Powers Unit3 Cell Transport

Unit 3 Cell Transport

Cell Transport

● Passive Transport

○

Diffusion

○

Facilitated diffusion

○

Osmosis

● Active Transport

○

Molecular transport

○

Bulk transport

Cell Transport

● One of the most important processes in a

cell is homeostasis
○

Homeostasis: a state of relatively constant
internal physical and chemical conditions

○

Regulates the movement of substances in
and out of the cell

Passive Transport

● Cells exist in liquid environments

● That liquid will be going in and out of

the cell via the cell membrane

● Passive Transport: The movement of

molecules across the cell membrane
without using cellular energy.

● If something or someone is passive,

they let things go easily. Same with
cells!

Types of Passive Transport

● Diffusion

● Facilitated Diffusion

● Osmosis

Diffusion

● Diffusion: the process by which particles move from an area

of higher concentration to an area of lower concentration

● Always higher to lower concentrations

● The driving force behind the movement of many substances

across the cell membrane

Facilitated Diffusion

● Some molecules need help to pass through

the cell membrane

● Larger molecules and charged molecules

○

Sugar (glucose), Cl-

● Facilitated diffusion: process of diffusion in

which molecules pass across the membrane
through cell membrane channels

● The membrane uses proteins to help move

the molecules

Does not use energy
from the cell

Discussion Questions:

1. What is the difference between

diffusion and facilitated diffusion?

Osmosis: An Example of Facilitated Diffusion

● Water cannot pass through the cell

membrane without the help of
aquaporins.
○

The lipid bilayer is hydrophobic

○

Aquaporin: water channel protein that
assists water through the cell membrane

● Osmosis:the diffusion of water through a

selectively permeable membrane.
○

Higher to lower concentration

Osmosis: How it Works

● Water moves through a selectively permeable membrane

○

From higher to lower concentration of solutes until
equilibrium is reached
■Solute = sugar, salt, etc.

■Solvent = water

Osmosis: How it Works

● When equilibrium is reached, there

will be the same amount of solute and
solvent molecules on both sides.
○

Isotonic: “same strength” - equal on
both sides

○

Hypertonic: “above strength” - more
solutes compared to water molecules

○

Hypotonic: “below strength” - less
solute compared to water molecules

Video!

Osmosis: https://www.youtube.com/watch?v=L-osEc07vMs

Osmotic Pressure

● Osmotic pressure: pressure that must be applied to prevent

osmotic movement across a selectively permeable
membrane.
○

Cells can shrink or swell if they are in a hypertonic or
hypotonic solution (solutes)
■Cells in a hypotonic solution - swell

■Cells in a hypertonic solution - shrink

Practice:

More Practice:

Osmotic Pressure:

● Since animal cells contain salts, sugars, proteins, and other

dissolved molecules, they are almost always hypertonic to
freshwater.
○

In plant cells, osmotic pressure causes the vacuole to swell
or shrink as water moves in and out of the cell

● Cells in large organisms are not in danger of bursting

○

Most of the cells do not come into contact with freshwater
■Surrounded in blood or other isotonic solutions

Osmotic Pressure:

● What happens when cells do come into contact with

freshwater?
○

Plant cells have cell walls that protect and prevent cells from
expanding or shrinking

○

Eggs laid in water lack water channels

Active Transport

● Active transport: the movement of materials against a

concentration difference which requires energy.

● Uses transport proteins to go against the concentration

difference

● Types of Active Transport

○

Molecular transport

○

Bulk transport
■

Endocytosis

■

Exocytosis

Active Transport - Molecular Transport

● Small molecules and ions are

carried across membranes by
protein pumps
○

Calcium, potassium, and sodium

● Uses a lot of energy/ATP

● Binds substances on one side and

then releases them on the other

Active Transport - Bulk Transport

● Larger molecules and solid materials also need to move

in and out of the cell

● Think big! (Costco)

● Endocytosis

● Exocytosis

Maybe not this big….

Endocytosis

Endocytosis: the process of taking material into
the cell by means of infoldings, or pockets, of
the cell membrane.
● The cell membrane infolds together to form

a vesicle or vacuole

● Large molecules, clumps of food, and whole

cells

Endocytosis
● Phagocytosis: extensions of cytoplasm

surround a particle and package it
within a food vesicle

■Literally means “cell eating”

○

The cell engulfs the particle

● Pinocytosis: cells take up liquid from

the surrounding environment

■Literally means “cell drinking”

○

tiny pockets form along the cell
membrane, fill with liquid, and pinch
off to form vacuoles

Exocytosis

● Exocytosis: a process in which cells

transport material out of the cell
○

The membrane of the vesicle or
vacuole fuses with the cell membrane,
forcing the contents out of the cell

○

Ex: Removal of water