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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 10-100um (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
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Osmosis
• Movement of water from a high water concentration to a low water concentration
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
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
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
• 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
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
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)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
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