Download Chapter 4 – Cells and their Environment

Chapter 4 – Cells and their
Environment
Mr. Lopez – Ag. Biology – Shandon High School
California Content Standards: 1a, 1b, 10b, 10d, IE1d
Section 1 - Passive Transport
• Homeostasis maintained by controlling the
movement of substances across the cell
membrane
• Movement of substances can be
accomplished in two ways: passive or
actively.
Section 1 - Passive Transport (continued)
What is passive transport?
• Movement across the cell membrane that
does not require energy
• Figure 1 on page 75 provides an example of
passive transport.
Section 1 - Passive Transport (continued)
Section 1 - Passive Transport (continued)
Difference in concentration of substances is
known as?
• Concentration gradient
When the concentration of a substance is
equally distributed, it is know as?
• Equilibrium
Section 1 - Passive Transport (continued)
What is diffusion?
• The movement of a substance from an area of
high concentration to an area of lower
concentration due to random motion
Section 1 - Passive Transport (continued)
• Molecules and ions enter and leave the cell
by diffusion
• Many times the concentrations of substances
very between the cell and the outside
• Yet remember that the membrane is
“selectively permeable” – Nonpolar lipid layer
repel ions and most polar molecules
Section 1 - Passive Transport (continued)
• Osmosis
– Diffusion of water through a selectively
permeable membrane
– Figure 2, shows how osmosis
occurs across the membrane.
Section 1 - Passive Transport (continued)
• Hypertonic Solution
– As water diffuses out of a cell, the cell shrinks
– Fluid outside the cell has a higher concentration
of dissolved particles
• Hypotonic Solution
– As water diffuses into a cell, the cell swells
– Fluid outside the cell has a lower concentration of
dissolved particles
Section 1 - Passive Transport (continued)
• Isotonic Solution
– No changes in size
– State of equilibrium is reached
– Water diffuses in and out at the same rate
Section 1 - Passive Transport (continued)
• Crossing the Cell Membrane
– Ions and polar molecules are able to enter cells
via the aide of transport proteins
– Transport proteins known as channels provide
polar passageways that allow specific substances
to pass through the cell
– For example, ions like sodium, Na+, potassium, K+,
calcium Ca2+, chloride, Cl-, cross into the cell via
ion channels
Section 1 - Passive Transport (continued)
Section 1 - Passive Transport (continued)
– Movement of charged particles also influenced by
the particle’s positive or negative electrical charge
– In general, the inside of cells are negatively
charged
– Therefore positively charged ions are more likely
to enter the cell
– Negatively charged ions are more likely to leave
the cell
Section 1 - Passive Transport (continued)
• What are carrier proteins?
– Binds to specific substances in membrane
– Carry the substance across the membrane
– Release the substance where it is needed by
concentration gradient
– This “ride-along” of the substance is known as
facilitated diffusion
Section 1 - Passive Transport (continued)