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What is the structure of a cycad trunk?
it is covered by leaf bases where other organisms live in
Difference between male and female cycad cone.
- female: rougher appearance in texture; fatter
- male: slender
- male cone has microsporangia
- female has ovules
Megasporophyll evolution: There was __
a gradual reduction that resulted in only two ovules
Developing seeds are located on the edges; can be numerous
In Zamia floridana, what is the microspore?
What does the antheridia do?
divides into the generative and the tube cell
Explain microgametophyte development.
- From the haploid microspore, you get a pollen grain with a prothallial cell, generative cell, tube cell, and tube cell nucleus (three cells)
- -- it is the antheridia which intiially divide into the generative and tube cell
Once it gets into an ovule, it will begin to germinate and a pollen tube begins to form from the tube cell
The generative cell will also divide and produce two more cells, the stalk cell (sterile) and the body cell (androgenous cell); at this point, there are now four cells (stalk, body, prothallial cell, and tube cell (which develops into the pollen tube))
Afterwards, the body cell divides into two sperm (all that is left of the antheridia is the stalk cell); there are five cells
the sperm contain flagella
When will the pollen grain germinate?
once inside the ovule; and then it produces a pollen tube
What is the method of division in Zamia microgametophyte development?
everyhting divides by mitosis because of hte haploid condition
What is a characteristic feature of this male gametophyte?
What is all that is left of the antheridium?
When does it become a mature
the fact that the sperm are the largest in the plant kingdom with multiple flagella
the sterile stalk cell
when the sperm develop
Summary of Zamia (cycad) microgametophyte development.
microspore is haploid and is made by the microsporocyte--> pollen grain with three cells (generative, tube cell, and prothallial cell)--> germination of pollen grain and formation of pollen tube--> generative cell divides into sterile stalk cell and androgenous body cell--> body cell divides to form two sperm
Zamia megagametophyte development
it begins with a megasporocyte surrounded by a megasporangium (nucellus) and containing integuments--> meiosis--> four megaspores--> three disintegrate to give one functional megaspore--> ovule contains the mature megagametophte and has an outer and inner fleshy layer and a middle stony layer and the archegonium are located near the pollen chamber--> mature seed forms
What may happen before megagametphyte developoment even occurs?
Explain what the pollen tube must do?
cells disintegrate and ooze out to form a pollination droplet; pollen grains stick; when it dries out, it gets pulled into the chamber with the pollen; pollen tubes then form the pollen tube
the pollen tube must digest its way through the megasporangium to reach the megaspore; it is parasitic in a sense
Once the pollen tube reaches the arch. chamber,, the tube bursts open; and, since the arch chamber has a lot of fluid in it, and some from the pollen tube, they swim to the archegonia ( not far, but still they swim)--> fertilization
What is the megasporangium surrounded by?
What is the nucellus?
What is the megasporocyte surrounded by?
What is an ovule?
nucellus and integuments
an immature seed
What is the method of division for the megasporocyte?
meiosis to produce four megaspores, three of which disintegrate
Explain the ovule containing the mature megagametophyte.
There is a micropyle at the very top (a small opening in the surface of an ovule, through which the pollen tube penetrates, often visible as a small pore in the ripe seed.)
Then (in descending order): there is a pollen chamber, a nucellus, an archegonial chamber, the archegonium (2-4), which are located within the megagametphyte, then the inner fleshy, middle stony, and outer fleshy layers
When is the temporary free-nuclear stage?
between the functional megaspore forming and the ovule containing the mature megagametophyte
Some ways that flowers differ
presence or absence of parts
fusion of parts
level of insertion of other parts relative to the ovary
flowers borne singly or in clusters (inflorescences)
Explain the presence or absence of parts
complete flower: all four parts (sepals petals stamens pistil) present
incomplete flower: one or more parts not present
perfect flower: both stamens and pistils present
imperfect: stamens OR pistils present, not both
What are the types of imperfect flowers?
staminate: only stamens present
pistillate: only pistils present
Explain monoecious species and dioecious.
mono: both staminate and pistillate flowers are on the same plant
dioecious: staminate and pistillate flowers are on different plants
Fusion of parts
connotation: fusion of like parts (ex: all petals fused to form a tube)
adnation: fusion of different parts (ex: stamens fused to teh petals)
Level of insertion
hypogynous: sepals, petals, and stamens attached to the receptacle below the ovary; all three parts not fused to each other; two parts may be fused; ovary is said to be superior (ex: tulip)
perigynous: sepals, petals, and stamens attached to the receptacle below the ovary; basal portion of all three parts fused to form a floral cup (hypanthium) that surrounds, and is free from, the ovary; ovary is said to be superior
epigymous: floral cup fused to the ovary and becomes part of the ovary wall; sepals, petals, and stamens attached above the ovary; ovary is inferior
radial: flowers bisected into mirror image halves in numerous ways
- actinomorphic (regular) flower: displays radial symmetry
- bilateral symmetry: flower bisected into mirror image halves in one way
- - zygomorphic or irregular flower: displays bilateral symmetry
A seed consists of __, either embedded in a __ or else iself containing __, surrounded by the __ and other modified tissues of the sporophyte.
- a dormant embryo
- food-storage tissue
- a rich supply of stored food (orignially supplied by the parent sporophyte)
A seed is a device ideally suited to )) of the land and __ under hte climatic conditions existing over much of the earth today. Although not a seed plant, the __ exhibits some of the features that led to attainment of the seed habit in now extinct ancestors of modern seed plants.
spike moss Selaginella
True or False:
Selaginella is ancestral to t he seed plants.
Requirements for the seed habitat
endosporal development of gametophytes, especially the female
retention of the megaspore permanetly within the megasporangium
continued suply of food from the sporophyte to hte female gametophyte, rather than storage of the limited food supply within the megaspore
independence from water for fertilization
enclosure of the megasporangium within additional tissue fo the sporophyte to permit development of the seed coat
ability of hte embryo to remain dormant through one or more unfavorable growing periods
What aspects of seed habit do Selaginella meet?
endosporal development of hte gametophytes while the meiospores are within the sporangia
fertilization prior to the shedding of the megaspores (in some species)
early stages of embryo development within the megaspore wall while the spore is retained within the megasporangium (in some species)
Features lacking in Selaginella
a continuing supply of food from the sporophyte to the embryo until the latter is mature
a tissue enveloping the megasporangium that could provide for a seed coat
independence from water for fertilization
a dormant period, or at least such a capability, for the embryo
Describe the structure of a matured seed
Development of the Ovule (Cycle)
homospory--> heterospory with several mega and microspores in the sporangium--> megasporangium with one functional egaspore--> ovule (immature seed) with micropyle (before fertilziation), archegonium (each has an egg), female gametophyte surrounding, nucellus (megasporangium), and integuments (develop into seed coat; can be thick or thin)--> matured seed
Do flower plants fall under the ovule.
no; only gymnosperm
Development of the ovule in erms of fusion
integumentary lobe with an exposed megasporangium--> megasporagnium closed around; integumentary lobes are independent and only fused at the base--> becomes more fused until eventually it has a micropyle and integument