Structure and Function of Organelles cell (plasma) membrane semi-permeable membrane which regulates the passage of substances into and out of the cell.

Structure and Function of OrganellesStructure and Function of Organelles cell (plasma) membranecell (plasma) membrane

semi-permeable membrane which regulates semi-permeable membrane which regulates the passage of substances into and out of the passage of substances into and out of the cellthe cell

composition: protein molecules dispersed composition: protein molecules dispersed throughout a double layer of lipid (fluid throughout a double layer of lipid (fluid mosaic)mosaic)

Animal Cell

Plant Cell

Eukaryotic Cell

Eukaryotic Cell

Factors affecting permeability of cell Factors affecting permeability of cell membrane to a particular substance: membrane to a particular substance:

1. 1. molecular size of the substance: molecular size of the substance: cell membrane generally is permeable to cell membrane generally is permeable to small molecules such as water (Hsmall molecules such as water (H22O), O),

carbon dioxide (COcarbon dioxide (CO22), glucose (C), glucose (C66HH1212OO66) )

and amino acidsand amino acids

Factors affecting permeability of cell Factors affecting permeability of cell membrane to a particular substance:membrane to a particular substance:

1. molecular size of the substance1. molecular size of the substance 2. electrical charge on the atom or molecule 2. electrical charge on the atom or molecule

of the substance of the substance

+

+

+

+++

+

+

+

+ +

+

- ---

-

- -

---

-

--

Na+

Cl-

Factors affecting permeability of cell Factors affecting permeability of cell membrane to a particular substance:membrane to a particular substance:

1. molecular size of the substance1. molecular size of the substance 2. electrical charge on the atom or molecule 2. electrical charge on the atom or molecule

of the substanceof the substance 3. solubility of the substance in water3. solubility of the substance in water

Factors affecting permeability of cell Factors affecting permeability of cell membrane to a particular substance:membrane to a particular substance:

1. molecular size of the substance1. molecular size of the substance 2. electrical charge on the atom or molecule 2. electrical charge on the atom or molecule

of the substanceof the substance 3. solubility of the substance in water3. solubility of the substance in water 4. solubility of the substance in lipid4. solubility of the substance in lipid

What determines the direction of the What determines the direction of the movement of molecules (diffusion) across movement of molecules (diffusion) across

the cell membrane?the cell membrane?

concentration of substances on each side of concentration of substances on each side of the membranethe membrane

Diffusion is a form of passive transport. (no energy required)

QuickTime™ and aMicrosoft Video 1 decompressorare needed to see this picture.

Click on image for movie.

OsmosisOsmosis

diffusion of water through a semi-diffusion of water through a semi-permeable membrane from an area where permeable membrane from an area where the water molecules are more concentrated the water molecules are more concentrated to an area where the water molecules are to an area where the water molecules are less concentratedless concentrated

Cells Cells

exposed to an isotonic solution will neither exposed to an isotonic solution will neither lose nor gain waterlose nor gain water

exposed to a hypotonic solution will swell exposed to a hypotonic solution will swell due to the uptake of water by the celldue to the uptake of water by the cell

exposed to a hypertonic solution will shrink exposed to a hypertonic solution will shrink due to the loss of water from the celldue to the loss of water from the cell

Active transport requires energy.Active transport requires energy.

A transport protein actively pumps a A transport protein actively pumps a specific solute across a membrane against specific solute across a membrane against the solute’s concentration gradient; i.e., the solute’s concentration gradient; i.e., away from where the solute is less away from where the solute is less concentrated. Membrane proteins use ATP concentrated. Membrane proteins use ATP as their energy source for active transport.as their energy source for active transport.

energy

energy