Question

1. Explain what is meant by Alternation of Generations in plants. be detailed
2. What are the significant advantages of seed production?

Answer 1

Alternation of generations, also called metagenesis or heterogenesis,

Alternation of generations.---Means...

The zygote is divides by mitosis to produce a diploid sporophytic plant body and this plant body produces haploid spores by the process of meiosis, which again divides by mitosis to produce haploid plant body.

Diagram shows the alterations of generation between a diploid sporophyte(bottom)and a haploid gametophyte (top).

• Two single-celled haploid gametes, each containing n unpaired chromosomes, fuse to form a single-celled diploid zygote, which contains n pairs of chromosomes, that is 2n chromosomes in total.
• The single-celled diploid zygote germinates, and then dividing by mitosis which maintains the number of chromosomes at 2n. That result in a multi-cellular diploid organism,that is called the sporophyte (because later it produces spores).
• When it reaches maturity, the sporophyte produces one or more sporangia /sporangium which are the organs that produce diploid spore mother cells (sporocytes). These divide by a process called meiosis that reduces the number of chromosomes by half. This initially results in four single-celled haploid spores, each containing n unpaired chromosomes.
• The single-celled haploid spore germinates, dividing by mitosis, which maintains the number of chromosomes at n. Which result a multi-cellular haploid organism, called the gametophyte (because it produces gametes at maturity).
• When it reaches maturity, the gametophyte produces one or more gametangia/ gametangium that is the organs that produce haploid gametes.

Hence the 'alternation of generations' in the life cycle is thus between a diploid (2n) generation of sporophytes and a haploid (n) generation of gametophytes.

Advantages of seed production

Seed production is production of high quality seed fundamental to modern agriculture.plant produce many seeds and seed contain embryo which later grow into new plant and the important of the seed production is that it help to preserve some old species of food grains so that seed can use for future generations so that seed will exist .

The seed quality is very important .Plants make seeds that can grow into new plants, but if the seeds just fall to the ground under the parent plant,they will not get sunlight so that it preserve the seed for the seed production.

Seed production enables the plant to become the dominant producers in the ecosystem(majority of plant diversity),the reduced gametophyte of seeded plant are protected in the ovules and pollen grains therefore they develop with in the walls of spores and that are retained within the tissue of parent sporophyte which enables the gametophyte to get nutrition from the sporophyte.