The early precambrian atmosphere consisted primarily of nitrogen and carbon dioxide with almost no oxygen.
<span>Today, the atmosphere contains about 20% oxygen, less carbon dioxide and similar amounts of nitrogen. </span>
<span>Photosynthetic green-leaf plants and trees are largely responsible for the change, converting carbon dioxide to oxygen.</span>
Enzymes are needed for metabolic pathways in the body, respiration, digestion and other important life processes. When enzymes function properly, homeostasis is maintained. However, if an enzyme is lacking or has an incorrect shape due to genetic mutation, this can lead to disease within an organism.
Answer: The correct answer is- Replication of DNA ( deoxyribonucleic acid) must happen before a body cell can begin mitotic cell division.
Mitotic division is a type of cell division in which a parent cell divides two identical daughter cells ( through a series of five stages that is- prophase, metaphase, anaphase, telophase, and cytokinesis) having same number of chromosomes as that of the parental cell.
It occupies the second stage of cell cycle, the first being interphase ( which has three stages that is G1, S, and G2 phase). Replication of DNA takes place in the interphase ( particulary in the S phase) so that cell is ready to divide in the mitotic phase.
Thus, replication of DNA ( deoxyribonucleic acid) must happen before a body cell can begin mitotic cell division.