Download Cell Transport

Structure and Function of the
Plasma Membrane
• Each living cell exists in a watery
environment, which allows dissolved materials
to move in and out the cell like oxygen, food
& nutrients.
• As the cell reacts with it’s ever changing
surroundings it actively tries to keep
conditions inside itself pretty constant. This
internal balancing of conditions is called
homeostasis.
The Cell Membrane
Function: All cells use the cell membrane to help
maintain homeostasis. This is due to the membrane
being selectively permeable meaning it can pick
and choose what comes into and out of the cell.
Structure: The membrane’s function is
directly related to its structure. It consists of a
lipid bilayer made of two layers of
phospholipids sandwiched together and
dotted with different types of proteins.
Notice the polar heads (water loving)
and non-polar tails (water fearing)
Passive Transport vs. Active
Weeee!!
Transport
!
• Passive transport –
– Cell doesn’t use energy
– Random movement of
molecules from a high to
low concentration.
high
low
• Active transport –
– Cell uses energy
– Directed movement of
molecules from a low to
high concentration.
This is
gonna
be hard
work!!
high
low
Passive Transport
3 types of passive transport:
• Diffusion - transport of substances
• Osmosis – transport of water
• Facilitative Diffusion – transport with the
help of carrier proteins (for molecules too
large to pass through the membrane
without help)
Diffusion
Transport of substances (other than water)
from areas of high to low concentration.
Diffusion occurs until the molecules are distributed evenly throughout.
Diffusion Through Cell
Uncharged and veryMembranes
small molecules
CO
move straight through the middle
non-polar region of the cell
membrane without breaking it until
equilibrium is reached (the same
amount of solutes on both sides).
These include very small molecules like
oxygen, carbon dioxide, and water.
For example: The capillary below is returning
blood to the lungs, thus has a high
concentration of carbon dioxide. The air sacs
in the lungs have a lower concentration of
carbon dioxide. Which way will the carbon
dioxide go?
CO2
2
CO2
CO2
CO2
CO2
CO2
CO2
bloodstream
air sacs
Osmosis
• The diffusion of water across a selectively
permeable membrane (high to low
concentration)
Notice the water rises
on the left side of the
tube, as water moves
from right to left.
The sugar concentration
is higher on the left,
so water moves
through the
membrane until the
solutions are about
equal in terms of
sugar concentration
Facilitated Diffusion
• Diffusion of molecules with the aid of
carrier proteins, located in the cell
membrane, from high to low
concentration
Larger and charged ions or molecules are repelled
by the cell membrane and must be transported
through “doors” in the membrane called transport
proteins. There are many different “doors” each
only allowing a specific type of molecule through.
Passive Transport vs. Active
Weeee!!
Transport
!
• Passive transport –
– Cell doesn’t use energy
– Random movement of
molecules from a high to
low concentration.
high
low
• Active transport –
– Cell uses energy
– Directed movement of
molecules from a low to
high concentration.
– 3 Types
• Protein Pumps
• Endocytosis
• Exocytosis
This is
gonna
be hard
work!!
high
low
Protein Pump
Sodium
Potassium Pumps
(Active Transport
using proteins)
1. Protein Pumps transport proteins that
require energy to do
work
•Example: Sodium /
Potassium Pumps
are important in nerve Protein changes shape to move
responses.
molecules: this requires energy!
Types of Endocytosis
Endocytosis – takes materials
into the cell (low to high
concentration)
Examples Endocytosis
Macrophage (white blood
cell) engulfing bacteria
Amoeba engulfing food.
Exocytosis:
materials exit the cell (low to high concentration)