This survey included the bryophytes (mosses, etc.),
which lack vascular tissue, plants like ferns, which have vascular tissue but
not seeds, and the seed plants, which reproduce using diploid seeds rather than
haploid spores. Seed plants also produce pollen, which transports sperm over great
distances, allowing sexual reproduction to occur on dry land. The seed plants
include the gymnosperms and the angiosperms. In this course, we will focus on
the angiosperms. The name angiosperm (vessel seed) refers to the fruit, which
contains the seed(s) and is unique to this group. All angiosperms belong to the
phylum Anthophyta, which means flowering plant. Flowers are also unique to this
group. They contain the sexual reproductive organs of the plant, and in many
species, attract the animals that pollinate them. In this lab, we will be
studying the life cycle and specialized reproductive structures of angiosperms.
All organisms have life cycles, the series of
developmental stages and reproductive events that occur in each generation and
produce the next. As we look across the living world, we observe great
diversity in the details of these life cycles. If the species is to persist,
reproduction must be part of the life cycle and it can be asexual or sexual.
Some species do one or the other. Others can do either, depending on
conditions, while yet others do both in a regularly alternating pattern. Many
plants can and do reproduce asexually. For instance, when a strawberry plant
sends out a stolon (runner) and it sets down roots and produces a new plant, it
has just reproduced asexually. The process involves only mitotic cell division.
Sexual reproduction always involves the combination of genes from two
individuals (parents) that produce the genome of the next generation. This
process is fertilization. Sexual reproduction in all eukaryotes involves
fertilization as well as meiotic cell division, which reduces the chromosome
number from diploid (2n: two of each type of chromosome, one from each parent),
to haploid (In: one of each type of chromosome). Without meiosis, the
chromosome number would double with each generation of sexual reproduction.
Sexual reproduction in all eukaryotes involves an alternation of generations
between haploidy and diploidy, summarized