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Transcript
Cells and Their Environment
Chapter 4
p 74-84
What is a cell membrane?
• The cell membrane protects the cell and
helps move substances and messages in out
of the cell.
• Made of a phospholipid bilayer.
• Plasma Membrane Video
Homeostasis
• A biological balance
• Cells, tissues, organs, and organisms must
maintain a balance.
• Cells do so by controlling and regulating what gets
into and out of the cell.
Cell Membrane
• Only small, nonpolar substances can cross
the cell membrane.
• How can polar substances move across the
cell membrane?.... Through proteins in the
lipid bilayer!
• Construction of Cell Membrane
Review Questions
1. Describe homeostasis?
2. What types of substances can pass through
the cell membrane?
3. What would happen if the cell membrane
were fully permeable to all substances?
Transport
• Passive
• Active
• Transport that does
not require chemical
energy to occur
• example: diffusion,
facilitated diffusion
and osmosis
• The movement of
any substance across
a cell membrane with
the use of chemical
energy
– ie: Na+/K+ pump
Passive Transport –
SIMPLE DIFFUSION
• Process by which molecules spread from an area
of high concentration to an area of low
concentration.
• Concentration gradient: a difference in the
concentration of a substance
• Examples:
– Oxygen diffusing into cells
– Beaker of water with food coloring
– Smell of perfume in a room
***Molecules are in constant motion
Passive Transport - Diffusion
• Molecules tend to “spread out” to reach
equilibrium.
Diffusion animations
• http://www.northland.cc.mn.us/biology/Biol
ogy1111/animations/transport1.html
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/c
hapter2/animation__how_diffusion_works.h
tml
Passive Transport - Osmosis
• Diffusion of water through a membrane from
an area of high concentration to an area of
low concentration.
What determines the direction in which water
molecules diffuse across a cell membrane?
**the concentration of water and of solutes
dissolved in the solution
• http://www.stolaf.edu/people/giannini/flash
animat/transport/osmosis.swf
• http://www.tvdsb.on.ca/westmin/science/sbi
3a1/Cells/Osmosis.htm
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/c
hapter2/animation__how_osmosis_works.ht
ml
• http://www.wiley.com/legacy/college/boyer
/0470003790/animations/membrane_transp
ort/membrane_transport.htm
• http://www.youtube.com/watch?v=ls_mdB
QVGJ4
Think about it…
What happened if you eat salty foods?
Grass wilts if you add too much
fertilizer…WHY?
Cells can be found in 1 of 3
solutions:
1. HypOtonic
2. Hypertonic
3. Isotonic
HYPOTONIC
• Concentration of
solute molecules in
the environment
outside of the cell is
lower than that in
the cell.
• Water moves in
Red blood cell
Hypertonic
• Concentration of
solute molecules
outside the cell is
greater than that in the
cell
• Water moves out
Isotonic
Concentration of solute
molecules outside cell
and inside are equal.
**equilibrium
Passive Transport –
Facilitated Diffusion
• Use of transport proteins to “help” move
molecules across a membrane
• Passive: energy Y or N?
• Gradient: H to L
• Example: glucose
Passive Transport - Filtration
• Type of Transport:
Passive
• Using pressure to push
something through the
cell membrane
• Energy needed??
• Example…what organ
in your body filters
Active Transport
• Movement of substances through a membrane
from a low to high concentration with the use of
energy.
• ATP: energy form
• Usually Low to high concentration
– “Against a gradient”
• Example: Na/K pump.
Active Transport
• http://www.brookscole.com/chemistry_d/te
mplates/student_resources/shared_resources
/animations/ion_pump/ionpump.html
Some molecules are too large to
pass thru membrane!!! Even with
use of energy
– Endocytosis…movement of
substances into the cell by
transport vesicles into the
cell.
– Exocytosis… movement of
substances outside of the cell
by transport vesicles into the
cell
Endocytosis
Exocytosis
http://www.coolschool.ca/lor/BI12/u
nit4/U04L05.htm
http://www.wiley.com/college/boyer/0470003790/animations/m
embrane_transport/membrane_transport.htm
http://www.teachersdomain.org/asset/tdc02_int_membr
aneweb/