Section ObjectivesExplain how the processes of diffusion,

passive transport, and active transport occur and why they are important to cells.

Predict the effect of a hypotonic, hypertonic, or isotonic solution on a cell.

Molecules move from high to low• Diffusion

– move from HIGH to LOW concentration

Diffusion• Move from HIGH to LOW concentration

– passive transport– no energy needed

diffusion osmosis

diffusion of water

Simple Diffusion • Move from HIGH to LOW

inside cell

outside cell

Which way will fat move?

fat

fat

fat

fat

fat

fat fat

fatfat

fat

fat

fat

fat

fat

LOW

HIGH

Movement through the channel

• Why do molecules move through membrane if you give them a channel?

?

?

HIGH

LOW

Facilitated Diffusion• Move from HIGH to LOW through a channel

inside cell

outside cell

sugar

sugar

sugar

sugar

sugarsugar

sugarsugar

sugarsugar

sugar

Which way will sugar move?

sugar

sugar

LOW

HIGH

Diffusion• Move from HIGH to LOW concentration

– directly through membrane• simple diffusion• no energy needed

– help through a protein channel• facilitated diffusion (with help)• no energy needed HIGH

LOW

Simple vs. facilitated diffusion

inside cell

outside cell

lipidinside cell

outside cell

H2O

simple diffusion facilitated diffusion

H2O

protein channel

Passive Transport

• Requires no energy from cell• Movement down the concentration

gradient

Facilitated Diffusion

Cellular Structure and Function

Movement of materials across the plasma membrane using protein channels.

Osmosis

Cellular Structure and Function

Diffusion of water across a selectively permeable membrane

Aquaporins are water channel proteins that allow water to pass through cell membrane through facilitated diffusion.

• Dynamic equilibrium is reached when the concentration

Osmosis is the passive transport of water

• In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration – Hypertonic: [hyper=above, over]

• Solutions in which more solute present (concentrated solution)

– Hypotonic: [hypo= below, under]• Solutions in which less solute is present (dilute

solution)

– Isotonic: [ iso= equal]• Solutions have equal concentrations of substances

Blood CellPlant Cell

Isotonic Solution

Cellular Structure and Function

Water and dissolved substances diffuse into and out of the cell at the same rate.

11,397x

Blood Cell

Hypotonic Solution

Cellular Structure and Function

Solute concentration is higher inside the cell. Water diffuses into the cell.

Plant Cell

13,000x

Plant Cell

Hypertonic Solution

Cellular Structure and Function

Solute concentration is higher outside the cell. Water diffuses out of the cell.

Blood Cell

13,000x

Water balance between cells and their surroundings is crucial to organisms

• Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution– The control of water

balance(osmoregulation) is essential for organisms

ISOTONIC SOLUTION

HYPOTONIC SOLUTION

HYPERTONIC SOLUTION

ANIMALCELL

PLANTCELL

Active transport

• Requires the cell to spend energy [ATP][ATP]

• Transport proteins can move solutes across a membrane against [up] a concentration gradient

Active Transport

Cellular Structure and Function

Movement of particles across the cell membrane using energy

Active Transport Using Carrier Proteins

Active Transport

• active transport :Movement of materials through a membrane against a concentration gradient and requires energy from the cell. ATP

Concentration gradient

Plasma membrane

Carrier proteins

Cellular energy

Cellular energy

Active transport• Cells may need molecules to move against

concentration “hill”– need to pump “uphill”

• from LOW to HIGH using energy

– protein pump– requires energy

• ATPATP

Exocytosis and endocytosis transport large molecules

1. Exocytosis [ exo = outside]movement of large materials OUT of the cell~a vesicle may fuse with the membrane and expel its contents

CYTOPLASM

FLUID OUTSIDE CELL

2. Endocytosis [ endo = inside]

movement of large materials to INSIDE of the cell

~membrane may fold inward, trapping materials from the outside