Cell Structure and Function

The Cell Theory All living things are made of one or more cells All cells come from pre-existing cells Cells are the basic unit for structure and function of all organisms

Cell structure All cells are surrounded by a plasma (cell) membrane Cells contain organelles - small structures inside cells that perform various jobs All cells can be divided into two main categories:

Prokaryotic vs. Eukaryotic Cells Prokaryotic - no nucleus - Very small (1-10 um) - Have very few organelles Eukaryotic - have a nucleus - Larger um (some larger) - Have many organelles

Eukaryotic Cells Plant and animal cells are eukaryotic as well fungi and protists (amoeba, paramecium, etc) Plant and animal cells have important differences (see diagrams)

Eukaryotic Cellular Organization Single celled organisms (unicellular) Multiple celled organisms (multicellular) - in multicellular organisms, cells become specialized (do a particular job)

Plasma (cell) membrane Consists of a double layer of lipids The outside and inside of the membrane is hydrophilic (“water-loving”) The interior of the membrane is hydrophobic (“water-fearing”) Substances must cross the membrane to enter and exit the cell

Types of Membrane Transport Passive Transport (requires NO energy) Moves substances from a high to a low concentration Diffusion & osmosis, facilitated diffusion Active Transport (requires energy) Substances move from a low to a high concentration Endocytosis & exocytosis

Concentration gradient Passive transport moves substances WITH (or DOWN) their concentration gradient Active Transport moves substances AGAINST their concentration gradients HIGH LOW ACTIVE TRANSPORT PASSIVE TRANSPORT

Diffusion Movement of a substance from a high concentration to a low concentration

Osmosis Movement of water from a high water concentration to a low water concentration

Osmosis in Different Cellular Environments Hypotonic - solution with a lower solute concentration than the cytoplasm of the cell Hypertonic - solution with a higher solute concentration than the cytoplasm of the cell Isotonic - has same solute concentration as the cytoplasm of the cell

Turgor pressure - pressure (from water) pushing against the cell wall of a plant (makes plant cells firm) Plasmolysis - shrinking of the cytoplasm of a cell caused by the loss of water (causes plants to wilt)

Facilitated Diffusion Diffusion using membrane protein channels Some substance must use protein channels since they cannot pass through the lipid layer of the membrane

Active Transport Requires the input of energy to move a substance against its concentration gradient (low to high) Energy is used in the form of ATP (energy molecule produced in mitochondria)

Types of Active Transport: Endocytosis, Exocytosis and Ion Pumps Endocytosis - cell takes in substances too large to pass through the membrane Exocytosis - cell gets rid of large substances Ion pumps - pump ions against their concentration gradient See endocytosis and exocytosis in action