Which statements about the modification of chromatin structure in eukaryotes are true?1. Acetylation of histone tails is a reversible process. 2. DNA is not transcribed when chromatin is packaged tightly in a condensed form. 3. Methylation of histone tails in chromatin can promote condensation of the chromatin. 4. Some forms of chromatin modification can be passed on to future generations of cells. 5. Acetylation of histone tails in chromatin allows access to DNA for transcription. 6. Deacetylation of histone tails in chromatin loosens the association between nucleosomes and DNA.

1. Some forms of chromatin modification can be passed on to future generations of cells.

2. Acetylation of histone tails is a reversible process.

5. DNA is not transcribed when chromatin is packaged tightly in a condensed form.

3. Acetylation of histone tails in chromatin allows access to DNA for transcription.

4. Methylation of histone tails in chromatin can promote condensation of the chromatin.

Explanation:

Chromatin is a structure formed during the packaging of the DNA structure which is formed by the histone proteins and DNA.

1. The chromatin at some position highly is condensed called heterochromatin whereas at some position is not condensed called euchromatin. The heterochromatin sine highly packaged is inactive for transcription.

2. The acetylation is the addition of the acetyl group which can also be removed by deacetylase enzyme, therefore, is a reversible process.

3. The methylation adds a methyl group to the nitrogenous base and suppresses the transcription.

Thus, the selected options are correct.

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.