Chapter 4 Notes

Cells and Their Environment

Molecules need to move across membranes in cells…

Image modiified from: http://www.accessexcellence.org/AB/GG/importProt.html

INfoodcarbohydratessugars, proteinsamino acidslipidssalts, O2, H2O

OUTwasteammoniasaltsCO2

H2O products

How does that happen?

I. Passive Transport

• Passive Transport-the movement of substances across the cell membrane without the use of energy by the cell.

• There are many types of passive transport:

A. Diffusion

• Diffusion- is the movement of a substance from an area of high concentration to an area of low concentration.

• Diffusion will eventually cause substances to be balanced (equilibrium) on both sides of the cell membrane.– Ex: ink or food coloring moving through water.

Diffusion-high to low concentration.

Animatioin from: http://www.biologycorner.com/resources/diffusion-animated.gif

B. Osmosis

• Osmosis- is the diffusion of water molecules across a selectively permeable membrane. (Egg Experiment)

• 1. Hypotonic-solute outside cell less than inside; water moves into cell; cell swells

• 2. Hypertonic-solute outside cell greater than inside; water moves out of cell; cell shrinks

• 3. Isotonic-solute outside cell equals inside; no net movement of water.

HYPOTONIC ISOTONIC HYPERTONIC

solute outside ‹ inside

Net movement of water into cell

Animal cells: swell & burst = CYTOLYSISPlant cells increase TURGOR PRESSURE

solute outside = inside

Net movement of water in and out of cell is equal

No change in size

solute outside > inside

Net movement of water out of cell

Animal cells: shrink = CRENATIONPlant cells: can’t shrink due to cell wallCell membrane pulls away from cell wall= PLASMOLYSIS

C.Facilitated Diffusion• Facilitated Diffusion-when a membrane

protein helps to transport a substance across a cell membrane.

1. Ion Channels-proteins that have a pore through which ions such as sodium, calcium, potassium can cross the cell membrane.

Types of Facilitated Diffusion

Animation from: http://www2.uic.edu/~myilma1/ionchannel.gif

Types of FacilitatedDiffusion

2. Carrier protein-proteins that bind to specific substances, carry it across the cell

membrane, and release it.Animation from: http://bio.winona.edu/berg/ANIMTNS/facdifan.gif

II. Active Transport

• Active Transport-the movement of a substance into an area of higher concentration by using energy from the cell in the form of ATP.

• There are many types of active transport:

1. Sodium-Potassium pump• sodium ions are pumped out of the cell.• Potassium ions are pumped into the cell.

http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/eustruct/images/sppump.gif

http://www.accs.net/users/kriel/chapter%20nine/

Animation from: http://academic.brooklyn.cuny.edu/biology/bio4fv/page/cell-movement.html

• 2. Endocytosis-substances that are too large to move into the cell membrane are moved by a vesicle that forms around it.

• 3. Exocytosis-substances that are too large to move out of the cell membrane are released by a vesicle that forms around it.

• 4. Membrane Receptor Proteins-proteins that help cell communicate with each other.

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/rectpr.htm