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.
The answer is A. Oligotrophic lakes are clear and hence
have little vegetation in them (hence no net primary production) that
could initiate the process of eutrophication. Eutrophication is brought about when bacteria
break down the high amount of organic matter hence reduce the oxygen supply in
the waters.
The human body attempts to cool down during exercise by producing sweat, while a dog's body attempts to cool down by panting
Answer:
mineral -
This is any element or inorganic compound. It is a naturally occuring solid chemical compound found in pure form. It is commonly found within rocks.
metal -
an element known for is lustrous, opaque, and malleable properties. Metals are good conductor of heat and electricity.
ore -
This is a natural rock from which minerals, elements or metals can be extracted through mining.
alloy -
An alloy is a group of metals or metals that have one or more other elements. Take for example, red gold is a combination of gold and copper while white gold is a combination of silver and gold.
Answer:
b
Explanation:
The R in RNA stands for Ribosomes which are proteins.
