Question

cell differentiation occurs when —
a. dna is deleted during the cell cycle
b. mutations develop in the dna of an organism
c. specific genes in dna are activated by environmental factors
d. different types of cells in the same organism contain different dna
1.
the order of the nitrogenous bases in dna determines the —
a. genetic code of an organism
b. polarity of a nitrogenous base
c. presence of a hydrogen bond
d. presence of a fifth nitrogenous base
2.
which pair of statements best contrasts nucleic acids found in eukaryotes and prokaryotes?
a. in eukaryotes, dna is linear and found in the nucleus.
in prokaryotes, dna is circular and is free floating.
b. in eukaryotes, dna is circular and found in the nucleus.
in prokaryotes, dna is linear and found in the nucleus.
c. in eukaryotes, dna is single stranded and found in the nucleus.
in prokaryotes, dna is double stranded and is free floating.
d. in eukaryotes, dna is double stranded and found in the nucleus.
in prokaryotes, dna is single stranded and is free floating.

Explanation:

1. Cell differentiation occurs when specific genes in DNA are activated by environmental factors. DNA is not deleted during cell cycle (A is wrong). Mutations are changes in DNA sequence and not the cause of normal cell differentiation (B is wrong). All cells in an organism (except some exceptions like mature red blood cells in mammals) have the same DNA (D is wrong).
2. The order of nitrogenous bases in DNA determines the genetic code of an organism. The polarity of a nitrogenous base is determined by its chemical structure (B is wrong). Hydrogen - bonds are formed between complementary base pairs and their presence is not determined by the order of bases (C is wrong). There are four main nitrogenous bases in DNA (adenine, thymine, cytosine, guanine), no fifth base (D is wrong).
3. In eukaryotes, DNA is linear and found in the nucleus. In prokaryotes, DNA is circular and is free - floating. Eukaryotic DNA is double - stranded (C and D are wrong about eukaryotic DNA being single - stranded). Prokaryotic DNA is not in the nucleus (B is wrong).

Answer:

1. C. specific genes in DNA are activated by environmental factors
2. A. genetic code of an organism
3. A. In eukaryotes, DNA is linear and found in the nucleus. In prokaryotes, DNA is circular and is free floating.