Answer:
The correct answer is option A. "The contents of blood come into closer contact with tissues in a closed system than an open system".
Explanation:
In a closed circulatory system, the blood has an specific path, circulating from arteries to veins and to smaller blood vessels throughout the body. This is in contrast with open circulatory systems at which the blood is not contained in arteries or veins but it suffuses the body. A closed circulatory system have many advantages over open circulatory system, however in a closed circulatory system the contents of blood are not into closer contact with tissues in than an open system. Actually, in an open circulatory system the blood is in closer contact with tissues.
Answer and Explanation:
A gene is a section of DNA. The change in the sequence of the DNA is known as mutation. Mutation always changes the sequence of the DNA. Sunlight can cause mutation. Sunlight produces structures named thymine dimers. Thymine dimers produce twist in the shape of DNA. These twists make DNA hard to copy, which can lead to mutation. It is essential to use sunscreen to block UVA and UVB rays to prevent thymine dimers from emerging in our cells. The US Food and Drug Agency recommends an SPF (sun protection factor) to defend against skin aging and skin cancer. X-ray radiation is a form used in x-rays. The energy level of the X-ray radiation is very high that can produce free radicals. Free radicals can steal electrons from DNA that can cause mutation. By using medical images, we can decrease exposure to X-rays. Less exposure to X-rays prevents mutation and also prevents the production of gene protein in other body parts.
Answer: ok...
Explanation:
The continual input of energy, mostly from sunlight, sustains the process of life. Sunlight allows plants, algae and cyanobacteria to use photosynthesis to convert carbon dioxide and water into organic compounds like carbohydrates. This process is the fundamental source of organic material in the biosphere.
The DNA polymerases are enzymes that create DNA molecules by assembling nucleotides, the building blocks of DNA. These enzymes are essential to DNA replication and usually work in pairs to create two identical DNA strands from one original DNA molecule. During this process, DNA polymerase “reads” the existing DNA strands to create two new strands that match the existing ones.
Every time a cell divides, DNA polymerase is required to help duplicate the cell’s DNA, so that a copy of the original DNA molecule can be passed to each of the daughter cells. In this way, genetic information is transmitted from generation to generation.
Before replication can take place, an enzyme called helicase unwinds the DNA molecule from its tightly woven form. This opens up or “unzips” the double stranded DNA to give two single strands of DNA that can be used as templates for replication.
DNA polymerase adds new free nucleotides to the 3’ end of the newly-forming strand, elongating it in a 5’ to 3’ direction. However, DNA polymerase cannot begin the formation of this new chain on its own and can only add nucleotides to a pre-existing 3'-OH group. A primer is therefore needed, at which nucleotides can be added. Primers are usually composed of RNA and DNA bases and the first two bases are always RNA. These primers are made by another enzyme called primase.
Although the function of DNA polymerase is highly accurate, a mistake is made for about one in every billion base pairs copied. The DNA is therefore “proofread” by DNA polymerase after it has been copied so that misplaced base pairs can be corrected. This preserves the integrity of the original DNA strand that is passed onto the daughter cells.

A surface representation of human DNA polymerase β (Pol β), a central enzyme in the base excision repair (BER) pathway. Image Credit: niehs.nih.gov
Structure of DNA polymerase
The structure of DNA polymerase is highly conserved, meaning their catalytic subunits vary very little from one species to another, irrespective of how their domains are structured. This highly conserved structure usually indicates that the cellular functions they perform are crucial and irreplaceable and therefore require rigid maintenance to ensure their evolutionary advantage.
True because some fossils only lived in certain places
