires EnergyLOW 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 Wonkacytolysis= cell bursts

• In a hypertonic solution, animal cells shrink (plasmolysis), and plant cell vacuoles collapse.

Cellmembrane

Higher Concentrationof Water

Lower Concentrationof Water

Water molecules

Sugar molecules

Section 7-3Osmosis

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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

• HIGHLOW• Requires NO energy

(ATP)

HighConcentration

LowConcentration

CellMembrane

Glucosemolecules

Proteinchannel

Active Transport

• Sometimes cells must move materials against concentration gradients (from low concentration to high to concentration)

• Requires energy (ATP needed)

Types of Active Transport1. 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 tobe carried Low

Concentration

CellMembrane

HighConcentration

Moleculebeing carried

LowConcentration

CellMembrane

HighConcentration

Energy Energy

Section 7-3

Active Transport

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ENDOCYTOSIS• “endo”= into or inside• “cyto”= cell• MOVEMENT INTO CELLhttp://02b5260.netsolhost.com/video-transport.htm

EXOCYTOSIS• “Exo”= exit, out of

• “cyto”=cell

• MOVEMENT OUT OF CELL

Checkpoint1. 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.