Download Cell Transport - Elmwood Park Memorial High School

Chapter 5
Section 1: Passive Transport
Passive Transport
• substances can cross the membrane without any input of
energy by the cell.
Diffusion
• Movement of molecules from an area of higher
concentration to an area of lower concentration.
• Simplest type of passive transport.
• Driven by kinetic energy.
Diffusion
• Molecules are in constant motion.
• Go in a straight line- hit something- then straight line in a
new direction.
•
MOLECULES MOVE DOWN THE
CONCENTRATION GRADIENT (HIGH TO LOW)
Concentration Gradient
• Difference in the concentration of molecules across a
distance.
Concentration Gradient
• SUGAR CUBE IN CUP OF WATER
Equilibrium
• Concentration of molecules is the same throughout the space the
molecules occupy.
• Movement of molecules balance one another and equilibrium is
maintained.
• Molecules are just as likely to move in one direction as another.
Diffusion Across Membranes
• Membrane is semipermeable.
• If the substance can pass- it will go from an area of high concentration
on one side to an area of lower concentration on the other side.
• Called simple diffusion
Diffusion Across Membranes
• Molecules that can dissolve in lipids may pass directly through the
membrane.
• Molecules that are small but not soluble in lipids may diffuse across
membrane through pores.
Solution
• Solution: solute dissolved in a solvent
• Sugar- solute
• Water- solvent
• In cells:
• Solute- organic and inorganic compounds
• Solvent- water
Osmosis
• The process by which water molecules diffuse across a cell membrane
from an area of higher concentration to an area of lower
concentration.
• Does not require cells to use energy
• Example of passive transport.
Direction of Osmosis
• Net direction of osmosis depends on the relative concentration of
solutes on the two sides of the membrane.
• HYPOTONIC
• HYPERTONIC
• ISOTONIC
.
Table 5-1 Direction of
Osmosis
Hypotonic
• Concentration of solute molecules outside the cell is lower than the
concentration in the cytosol.
• Water diffuses into the cell until equilibrium is established.
.
Hypertonic
• Concentration of solute molecules outside the cell is higher than the
concentration in the cytosol.
• Water diffuses out of the cell until it reaches equilibrium.
Isotonic
• Concentrations of solutes outside and inside the cell are equal.
• Water diffuses into and out of cell at equal rates.
• No net movement of water.
.
Contractile Vacuoles
• Organelles that remove water.
• Collect excess water and then contract, pumping water out of the cell.
• This action requires energy.
Contractile Vacuoles
• Figure 5-2
• Paramecium
Osmosis
• Cells response to hypotonic environment by pumping solutes out of
the cytosol
• Water molecules are less likely to diffuse into the cell.
Osmosis
• Plants are surrounded by water- so water diffuses by osmosis into the plant.
• Cell wall is strong enough to resist the pressure exerted by the water inside
the cell.
• TURGOR PRESSURE- pressure that water molecules exert against the cell
wall.
Plasmolysis
• The contraction or shrinking of the cell membrane of a
plant cell in a hypertonic solution in response to the loss
of water by osmosis.
Human Red Blood Cells
• Lack contractile vacuoles, solute pumps, and cell walls.
• Change shape when in hypertonic or hypotonic environment.
• Hypertonic environment- water leaves cells making them shrivel.
• Hypotonic- water diffuses into cells causing them to swell and
eventually burst.
• Cytolysis- bursting of cells.
Human Red Blood Cells
Figure 5-4
Facilitated Diffusion
• Type of passive transport.
• Molecules that cannot readily diffuse through the cell
membrane even when there is a concentration
gradient across the membrane.
• Either not soluble in lipids or too large.
• Movement assisted by carrier proteins.
Carrier Proteins
• Figure 5-5
Transport of Glucose
• Facilitated diffusion
• 1. can help substances move into or out of a cell.
• 2. carrier proteins involved in facilitated diffusion are
each specific for one type of molecule
Ion Channels
• Transport ions from an area of higher concentration
to an area of lower concentration.
• Na+, Cl-, Ca2+
• Ions cannot diffuse across the membrane without
assistance.
• Each ion channel is specific to one type of ion.
Ion Channels
• Some ion channels are always open
• Other ion channels have gates
• Gates may open or close in response to three kinds of stimuli
• Stretching of the cell membrane
• Electrical signals
• Chemicals in the cytosol or external environment
Quick Quiz
• True/False- In diffusion substances always move down
the concentration gradient.
• True/False- Osmosis is a type of diffusion.
Chapter 4
Section 2: Active Transport
Objectives: 11/26
• Do Now
• Day 3 of Lab
• Lab Questions
• Lab Error
• Reading Comprehension
Day 3 of Lab
•
•
•
•
Dump out the corn syrup and water from the cups.
Do not pop the egg.
Measure the circumference of the egg.
After you take measurements, place the egg in the front of
the room.
• Clean up lab station
• Work with lab group to complete the post lab questions.
• Hand in lab paper, work on reading comprehension
Active Transport
• In some cases- cells must move materials from an area of lower
concentration to an area of high concentration.
• up the concentration gradient
• This type of transport requires the cell to expend energy
• The energy needed is supplied directly or indirectly by ATP
Types of Active Transport
• Sodium-Potassium Pump
• Endocytosis
• Exocytosis
Cell Membrane Pumps
• Ion channels and carrier proteins help with active
transport.
• Cell membrane pumps- move substances from lower
concentration to higher concentration.
Sodium-Potassium Pump
• Carrier protein that transports Na+ ions and K+ ions up their
concentration gradients.
• Some animals cells must have higher concentrations of these- so the
sodium-potassium pumps maintain the concentration differences.
Sodium Potassium Pump
Sodium – Potassium Pump
pumps three
Sodium ions
out of cell
pumps two
Potassium ions
into cell
Movement in Vesicles
• Endocytosis and Exocytosis
• Used to transport large quantities of small molecules into and out of
cells.
• Require cells to expend energy.
Endocytosis- 2 main types
• Pinocytosis- transport of solutes or fluids
• Phagocytosis- movement of large particles or whole cells.
• Certain cells in animals use phagocytosis to ingest bacteria and
viruses
• phagocytes
Endocytosis- 2 main types
• Pinocytosis- transport of solutes or fluids
• Phagocytosis- movement of large particles or whole cells.
• Certain cells in animals use phagocytosis to ingest bacteria and
viruses
• phagocytes
Endocytosis
42
Exocytosis
• Process by which a substance is released from the cell through a
vesicle that transports the substance to the cell surface and then fuses
with the membrane to let the substance out of the cell.
• Reverse of endocytosis
• Release protein, waste products, or toxins
Exocytosis
44