4.4 Cell Transport
Cell Transport

What do cells need to transport across
the membrane?
◦ Nutrients, waste, water, oxygen
Types of Transport

Passive transport: movement of
materials across a membrane without the
use of energy (ATP)
◦ Molecules move from high concentration to
low concentration
◦ “down the concentration gradient”
◦ Three types:
 Diffusion
 Osmosis
 Facilitated diffusion
Types of Transport:
Passive transport
Passive Transport:
Diffusion

Diffusion: movement of molecules across
a selectively permeable membrane
◦ Molecules move from high concentration to
a low concentration; down or “with” the
concentration gradient
Passive Transport:
Diffusion

= solute
= solute
Which solute will pass the barrier? Why?
Passive Transport:
Diffusion

Example: Oxygen diffuses into the blood
stream because of high oxygen
concentration in the lungs
Passive Transport:
Osmosis

Osmosis: movement of water across a
selectively permeable membrane
◦ Water moves from a high concentration of
water (low [solute]) to a low concentration
of water (high [solute])
◦ Remember:
 A lot of water = not much solute
 A little bit of water = LOTS of solute
Passive Transport:
Osmosis
Passive Transport:
Osmosis
Passive Transport:
Facilitated Diffusion

Facilitated diffusion: diffusion of large
particles across a membrane with the
help of membrane proteins
◦ Molecules move from high concentration to
low concentration
Passive Transport:
Facilitated Diffusion
Glucose
molecules
High
Concentration
Cell
Membrane
Low
Concentration
Prote
chan
Quick Review:
Does passive transport require energy?
 Give 3 examples of passive transport
 What direction to molecules move in
passive transport?
 How does diffusion differ from facilitated
diffusion?
 What type of passive transport describes
how water moves?

Types of Solutions

Movement of water depends on the
[solute]
◦ Water always moves towards the area of low
[water] or high [solute]
Types of Solutions

Hypertonic solution:
◦ Has a higher [solute] than another solution
Low[solute]
High [solute]
Types of Solutions

What will happen to a cell in a
hypertonic solution?
◦ Water moves OUT of the cell towards the
area of high [solute]
◦ Cell shrinks (plasmolysis)
Types of Solutions

Hypotonic Solution:
◦ Has a lower [solute] than another solution
High [solute]
Low [solute]
Types of Solutions

What will happen to a cell in a
hypotonic solution?
◦ Water will move in to the cell
towards an area of high [solute]
◦ Animal cell: lysis (burst)
◦ Plant cell: turgid (fat plant cells)
◦ Ideal environment for plants
Types of Solutions:

Isotonic solutions:
◦ Two solutions have the same concentration of
solute
Types of solution

What will happen to cells
placed in isotonic solutions?
◦ Water moves into & out of the
cell equally
◦ Cells stay the same
◦ Ideal environment for animals
Cell Transport
Active Transport

Active transport: proteins are used to
move molecules (minerals & nutrients)
across the membrane by using ATP
energy
◦ Molecules move from low concentration to
high concentration
Types of Active Transport

Endocytosis: process when a cell
surrounds and takes in large materials or
large amounts of materials from the
environment
Active Transport: Endocytosis
The amoeba heads toward
the unsuspecting
paramecium.
It begins to spread out
its body to catch its
prey.
Too late for the
paramecium, it's been
caught!
Active Transport: Endocytosis
The amoeba spreads out
even more to surround its
lunch.
The paramecium will
soon be completely
inside the amoeba!
The amoeba will absorb
its lunch now that it is
inside its cell membrane.
Types of Active Transport:

Types of endocytosis:
◦ Pinocytosis: movement of liquids into the cell
◦ Phagocytosis: movement of solids into the
cell
Type of Active Transport

Exocytosis: the exit or secretion or
materials from the cell
◦ Ex: cell getting rid of waste
2
1
3
Active Transport

Endocytosis and Exocytosis often work
together
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