Handout 9-Reproduction of Flowering Plants
intra-species
the flower recognize its own pollen
What is the male gametophyte in a flower?
The pollen grain which consists of the generative (divides by mitosis to form 2 sperm cells) and tube cells (becomes the pollen tube)
In angiosperms, which generation is the dominant one?
The sporophyte generation; it is larger and more independent of the gametophyte generation, whereas the gametophyte generation is smaller and more dependent on the sporophyte generation
What does the sexual life cycles always involve?
meiosis and fertilization
What are the two products of double fertilization?
zygote and endosperm
Are the zygote, endosperm, petal, pollen, embryo sac, ovary wall haploid, diploid, or triploid?
zygote: diploid endosperm: triploid petal: ? pollen: haploid embryo sac: haploid ovary wall: ?
What are some examples of flower adaptations to attract specific pollinators? What's the adaptive advantage of doing that?
"pollination syndromes" -difference in flower colors attract different pollinators (bee: yellow or blue; bats: white) -nectar: rewards pollinators so promoting the relationship between the plant and its pollinator -The ability of the flowers to develop specific structures that target a specific pollinator and the ability of the pollinator to develop a keen sense of detection of the flower help increase the flowers reproduction success -Ex: of specific adaptation: yucca plant is pollinated by a specific species of moth which pack pollen in its appendages, so the moth deposits eggs directly into the ovary, the larvae eat some developing seeds, but the benefit of having an efficient and reliable pollinator outweigh the out, unless the moth deposits too many eggs, ANOTHER EX: fly-pollinated flowers ar reddish and fleshy and emit odor like rotten meat, the flies mistaken the flower for a rotting corpse and lay their eggs, in the process is pollinate the flowers.
In the history of evolution of life on earth, flowering plants evolved a great diversity at the same time that insects evolved great diversity. Explain the coincidence.
(beneficial relationship): coevolution; evolution of two interacting species each in response to selection imposed by the other, Ex: some species have flower petals fused together, forming long, tube-like structures bearing nectaries tucked deep inside, this would favor long-tongued rivals, so the pollinating moth would also have long proboscis (straw-like mouthpart) to get the nectar; any special structures that would enhance the flower-pollinator mutualism would work
evolutionary advantage of avoiding self-pollination
-Different individuals have different staminate flowers (lacking carpels) or carpellate flowers (lacking stamens) -flowers with functional stamens and carpels that mature at different times or structurally arranged in a way that it's unlikely that an animal pollinator could transfer pollen from an anther to a stigma of the same flower -self-incompatibility: the ability of a plant to reject its own pollen
What kind of barriers against self-fertilization do plants have?
-Variation if the shape of the flowers (staminate flowers (lacking carpels) or carpellate flowers (lacking stamens)); this prevents pollination -the carpel and stamen mature at different time, plants have marker genes that recognize that the pollen is produced by itself, and so it can reject the pollen by inhibiting the further formation of the pollen tube
Compare the evolutionary advantages of sexual and asexual reproduction.
Advantage of asexual reproduction: no need for a pollinator, allows plant to pass on all of its genetic legacy, whereas sexual reproduction: plant passes on only half of its alleles, progeny from asexual reproduction are stronger than sexual reproduction, (vegetative reproduction) -Contrast, seed germination if a tough stage, consume lots of energy, sexual reproduction generates genetic variation, seeds (mostly sexual) can be distributed far away
Give two examples of asexual (vegetative) reproduction in plants.
Aspen trees: each trees derives from the root system of one parent -> adventitious shoots that become separate shoot systems -dandelions: produce seeds without fertilization (apomixis)
What is involved in double fertilization, and what are the two products of double fertilization?
Double fertilization: The union of two sperm cells with different nuclei of the female gametophyte; So what happens? -pollen grain->lands on stigma->absorbs water and germinates by producing pollen tube->grows toward the ovary->nucleus of generative cell divides by mitosis and forms two sperms->discharged from the tube ->one sperm fertilizes the egg and form the zygote and other sperm combines with the two polar nuclei to form a triploid: endosperm -Double fertilization ensures that endosperm develops only in ovules where the egg has been fertilized, thereby preventing angiosperms from squandering nutrients on infertile ovules
What are some examples of flower adaptations to attract specific pollinators? What's the adaptive advantage of doing that?
Ex: Bee-pollinated flowers have a delicate, sweet fragrance; bees are attracted to bright colors, primarily yellow and blue; red appears dull; bees can see UV radiation; so dandelion have UV markings to guides the bees to the nectaries Pollination by moths and butterflies: they detect odors, so the flowers they pollinate are often sweetly fragrant; moths perceive white or yellow better; (more on pg. 805)
Double fertilization, which is a hallmark of angiosperm sexual reproduction, results in two diploid cells.
False; one cell---the zygote---is diploid and the other cell, which will develop into the nutritive endosperm of the see, is triploid
What's the difference between pollination and fertilization?
