Economic importance of algae - Algae have diverse economic uses.
(a) Food source: Many species of marine algae such as Porphyra, Sargassum, and Laminaria are edible and used as food.
(b) Food supplements: Chlorella and Spirulina are rich in proteins and are used as food supplements.
(c) Commercial importance: It is used for the production of Agar which is obtained from Gelidium and Gracilaria. Agar is used for growing microbes in laboratories and in ice creams and jellies.
(d) Production of hydrocolloids: Certain brown (align) and red algae (carrageen) are used for the production of hydrocolloids.

Economic importance of gymnosperms – Gymnosperms are of great economic value. They are used in the following ways.
(a) Construction purposes: Many conifers such as pine, cedar, etc., are sources of the soft wood used in construction and packing.
(b) Medicinal uses: An anticancer drug Taxol is obtained from Taxus a gymnosperm. Many species of Ephedra produce ephedrine, which can be used in the treatment of asthma and bronchitis.
(c) Food source: The seeds of Pinus are edible and used as food.
(d) Source of resins: Conifers such as Pinus australis is an excellent producers of resins. Resins are used in various industries such as varnishes, plasters and enamel paint because they are resistant to decay.

Liverwort: In liverworts, the reduction division takes place in the capsule during the sexual reproduction.
Moss: In mosses the reduction division takes place in the capsule during the sexual reproduction.
Fern: Reduction division takes place in the sporangia, thereby producing many spores during the sexual reproduction.
Gymnosperm: Reduction division takes place in the microsporangia present and in the megasporangia during sexual reproduction.
Angiosperm: In angiosperms, reduction division takes place in the anthers of the stamen (producing haploid pollen grains or male gametes) and in the ovary of the pistil (producing eggs or female gametes ) during the sexual reproduction phase.

The ploidy of the following are:
(a) Protonemal cell of a moss – Haploid
(b) Primary endosperm nucleus in a dicot – Triploid
(c) Leaf cell of a moss – Haploid
(d) Prothallus of a fern – Haploid
(e) Gemma cell in Marchantia – Haploid
(f) Meristem cell of a monocot – Diploid
(g) Ovum of a liverwort – Haploid
(h) Zygote of a fern – Diploid

Archegonium is the female sex organ that produces the female gamete or egg. It is present in the life cycles of mosses (bryophytes), pteridophytes, and gymnosperms.
Life cycle of a moss.
Gametophytic stage is the predominant stage of the moss lifecycle. The Gametophytic stage consists of two stages
(i). Protenema stage – this is the first stage which develops directly from a spore.
(ii). Leafy stage – this is the second stage which develops from the secondary protonema as a lateral bud.
They consist of upright slender axes which bears spirally arranged leaves. Rhizoids are the multicellular structure that attaches the mosses to the soil. This stage bears the sex organs. The male (antheridia) and female (archegonium ) sporangia are formed at the apex of the leafy shoots. Cells within the sporangium of the sporophyte undergo meiosis to produce male and female spores, respectively. These spores divide mitotically to produce multicellular male and female gametophytes. The sperm and eggs are produced mitotically in the antheridia and archegonia, respectively. Sperm are carried to the archegonia in water droplets. After fertilisation, the sporophyte generation develops in the archegonium and remains attached to the gametophyte and the cycle is completed. 

Algae are classified on the following factors:
(a) Major photosynthetic pigments present.
(b) Form of stored food.
(c) Cell wall composition.
(d) Number of flagella and position of insertion.
(e) Habitat.