16. Plant Diversity Flashcards
Understand (from phylogenetic tree) that charophytes are closest relatives of land plant (embryophytes)
List four key traits of land plants that are absent in green algae charophytes
- Alternation of generations -
- Walled spores
- Multicellular gametangia
- Apical meristems
What does alternations of Generations describe?
5 MAIN STEPS
“Alternation of generations” is a reproductive strategy observed in the life cycles of some organisms, particularly plants and certain algae. It involves two distinct multicellular stages in the life cycle: the haploid (n) gametophyte stage and the diploid (2n) sporophyte stage.
In this pattern, the gametophyte produces haploid gametes (such as eggs and sperm) through mitosis. These gametes fuse during fertilization to form a diploid zygote. The zygote then develops into a multicellular sporophyte through mitosis, which produces haploid spores through meiosis. These spores, in turn, develop into the next generation of gametophytes, completing the cycle.
This alternation between haploid and diploid stages is a key feature of plant life cycles and contributes to their reproductive diversity and adaptability. It allows for genetic diversity, dispersal, and adaptation to different environmental conditions.
What are Walled Spores?
Walled spores are reproductive structures produced by certain organisms, particularly fungi, algae, and some plants.
What are Multicellular gametangium?
Gametangium = specialized organ or cell in which gametes are found in algae, ferns, and some other plants
What are Apical meristems?
Growth regions in plants found within root tips and tips of new shoots and leaves
What is a Gametophyte?
The multicellular gametophyte is haploid and produces haploid gametes by mitosis
What is a Zygote?
Fusion of the gametes (eggs and sperm) results in fertilization, which gives rise to the diploid zygote
‒ The diploid embryo is retained within the tissue of the female gametophyte
‒ Nutrients are transferred from parent to the embryo through specialized placental transfer cells
What is a diploid sporophyte?
The zygote divides by mitosis and develops into a multicellular, diploid sporophyte
The sporophyte produces haploid spores by meiosis
Spores divide by mitosis and develop into the gametophyte
- Describe life cycle of non-vascular plants (mosses, liverworts and hornworts)
7 KEY MOMENTS
- The multicellular/haploid gametophyte produces haploid gametes by mitosis
- Gametes fuse giving rise to the diploid zygote
- The diploid embryo is retained within the tissue of the female gametophyte
- Nutrients are transferred from parent to the embryo through specialized placental transfer cells
- The zygote divides by mitosis and develops into a multicellular, diploid sporophyte
- The sporophyte produces haploid spores by meiosis
- Spores divide by mitosis and develop into the gametophyte
2 Important things to remember about the life cycle of non-vascular plants.
gametophytes are dominant part of life cycle;
male and female gametophytes are separate organism
What are the similarities and differences
between zygotes and spores?
- SIMILARITY =
Zygotes and spores are both single cells that divide by mitosis to form a multicellular individual - DIFFERENCE =
Zygotes result from the fusion of two cells, such as sperm and an egg (so they are diploid), but spores are not formed by the fusion of two cells (so they are haploid) - DIFFERENCE = Zygotes produce sporophytes while spores produce gametophytes
What is a Sporangia?
an organ in which the sporophyte produces spores
What are Sporocytes?
Diploid cells which undergo meiosis to generate haploid spores
What is Sporopollenin?
Spore walls contain sporopollenin, which protects against desiccation (drying up) making them resistant to harsh environments
What are Gametangia?
Sex Organs in which Gametes are produced
What are Female gametangia?
archegonia, produce eggs and are the site of fertilization
What are Male gametangia?
antheridia are the site of sperm
production and release
What are Apical meristems?
Apical meristems comprise of embryonic cells and are the growth regions at plant tips (root tips and shoot tips), thereby allowing plants to sustain continual growth in their length
What are Bryophytes?
