$(a)$ Why do we say that homozygous plants produce pure progeny?
$(b)$ Define heterozygous.
$(c)$ Explain how the process of speciation takes place.

(N/A) Homozygous plants possess identical alleles for a particular trait (e.g.,$TT$ or $tt$). During gamete formation,all gametes carry the same allele,ensuring that all offspring inherit the same genetic makeup,thus producing pure progeny.
$(b)$ An organism is called heterozygous if it possesses two different alleles for a specific trait (e.g.,$Tt$).
$(c)$ Speciation occurs due to the following factors:
$(i)$ Natural selection: Differential survival and reproduction based on environmental pressures.
$(ii)$ Geographical isolation: Physical barriers preventing gene flow between populations.
$(iii)$ Genetic drift: Random changes in allele frequencies in a small population.
$(iv)$ Reproductive isolation: Accumulated variations in $DNA$ or chromosome numbers prevent interbreeding between groups,leading to the formation of a new species.