Low-head dams are dangerous structures that basically extend from one side of a riverbank to the other. Low-head dams block the water way partially and the water moving over the dam produces a strong circular current at the lower part of the dam. Low-head dams are dangerous to small boats and paddle craft because the strong circular current below the dam can trap small boats and paddle craft and pull them under the dam.
The exchange of genetic material between non-sister chromatids that may result in new gene combinations on the chromosomes is called the random assortment. It involves formation of random combinations of chromosomes in meiosis and of genes on different pairs of homologous chromosomes by the passage according to the laws of probability of one of each diploid pair of homologous chromosomes into each gamete independently to each other pair.
1. formaldehyde
2. paradichlorobenzene
3. tobacco smoke
4. toronto smog
5. pesticides
Simple diffusion is the process by which a substance moves across a cell membrane from an area of high concentration to an area of low concentration. Substances that move by simple diffusion are able to diffuse directly across the phospholipid bilayer of the cell membrane. These substances are generally small and neutral, as large or charged particles cannot cross the phospholipid bilayer. Some examples of molecules that move by simple diffusion are carbon dioxide and oxygen.
Facilitated diffusion is the process by which a substance moves across a cell membrane from an area of high concentration to an area of low concentration with the aid of a membrane protein. Substances that move by facilitated diffusion are not able to diffuse directly across the phospholipid bilayer of the cell membrane. These substances are generally large and/or charged. They therefore travel through a protein channel in the cell membrane along their concentration gradient. Some examples of substances that can move by facilitated diffusion are glucose, sodium ions and chloride ions.
The similarities between facilitated diffusion and simple diffusion are:
They both involve the movement of a substance across a cell membrane along its concentration gradient (from an area of high concentration to an area of low concentration).
They are both examples of passive transport, as neither requires energy from the cell to move the substance across the membrane.
