Cellular Transport

Review of Diffusion

• Movement of particles from an area of higher concentration to an area of lower concentration.

Osmosis• Diffusion of water across a selectively

permeable membrane.• Controlled by concentration gradients.

– Regulation of osmosis by the cell maintains homeostasis.

Cells in Isotonic Solutions• Concentration of both dissolved substances and

water in the solution is the same as the concentration of dissolved substances and water in the cell.

• Osmosis occurs with water diffusing in and out of the cell at the same rate.

• Cell retains its original shape.

Cells in Isotonic Solutions

Cells in Hypotonic Solutions• Concentration of dissolved substances is

lower in the solution outside the cell than the concentration of dissolved substances inside the cell.

• More water outside the cell than inside the cell.

• Water moves through the plasma membrane into the cell.

• Cell swells and the internal pressure increases.

Cells in Hypotonic Solutions

•http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

Cells in Hypotonic Solutions• If the solution is extremely hypotonic,

pressure may be so great that animal cells may burst.

• Plant cells will not usually burst because they contain a rigid cell wall against which the plasma membrane is pressed, causing the cell to become more firm.

Cells in Hypertonic Solutions• Concentration of dissolved substances outside

the cell is higher than the concentration of dissolved substances inside the cell.

• Water is greater inside the cell and flows out of the cell across the plasma membrane.

Cells in Hypertonic Solutions

http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

Cells in Hypertonic Solutions

• Animal cells will shrivel because of the decreased pressure.

• The cell wall maintains the shape of plant cells, but the plasma membrane pulls away from the cell wall, causing the plant to wilt.

Passive Transport• Movement of particles across the

membrane in which the cell does not need to use energy to move particles.

• 2 Main Types:– Simple Diffusion– Facilitated Diffusion

Simple Diffusion

Facilitated Diffusion

• Passive transport of materials across the membrane using transport proteins.

• Two types of transport proteins:– Channel Proteins– Carrier Proteins

Channel Proteins• Type of transport protein.• Form channels that allow

specific molecules to flow through.

• Movement of material is with the concentration gradient.

• No energy input by the cell is required.

Carrier Proteins

• Change shape to allow a substance to pass through the plasma membrane.

Active Transport• Movement of particles from a region of

lower concentration to an area of higher concentration (against the concentration gradient.

• Cell must expend energy to counteract the force of diffusion moving particles in opposite direction.

Steps in Active Transport1. Carrier protein bonds with the substance

to be transported.• In general, each type of carrier protein has a

shape that fits a specific molecule or ion.

2. When the proper molecule bonds with the protein, chemical energy allows the cell to change the shape of the carrier protein.

Steps in Active Transport

3. The substance to be moved is released on the other side of the protein.

4. The original shape of the protein is restored.

Active Transport

Endocytosis• Process by which a cell surrounds and

takes in material from its environment.• The material doesn’t pass through the

membrane but is engulfed by a portion of the plasma membrane.

• The portion of the plasma membrane then breaks away and the resulting vacuole, along with its contents, moves to the inside of the cell.

Endocytosis

Exocytosis• Expulsion or secretion of materials from a cell.• Used to expel wastes and to secrete substances

such as hormones produced by the cell.