The Cell Membrane and

Types of Transport

Homeostasis keeping the cell stable

•  Homeostasis is the need for organisms to maintain stable, internal conditions.

•  In order to maintain homeostasis, all organisms have processes and structures that keep conditions in their bodies stable

•  The main organelle involved in maintaining homeostasis is the cell membrane •  Remember: what is the function of the cell membrane?

The Cell Membrane maintaining homeostasis

•  The cell membrane regulates the passage of material into and out of the cell. •  Depending on the needs of

the cell, excess (extra) substances must move out of the cell and needed substances must move into the cell.

•  Substances that move in and/or out: food, oxygen, carbon dioxide, and waste

The Cell Membrane Fluid Mosaic Structure

•  The cell membrane is semipermeable. •  Semipermeable = only some

substances can move into and out of the cell

•  The Cell Membrane is also known

as a Phospholipid Bilayer •  It is composed of two layers

of phospholipids which are embedded with proteins.

Phospholipid Structure: Hydrophobic Tails= Water fearing Hydrophilic Heads= Water loving

2 Types of Transport Active vs. Passive Transport

•  There are 2 types of transport that the cell membrane uses to maintain homeostasis: •  Passive Transport •  Active Transport

•  Passive Transport = does not require energy •  Molecules move DOWN a concentration

gradient (high to low)

•  Active Transport = requires energy •  Molecules move UP/AGAINST a

concentration gradient (low to high)

Passive Transport 3 types

•  Passive transport is defined as “a process by which substances move across the cell membrane but do not require energy from the cell”

•  Passive due to not requiring energy.

•  Molecules move down the concentration gradient

•  There are 3 types of passive transport: 1.  Diffusion 2.  Osmosis 3.  Facilitated Diffusion

Diffusion a type of passive transport

•  Diffusion is the spreading out (movement) of molecules across a cell membrane until they are equally concentrated on both sides of the cell membrane.

•  Diffusion results from the random movement of molecules down a concentration gradient

•  In diffusion, substances are able to pass directly across the cell membrane without the need for a protein or energy.

Facilitated Diffusion a type of passive transport

•  Facilitated diffusion is the process by which some substances enter the cell membrane with the aid of transport proteins.

•  Facilitated diffusion occurs down a concentration gradient and does not require energy from the cell.

•  Some substances have chemical structures that prevent them from passing directly through a cell membrane. •  Therefore, transport proteins allow these substances to

pass across the cell membrane.

Facilitated Diffusion