Plant Reproduction Flashcards
Diagram the ABC gene hypothesis in flower development.
If A gene is present we only get sepals, if A and b genes are present we get petals and sepals, if only B is present we get no sepals and petals only stamen, if b and c are present we get stamens and if all are present we get all 4
Explain how sperm travels to the egg in the four major plant phyla.
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Explain fruit development and how it relates to flower structure.
A fruit is the mature ovary (typically) of a flower. While the seeds are developing from ovules, the flower develops into a fruit The fruit protects the enclosed seeds and, when mature, aids in their dispersal by wind or animals. Fertilization triggers hormonal changes that cause the ovary to begin its transformation into a fruit. If a flower has not been pollinated, fruit typically does not develop, and the flower usually withers and falls away.
the ovary wall becomes the pericarp, the thickened wall of the fruit
Explain the purpose of seed dormancy
prevents seeds from germinating during unsuitable ecological conditions that would typically lead to a low probability of seedling survival
An important function of seed dormancy is delayed germination, which allows dispersal and prevents simultaneous germination of all seeds.
Seeds make it possible for embryos to survive in harsh conditions.
Sporogenesis
development of the mega/micro spores via meiosis
Gametogenesis
development of the gametes via mitosis
Antheridiogen
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pistil
A single carpel or a group of fused carpels.
anther
In an angiosperm, the terminal pollen sac of a stamen, where pollen grains containing sperm-producing male gametophytes form.
Thrum flower
Long stamens, short styles
Pin flower
Long styles, short stamens
Micropyle
Space between integuments
remains open until pollination can occur
Epicotyl
embryonic axis above the cotyledons
Hypocotyl
embryonic axis below the cotyledons
Radicle
embryonic root
Seed
An adaptation of some terrestrial plants consisting of an embryo packaged along with a store of food within a protective coat.
Simple fruit
derived from a single carpel or fused carpels (ie. Most frui
Aggregate fruit
from a single flower, with each carpel forming a fruit (ex. Raspberries)
Multiple fruit
develops from a cluster of flowers that fuse together (ex. Pineapples)
Accessory fruit
fruit formed from other floral parts that are not the carpels (ex. Apples and strawberries)
Dormancy
A condition typified by extremely low metabolic rate and a suspension of growth and development.
Imbibition
The physical adsorption of water onto the internal surfaces of structures.
What are the 3 Fs of Angiosperms?
Flowers, Double fertilization, fruits
What are flowers composed of?
Flowers are composed of 4 whorls of floral organs
Carpels -> megasporophylls composed of stigma, style, ovary(MEGASPORANGIA)
Stamens->microsporophylls composed of anthers(SPORANGIA), filaments
Petals -> showy, inner whorl
Sepals -> green (usually), outer whorl
Carpels
megasporophylls composed of stigma, style, ovary(MEGASPORANGIA)
The ovule-producing reproductive organ of a flower, consisting of the stigma, style, and ovary.
Stamens
microsporophylls composed of anthers(SPORANGIA), filaments
The pollen-producing reproductive organ of a flower, consisting of an anther and a filament.
Petals
showy, inner whorl
A modified leaf of a flowering plant
Petals are the often colourful parts of a flower that advertise it to insects and other pollinators
Sepals
green (usually), outer whorl
A modified leaf in angiosperms that helps enclose and protect a flower bud before it opens
receptacle
site of attachment of all whorls
incomplete flower
missing 1 or more whorls, includes unisex flowers
inflorescences
clusters of flowers (as opposed to a single flower)- wheat
Carpellate flower
female only(missing stamen),
staminate flower
male only
In what ways do flowers vary?
Vary in shape, size ,colour ,odour, whorl arrangements ,time of opening (ie flowering time)
Pollination
is the transfer of pollen to the part of a seed plant containing the ovules
In angiosperms, this transfer is from an anther to a stigma.
What do flowers aid in?
aid in pollination
What are different modes of pollination?
Wind pollinated flowers:
Animal/insect pollinated flowers
Wind pollinated flowers
Release lots of smaller pollen grains
Are the bane of anyone who has seasonal allergies
Animal/insect pollinated flowers:
Reward the pollinator with food (nectar)
Many animal pollinators are loyal to the flowers species
co-evolution
• Natural selection will increase selective pressure for floral traits that make it more prized to the pollinator (more likelihood for pollination
The animal pollinator will also evolve to be better able to get the prized nectar
Sporogenesis
development of the mega/micro spores via meiosis
Gametogenesis
development of the gametes via mitosis
Describe the male gametophyte development
within pollen grains
1) Contained within the anther is the microsporangium (2n)
2) Within the microsporangium (2n), microsporocytes (2n) undergo meiosis to produce microspores (n)
3) Each microspore (n) will undergo mitosis to develop into the pollen grain, containing the saprophytic exine (pollen wall) and the male gametophyte (n)
4) The male gametophyte contains the generative cell, which will undergo mitosis to produce 2 sperm during pollination, and
5) The tube cell will eventually produce the pollen tube for fertilization
What factors can affect the gametophytes function?
