Insulin is a protein hormone produced by the pancreas in humans that regulates the metabolism of food. In 1978, scientists successfully spliced the human gene for insulin into the bacterium E. coli. This enabled insulin to be produced by the bacteria. This
insulin could then be extracted and used as a medication to treat people with diabetes. Since then, the gene for insulin has also
been spliced into yeast cells and plant cells for the same purpose.

both male and female gametes are produced by meiosis of the germ cells. therefore, both male and female gametes are haploid. one male and one female gamete unite during the fertilization to form the diploid zygote. in seed bearing plants, pollen grain is the male gametophyte, which produces sperm cells.

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.