Pollination is the transfer of pollen grains from an anther to the stigma while fertilization is fusion of the sperm and egg to form a zygote and sperm and two polar nuclei to form an endosperm
Identify each of the following and its function: flower, petal, sepal, carpel, anther (on stamen)
Flower: reproductive shoots of angiosperm sporophytes; Petal: brightly colored "leafy like;" advertise the flower to insects and other pollinators Sepal: leafy in appearance; enclose and protect unopened floral buds Carpels: consist of stigma, style, and ovary *pistil; area where pollination and fertilization occur anther: terminal end of stamen; contains the microsporangia (pollen sacs) (produce pollins)
Sexual reproduction in plants
Flowers: reproductive shoots of angiosperm sporophytes Stamens and carpels are reproductive organs, Male reproductive part: stamen: filament and anther; anther contains microsporangia (pollen sacs) that produce pollen; Female reproductive part: carpel: ovary(ovules), style, and stigma, -complete flowers: sepals, petals, stamens, or carpels -found in most angiosperms, fusion of gametes
What is the male gametophyte (multicellular haploid structure) in a flower?
It is the pollen grain, not the sperm; anther: contains microsporangia which produces microspores through meiosis and each under goes mitosis to produce a male gametophyte: consists of generative cell and tube cell;
Monocots vs. Dicots flower
Monocots: flower part in 3's and dicots: flower part in 4's or 5's ( or multiples)
Which of these structures is not a part of the sporophyte generation: flower, pollen grain, anther, and leaf
Pollen grain is not a part of the sporophyte generation . Instead, it represents the male gametophyte generation
What is the difference between pollen grain and a sperm nucleus?
Pollen grain is the male gametophyte, it's involved in pollination only, the sperm nuclei are produced by the cell division of the generative cell and involve in the process of fertilization
Microspores and megaspores are form by meiosis and they undergo mitosis to produce the gametophytes
Sporophyte: microsporocyte (male) and megasporocyte (female) which undergo meiosis to produce 4 microspores (n) and 4 megaspores (n), respectively; these haploids undergo mitosis to produce the gametophyte: pollen grain (male) and embryo sac (female)
What is a pollen grain?
The generative and tube cells and spore wall constitute the pollen grain; may be transferred to a receptive surface of a stigma; produces a pollen tube that delivers sperms to ovary
What is the function of fruit?
aids in their dispersal of the seed by animals
Microspores and megaspores undergo which type of division?
mitotic; the haploid microspores and megaspores undergo mitosis to produce the male and female gametophytes
Write out a general, simple life cycle (diploid-meiosis-haploid-fertilization-diploid). In what organs do meiosis and fertilization occur in a flowering plant?
alternation of generation: diploid plant (sporophyte) produces haploid spores by meiosis->these spores divide by mitosis which leads to multicellular gametophytes (male and female haploid plants that produce gametes->fertilization: fusion of gametes which results in diploid zygotes which divides by mitosis to form new sporophytes (in angiosperms, the sporophytes is the dominant generations) Organs for meiosis: stamens Organs fertilization: carpels
asexual reproduction in plants
budding, fragmentation, cutting, grafting, and runners
What is the female gametophyte?
embryo sac
inter-species
flower and pollinators
How inter-species interactions are important for plant reproduction
flowers and their pollinators; important for pollination and fertilization of the plants part, produce genetic variability offsprings
The fruit develops from what flower part?
fruits develop from the ovaries of flowers
Give two examples of asexual (vegetive) reproduction in plants
growth by mitosis: runners (strawberry patches), root spreading (ex: aspen trees), budding or fragmentation (pieces of potato with the vegetative bud)
In the history of evolution of life on earth, flowering plants evolved a great diversity at the same time that insects evolved great diversity. Explain the coincidence
natural selection
Does the fruit nourishes the embryo?
no
When a pollen grain nucleus fertilizes an egg nucleus for the same individual plant (=self pollination), is that the same as asexual reproduction? Why or Why not?
no, it's sexual reproduction because meiosis had occurred
Adaptive advantages of out-crossing (creation of barriers against self-fertilization)
promotes genetic variability
What's the disadvantage of seed dispersal?
required energy from the maternal plants
Which of the following is the correct sequence during the alternation of generation life cycle in a flowering plant?
sporophyte-> meiosis -> gametophyte -> gametes -> fertilization -> diploid zygote
What is fragmentation?
the separation of a parent plant into parts that develop into whole plants; most common mode of asexual reproduction, (ex: aspen tree)
What's the benefit of seed dispersal?
to reduce competition with parents and siblings, reduce seed predators
Discuss two strategies (one structural adaptation and one biochemical adaption) used by plants to deter herbivores. Describe plant strategies to defend against pathogens
trichomes, cactus spine, thorns, Biochemical: cyanide,