Botany MCQs for NEET — Practice Questions with Answers

The NCERT text states: 'In such plants [where pollen grains are shed at two-celled condition], the generative cell divides and forms the two male gametes during the growth of pollen tube in the stigma.'

Triple fusion involves the fusion of one male gamete with the two polar nuclei, forming the Primary Endosperm Nucleus (PEN). This PEN then develops into the endosperm, which serves as nutritive tissue for the developing embryo.

The generative cell of the pollen grain undergoes mitosis to produce the two male gametes. The vegetative cell, on the other hand, develops into the pollen tube.

Following fertilization, the ovule matures and develops into a seed. The ovary, enclosing the ovules, develops into the fruit.

Double fertilization is characterized by two distinct fusion events: (1) Syngamy, the fusion of one male gamete with the egg cell to form the zygote, and (2) Triple fusion, the fusion of the other male gamete with the two polar nuclei to form the primary endosperm nucleus.

The entry of the pollen tube through the filiform apparatus into one of the synergids often leads to the degeneration of that synergid. The other synergid may also degenerate shortly after fertilization.

The NCERT text states: 'All these events–from pollen deposition on the stigma until pollen tubes enter the ovule–are together referred to as pollen-pistil interaction. As pointed out earlier, pollen-pistil interaction is a dynamic process involving pollen recognition followed by promotion or inhibition of the pollen.'

The context states: 'It also increases the genetic variability in the population of organisms from one generation to the next. Variations are very important for the process of evolution.' and earlier mentions 'Meiosis involves pairing of homologous chromosomes and recombination between non-sister chromatids of homologous chromosomes.' Crossing over (recombination) directly leads to new combinations of alleles on chromosomes, thus increasing genetic variability.

The NCERT text explicitly states: 'Meiosis is the mechanism by which conservation of specific chromosome number of each species is achieved across generations in sexually reproducing organisms, even though the process, per se, paradoxically, results in reduction of chromosome number by half.'

The text states: 'This specialised kind of cell division that reduces the chromosome number by half results in the production of haploid daughter cells.' If $2n = 46$, then the haploid number ($n$) would be $46/2 = 23$ chromosomes in the gametes.