The DNA replication by the action of DNA polymerase takes place in the 3' to 5' direction on the leading strand. The lagging strand which has the opposite orientation or polarity as that of the leading strand requires a more time to get synthesised. The DNA replication of the lagging strand happens in short segments where a RNA primer forms a compliment with a part of the DNA segment on its 3' end. This RNA primer helps initiate the replication of the Okazaki fragments. When the replication on the lagging strand reaches its end, the RNA primer forms a compliment with the last bit of the strand. This small segment gets missed in the end as no more DNA is left to form a RNA primer-DNA compliment. Such shortening of the lagging strand in the replication process is the end-replication problem.
Telomeres are protective ends of the DNA strands. These ends contain a poly-A tail. When the lagging strand replication reaches its end, the RNA primer forms a compliment with the telomere and initiates the replication. This leads to the shortening of the telomere and not the coding segments on the lagging strand of DNA. The telomerase repairs the shortened telomere by re-synthesising it.
<u>B. Secondary xylem</u> tissue makes up most of the wood of a tree.
<h3><u>What exactly is secondary xylem?</u></h3>
Secondary xylem is a sort of xylem produced by secondary growth. During initial growth, in contrast, the primary xylem develops. As a result, the secondary xylem is linked to the primary xylem by lateral growth as opposed to the vertical extension.
The kind of cambium that gives rise to each difference is another point of differentiation. The vascular cambium produces the secondary xylem, while the procambium produces the primary xylem.
Unlike trees and shrubs, non-woody plants lack secondary xylem. It gives such plants mechanical support by depositing lignin into their cell walls, thickening them. Compared to the major xylem, the secondary xylem is made up of tracheids and veins that are shorter and wider. In comparison to the primary xylem, it is also richer in xylem fibers.
Possible growth rings in the secondary xylem (or annual rings). Sapwood and heartwood are two differentiators of the secondary xylem in big woody plants.
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If the conclusions do not support their hypothesis they would start the experiment all over again and see what they did wrong. <span />
Answer:
D. Alveoli
Explanation:
Functionally, the respiratory system is separated into a conducting zone and respiratory zone:
Conducting zone consists of the nose, pharynx, larynx, trachea, bronchi, and bronchioles. These structures form a continuous passageway for air to move in and out of the lungs.
Respiratory zone is found deep inside the lungs and is made up of the respiratory bronchioles, alveolar ducts, and alveoli. These thin-walled structures allow inhaled oxygen (O2) to diffuse into the lung capillaries in exchange for carbon dioxide (CO2).
The respiratory zone begins where the terminal bronchioles join a respiratory bronchiole, the smallest type of bronchiole, which then leads to an alveolar duct, opening into a cluster of alveoli.
Gametes
When a cell divides by way of mitosis, it produces two clones of itself, each with the same number of chromosomes. When a cell divides by way of meiosis, it produces four cells, called gametes. Gametes are more commonly called sperm in males and eggs in females.
