Passive and Active Transport

Importance

Every living cell exists in a liquid environment.

One of the most important functions of the cell membrane is to keep the cell’s internal conditions relatively constant. It does this by regulating the movement of molecules from one side of the membrane to the other side.

Passive Transport

Cell membranes help organisms maintain Homeostasis by controlling what substances may enter or leave cells

Doing this WITHOUT energy is called passive transport Diffusion Facilitated Diffusion Osmosis

Diffusion

The simplest form of passive transport

Does not require energy

Is the movement of molecules from an area of HIGH concentration to an area of LOW concentration

High concentration of dye

Low concentration of dye

Ex: Perfume or Cologne

Facilitated Diffusion

Most molecules cannot cross the cell membrane by simple diffusion

Some Molecules are CARRIED across by CARRIER PROTEINS EMBEDDED IN the Cell Membrane

Requires NO energy

Carrier Proteins CHANGE SHAPE when Molecules ATTACH to them

The Change in Shape of the Carrier Protein ENABLES the Molecule to CROSS the Membrane.

The use of carrier proteins is called facilitated diffusion.

Osmosis

The diffusion of WATER over a semi-permeable membrane

Does NOT require energy

From HIGH concentration of WATER to LOW concentration of WATER

Osmotic Conditions

Isotonic Hypertonic Hypotonic

Quick Chemistry Review

Solute: substance being dissolved Solvent: water (does the dissolving) Solution: combined mixture

Isotonic “same strength”

In an Isotonic solution The amounts of solutes inside

is the same as outside of cell Under these conditions, water

diffuses into and out of the cell at EQUAL RATES, so there is NO net movement of water

Remains at equilibrium “Like a full restaurant – one family must leave for another to enter”

Cells in isotonic solutions…

No net movement of water Cells are normal

Hypertonic “above strength”

The concentration of solute molecules outside the cell is higher than the concentrations of solutes inside the cell.

WATER DIFFUSES OUT OF THE CELL until Equilibrium is established

Plasmolysis: the cell shrinks

“Hyper kids run out of school”

Cells in hypertonic solutions…

Water moves out of the cell Cells shrivel (plasmolysis)

Hypotonic “blow strength”

The concentration of solute molecule outside the cell is lower than the concentration of solutes inside the cell

WATER DIFFUSES INTO THE CELL until Equilibrium is established

Cytolysis: the cell explodes

Cells in hypotonic solutions…

Water moves into the cell Animal cells burst (cytolysis) Plant cells become turgid

Cells in Osmotic Environments

Plasmolysis

(Elodea cell)

Cytolysis

(Tumor cell)

Isotonic

(Elodea cell)

Active Transport

In many cases, cells must move materials from an area of low concentration to high concentration

This requires energy When energy is used to transport

molecule across a membrane, this is called active transport

Small molecules and ions are carried across membranes by proteins in the membrane that act like pumps

Large molecules need to be transported in Bulk

Bulk transports include endocytosis, and exocytosis

Endocytosis

During ENDOCYTOSIS the Cell Membrane  folds into a POUCH that encloses the Particles.

The Pouch pinches off INSIDE the Cell to form a VESICLE (membrane-wrapped bubbles).

The VESICLE can then fuse with other Organelles or release its contents into the cytoplasm

Pinocytosis and Phagocytosis

Two forms of Endocytosis Pinocytosis is often referred to as “cell

drinking” Bring in fluids and solutes

Phagocytosis is often referred to as “cell eating” Brings in food or other cells

Exocytosis

The opposite of endocytosis Gets rid of wastes