Q; a nucleotide consists of ?
a: a sugar, a protein and uracil
b: a phosphate, a sugar and a nitrogen base
c: a phosphate, an amino acid and a nitrogen base
d: a sugar and a nitrogen base

Option B, A phosphate, a sugar and a nitrogen base

Explanation:

Nucleotide is a basic building unit of DNA. Each nucleotide comprises of three major constituents – a) A sugar, b) A phosphate and c) a nitrogenous base.  

While forming a DNA molecule, deoxyribose acts as a specific sugar. When the nucleotides are linked together, they are supported by the phosphate bond and sugar as backbone. The two strands of DNA attaches to each other through the  nitrogenous bases in a way that nitrogenous base of one nucleotide attached to the nitrogenous base of other nucleotide through hydrogen bonds.  

Hence, option B is correct

it has one origin of replication, but it proceeds in two directions - d)

tsd is temerature dependent sex determination.

tsd: it is a type of environmental sex determination in which the temperature experienced during embryonic/ larval development (ambient temperature for development) determine the sex of the offspring.

crocodile displays the tsd where the ambient temperature of the developing egg determines the individual's sex. for example in the american alligator's eggs, incubation at 33 ºc produces mostly males, while incubation at 30 ºc produces mostly females. so if the american alligator's egg will get the ambient temperature (33 degree celcius)during embryonic development from egg, the offspring will be male and same for the female sex determination.