Cell Transport
Why do cells need a transport system?
- to move food, water, and wastes around the cell, as well as into and out of a cell
- to get rid of materials that could be bad for a cell
- to move proteins made in cells to other parts of cells as well as other cells
Passive vs Active Transport
- passive transport does not require energy because particles move from an area of high concentration to an area of low concentration
- active transport requires energy because particles are either too large to move passively, or they are moving from an area of low oncentration to an area of high concentration
PASSIVE TRANSPORT
- diffusion - the movement of particles (often gases) from high to low concentration
- What causes diffusion? – Collisions between molecules cause them to continually spread out until they are evenly distributed throughout the cell
· OXYGEN – easily diffuses across the cell membrane – one-celled organisms in pond water rely on this process – so the pond has to have more O2 than the inside of the cell
- osmosis - the movement of water from an area of high to low concentration
- facilitated diffusion -
- transport proteins
ACTIVE TRANSPORT
If a molecule is to be transported from an area of low concentration to an area of high concentration, work must be done to overcome the influences of diffusion and osmosis. Since in the normal state of a cell, large concentration differences in K+, Na+ and Ca2+ are maintained, it is evident that active transport mechanisms are at work.
Many crucial processes in the life of cells depend upon active transport. Included in the illustration above is the sodium-potassium pump which is a vital cell process. Active transport mechanisms may draw their enegy from the hydrolysis of ATP, the absorbance of light, the transport of electrons, or coupling with other processes that are moving particles down their concentration gradients.
A vital active transport process that occurs in the electron transport process in the membranes of both mitochondria and chloroplasts is the transport of protons to produce a proton gradient. This proton gradient powers the phosphorylation of ATP associated with ATP synthase.
Examples of active transport
Many crucial processes in the life of cells depend upon active transport. Included in the illustration above is the sodium-potassium pump which is a vital cell process. Active transport mechanisms may draw their enegy from the hydrolysis of ATP, the absorbance of light, the transport of electrons, or coupling with other processes that are moving particles down their concentration gradients.
A vital active transport process that occurs in the electron transport process in the membranes of both mitochondria and chloroplasts is the transport of protons to produce a proton gradient. This proton gradient powers the phosphorylation of ATP associated with ATP synthase.
Examples of active transport
- sodium-potassium pumps - a critical protein found in the membranes of all animal cells that functions in the active transport of sodium and potassium ions across the cell membrane against their concentration gradients. For each ATP the pump breaks down, two potassium ions are transported into the cell and three sodium ions out of the cell.
- endocytosis - an energy-using process by which cells absorb molecules (such as proteins) by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane. The opposite process is exocytosis.
Sodium-Potassium Pump Endocytosis and Exocytosis
Assessment - Transport quizlet
Use the link below to access the Quizlet on cell transport. There you will find a number of helpful resources along with a quiz that can assess your understanding of cell transport.