Biology B3 Revision

Plants And Animals.

In both plants and animal cells there are:

• A nucleus
• Cell membrane
• Cytoplasm ( gel like solution containing enzymes)
• Mitochondria

Just in plant cells are:

• Rigid cell wall made of cellulose - supports the cell
• Large vacuole - contains cell sap and helps provide support
• Chloroplasts

Most of the reactions involved in respiration take place in the mitochondria.Respiration turns glucose and oxygen into water and carbon dioxide, therefore releasing energy.

                  Plant Cell                                             Animal Cell

DNA is found in the nucleus of every cell. It is a double handed strelix. Each of the two strands is made up of lots of small groups called nucleotides. Each nuclotide contains a small molecule called a base. DNA has just four different bases: A, C, G and T. Each base forms cross links to a base on the other strand. This keeps the two DNA strands tightly wound together. A always pairs up with T and C always pairs up with G. This is called complementary base-pairing.

DNA copies itself every time a cell divides, so that each new cell still has the same amount of DNA. In order to copy itself, the DNA double helix first 'unzips' to form two single strands. As the DNA unwinds itself, new nucleotides (floating about freely in the nucleus) join on only where the bases fit, making an exact copy of the DNA on the other strand. The result is two molecules of DNA identical to the original molecule of DNA.