Question

Examine the life cycles of the 3 main groups of plants. What do you notice about the sporophyte and gametophyte stages as plants evolved from mosses to ferns to pine trees?

Answer 1

There are three different plant life cycles: haploid (1n), diploid (2n), and the more common haploid-diploid (1n-2n).

Haploids contain one set of chromosomes in their respective cells. The diploids contain two sets of chromosomes. The haploid and diploid cells divide over mitosis for plants. The haploid form of the plants is called the gametophyte, and a sporophyte is called the diploid form.

We are seeing a gradual transition from primitive to modern characteristics as we move from mosses to ferns. There are two big phenomena to keep track of. The first is a life-cycle transition, the second is a shift in basic internal structure. First, between a haploid gametophyte stage and a diploid sporophyte stage, all plants undergo an alternation of generations.In a special structure called a gametangium ,gametophytes produce gametes (sperm and eggs), while sporophytes produce spores in a special structure called a sporangium. Second, every plant needs to bring water to its cells. Primitive bryophytes such as mosses and liverworts are so small they can rely on diffusion to move water inside and out of the plant.Mosses have a few water strands in their central stem, but nothing like the broad and well-organized tracheophyte tube network, or "tube plants." In the more advanced ferns and "fern allies," the vascular tissues are made up of xylem and phloem, which conduct water, nutrients and food in the plant body.