Sporophyte - Wikipedia
wild of the two different generations (gametophytic and sporophytic) with regard to heavy metals. The data are discussed in relation to the role performed. The relationship between the gametophyte and sporophyte varies among different groups of plants. Gametophyte is the dominant, which is recognizable stage. To investigate the effects of gametophytes on their sporophytes, we studied the relationship between organic matter production by.
Sexual reproduction results in gametes that combine two cells from different individuals. Meiosis also produces gametes. Haploids contain one set of chromosomes in each of their cells.
Diploids cells contain two chromosome sets. For plants, haploid and diploid cells divide via mitosis.
Offspring alternate from diploid sporophytes to haploid gametophytes and back again in generations. This means plants generate two different kinds of plants with the same genetic material. Sporophytes represent the diploid phase of plants. Gametophytes represent the haploid phase of plants.
- Figure 30.1 Three variations on gametophyte/sporophyte relationships
- Alternation of generations
- Gametophyte and Sporophyte
Characteristics of Sporophytes Sporophytes are diploid plants that use meiosis to produce spores. These spores are haploid cells that grow into haploid gametophytes. Megaspores grow into female gametophytes, and microspores grow into male gametophytes. Meiosis occurs in the sporangium of a sporophyte and results in haploid spores.
These spores contain one cell that can become another new plant without mating.
Sporophytes have evolved in vascular plants to become larger, more dominant and longer-lived compared to gametophytes. Characteristics of Gametophytes Gametophytes are haploid plants that use mitosis to make haploid gametes. Unequal heteromorphy or anisomorphy. Gametophyte of Mnium hornuma moss.
In liverworts, mosses and hornworts, the dominant form is the haploid gametophyte. The diploid sporophyte is not capable of an independent existence, gaining most of its nutrition from the parent gametophyte, and having no chlorophyll when mature. In ferns, both the sporophyte and the gametophyte are capable of living independently, but the dominant form is the diploid sporophyte.
The haploid gametophyte is much smaller and simpler in structure. In seed plants, the gametophyte is even more reduced at the minimum to only three cellsgaining all its nutrition from the sporophyte.
The extreme reduction in the size of the gametophyte and its retention within the sporophyte means that when applied to seed plants the term 'alternation of generations' is somewhat misleading: Both gametes the same isogamy. Like other species of CladophoraC. Both of similar motility.
Species of Ulvathe sea lettuce, have gametes which all have two flagella and so are motile. However they are of two sizes: The larger sessile megagametes are eggs ovaand smaller motile microgametes are sperm spermatozoa, spermatozoids. The degree of motility of the sperm may be very limited as in the case of flowering plants but all are able to move towards the sessile eggs. When as is almost always the case the sperm and eggs are produced in different kinds of gametangia, the sperm-producing ones are called antheridia singular antheridium and the egg-producing ones archegonia singular archegonium.
Gametophyte of Pellia epiphylla with sporophytes growing from the remains of archegonia. Antheridia and archegonia occur on the same gametophyte, which is then called monoicous. Many sources, including those concerned with bryophytes, use the term 'monoecious' for this situation and 'dioecious' for the opposite.
The liverwort Pellia epiphylla has the gametophyte as the dominant generation. The moss Mnium hornum has the gametophyte as the dominant generation. However, the parent sporophyte may be monoecious, producing both male and female gametophytes or dioecious, producing gametophytes of one gender only. Seed plant gametophytes are extremely reduced in size; the archegonium consists only of a small number of cells, and the entire male gametophyte may be represented by only two cells.
All spores the same size homospory or isospory. Horsetails species of Equisetum have spores which are all of the same size. When the two kinds of spore are produced in different kinds of sporangia, these are called megasporangia and microsporangia. A megaspore often but not always develops at the expense of the other three cells resulting from meiosis, which abort.
Megasporangia and microsporangia occur on the same sporophyte, which is then called monoecious. Most flowering plants fall into this category.
Gametophyte and Sporophyte
Thus the flower of a lily contains six stamens the microsporangia which produce microspores which develop into pollen grains the microgametophytesand three fused carpels which produce integumented megasporangia ovules each of which produces a megaspore which develops inside the megasporangium to produce the megagametophyte.
In other plants, such as hazel, some flowers have only stamens, others only carpels, but the same plant i. Flowers of European Holly, a dioecious species: An individual tree of the European holly Ilex aquifolium produces either 'male' flowers which have only functional stamens microsporangia producing microspores which develop into pollen grains microgametophytes or 'female' flowers which have only functional carpels producing integumented megasporangia ovules that contain a megaspore that develops into a multicellular megagametophyte.
There are some correlations between these variations, but they are just that, correlations, and not absolute. For example, in flowering plants, microspores ultimately produce microgametes sperm and megaspores ultimately produce megagametes eggs. However, in ferns and their allies there are groups with undifferentiated spores but differentiated gametophytes.
For example, the fern Ceratopteris thalictrioides has spores of only one kind, which vary continuously in size. Smaller spores tend to germinate into gametophytes which produce only sperm-producing antheridia. The diagram shows the alternation of generations in a species which is heteromorphic, sporophytic, oogametic, dioicous, heterosporic and dioecious.
A seed plant example might be a willow tree most species of the genus Salix are dioecious.
Alternation of generations - Wikipedia
An immobile egg, contained in the archegonium, fuses with a mobile sperm, released from an antheridium. The resulting zygote is either 'male' or 'female'. A 'male' zygote develops by mitosis into a microsporophyte, which at maturity produces one or more microsporangia. Microspores develop within the microsporangium by meiosis. In a willow like all seed plants the zygote first develops into an embryo microsporophyte within the ovule a megasporangium enclosed in one or more protective layers of tissue known as integument.
At maturity, these structures become the seed. Later the seed is shed, germinates and grows into a mature tree. A 'male' willow tree a microsporophyte produces flowers with only stamens, the anthers of which are the microsporangia. The resulting meiospores develop into a gametophyte. Both the spores and the resulting gametophyte are haploid, meaning they only have one set of chromosomes. The mature gametophyte produces male or female gametes or both by mitosis. The fusion of male and female gametes produces a diploid zygote which develops into a new sporophyte.
This cycle is known as alternation of generations or alternation of phases. In flowering plantsthe sporophyte comprises the whole multicellular body except the pollen and embryo sac Bryophytes mossesliverworts and hornworts have a dominant gametophyte phase on which the adult sporophyte is dependent for nutrition. The embryo sporophyte develops by cell division of the zygote within the female sex organ or archegoniumand in its early development is therefore nurtured by the gametophyte.
Cleistocarpous sporophyte of the moss Physcomitrella patens Most algae have dominant gametophyte generations, but in some species the gametophytes and sporophytes are morphologically similar isomorphic. An independent sporophyte is the dominant form in all clubmosseshorsetailsfernsgymnosperms, and angiosperms that have survived to the present day. Early land plants had sporophytes that produced identical spores isosporous or homosporous but the ancestors of the gymnosperms evolved complex heterosporous life cycles in which the spores producing male and female gametophytes were of different sizes, the female megaspores tending to be larger, and fewer in number, than the male microspores.