Climate change can affect the viability and fertility of the pollen grains
• High temperatures can induce apoptosis (programmed cell death) within the anthers
Describe the male gametophyte development
within pollen grains
1) Contained within the anther is the microsporangium (2n)
2) Within the microsporangium (2n), microsporocytes (2n) undergo meiosis to produce microspores (n)
3) Each microspore (n) will develop into the pollen grain, containing the saprophytic exine (pollen wall) and the male gametophyte (n)
4) The male gametophyte contains the generative cell, which will undergo mitosis to produce 2 sperm during pollination, and
5) The tube cell will eventually produce the pollen tube for fertilization
Describe the female gametophyte development
1) Carpels(megasporophylls) contain ovules which contain the megasporangium (2n)
2) The megasporangium contains the megasporocyte (2n), which undergoes meiosis to produce 1 surviving megaspore (n) (the other 3 degenerate)
3) Two integuments (2n) will develop and surround the ovule, eventually becoming the seed coat
• Space between integuments is the micropyle (remains open until pollination can occur)
4) The megaspore will undergo mitosis 3 times (without cytokinesis) to produce a 8 nuclei embryo sac (female gametophyte)
5) The plant hormone auxin will determine the fate of each cell in the female gametophyte
6) At the micropylar end, 1 egg cell and 2 synergids are formed
7) At the opposite end, 3 antipodal cells are formed (function unknown)
8) The last 2 nuclei become the polar nuclei, which will be used in endosperm production
the ovule which will become a seed if fertilized, and now contains the embryo sac enclosed within the megasporangium and the integuments
angiosperm life cycle
gametophyte development
Sperm Delivery by Pollen Tubes
Double Fertilization
Seed Development
Describe pollination
The microsporangium will break open, releasing the pollen grains onto the surface for dispersal
The pollen grain is carried to the stigma of the carpel, where it absorbs water and germinates its pollen tube (what cell does this
As the pollen tube elongates down the style, the generative cell divides by mitosis, producing the two sperm
The tube nucleus then carries the two sperm cells through the pollen tube to the female gametophyte (lead by chemicals secreted by synergids)
Indirect pollination
pollen does not land directly on the ovule
direct pollination
lands directly- gymnosperms
microspore
A spore from a heterosporous plant species that develops into a male gametophyte.
pollen grain
In seed plants, a structure consisting of the male gametophyte enclosed within a pollen wall
embryo sac
The female gametophyte of angiosperms, formed from the growth and division of the megaspore into a multicellular structure that typically has eight haploid nuclei
megaspore
A spore from a heterosporous plant species that develops into a female gametophyte
pollen tube
A tube that forms after germination of the pollen grain and that functions in the delivery of sperm to the ovule.
endosperm
In angiosperms, a nutrient-rich tissue formed by the union of a sperm with two polar nuclei during double fertilization. The endosperm provides nourishment to the developing embryo in angiosperm seeds.
Basal cell
produces a thread of cells called the suspensor, which anchors the embryo to the parent plant and transfers nutrients
Cotyledons
“first leaves”)
How many Cotyledons do mono and eudicots have?
Monocots have 1
Eudicots have 2 that’s why its called dicot
fruit
is the mature ovary (typically) of a flower
Fruits contain the seeds and are the result of the ovary swelling
• Ie.Ovules->seeds, flowers->fruits
integuments
(layers of protective sporophytic tissue that will develop into the seed coat
Describe double fertilization
Fertilization occurs when one of the sperm cells fuses with the egg cell
The second sperm continues past the egg cell into the central cell where it combines with the 2 polar nuclei, forming a 3n endosperm
This ensures that only fertilized ovules have a food supply for the developing embryo.
What happens after double fertilization?
After double fertilization, each ovule develops into a seed. Meanwhile, the ovary (typically) develops into a fruit, which encloses the seeds and aids in their dispersal by wind or animals
Describe endosperm development
Endosperm usually develops before the embryo does
After double fertilization triploid(3n)nucleus divides by mitosis into a super cell that has a milky consistency (think coconut “milk”)
After cytokinesis partitions the nuclei, the endosperm becomes solid (think coconut “meat”)
Why is the endosperm important to us?
