Final answer:
Water ferns like Marsilea are heterosporous, but not all ferns are; most ferns are homosporous. The statement that sporangia form on the underisde of the gametophyte is false in ferns, as they form on the sporophyte. In mosses, it's true that the sporophyte produces haploid spores.
Step-by-step explanation:
The assertion that 'Water ferns are all heterosporous' can be considered as mostly false. While water ferns, such as species in the genus Marsilea, are heterosporous, not all ferns as a larger group are exclusively heterosporous. In general, ferns tend to be homosporous, producing one type of spore that develops into a bisexual gametophyte. However, there are some ferns which indeed are heterosporous, producing two distinct types of spores: megaspores and microspores, which will develop into female and male gametophytes, respectively.
When considering the fern life cycle, it is important to note that the statement 'Sporangia form on the underside of the gametophyte' is false. Sporangia, which produce haploid spores, typically form on the underside of the sporophyte generation, not the gametophyte. The sporophyte generation of ferns is diploid and grows from the haploid gametophyte, which carries out photosynthesis and supports the young sporophyte.
Lastly, in the context of mosses and the moss life cycle, the statement 'The sporophyte produces haploid spores' is true. The mature gametophyte of mosses is haploid, and the sporophyte, which is diploid, produces haploid spores through meiosis.