HOMEOSTASIS and TRANSPORT

A4

A4. Homeostasis and Transport1. Describe how the structure of the plasma membrane

allows it to function as a regulatory structure and/or protective barrier for a cell.

2. Compare the mechanisms that transport materials across the plasma membrane.

3. Explain how organisms maintain homeostasis.

4. Describe how membrane-bound organelles facilitate the transport of materials within a cell.

A4. Vocabulary

plasma membrane lipid bilayerphospholipid impermeableselectively permeable protein channelprotein pump osmosisdiffusion facilitated diffusionactive transport passive transportendocytosis exocytosisisotonic equilibriumhypertonic concentration gradienthypotonic homeostasis

Cell Membrane Structure and function

• Cell membranes are composed of phospholipids• Phospholipids are arranged in two layers (bilayer)• Each phospholipid has a “head” and two “tails”– The head loves water (hydrophilic)– The tails hate water (hydrophobic

• The lipid bilayer is flexible but strong

A phospholipid bilayer

Cell Membrane Structure and FunctionDRAW THIS

in your NOTES!!

Cell Membrane Structure and Function

• The cell membrane acts as a fluid…– It is not rigid– Proteins and phospholipids can move around

• The cell membrane is a mosaic…– Many different parts make up the cell membrane

Fluid Mosaic Model

Cell Membrane Structure and Function

• Barrier between the cytoplasm and the environment

• Protects and supports the cell• Controls everything that enters and leaves the

cell

Functions of the Cell Membrane

Cell Membrane Structure and Function

Membranes are selectively permeable • Some things can cross the membrane (permeable)– Gases, water, small particles

• Some things can cross the membrane with the help of a protein channel or pump– Ions, proteins, large particles

• Some things can’t cross the membrane (impermeable)

Permeability

Let’s Build a Model of a cell membrane!

• Cotton swabs represent phospholipids• Other components are embedded within the

phospholipid bilayer• Can you move the components back and

forth?

Can you do it?

• Give as many names for the boundary of the cell as you can…

Mechanisms of Passive Transport

• requires NO energy• Depends on a concentration gradient (difference)– Concentration = relative amount of substance

• SUBSTANCE moves from HIGH concentration (of

substance) to LOW concentration (of substance)

• Some materials can pass freely, other materials need a protein channel

Passive Transport Defined

Mechanisms of Passive Transport

Passive Transport is like…

A ball rolling down a hill

Mechanisms of Passive Transport

• Passive transport• Depends on a concentration gradient– Concentration = relative amount of substance– Gradient = difference

• MOVEMENT from HIGH concentration to LOW concentration–Down the concentration gradient

1. Diffusion (a.k.a. simple diffusion)

Mechanisms of Passive Transport

• Passive – requires NO energy• Depends on a concentration gradient (difference)– Concentration = relative amount of water

• MOVEMENT from HIGH concentration to LOW concentration

• just like simple diffusion EXCEPT needs a protein channel

2. Facilitated Diffusion

Mechanisms of Passive Transport

• Diffusion of water• WATER moves from HIGH concentration (of water) to

LOW concentration (of water)

• Aquaporins = protein channels for water to pass• Plays a role in maintaining homeostasis (water balance)

3. Osmosis

Osmosis

Which way will the water molecules move?

Why wouldn’t the green or purple molecules move?

Mechanisms of Active Transport

• Requires energy• Material flows AGAINST the concentration

gradient– From LOW concentration to HIGH concentration

• Requires protein pumps (need energy to work)

Defined

Movement within a cell

• Use ATP energy to move or “pump” material into an area that already has a high concentration

• It’s like pumping air into a basketball

1. Protein Pumps

Movement within a cell

1. Protein Pumps

Movement within a cell

• Used to transport very large molecules or food• Endocytosis = bringing materials into the cell• Exocytosis = taking materials out of the cell• Cell membrane/vesicles play a role

2. Bulk Transport

Movement within a cell

2. Bulk Transport

Homeostasis

• Maintaining stability in the cell or body• Variables within the body can fluctuate– Temperature, pH, water balance

• Important to maintain homeostasis near set point• Cell membrane aids in maintaining homeostasis

Defined

Homeostasis

• Diffusion of water• Passive (no energy required)• Water will move across the membrane down its

concentration gradient• Cell membrane regulates the amount of water

inside a cell

Osmosis and water balance

Homeostasis

• Amount of water inside = amount of water outside• Water moves back and forth across the membrane

equally in both directions• Equilibrium = equal concentrations of water on

both sides of the membrane

ISOTONIC Conditions

Homeostasis

• Amount of solute surrounding cell is high (high solute = low water)

• Water moves out of the cell to balance concentrations of water on both sides of membrane

• Cell shrinks (dehydrates)• EX: saltwater

HYPERTONIC Conditions

Homeostasis

• Amount of solute surrounding cell is low (low solute = high water)

• Water moves INTO the cell to balance concentrations of water on both sides of membrane

• Cell swells (animal cells could burst)• EX: pure water

Hypotonic conditions

Homeostasis

Osmosis

Why would plant cells be

better off than animal cells?

What would happen to the

cells of a freshwater fish

if it was put into a saltwater

tank?

Cell Transport Review

• Divide your poster into six sections• In each section, diagram one of the following

modes of transport– Simple diffusion– Facilitated diffusion– Osmosis– Active transport via protein pumps– Exocytosis– endocytosis

Keystone Questions

1. Carbon dioxide and oxygen are molecules that can move freely across a plasma membrane. What determines the direction that carbon dioxide and oxygen move?

A. Orientation of cholesterol in the plasma membraneB. Concentration gradient across the plasma membraneC. Configuration of phospholipids in the plasma membraneD. Location of receptors on the surface of the plasma

membrane

Keystone Questions

2. A sodium-potassium pump within a cell membrane requires energy to move sodium and potassium ions out of a cell. The movement of glucose into or out of a cell does not require energy. Which statement best describes the movement of these materials across a ac cell membrane?

A. Sodium and potassium ions move by active transport, and glucose moves by osmosis

B. Sodium and potassium ions move by active transport and glucose moves by facilitated diffusion.

C. Sodium and potassium ions move by facilitated diffusion and glucose moves by osmosis

D. Sodium and potassium ions move by facilitated diffusion and glucose moves by active transport

Keystone Questions

3. Which example is an activity that a fish most uses to maintain homeostasis within its body?

A. Using camouflage to avoid predatorsB. Feeding at night to regulate body temperatureC. Moving to deeper water to regulate metabolic wastesD. Exchanging gases through its gills to regulate oxygen

levels.

Keystone Questions

4. Diffusion occurs becauseA. Molecules are attracted to one anotherB. Molecules constantly move and collide with one

anotherC. Cellular energy forces molecules to collide with one

anotherD. Cellular energy pumps molecules across the cell

membrane

Keystone Questions

5. During diffusion, when the concentration of molecules on both sides of the membrane are equal, molecules will

A. Move across the membrane to the outside of the cellB. Stop moving across the membraneC. Continue to move across the membrane in both

directionsD. Move across the membrane to the inside of the cell