Having two different alleles for a gene means the genotype is heterozygous. In diploid organisms, you inherit one allele from each parent at the same gene locus, and if those alleles are different forms of the gene, that combination is heterozygous. If the two alleles were identical, that would be homozygous. Monohybrid refers to studying inheritance for a single gene, and polygenic describes traits influenced by many genes, so they’re about patterns of inheritance or the number of genes involved, not the identity of the two alleles at one locus.

Excretion is the removal of metabolic wastes from the body. As cells carry out metabolism, they produce waste products that can be toxic if they build up. The excretory systems—kidneys, liver, lungs, and skin—work to dispose of these wastes: urea and other nitrogenous wastes from the breakdown of proteins, excess salts and water, and gases like carbon dioxide from respiration. Removing these wastes helps keep the internal environment stable, including proper fluid balance and pH. Oxygen is something the body uses to release energy, not a waste to be expelled. Hormones are signalling molecules released by glands in a controlled way, not wastes in the sense of excretory waste, though some can be eliminated in urine to regulate body chemistry. Nutrients are absorbed and used by the body rather than being wastes. So the term that describes what is removed by excretion is metabolic wastes.

The male reproductive part of a flower is the stamen. It is made up of two pieces: a filament, which is the slender stalk that positions the other part, and an anther, the sac at the tip where pollen grains form. In the anther, pollen sacs develop pollen through cell division, and when mature the anther releases pollen so it can be carried to the female part for fertilization. This is distinct from the female structure, which is the carpel (also called the pistil) that includes the stigma, style, and ovary, with ovules inside the ovary. So the statement describes the stamen, the male part.

Nitrification is the conversion of ammonia into nitrite and then nitrate through two linked oxidation steps carried out by specialized bacteria. In the first step, ammonia-oxidizing bacteria take ammonia (NH3) and oxidize it to nitrite (NO2−), gaining energy in the process. In the second step, nitrite-oxidizing bacteria convert nitrite to nitrate (NO3−), releasing more energy. Both steps require oxygen, so this process happens under aerobic conditions. This distinguishes nitrification from ammonification, which releases ammonia during decomposition; from denitrification, which reduces nitrate to nitrogen gas under low-oxygen conditions; and from nitrogen fixation, which converts atmospheric N2 into ammonia.