Chapter 4

Cells and Their Environment

Section 1: Passive Transport

Cell need to maintain Homeostasis Controlling what moves across the

cell membrane1) Energy is need to move materials = ACTIVE TRANSPORT

2) Energy is NOT need to move materials = PASSIVE TRANSPORT

Passive Transport

Molecules enter and exit an area because of their own motionMolecules will ALWAYS move from areas of HIGH concentration to areas of LOW concentrationA difference in concentration of substances is called a CONCENTRATION GRADIENT

Passive Transport All cells strive for EQUILIBRIUM Is a condition in which the concentration

of a substance is equal through a space

DIFFUSION is the movement of molecules from an area of high concentration to an of low concentrationSmall molecules or Nonpolar molecules can diffuse across the cell membraneDiffusion is the simplest type of Passive Transport

Osmosis

Is the diffusion of WATER through the cell membraneIs a type of Passive TransportOccurs as “free” water molecules move into the solution with lower concentration3 possibilities for the direction of water movement

Osmosis – Directions of Movement

#1 – Water Moves Out (Hypertonic) Cell Shrinks Outside the cell = Lower Concentration Inside the cell = Higher Concentration#2 – Water Moves In (Hypotonic) Cell Swells Outside the cell = Higher Concentration Inside the cell = Lower Concentration

Osmosis – Directions of Movement

#3 –No Net Water Movement (Isotonic) Cell Stays the same Free water molecules inside & out are

EQUAL Cell is in a state of Equilibrium

Hypotonic solution could cause the cell to burst Cell walls in plants & fungi help prevent

bursting

Crossing the Cell Membrane

Most ions & polar molecules can NOT cross the cell membraneBut CAN cross with the help of ChannelsION CHANNELS Na, K, Ca, and Cl ions Is a transport protein with a polar pore

through which ions can pass Some channels are always open Some channels have gates

Crossing the Cell Membrane

Diffusion of ions through ion channels is a form of Passive TransportNo energy is used because ions move down their concentration gradientsMovement of ions is influenced by their charge Inside the cell Negatively Charged “Opposites Attract”

Facilitated Diffusion (Pg. 80 - Figure 4)

CARRIER PROTEINS – a kind of transport protein that can bind to a specific substance on one side and be carried to the other side of a cellTransport – Sugar & Amino AcidsWhen carrier proteins transport Sugar & amino acid is is called FACILITATED DIFFUSIONFacilitated diffusion is a type of Passive Transport

Section 1 Review1. What is the difference between diffusion and osmosis?2. Describe how diffusion of ions across a cell membrane differs from the diffusion of nonpolar molecules across the cell membrane.3. How does facilitated diffusion work?4. T/F Diffusion occurs as a result of the random motion of substances.4. Why are green leafy vegetables sprayed with water at supermarkets?

Section 2: Active Transport

Moves substances AGAINST their concentration gradients From an area of LOW concentration to an area of HIGH concentrationREQUIRES ENERGYEnergy comes from ATPMembrane Pumps

Sodium-Potassium Pump

Transports 3 Na ion out & 2 K ions into the cellATP supplies the energy to move the Na and K ionsFIGURE 5 – page 82 – STUDY!Important for 2 Reasons #1 – Prevents Na from accumulating inside

If accumulation occurs the cell could burst

#2 – Helps Maintain the concentration gradient

Movement in Vesicles

Large molecules are moved across the cell membrane by VESICLES Proteins & Polysaccharides

Movement of substances into the cell by vesicles is called ENDOCYTOSIS Cell membrane forms a pouch around a

substance Pinches off & forms a vesicle

Movement in Vesicles

The movement of substances outside of a cell is called EXOCYTOSIS Vesicles fuse with the cell

membrane and expel their contents outside the cell

Cells use exocytosis to transport proteins that are modified by the Golgi Apparatus

Membrane Receptor Proteins

Signal Molecules HormonesRECEPTOR PROTEINS – pick up these signals and respond to the ones that are importantSignal Molecules binding to a receptor protein cause a change in receiving cells

Changes in Receiving Cell

1) Change in Permeability Cause the ion channel to open Important in the nervous system2) Second Messengers Act as a signal molecule in the

cytoplasm Activating enzymes, triggering

chemical reactions or change the permeability of the cell

Changes in Receiving Cells

3) Enzyme Action Receptor Protein may act as an

Enzyme Speeds up chemical reactions Activate other enzymes Drug affect the binding sites of

molecules to receptor proteins

Section 2 Review

1. What is the difference between passive and active transport?2. Which ion(s) move against a concentration gradient in a sodium-potassium pump?3. What serves as an “escort” to enable substances to move across a cell membrane by active transport and by endocytosis or exocytosis?4. What are the 3 functions of receptor proteins?