Question

summarize the steps of sexual reproduction

Answer 1

Sexual reproduction involves the mixing of genes from two different parents to give offspring with a genetic make-up similar to, but different from, each parent. In bryophytes the process requires the production of male gametes (sperm), female gametes (eggs) and some means of getting the sperm to the eggs. The gametes are produced on the gametophytes. The sperm are produced within tiny, typically stalked, club-shaped structures called antheridia and you can also see bryophyte sperm referred to as antherozoids. The stalk anchors the antheridium to the gametophyte. Each antheridium produces numerous sperm. The eggs are produced in tiny, typically somewhat flask-like structures called archegonia. Each archegonium holds one egg (in a swollen section called the venter) and the sperm enter through the channel in the narrower, tubular section (or neck). On the side of the venter opposite the neck is the foot which anchors the archegonium to the gametophyte. In the early stages of archegonial development that channel does not exist, the area being filled with cells. At maturity the cells in the centre of the neck disintegrate to create the channel. The channel is filled with mucilage that results from the breaking down of the cells that initially occupied the channel.

A fertilized egg in an archegonium develops into the sporophyte. The sporophyte consists of a spore-containing capsule which, depending on the species, may be stalked or stalkless. Each spore contains a mix of genes from the two parents and on successful germination will give rise to a new gametophyte.

The following diagrams show some moss archegonia and antheridia. The figures have been copied from John Lindley's The Vegetable Kingdom, published in 1853. The archegonia are on the left and have been coloured green You can see the swollen venters near the archegonial bases. At the top of the neck each archegonium has a somewhat funnel-shaped mouth. The antheridia are on the right, have been coloured blue and the middle antheridium is releasing a sperm mass, coloured brownish-orange. Archegonia and antheridia grow intermixed with hair-like to club-like paraphyses, left uncoloured in the diagrams. The previous paragraph mentioned that the antheridia and archegonia are tiny. Size varies, depending on species, but typically these gamete-producing organs are well under a millimetre in length.