Answer:
In 1928, Fred Griffith performed an experiment revealing that genetic material can be passed between two different stains of the bacteria.
Explanation:
In 1928, Frederick Griffith, a British bacteriologist conducted some experiments to develop a pneumonia vaccine. He used mice and two strains of Streptococcus pneumoniae bacteria, known as R and S in his experiments.
The live R strain bacteria had a rough appearance and were nonvirulent. When he injected R bacteria into mice, they did not cause pneumonia. The live S strain bacteria had a smooth appearance due to their polysaccharide coating and were virulent. When injected into mice, the mice died as a result of pneumonia. The polysaccharide coating protected the S bacteria from the immune system of the mice.
Griffith then injected mice with heat-killed S bacteria (the heat killed the bacterial cells) and they did not cause pneumonia in mice. But when he injected a combination of non-lethal R bacteria and non-lethal heat-killed S bacteria into mice, the mice died from pneumonia. When he examined the blood sample from the dead mice, he found that the blood sample contained live S bacteria. This finding leads him to the conclusion that the nonvirulent R-strain bacteria had been "transformed" into virulent and lethal S-strain bacteria by taking up a "transforming principle" from the heat-killed S bacteria.
This experiment was then used for additional experiments conducted by Avery, McCarty, McLeod and then by Hershey and Chase. They found the evidence that the transforming principle from Griffith's experiment was actually the hereditary material, DNA. The DNA of the S strain bacteria had survived the heating process. This DNA that contains the genes for the production of the protective polysaccharide coating was taken up by the R strain bacteria. The transformed R strain bacteria were now protected from their host's immune system and this process of transferring genetic information between different bacterial strains is known as transformation.
Answer:
The water cycle.
Explanation:
The sun drives the movement of water through a process called the water cycle. In this process, water is evaporated from the sun's heat that reaches Earth. This water rises into the atmosphere in the for of water vapor. This water vapor then collects in the atmosphere along with other particles such as fine dust. This water then precipitates back onto the Earth. Presumably, the water precipitation may fall onto a land formation and integrate back into the ecosystem in the form of ground water or join a steam/river and end up in a lake or the ocean. The water then continues this cycle.
The reason why nost scientists thought that the first true cells formed on Earth were anaerobic is being shown in the second option :B. because there was no oxygen on early Earth. Paying attention to this fact scientists discovered that first cells were prokaryotes and greatest part of them created oxygen as a toxic by-product of their own metabolism which make them understand how the planet was provided with oxygen and made a conclusion that first cells were anaerobic.
Answer:
DNA replication a process of copying of a cell's DNA. DNA replication is semiconservative process which means that each strand in the double helix helps in the synthesis of new, complementary strand and conserve the parent template.
The Molecular mechanism of DNA replication is as following:
- The double starnded DN in binded with hydrogen bond, the enzyme helicase opens up the DNA at the replication fork.
- A single stranded binding protein prevent the rewinding of DNA and so binds to the DNA around the replication fork
- Topoisomerase prevent supercoiling at replication fork.
- The ezymes primase come in action and produces RNA primers which are complementary to the DNA strand.
- DNA polymerase III help to extends the primers and allow them to add to the 3' end, to make new DNA.
- DNA Polymerase then remove RNA primers and replace with DNA.
- DNA ligase blocks the the gaps between DNA fragments.
So, this is the molecuar mechanism of DNA replication.
Answer: A. reporting results of scientific analysis.
A physical evidence, also called real evidence. It is a tangiable evidence, which can be touched, picked and collected from the scene of crime or any other place. It can be used to prove a crime has occurred. Physical evidences includes fingerprints, footprints, fibers, paint and building materials.
A specimen sample is taken from the suspects or victims and compared with suspected samples obtained from the scene of crime. The comparitive analysis of physical evidences can be used as a scientific evidence against criminal.
Therefore, reporting results of the scientific analysis is the task she should perform.
