Ch. 30 Plant Diversity: Seed Plant Evolution
a) an immature gametophyte b) from a microsporangia then through meiosis produce microspores which form pollen c) to disperse onto a female gametophyts anf ultimately to fertilize eggs by either wind, animal, or water dispersal d) they arent dependent on water for fertilization so they can live on dry environment. They also promote genetic variation & outcrossing with its shape.
(a) What is a pollen grain? (b) How does it form? (c) What is its function, and how does it accomplish this function? (d) In an evolutionary context, why was pollen an im portant step in allowing seed plants to become the dominant plants?
One sperm is needed to fertilize the egg and a second sperm is needed to fertilize the polar nuclei.
Double fertilization means...
Reduced gametophytes
Microscopic male and female gametophytes (n) are nourished and protected by the sporophyte (2n)
fertilized ovule in a gymnosperm
A megaspore develops into a female gametophyte, which produces an egg. The pollen grain, which had entered through the micropyle, contains a male gametophyte. The male gametophyte develops a pollen tube that discharges sperm, thereby fertilizing the egg.
Mature ovary
A fruit is usually a...
A mature ovary
A fruit is...
megasporangium
A plant structure in which megaspores are formed, such as those of the female cones of pines.
megaspore
A spore from a heterosporous plant species that develops into a female gametophyte.
Pine cones and flowers both have sporophylls, modified leaves that produce spores. Pine trees have separate pollen cones (with pollen grains) and ovulate cones (with ovules inside cone scalеs). In flowers, pollen grains are produced by the anthers of stamens, and ovules are within the ovaries of carpels. Unlike pine cones, many flowers produce both pollen and ovules.
Compare and contrast a pine cone and a flower in terms of structure and function.
To reach the eggs, the flagellated sperm of seedless plants plants must swim through a film of water, usually over a distance of no more than a few centimeters. In contrast, the sperm of seed plants do not require water because they are produced within pollen grains that can be transported long distances by wind or by animal pollinators. Although flagellated in some species, the sperm of seed plants do not require mobility because pollen tubes convey them from the point at which the pollen grain is deposited (near the ovules) directly to the eggs.
Contrast how sperm reach the eggs of seedless plants with how sperm reach the eggs of seed plants.
In a gymnosperm seed, fertilization initiates the transformation of the ovule into a seed, which consists of a sporophyte embryo, a food supply, and a protective seed coat derived from the integument.
Describe the embryo, food source, and seed coat of a seed plant.
In angiosperms, pollination is the transfer of pollen from an anther to a stigma. Fertilization is the fusion of the egg and sperm to form the zygote; it cannot occur until after the growth of the pollen tube from the pollen grain.
Distinguish between pollination and fertilization.
The pine life cycle illustrates heterospory, as ovulate cones produce megaspores and pollen cones produce microspores. The reduced gametophytes are evident in the form of the microscopic pollen grains that develop from microspores and the female gametophyte that develops from the megaspore. The egg is shown developing within an ovule, and a pollen tube is shown conveying the sperm.
Explain how the pine life cycle in Figure 30.4 reflects the five adaptations common to all seed plants.
Unfertilized ovule in a gymnosperm
Fleshy megasporangium is surrounded by a protective layer of tissue called an integument. The micropyle, the only opening through the integument, allows entry of a pollen grain.
C. Ovaries
Gymnosperms and angiosperms have the following in common except A. Seeds B. Pollen C. Ovaries D. Ovules
Ovules and seems are within the flower ovary Ovule has a double integument Embryo has specialized food supply (3n)
How has flowering plants increased its protection for ovule and embryo?
3: seed coat, food supply, and embryo
How many generations are contained within a single seed?
Long styles help to weed out pollen grains that are genetically inferior and not capable of successfully growing long pollen tubes.
If flowers had shorter styles, pollen tubes would more easily reach the embryo sac. Suggest an explanation for why very long styles have evolved in most flowering plants.
Anther
Male part of the flower where sperm (pollen) are produced by meiosis
Stamen
Male part of the flower; made up of an anther and a filament.
water, wind, animals, launch
Seed dispersal methods
endosporic development
Spores are not released
Ovules
Structure that develops within ovary of seed plant and contains female gametophyte. Located in the ovary. The ovule contains an egg which developes into a seed after it is fertilized.
both an aggregate fruit and an accessory fruit.
The black dots that cover strawberries are actually fruits formed from the separate carpels of a single flower. The fleshy and tasty portion of a strawberry derives from the receptacle of a flower with many separate carpels. Therefore, a strawberry is...
Carpels
The female reproductive organ of a flower, consisting of the stigma, style, and ovary.
pollen grains
The structures that contain the immature male gametophytes.
Spores are usually single-celled, whereas seeds are multicellular, consisting of an embryo protected by a layer of tissue, the seed coat. A seed can remain dormant for years after being released from the parent plant, whereas most spores have shorter lifetimes. Unlike spores, seeds have a supply of stored food.
What advantages do seeds provide over spores?
megasporangium- structure containing megaspores Megaspore- reproductive cells that will develop into a female gametophyte Megagametophytes- female gametophyte
What are pine megasporangium, megaspores, and megagametophytes?
Microsporangia-structure containing microspores Microspores-reproductive cells that will develop into a male gametophyte Microgametophytes- pollen grain when immature or a male gametophyte
What are pine microsporangia, microspores, and microgametophytes?
Signal & reward Animals (convolution and mutualism with pollinators) Wind and water
What are some seed dispersal methods of flowering plants?
