Botany MCQs for NEET — Practice Questions with Answers

The NCERT text explains: 'This ability of the plants is due to the presence of meristems at certain locations in their body. The cells of such meristems have the capacity to divide and self-perpetuate. The product, however, soon loses the capacity to divide and such cells make up the plant body. This form of growth wherein new cells are always being added to the plant body by the activity of the meristem is called the open form of growth.' (Chapter: PLANT_GROWTH_AND_DEVELOPMENT, Section 13.1.1).

Relative growth rate is calculated per unit initial parameter. If both leaves increase by the same absolute amount (5 cm²), the leaf with a smaller initial area will have a higher relative growth rate (percentage increase) compared to a larger leaf. For example, if Leaf A is 10 cm² and grows to 15 cm², its relative growth is 50%. If Leaf B is 100 cm² and grows to 105 cm², its relative growth is 5%. (Chapter: PLANT_GROWTH_AND_DEVELOPMENT, Section 13.1.4 and Figure 13.7).

The process of double fertilization involves two main fusions. One male gamete fuses with the egg cell to form the zygote, and the other male gamete fuses with the two polar nuclei in the central cell to form the Primary Endosperm Nucleus (PEN), which develops into the endosperm. This is a characteristic feature of angiosperm fertilization.

The Primary Endosperm Nucleus (PEN) is formed by the fusion of one male gamete (haploid, n) with the two polar nuclei (each haploid, n) present in the central cell. Therefore, the resulting PEN is triploid (n + n + n = 3n).

According to the process of double fertilization, one of the two male gametes released by the pollen tube fuses with the egg cell. This fusion is called syngamy or generative fertilization and leads to the formation of the diploid zygote.

The NCERT text states: 'The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tubes into the synergid.'

Triple fusion is the fusion of one male gamete with the two polar nuclei. The polar nuclei are located in the large central cell of the embryo sac. Therefore, triple fusion occurs in the central cell.

The NCERT text states: 'the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell.' This large central cell, containing the two polar nuclei, fuses with one male gamete during triple fusion to form the primary endosperm nucleus, which later develops into the endosperm.

The pollen grain germinates on the stigma, and the pollen tube grows through the tissues of the style and reaches the ovary. From the ovary, it enters the ovule through the micropyle, and then specifically enters one of the synergids. (Ref: 'Pollen tube grows through the tissues of the stigma and style and reaches the ovary... Pollen tube, after reaching the ovary, enters the ovule through the micropyle and then enters one of the synergids through the filiform apparatus').

The chapter is titled 'Sexual Reproduction in Flowering Plants' (Angiosperms) and discusses double fertilization as a key event in their reproductive cycle. Double fertilization involving the formation of both a zygote and primary endosperm nucleus is exclusive to angiosperms.