Download Passive and Active Transport

Passive and Active Transport
Biology I
Main Idea
• Cellular transport moves substances
within the cell and moves substances into
and out of the cell.
Diffusion
• Particles in gases, liquids, and solids
move in random motion (called Brownian
motion).
• This random motion causes diffusion,
which is the net movement of particles
from an area where there are many
particles of the substance to an area
where there are fewer particles of the
substance.
Diffusion
• The amount of substance in a particular area is
called concentration.
• Diffusion occurs from areas of high
concentrations to areas of low concentration.
• There must be a concentration gradient, a
difference between concentrations across a
membrane, for cellular transport to occur.
• No energy is needed because the particles are
already in motion.
Diffusion
• The particles will continue to move
randomly but will not change the
concentration difference.
• At the point where there is continuous
movement, but no overall change,
dynamic equilibrium is reached.
• Diffusion at Work
Diffusion
• All types of diffusion are passive transport
mechanisms.
• Three main factors that affect the rate of
diffusion:
– Concentration
– Temperature
– Pressure
Facilitated Diffusion
• Facilitated diffusion uses transport
proteins to move other ions and small
molecules across the plasma membrane.
• Substances move into the cell through a
water-filled channel or a carrier protein.
• Channel proteins open and close, whereas
carrier proteins change shape.
• Requires no extra input of energy
Facilitated Diffusion
Osmosis
• Special type of diffusion involving water
• Water can pass freely into and out of the
cell.
• Osmosis is the diffusion of water across a
selectively permeable membrane.
• Very important in maintaining
homeostasis!
Osmosis
• Water molecules will diffuse towards the
area of low water concentration.
• 3 types of solutions possible:
– Isotonic
– Hypotonic
– hypertonic
Osmosis
• When a cell is in a solution that has the
same concentration of water and solutes
(ex. Ions, sugars, proteins, etc.) as its
cytoplasm, the cell is said to be in an
isotonic solution.
– Solutes are anything dissolved in water.
Osmosis
• If a cell is in a solution that has a lower
concentration of solute, the cell is in a
hypotonic solution.
• There is more water on the outside of the
cell than the inside.
• Causes swelling as the vacuoles in the cell
fill with water
Osmosis
• When a cell is placed in a hypertonic
solution, the concentration of the solute
outside the cell is higher than inside.
• Net movement of water is out of the cell.
• Vacuoles are emptied of water, causing
cells to shrink.
Osmosis
Active Transport
• Sometimes substances must move from
an area of low concentration to high
concentration.
• The movement of substances across the
plasma membrane against a concentration
gradient is called active transport.
• Requires energy!
• Helps maintain homeostasis
Active Transport
• Occurs with the aid of carrier proteins, called pumps
• Active Transport Animation
• Endocytosis is a process by which a cell surrounds and
takes in material from its environment.
– Does not pass directly through the membrane
– Engulfed
– Two examples: phagocytosis (eating) and pinocytosis (drinking)
• Exocytosis is the expulsion or secretion of materials
from a cell.
– used to expel wastes and secrete hormones
Active Transport