A flowering plant species has a diploid chromosome number of $2n = 24$ in its vegetative (leaf) cells. Calculate the exact number of chromosomes present in the following cells: (a) Pollen grain, (b) Antipodal cell, (c) Endosperm cell, (d) Zygote, and (e) Integument cell. Show all necessary steps and biological reasoning for each calculation.

Question

Accepted Answer

Given Data:

Diploid chromosome number of vegetative (leaf) cells ($2n$) = $24$
Therefore, the haploid number ($n$) = $\frac{24}{2} = 12$

Step-by-Step Calculations for Each Cell Type:

(a) Pollen grain:

Reasoning: A pollen grain is formed by the meiotic division of microspore mother cells and represents the male gametophyte, which is haploid ($n$).
Calculation: Number of chromosomes = $n = 12$.

(b) Antipodal cell:

Reasoning: Antipodal cells are cells of the female gametophyte (embryo sac) formed by mitotic divisions of the functional megaspore, making them haploid ($n$).
Calculation: Number of chromosomes = $n = 12$.

(c) Endosperm cell:

Reasoning: In angiosperms, the endosperm is formed as a result of triple fusion involving three haploid nuclei (one male gamete + two polar nuclei), making it triploid ($3n$).
Calculation: Number of chromosomes = $3 \times n = 3 \times 12 = 36$.

(d) Zygote:

Reasoning: A zygote is formed by the fusion of a male gamete ($n$) and an egg cell ($n$), restoring the diploid condition ($2n$).
Calculation: Number of chromosomes = $2n = 24$.

(e) Integument cell:

Reasoning: Integuments belong to the ovule wall which is a vegetative (sporophytic) part of the plant, thus remaining diploid ($2n$).
Calculation: Number of chromosomes = $2n = 24$.