Slide 1
We will now begin
discussing the four main groups of plant diversity and we will start with the
non-vascular plants.
The non-vascular plants were the first group of plants to evolve and they retain primitive characterstics such as a lack of vascular tissue.
Slide 2
The Non-vascular plants are sometimes referred to as the Bryophytes.
However, the non-vascular plants are not a monophyletic group and this classification system is being updated.
All members of this group lack vascular tissue which means they hae no tissue to move water and nutrients around the body of the plant. As a result, these plants remain small because they rely on passive diffusion to move water and nutrients around the plant.
This group of plants has no pollen,
seeds, flowers or fruit and they reproduce via spores that are released from
the parent plant.
Slide 3
Plants are sexually reproducing organisms and they make gametes - both sperm and eggs. The sperm of the non-vascular plants are flagellated and they need a moist environment so that they can swim to fertilize the egg of a female plant.
Therefore, the nonvascular plants are found in moist environments - at least during their reproductive stage.
They are anchored to the soil substrate that they grow on by structures known as rhizoids - these are not roots because true roots have vascular tissue.
Because they lack vascular tissue nutrients and water must diffuse into the cells of the plant. This keeps the plant small.
The non-vascular plants have an alternation of generation life cycle like all plants. The non-vascular plants are unique in that the gametophyte is the prominent stage in the life cycle (all other plant groups have a prominent sporophyte).
Slide 4
The non-vascular plants
includes not only the mosses but also plants known as liverworts and
hornworts.
Slide 5
There are about 12,000 species of mosses alone and
they grow in shady wet environments like this beautiful and peaceful moss
garden in Kyoto, Japan.
Slide 6
Recall that alternation of
generations is a life cycle in which there is an alternation between a
multicellular haploid and multicellular diploid stage in the life cycle.
The keyword here is multicellular - both the haploid and the diploid stage are multicellular. This is in contrast to humans, for example, We have a multicellular diploid stage but the haploid cells in the human life cycle only include the sperm and eggs and they are unicellular.
The diploid stage is the sporophyte and it produces the spores and the haploid stage is the gametophyte and it produces the gametes.
Slide 7
In this tutorial we will examine the alternation of generations life cycle in more detail.
If we start with the multicellular diploid stage - the sporophyte...
Slide 8
We see that it creates spores via meiosis (spores are haploid).
Slide 9
These spores are released from the parent sporophyte and they germinate and grow via mitosis into a multicellular haploid gametophyte.
Slide 10
The gametophyte produces gametes - both eggs and sperm - via mitosis (remember, the gametophyte cells are haploid so they produce haploid gametes by mitosis).
Slide
11
Fertilization of an egg by a sperm produces a diploid zygote and this zygote grows via mitosis into a new multicellular sporophyte individual.
Alternation of generations is a feature of all plants but it looks slightly different in the different types of plants.
Slide 12
In the mosses and other non-vascular plants - it is the gametophyte that is prominent.
There is a separate male and female gametophyte - the male produces sperm and the female produces eggs. The sperm must swim to the egg and fertilization produces the diploid zygote.
The zygote grows into a sporophyte. In the mosses this sporophyte is small and completely dependent on the gametophyte for nutrition (the sporophyte cannot photosynthesize).
This is what it means for the gametophyte to be prominent.
The sporophyte produces spores via meiosis and produces spores that will grow into new gametophytes.
The mosses are heterosporous - there are two different
types of spores - one type gives rise to male gametophytes and one type gives
rise to female gametophytes.