Answer:
Ribosomes
Explanation:
Rough endoplasmic reticulum, choloroplast and nucleus all are important organelles and are membrane bound except for ribosome
Answer:
Semi-conservative replication
Explanation:
After the double-helix discovery of Watson and Crick, there were three possible models about the DNI replication:
- The Conservative model stated that the two strands of DNI together were the template of another new molecule. The final product was the original double-stranded molecule and the new molecule.
- The semi-conservative model stated that the original DNI molecule separated into two strands, and each of them served as a template for the synthesis of a new complementary strand. The replication product would be two double-stranded DNA molecules, each carrying an original strand a new one.
- The Dispersive moles stated that the replication product would be two molecules made by a mixture of segments of the original and the new molecules.
Meselson and Stahl joined to discover which of the models was the correct one. To do it they used E. coli and Nitrogen isotopes.
- First, they extracted DNI from bacteria grown in a medium with N¹⁴ and got its density band by centrifugation.
- Then they grew bacteria in a medium with N¹⁵, extracted their DNI molecules, centrifugated them, and got the density band, which was heavier than the firsts ones.
- The researchers then transferred bacteria grown in medium with N¹⁵ to a medium with N¹⁴, and they allowed only one replication process to occur. DNI was extracted and centrifugated again, and a new band appeared. This band was an intermediate form between bands of DNI-N¹⁵ and DNI-N¹⁴.
This event <em>eliminated the conservative model</em>. If this model were correct, the expected result would be to get two bands: one corresponding to the density DNI-N¹⁵ and the other corresponding to the density DNI-N¹⁴.
- Bacteria grown in a medium with N¹⁵ and then transferred to a medium with N¹⁴ were finally allowed to replicate twice. Their DNI was extracted and centrifugated. The result was two bands: one of them coincided with the intermediate band, and the other one with the DNI-N¹⁴.
<u>This result was conclusive</u> because if the dispersal model were correct, these two bands should not appear, as all the DNI strands would have part of the original molecule.
With this experiment, Meselson and Stahl proved that the correct replication model was the semi-conservative one.
An adaptation occurs when a species is set through a new constraint. This can be change in climate, defense mechanisms, food source, etc. Which will have to occur before an adaptation is made. For an example: in North America the climate slightly swifted. This meant smaller mammals such as rabbits would need to have a thicker coat of fur or shelter. Let's say all the thin furred rabbits died and all that remained were the thick furred rabbits. Over a span of time the rabbits have adapted through the climate. Meaning most of the population is thick furred through their DNA. Conclusively, it's a genetic characteristic that can happen very rapidly or slowly.
I hope this solved your question!
Fossils are typically recovered within Sedimentary Rock exposures. This is because Sedimentary rock is the rock found closest to that of Earth, and is practically exposed 24/7 to all of Earth's natural disasters and what-not.
