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Ch.9 Flowers and reproduction (Flower structure and cross-pollination…
Ch.9 Flowers and reproduction
Asexual Reproduction
Fragmentation
one of the most common forms of asexual reproduction
A plant spreads vines, and individual part become self- sufficient
if middle portions die, the outside portions act as individuals
Sexual reproduction
in angiosperms, involves flowers
flower house the necessary cells
The plant life cycle
Sporophyte phase/generation
Trees, shrubs, herbs
Sporophytes are always diploid
Contain cells capable of meiosis
Produces haploid spores
Undergo mitosis and form a haploid gametophyte
A plant that produces gametes
Gametes
Sperm
Zygote
forms a new individual
Microgametes
Eggs
Megagametes
Produced by meiosis
oogamous plants
have seperate individuals to produce male and female gametes
Male
microgametophyte
form microspores
Female
Megagametophyte
form megaspores
Heterospory: having 2 types of spores
Alteration of generations
a life cycle with two generations
Heteromorphic generations
Gametophytes do not resemble sporophytes
Flower structure
Flower
Basically a stem with leaf-like structures
Never become woody
No secondary growth
Pedicel
Flower stalk
Receptacle
The very end of the axis where the other flower parts are attached
Floral appendages
Complete flowers
Have all 4 types
Sepals
Lowermost and outermost appendages
Modified leaves
Surround and enclose other flower parts as they mature
Typically the thickest, toughest, and waxiest
All sepals together= calyx
Petals
Above sepals on the receptacle
Make up the corolla
Sepals+petals=perianth
Leaflike, broad, flat, and thin
Contain pigments other than chlorophyll
Attract the correct pollinators
Have specific size, shape, and colors
Stamens
Above the petals
Collectively form the androecium
Referred to as the "male" parts of the flower
Produce pollen, but not gametes
Have two parts
Filament
stalk
Anther
where pollen is produces
Composed of diploid cells
Carpels
Constitute the gynoecium
Located at the highest level on the receptacle
Three parts
Stigma
Cathches pollen grains
style
Elevates the stigma to a useful position
ovary
where megaspores are produced
Contains placentae
bears ovules
carries water and nutrients from the placenta to the ovule via a funiculus
Contains a nucellus
1 more item...
Develop into seeds after its egg is fertilized
Gametophytes
Microgametophyte
Male
Microspores develop into microgametophytes
Microspore nucleus
migrates to the side of the pollen grain next to the wall
Divides mitotically
Produces
A large vegetative cell
A small, lens-shaped, generative cell
1 more item...
Pollen grain
lands on a stigma
germinates by producing a pollen tube
penetrates the loose open tissues of the stigma
will grow down towards the ovary
Carries sperm cells to the ovule
Megagametophyte
Embryo sac
a multinucleate megagametophyte
One large central cell
with two polar nuclei
Three small antipodal cells
Egg apparatus
Two synergids
Egg
Fertilization
Plasmogamy
Fusion of the protoplast of the gametes
Karyogamy
Fusion of the nuclei
Double fertilization
Both sperm nuclei undergo fusions
Embryo and seed development
Suspensor
Formed by the zygote growing into a small cluster of cells
Pushes the embryo deep into the endosperm
Cells at one end will divide mitotically
Forming an embryo
The end of the embryo farther from the suspensor
initiates two primordia
grow into two cotyledons
Heart stage
Torpedo stage
A short axis is established with a
radicle
embryonic root
epicotyl
embryonic stem
hypocotyl
root/shoot junction
Seeds
Albuminous
a mature seed in which endosperm is abundant
Exalbuminous
Endosperm is sparse or absent at maturity
Fruit development
Formed from a maturing ovary
Three layers become distinct during growth
Exocarp
Outer layer
Skin or peel
Mesocarp
Flesh/middle layer
Endocarp
Innermost layer
May be thin
May be thick and tough
E.g. cherry pit
Pericarp
entire fruit wall
May contain all three layers, or one or two may be absent
Flower structure and cross-pollination
Cross pollination
Pollination of a carpel by pollen from a different individual
Results in increased genetic diversity
Self pollination
Pollination of a carpel by pollen from the same flower or plant
Compatibility barriers
Chemical reactions between pollen and carpels that prevent pollen growth
Inhibits self pollination
Essential organs
Stamens and carpels
produce critically important spores
if either is absent, sexual reproduction is dramatically affected
These are called incomplete/imperfect flowers
Perfect flower
contains both
Nonessential organs
sepals and petals
do not produce spores
Dioecy/ Dioecios plants
These species have individuals that produce ONLY either staminate or carpellate flowers
Life cycle consists of 4 types of plants
1) microgametophytyes
2) megagametophytes
3) staminate sporophytes
4) carpellate sporophytes
Ensures cross pollination
Monoecy/ monoecious plants
have staminate and carpellate flowers on the same plant
Animal-Pollinated flowers
resulted in mutations for pigments, secretions, and fragrances
Increases probability of pollination as compared to wind
Coevolution
Plants/insects become adapted to better suit each other
E.g flower shape
Radially symmetrical
bilaterally symmetrical
Wind pollinated flowers
No need to attract pollinators
Saves energy to be used elsewhere
grow and dense populations in range lands or forests
Inflorescences and Pollination
Inflorescence
many flowers grouped together
Gives a collective visual signal to pollinators
Two basic arrangements
determinate inflorescence
has only a limited potential for growth
because the apex is converted to a flower
Indeterminate inflorescence
new flowers continue to initiate from the apex
Fruit types and seed dispersal
True fruits and accessory fruits
True fruit
Contains only ovarian tissue
Accessory fruit
Contains any type of non-ovarian tissue
Simple fruit
Develops from a single ovary, or the fused ovaries of one flower
Classification of fruit types
Dry fruit
Not typically eaten by normal seed-dispersing animals
Further classification
Dehiscent
break open to release the seeds
Indehiscent
have to be mechanically broken open
Fleshy fruit
are eaten during the natural seed distribution process