Endosperm is an important food source (popcorn, rice, wheat
How is the endosperm used in different plants?
In grains and most other species of monocots, as well as many eudicots, the endosperm stores nutrients that can be used by the seedling after germination. In other eudicot seeds, the food reserves of the endosperm are completely exported to the cotyledons before the seed completes its development; consequently, the mature seed lacks endosperm.
Describe the Development of the embryo
The first mitotic division of the zygote splits the fertilized egg
• Terminal cell -> becomes the embryo
• Basal cell -> produces a thread of cells called the suspensor, which anchors the embryo to the parent plant and transfers nutrients
The terminal cell divides many times and forms the embryo attached to the suspensor
Cotyledons(“first leaves”)begin forming
between the cotyledons are the shoot apex and root apex, which are meristems that will produce the shoots and roots after germination
suspensor
which anchors the embryo to the parent plant. The suspensor helps in transferring nutrients to the embryo from the parent plant and, in some species of plants, from the endosperm.
What is the last stage of seed development?
The last stage of seed development is dehydration
What happens during the last stage of seed development?
Water content will reduce to 5-15% seed weight
The seed enters dormancy, where it stops growing and metabolism halt
What does it contain during the last stage of seed development?
At this stage, the seed contains
The embryo with its cotyledons and endosperm
Hypocotyl -> embryonic axis below the cotyledons
Radicle->embryonic root
Epicotyl -> embryonic axis above the cotyledons
the embryo and its food supply are enclosed by a hard, protective seed coat formed from the integuments of the ovule. In some species, dormancy is imposed by the presence of an intact seed coat rather than by the embryo itself.
seed coat
A tough outer covering of a seed, formed from the outer coat of an ovule. In a flowering plant, the seed coat encloses and protects the embryo and endosperm.
What do monocots have during the last stage?
Monocot seeds have only 1 cotyledon but also have
Coleoptile -> protective sheath surrounding the shoot
Coleorhiza -> protective sheath surrounding the root
When do seeds germinate?
Germination occurs when water is taken up into the seed (imbibition) due to the low water potential of the dry seed
Causes rapid swelling of the seed, rupturing the seed coat and triggering metabolism
Endosperm is digested and transferred to the growing embryo (seed with low concentration soil with high water will go into seed)
Root always forms first
Describe asexual reproduction in plants
In asexual reproduction, offspring are derived from the parent plant without fusion of an egg + sperm Fragmentation->pieces can regenerate into a whole plant Adventitious plantlets (ex Kalanchoe, “Mother of Thousands”, spider plants) (genetically identical to parent plant) root is coming from something not a root Splitting of the root mass/ball (can do this with shrubs, Aspens) Apomixis->development of seeds without fertilization (ex dandelions.....cloning with dispersal!)
Apomixis
development of seeds without fertilization (ex dandelions…..cloning with dispersal!)
Advantages for asexual reproduction
Don’t need a pollinator
Passes on all its genes to its offspring
Vegetative reproduction
• Food sources from the parent, so more rapid growth compared to sexually formed embryo
Disadvantages of asexual reproduction
No genetic variation
Not as long-distant dispersal
No seed dormancy
Describe mechanisms how self-fertilization can be prevented in plants.
Plants can be dioecious(i.e.unisexual) with either staminate flowers (male) or carpellate flowers (female) (gymnosperms are monoecious)
Differences in maturation time between stamens and carpels on the same flower
Self-incompatibility->rejects its own pollen
Flower structure and arrangement of stamens and carpels
What is selfing?
allows for sexual reproduction in plants where pollinators may be scare
Risk having weaker (less fit) offspring
Desirable in crop plants though since each ovule can be fertilized to produce a seed
What is the cause of Self-incompatibility?
cased on S-genes -> if the specific allelic combination of S alleles in the pollen match the S alleles of the stigma, it is rejected
Describe the mechanisms of seed dispersal in gymnosperms and angiosperms.
a. Explain the benefit of seed dispersal.
in gymnosperms, seeds are on ovulate cones as a result of direct fertilization
• Dispersal is likely by wind (bracts helicopter away from parent tree once cone opens)
In angiosperms, seeds are within fruits as a result of indirect fertilization
• Dispersal is due to a variety of means Animals -> dogs with burrs, eating and digestion by animals
Wind -> winged seeds of maple seeds, dandelion seeds, tumbleweeds
Water -> coconut and other buoyant seeds
Compare pollination between gymnosperms and angiosperms.
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