Chapters 3.3 & 3.4& 3.5

Chapter 3.3 Cell membrane

Functions: contains cell contents, controls what enters and exits a cell

Fluid mosaic model: describes the arrangement of molecules that make up a cell membrane.

**The Membrane is flexible like a fluid and has a variety of 

molecules like the variety of tiles in a mosaic

                   













                                                           

Phospholipids: form a double layer surrounding a cell. 

charged/polar phosphate group, and glycerol

 no charge/non polar two fatty acid chains. 

head: hydrophilic (water loving) 

    


tails: hydrophobic (water fearing)

Other Molecules that make up the cell membrane: 

 cholesterol: strengthens membranes

proteins: help cell identification, movement of molecules across 

membranes and cell signaling, 

carbohydrates: aid cell identification  

Selective permeability/Semipermeable:allows some materials to

 Cross; in order for cell to maintain homeostasis;


Sketch Selective Permeability

Receptors: detect a signal molecule and perform an action in response

ligand is a molecule that acts as a signal when it binds to a receptor. Can cross the cell membrane

Intracellular: located inside a cell; bind to molecules that can cross the membrane

Membrane : located in the membrane; binds to molecules than cannot cross the membrane;

change in shape transmits the message to the cell interior

Diffusion & Osmosis 3.4

Passive transport: 

the 

movement of 

molecules across a 

membrane 


without

 energy input from 

the cell

Diffusion: movement of molecules from higher to lower concentration

Osmosis: the diffusion of water

How do different solutions affect cells?

** hypertonic solution has a higher concentration of dissolved particles than a cell. This means water concentration is higher inside the cell than outside. Thus, water flows out of the cell, causing it to shrivel or even die.

**isotonic solution to a cell if it has the same concentration of dissolved particles as the cell. Water molecules move into and out of the cell at an equal rate, so the cell’s size remains constant.

**hypotonic solution has a lower concentration of dissolved particles than a cell. This means water molecules are more concentrated outside the cell than inside. Water diffuses into the cell. If too much water enters a cell, the cell membrane could potentially expand until it bursts.

Facilitated diffusion: the diffusion of molecules across a 

membrane through transport proteins; requires no energy input 

from the cell

Active Transport, Endocytosis & Exocytosis Chapter 3.5

**Active transport: drives 

molecules across a membrane 

from lower to higher 

concentration (against a 

concentration gradient) 

**Most active transport proteins use energy from the breakdown  

of ATP (IS ENERGY)

ACTIVE & PASSIVE TRANSPORT RECAP

Endocytosis: process of taking in

liquids or larger molecules into a  
cell by engulfing in a vesicle; 

requires energy 


Exocytosis: process of releasing 

substances out of a cell by fusion of a vesicle with the membrane 

requires energy

Phagocytosis (cell eating):is a 

type of endocytosis in which the 

cell membrane engulfs large 

particles. 

Chapter 3.3,3.4&3.5 Quiz