Question

Describe sexual reproduction in ferns and pines, the different mechanisms of the transfer of sperm from male to female, and a description of the development of the seed and its definition.

Answer 1

Ferns use both sexual and asexual reproduction methods. In sexual reproduction, a haploid spore grows into a haploid gametophyte. If there is enough moisture, the gametophyte is fertilized and grows into a diploid sporophyte. The sporophyte produces spores, completing the life cycle.

In ferns, the diploid sporophyte produces haploid spores by meiosis, the same process that produces eggs and sperm in animals and flowering plants. Each spore grows into a photosynthetic prothallus (gametophyte) via mitosis. Each prothallus produces gametes via mitosis. Often, a prothallus produces both sperm and eggs on the same plantlet. While the sporophyte consisted of fronds and rhizomes, the gametophyte has leaflets and rhizoids. Within the gametophyte, sperm is produced within a structure called an antheridium. The egg is produced within a similar structure called an archegonium. When water is present, sperm use their flagella to swim to an egg and ​fertilize it. The zygote grows via mitosis into the diploid sporophyte, completing the life cycle.

In pines, male and female reproductive structures are organized in male and female cones respectively. Female cones usually grow in upper branches where they may be fertilized by the pollen blown by the wind from the male cones. A pollen tube is formed in the pollen grain allowing the migration of pollen nucleus into the female gametophyte.  It results in the fertilization and formation of a zygote which grows into an embryo and naked seeds are formed which are dispersed in the air to start the life cycle once again.

In ferns, water is needed for the fertilization and in pines, the wind is needed for the dispersal of pollen grains that land on the female cone for fertilization.