Transcript SBI4U - Membrane Transport

Transport Across Membranes
2.4
Transport Across Membranes
• the movement of materials into and out
of the cell is critical to a cell’s survival
and functioning
Passive Transport
• the movement of materials across the
cell membrane without the use of
chemical energy (ATP)
• occurs because of diffusion
Diffusion
• the net movement of
a substance from an
area of higher
concentration to an
area of lower
concentration
• dynamic equilibrium
Simple Diffusion
• substances move across membrane
unassisted
• small non-polar molecules (O2, CO2,
steroid hormones, some drugs) and
small polar molecules (H2O, glycerol)
• larger molecules and ions can not pass
through membranes unassisted
Homework, p.97 #6
6a. How do size, polarity, and charge
influence the ability of a substance to
diffuse across a membrane?
6b. Which combinations of these factors
require cells to use active transport to
move a substance across a membrane?
Facilitated Diffusion
• diffusion across membrane assisted by
integral membrane proteins called
transport proteins
• channel proteins vs. carrier proteins
• ions, water, amino acids, sugars, etc.
Homework, p.97 #2
• Facilitated diffusion is specific. What
does this mean?
Osmosis
• the diffusion of water
across a membrane
• water follows
concentration
gradient (low solute
concentration to
high) until
equilibrium
Homework, p.97 #1
• Your biology study partner asks you a
question about the concentration
gradient of water. What is meant by the
term “concentration gradient”? Is your
study partner using the term correctly in
reference to water? Explain why or why
not.
Osmosis
• direction of osmosis changes depending
on type of solution surrounding the cell:
• isotonic solution
• hypotonic solution
• hypertonic solution
Cell in Isotonic Solution
10% NaCL
90% H2O
ENVIRONMENT
CELL
10% NaCL
90% H2O
NO NET
MOVEMENT
What is the direction of water movement?
equilibrium
The cell is at _______________.
copyright cmassengale
13
Cell in Hypotonic Solution
10% NaCL
90% H2O
CELL
20% NaCL
80% H2O
What is the direction of water movement?
copyright cmassengale
14
Cell in Hypertonic Solution
15% NaCL
85% H2O
ENVIRONMENT
CELL
5% NaCL
95% H2O
What is the direction of water movement?
copyright cmassengale
15
Homework, p.97 #4
• Distilled water is considered hypotonic
to body cells. Explain.
Cells and Tonicity
Red Blood Cells
Homework, p.97 #3
3. A red blood cell was placed in a beaker
of solution. The cell immediately began
to swell and finally burst. Explain what
happened, referring to the cytosol of the
cell and the solution in the beaker.
hypotonic
hypertonic
isotonic
hypertonic
isotonic
hypotonic
copyright cmassengale
20
How does this impact…
• …a single-celled organism living in a
freshwater environment?
• …a single-celled organism living in a
salt-water environment?
• …the roots of a plant in the spring after
salt has been sprinkled during the
winter?
More applications…
• Why can’t you water a plant with salt
water?
• Why do vegetables in the grocery store
get sprayed with water periodically?
(What would happen if they were
sprayed with salt water?)
Active Transport
Active Transport
• the movement of materials against the
concentration gradient
• requires cellular energy (ATP)
Primary Active Transport
• pumps move
positively charged
ions (H+, Ca2+, Na+,
K+) across
membranes
• creates
electrochemical
gradient
Secondary Active Transport
• uses gradient established by a primary
active transport pump
Homework, p.97 #5
5. Compare the energy requirements of
passive transport, primary active
transport, and secondary active
transport.
Homework, p.97 #7
7a. How does the concentration of a
solute on the two sides of a membrane
affect passive transport?
7b. How does this concentration affect
primary and secondary active transport?
Bulk Transport
• movement of larger substances across
a cellular membrane
• requires energy (ATP)
• exocytosis & endocytosis
Endocytosis
Exocytosis
Homework, p.97 #8
8a. What process is shown in the
micrographs in Figure 13?
(8b. Draw a labelled scientific drawing of
the micrographs.)
Credits
• Slides #10, 11, 12, and 15 taken from
Powerpoint presentations created by
Cheryl Massengale, educator
extraordinaire & creator of
http://www.biologyjunction.com/