Biology · Plant Kingdom · NEET
The gametophyte is haploid (n). It is the plant body that grows from a haploid spore, so every cell in it has only one set of chromosomes. Because it is already haploid, it makes gametes by simple mitosis (no meiosis needed). Examples of the gametophyte are the leafy moss plant, the fern prothallus, and the main Spirogyra body.
The sporophyte is diploid (2n). It grows from the diploid zygote, so every ordinary cell in it has two sets of chromosomes. The sporophyte is the plant body that makes spores. In ferns, gymnosperms and flowering plants, the big dominant plant you see is the sporophyte.
A spore is haploid (n). This is the most common trap. A spore is made by meiosis inside the diploid sporophyte, so the halving already happened and the spore has only one set of chromosomes. Do not confuse the haploid spore with its parent cell, the spore mother cell, which is diploid (2n).
The spore mother cell is diploid (2n). It sits inside the diploid sporophyte and it is the cell that undergoes meiosis. Meiosis is reduction division, so a 2n spore mother cell produces n (haploid) spores. Rule to remember: a mother cell of meiosis is always 2n, and its products are n.
Gametes (the male gamete or antherozoid and the female gamete or egg) are haploid (n). They are made by the haploid gametophyte using mitosis, so they stay n. When two n gametes fuse, they add up to 2n and form the diploid zygote, which is where diploidy comes back.
The zygote is diploid (2n). It forms when a haploid male gamete (n) fuses with a haploid female gamete (n): n + n = 2n. The zygote is the first cell of the sporophyte, which is why the whole sporophyte that grows from it is also 2n.
Trace the cell back to the last big event that made it. If it came after meiosis (spores, gametophyte, gametes) it is haploid (n). If it came after fertilisation, or is inside the sporophyte (zygote, sporophyte, spore mother cell), it is diploid (2n). Simple rule: meiosis makes n, fertilisation makes 2n. This one rule covers every plant group in NEET.
Zygotic meiosis is characteristic of
Match the plant with the kind of life cycle it exhibits: (a) Spirogyra (b) Fern (c) Funaria (d) Cycas | (i) Dominant diploid sporophyte vascular plant with highly reduced gametophyte (ii) Dominant haploid free-living gametophyte (iii) Dominant diploid sporophyte alternating with reduced gametophyte called prothallus (iv) Dominant haploid leafy gametophyte with partially dependent sporophyte
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Ploidy is the number of chromosome sets in a cell. Haploid (n) means one set; diploid (2n) means two sets. In plants, meiosis turns 2n into n and fertilisation turns n back into 2n.
Spores, the entire gametophyte body, and the gametes (egg and sperm/antherozoid). All of these come after meiosis, so they carry only one set of chromosomes.
The zygote, the entire sporophyte body, and the spore mother cell. All of these come after fertilisation or are inside the 2n sporophyte, so they carry two sets of chromosomes.
In flowering plants the endosperm is triploid (3n) because it forms from one sperm (n) fusing with two polar nuclei (n + n). You meet this later in Sexual Reproduction, not in Plant Kingdom, but it is worth noting so 3n does not surprise you.
Yes. In every plant group the gametophyte, spores and gametes are haploid (n), and the zygote, sporophyte and spore mother cell are diploid (2n). Only which body is dominant changes between groups; the ploidy labels never change.
