What valve prevents back flow into the left ventricle of the heart?
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Answer:
Cell size is determined by joint regulation of cell size and cell cycle duration.
Size dependent modulation of growth rate allows maintenance of cell size homeostasis.
Central carbon metabolism is key regulator of both cell size and cell cycle.
Size dependent regulation of metabolism and growth rate implies cell size sensing. As the cell increases in size the volume of the cell increases more rapidly than the surface area which causes a decrease in the cell's ratio of surface area to volume and makes it more difficult for the cell to move needed materials in and waste products out.
DNA- variety of genes are involved in the control of cell growth and division. The cell cycle is the cell’s way of replicating itself in an organized, step-by-step fashion. Tight regulation of this process ensures that a dividing cell’s DNA is copied properly, any errors in the DNA are repaired, and each daughter cell receives a full set of chromosomes. The cycle has checkpoints (also called restriction points), which allow certain genes to check for problems and halt the cycle for repairs if something goes wrong. If a cell has an error in its DNA that cannot be repaired, it may undergo programmed cell death (apoptosis). Apoptosis is a common process throughout life that helps the body get rid of cells it doesn’t need. Cells that undergo apoptosis break apart and are recycled by a type of white blood cell called a macrophage. Apoptosis protects the body by removing genetically damaged cells that could lead to cancer, and it plays an important role in the development of the embryo and the maintenance of adult tissues. Cancer results from a disruption of the normal regulation of the cell cycle. When the cycle proceeds without control, cells can divide without order and accumulate genetic defects that can lead to a cancerous tumor.
Nutrients and waste- The larger a cell becomes, the more demands the cell places on its DNA. In addition, the cell has more trouble moving enough nutrients and wastes across the cell membrane. The resulting decrease in the cell's ratio surface area to volume makes it more difficult for the cell to move needed materials in and waste products out.
Surface area of the cell- The amount of surface area available to each unit of the cell depends on the size of the cell. As a cell grows, it's surface area/volume ration decreases. At some point of the cells growth, the surface area/volume ratio becomes so small that the surface area is too small to supply raw materials to its volume. materials cannot enter the cell if the surface is too large. ... the cell may become too large to take in enough food and to remove enough wastes. waste products cannot leave the cell if the cell is too small.
Cell volume-
Explanation:
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In humans, cells other than human sex cells, are diploid and have 23 pairs of chromosomes. Human sex cells (egg and sperm cells) contain a single set of chromosomes and are known as haploid.
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