Sporangia develops inside flowers (highly modified structures) Carpels and fruits Double fertilization & triploid endosperm as nutrition for embryo Sophisticated vascular tissues (xylem & phloem) Loss of swimming sperm (no flagella) Increased protection of ovules (double integument)
What are some shared, derived traits of flowing plants?
Heterospory Reduced gametophytes Pollen & pollination Ovules Seeds
What are some shared, derived traits of seed plants?
1) Seed coat (from integument) 2) Nutrient source (megagametophyte tissue) 3) Embryo (new sporophyte)
What are the 3 parts of a pine seed?
In heterospory the large megaspore which contains female gametophyte derives it's food from the sporophyte, and is independent of the external conditions as it might interfere with the growth of a free living gametophyte. Reduces self-fertilization allowing more outcrossing Megaspore can grow to a size that better supports new embryo Increased protection and increased nutrition of offspring
What are the advantages of heterospory over homospory?
The tiny gametophytes can develop from spores retained within the sporangia of the prenatal sporophyte-this allows protection of the gametophyte from environmental stresses. It also enables the developing gametophyte to obtain nutrients from the prenatal sporophyte.
What are the advantages of microscopic, dependent gametophytes?
It protects the egg and provides food for the embryo.
What are the advantages of ovules?
Protects the gametophyte Easily dispersed with wind, animals, and people Is not depended on water for reproduction so it can live in dry habitats Sperm don't require motility because they are carried to the eggs by pollen tubes
What are the advantages of pollen?
Megagametophyte consists of only 7 cells There is no archegonium The microgameophyte develops in only 2 mitotic events
What are the trends of reduction in size and in complexity of flowing plants?
Seeds
What do ovules develop into?
The reduced gametophytes of seed plants are nurtured by sporophytes and protected stress, such as drought conditions and UV radiation. Pollen grains, with walls containing sporopollenin, provide protection during transport by wind or animals. Seeds have one or two layers of protective tissue, the seed coat, that improve survival by providing more protection from environmental stresses than do the walls of spores. Seeds also contain a stored supply of food, which provides nourishment for growth after dormancy is broken and the embryo emerges as a seedling.
What features not present in seedless plants have contributed to the success of seed plants on land?
1) in most conifer species, each tree has both ovulate and pollen cones 2) microsporocytes divide by meiosis, producing haploid microspores. A microspore develops into a pollen grain (a male gametophyte enclosed within the pollen wall) 3) an ovulate come scale has 2 ovules, each containing a megasporangium. 4) pollination occurs when a pollen grain reaches the ovule. The pollen grain then germinates, forming a pollen tube that slowly digests it's way through the megasporangium 5) while the pollen tube develops, the megasporocyte undergoes meiosis, producing 4 haploid cells. 1 survives as a megaspore 6) the megaspore develops into a female gametophyte that contains 2 or 3 archegonia, each of which will form an egg 7) by the time the eggs are mature, sperm cells have developed in the pollen tube, which extends to the female gametophyte. Fertilization occurs when sperm and egg nuclei unite 8) fertilization usually occurs more than a year after pollination. All eggs may be fertilized, but usually only 1 zygote develops into an embryo. The ovule becomes a seed, consisting of an ámbito, food supply, and seed coat.
What is the Pinus life cycle in 8 steps?
Gymnosperms bear naked seeds on modified leaves (sporophyll), typically in cones(strobili) while angiosperms seeds are enclosed in chambers of flowers that mature into fruits.
What is the difference between gymnosperms and angiosperms?
Double fertilization synchronizes the development of food storage in the seed with the development of the embryo. It's an adaption that prevents flowering plants from wasting nutrients on infertile ovules
What is the function of double fertilization in angiosperms and in what way is it advantageous?
1) in the megasporangium of each ovule, the megasporophyte divides by meiosis, producing 4 megaspores. 1 survives and gives rise to a female gametophyte 2) on the anther, each microsporangia contains microsporocytes that divide by meiosis, producing microspores 3) a microspores develops into a pollen grain. The generative cell of the gametophyte will divide, forming 2 sperm. The tube cell will produce the pollen tube 4) after pollination, eventually 2 sperm cells are discharged in each ovule 5) double fertilization occurs. 1 sperm fertilizes the egg, forming a zygote. The other sperm fertilizes the central cell, forming the endosperm (food supply, 3n) 6) the zygote develops into an embryo that is packaged along with food into a seed 7) when a seed germinates, the embryo develops into a mature sporophyte
What is the life cycle of a flowering plant in 7 steps?
megagametophyte: Only 1 megaspore mother cell develops on each megasporangium Megagametophyte is microscopic and dependent Few archegonia develop Microgametophyte: The micogamtophye is just a few cells No antheridium Only 1 functional sperm
What is the trend in reduction in size and in complexity of gymnosperms?
Within the integument within an ovule contained within an ovary of a flower
Where in an angiosperm would you find a megasporangium?
D. Alternation of generations
Which of the following is not a characteristic that distinguishes gymnosperms and angiosperms from other plants? A. Dependent gametophytes B. Ovules C. Pollen D. Alternation of generations
C. Microspore-n
With respect to angiosperms, which of the followinf is incorrectly paired with its chromosome count? A. Egg-n B. Megaspore-2n C. Microspore-n D. Zygote-2b
strobilus
a cluster of modified leaves with sporangia
integument
covering that protects the ovules inside the ovary of a female plant
Seeds
fertilized ovules; structures that contain a young plant inside a protective covering
sporophylls
modified leaves that bear sporangia
triploid endosperm
nourishes the developing embryo
