UNIT 4. MOVEMENT ACROSS CELL MEMBRANE

1. Passive Transport

2. Active Transport

3. Endocytosis

4. Exocytosis

4 Major Types of Movements Across Cell Membrane

Passive Transport

4 Major Types of Movements Across Cell Membrane:

● No energy required

● Move due to gradient

● Movement is down the concentration gradient

● High concentration moves toward low concentration

1. Passive Transport

2. Facilitated Diffusion

3. Osmosis

3 Types of Passive Transport

Simple Diffusion

3 Types of Passive Transport:

• molecules move to equalize concentration

• Movement of small, nonpolar molecules directly through the lipid bilayer

• Example: Oxygen (O₂) entering cells, Carbon dioxide (CO₂) leaving cells

Facilitated Diffusion

3 Types of Passive Transport:

• Movement of specific, polar or charged molecules down a concentration gradient

• Pass through membranes via specific carrier protein

• Selection is by size, shape, charge

• Example: Glucose transport via GLUT transporters, ions via ion channels

Channels

(are specific) help polar or charged molecules or ions enter or leave the cell

transport proteins

Channels usually are ______________

Aquaporin

a membrane protein channel that facilitate the movement of water

Osmosis

3 Types of Passive Transport:

- Special form of diffusion

- Fluid flows from the lower solute concentration to higher

- Requires selective permeable membrane

- Diffusion of water across a selectively permeable membrane

1. Hypotonic Solutions

2. Isotonic solution

3. Hypertonic solution

3 Types of Solutions:

Hypotonic Solution

3 Types of Solutions:

• Solute concentration outside < inside

• Water moves into the cell

• cell may swell/lyse

• important in turgor pressure in plant cells

Isotonic Solution

3 Types of Solutions:

• Solute concentration outside = inside

• Water moves equally in both directions

• cell remains stable

• Example: 0.9% NaCl (normal saline) for human cells

Hypertonic Solution

3 Types of Solutions:

• Solute concentration outside > inside

• Water moves out of the cell

• cell shrinks/shrivels (crenation)

• Example: 10% NaCl solution for human cells

• Hypotonic = lysed

• Isotonic = normal

• Hypertonic = shriveled

Effects of Osmosis in Animal cell

• Hypotonic = Turgid (normal)

• Isotonic = Flaccid

• Hypertonic = Plasmolyzed

Effects of Osmosis in Plant cell

Active Transport

4 Major Types of Movements Across Cell Membrane:

• Molecular movement

• Requires energy (ATP)

• against concentration gradient (low HC —> High HC)

• Ex: Sodium-potassium pump (Na⁺/K⁺-ATPase) moves 3 Na⁺ out and 2 K⁺ in

Endocytosis

4 Major Types of Movements Across Cell Membrane:

• Process of taking in large particles or liquids

• invagination of the plasma membrane

• Movement is into cell

A. Pinocytosis

B. Phagocytosis

2 Types of Endocytosis:

Pinocytosis

2 Types of Endocytosis:

• '“cell drinking”

• Engulfs liquids and dissolved solutes

• Example: Nutrient uptake in intestinal cells

Phagocytosis

2 Types of Endocytosis:

• “cell eating”

• Engulfs large particles or microbes

• Example: Macrophages ingesting bacteria

Exocytosis

4 Major Types of Movements Across Cell Membrane:

• Reverse of endocytosis

• Cell discharges material

• Releases substances from the cell into the extracellular space

• Vesicles fuse with the plasma membrane to expel contents

• Example:

  • Neurotransmitter release at synapses

  • Hormone secretion (e.g., insulin from pancreatic β-cells)