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Exchange with the
Environment
Cell Transport
Cell Processes
 For
a cell to survive, it must
get nutrients and water. It must
also get rid of wastes
 How can the cell get materials
in and out through the cell
membrane?
Cell membrane


Made up of a phospholipid bilayer and
several proteins
Phospholipid:


Hydrophillic phosphate head
Hydrophobic fatty acid tail
Image from:
http://academic.brooklyn.cuny.
edu/biology/bio4fv/page/phos
phb.htm
Cell membrane
Cell membrane: Proteins

Integral Proteins




Embedded in lipid bilayer
Receptor proteins and transport proteins
Transmit signal or materials into/out of the cell
Peripheral Proteins



Only on one side of membrane
Some act as enzymes
Some act as cell markers
Fluid mosaic model of cell
membrane



Phospholipid bilayer acts as a fluid
Lipids and proteins can move in the layer
Sterols (including cholesterol) are used to
help keep membrane structure
Cell membrane
Cell Membrane
Diffusion
 The
movement of particles from
an area of high concentration to
an area of low concentration
down the concentration gradient
 Occurs outside of cells and
across cell membranes
Diffusion
Picture from:
http://hyperphysics.phyastr.gsu.edu/hbase/kinetic/diffu
s.html
Osmosis
The
diffusion of water
across a cell membrane
If solution outside a cell
has more water than the
cell then water will move
into the cell
Osmosis
Image from:
http://hyperphysics.phyastr.gsu.edu/hbase/kinetic/diffus.ht
ml#c3
Movement of small
particles
 Not
all particles are able to slip
through a cell membrane
through diffusion
 Example: sugars and starches
aren’t small enough to move
between the phospholipid
molecules
Types of solutions
 Isotonic
 Has
same concentration as a
cell, the cell neither loses nor
gains water
 Hypotonic
 Has
less concentration than
cell, cell gains water
Types of solutions
 Hypertonic
 Has
more concentration than cell,
cell loses water
Osmosis in cells

Paramecia

Control water flow by using a contractile vacuole


Collect excess water and pump it out of the cell
Plant cells





Live in hypotonic environment
Survive because of cell wall
Pressure of water against cell wall: turgor pressure
Too much water leaves the cell: plasmolysis
Water storage in Central Vacuole
Transport of particles

Some particles have to go through
“doorways” to enter the cell

Because they are too large or not
soluble through cell membrane
These “doorways” are protein
channels
 These proteins are carrier proteins

Facilitated Diffusion
 Diffusion
of particles through protein
channels in a cell membrane
 Particles move from high
concentration to low concentration
 Example: glucose and salts
 Does NOT require energy
Image from:
http://www.bios.niu.edu/sims/metabolism/meta
bolism1.htm
Ion Channels



Allow ions to move across the cell
membrane
Specific to specific ions
Some are “gated”
Active transport
 Movement
of particles against the
normal direction of diffusion
 Particles move from LOW
concentration to HIGH
 Requires energy from the energy
molecule ATP
 Example: sodium/potassium
pump
Image from: http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/prostruct/images/u1fig7a.jpg
Image from: http://www.sp.uconn.edu/~terry/images/anim/antiport.gif
Moving larger particles

Endocytosis
 Cell membrane surrounds a particle,
and encloses it in a vesicle
 Phagocytosis
When large particles are taken in by
endocytosis
 Pinocytosis
Transport of fluids or solutes
Image
from:
http://ww
w.sirinet.n
et/~jgjohn
so/endocy
tosissmall
.jpg
Endocytosis
Image from:
http://www.sp.uconn.edu/~bi1
07vc/images/cell/clathrin.jpg
Exocytosis
 Used
to remove large particles
from the cell
 Vesicles formed at the ER or
Golgi move to the cell
membrane for release
Exocytosis
Image from: http://cellbio.utmb.edu/cellbio/end7.jpg
Modeling the cell
membrane