* Pollen is the male gametophyte in flowering plants. Its main purpose is to deliver the male gametes (sperm) to the female ovule for fertilization.

* Gametes are always haploid – they contain only one set of chromosomes.

* Pollen is produced through meiosis, a cell division process that reduces the number of chromosomes in a cell by half. This is why pollen grains have half the number of chromosomes as the parent plant.

Diploid cells, on the other hand, contain two sets of chromosomes, one from each parent. This is the case for the sporophyte generation of plants, which includes the plant's body.

To summarize:

* Pollen is haploid because it contains only one set of chromosomes.

* Pollen is a gametophyte – its purpose is to deliver the male gametes for fertilization.

* Diploid cells contain two sets of chromosomes and are part of the sporophyte generation.