Bryophytes are non-vascular and represented today by:
– Liverworts
– Hornworts
– Mosses
-Gametophytes are dominant part of the life cycle: larger in terms of size and longer-living than sporophytes…also gametophyte produces most of the food required by the individual
– Sporophytes are present only part of the time and are dependent on gametophytes
What are Rhizoids?
Rhizoids anchor gametophytes to a substrate
The life cycle of moss (non-vascular plant)
- Sperm swim through water to reach and fertilize the egg (fertilization occurs within the archegonium)
- Diploid zygote develops within archegonium, which then becomes an embryo via mitosis
- Embryo will give rise to the diploid sporophyte (this sporophyte will grow out of the archegonium)
- Sporophyte will produce spores which will be contained within the sporangia (sporocytes will go through meiosis to produce haploid spores)
What is Vascular Tissue?
Vascular tissue (i.e., xylem and phloem) allowed vascular plants to grow tall compared to the non-vascular plants
bryophytes vs. sporophytes
- In contrast with bryophytes, sporophytes of
seedless vascular plants are a dominant part of the life cycle compared to the gametophyte - Sporophytes are much larger in size and longer-lived than bryofights
- We will look at the fern life cycle as an example of a seedless vascular plant for this lecture
What are sporophylls?
spore-bearing leaves of the sporophyte,
there are sporangia present
What is a Sorus?
Group of sporangium
(plural is sori)
What is hermaphroditic?
both antheridia and archegonia are found
What is common to all seed vascular plants?
– Reduced gametophytes
(instead, sporophytes are a dominant part of the life cycle)
– Heterospory
– Ovules
– Pollen
Gametophyte / sporophyte relationships in different plant groups
What does it mean to be homosporous?
Non-vascular plants and most seedless vascular plants like ferns are homosporous – they produce one type of spore of the same size
What is Heterospory?
Heterospory is the production of spores of two different sizes and sexes by the sporophytes
Seed vascular plants (i.e., gymnosperms and angiosperms) are heterosporous
What is Megasporangia?
Megasporangia produce megaspores that give rise to female gametophytes
What is Microsporangia?
Microsporangia produce microspores that give rise to male gametophytes
What are Ovules?
Unfertilized, immature seed = ovule
(so a fertilized ovule is called a seed)
– Ovules of gymnosperms develop on scales of cones
– Ovules of angiosperms are enclosed in chambers called ovaries (a fruit is a fertilized, fully grown, ripened ovary that contains the seeds)
What is a Megasporangium?
Megasporangium = Diploid
inner cell mass of ovule, comprising of diploid sporophytic cells
What is a Megasporocyte
Megasporocyte = Diploid
a diploid cell that undergoes meiosis to produce four haploid megaspores – at least one of the spores develops into the haploid female gametophyte (which includes an egg cell)
What is a Integument?
Integument =
layer of sporophyte tissue (diploid) that envelops and protects the megasporangium and the megaspore – the integuments develop into the seed coat when the ovule matures after fertilization
At Maturity, what does the mature seed contain?
At maturity, the mature seed contains:
– the diploid integument which develops into the seed coat
– the haploid female gametophyte (food supply), and
– the diploid embryo (which will germinate to become a new sporophyte)
What is a Microsporangium?
Microsporangium is a pollen sac that contain microsporocytes, which develop into microspores
- diploid
What is a Microsporocyte?
Microsporocyte =
a diploid cell that undergoes meiosis to produce four haploid microspores – each microspore will ultimately form a haploid pollen grain (which is the male gametophyte)
§ The pollen grains then produce sperm cells via mitosis
What are Microspores?
What are Megaspores?
microspores that give rise to male gametophytes
megaspores that give rise to female gametophytes
HAPLOID
What is sporopollenin?
The tough pollen wall, which contains
sporopollenin, which protects the pollen grain as it is transported from the parent plant by wind or by hitchhiking on the body of an animal
What is Pollination?
Pollination is the transfer of pollen from the male to the female part containing the ovules
