Post on 08-Feb-2022
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Plant Reproduction
Prepared by Diana Wheat
For LBCC – General Biology 103
Revised Spring 2011
Objectives
� To define the alternation of generations.
� To explain how pollination leads to fertilization.
� To address double fertilization.
� Introduce anatomy of a flower
� Relate fruits & seeds to flower.
� Classify different fruit types.
� Address seed dispersal
Now onto plants
Alternation of generations
The life cycle typically found in
plants in which the spore producing generation alternates with the
gamete producing generation.
Plants have 2 forms…….
The different forms
Gametophyte: The multicellular, haploid stage in the life cycle of
plants.
Sporophyte: The diploid form of a
plant that produces , haploid, asexual spores through the process
of meiosis – reduction division.
Flower are modified structures
Innovations for reproduction.
Flower Anatomy
� Sepals, which enclose
the flower
� Petals, which are brightly colored and
attract pollinators
� Stamens, which
produce pollen
� Carpels, which produce ovules
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The Angiosperm Life Cycle
In the angiosperm life cycle
� Double fertilization occurs when a pollen tube discharges two sperm into the female gametophyte within an ovule
� One sperm fertilizes the egg, while the other combines with two nuclei in the center cell of the female gametophyte and initiates
development of food-storing endosperm
The endosperm
� Nourishes the developing embryo
The Participants
Pollen: Male gametophyte of seed plants.
Ovule: Female gametophyte of seed plants.
The ProductsThe Products
Seed Seed –– From the ovuleFrom the ovule
Seed Coat Seed Coat ––
From the Ovule WallFrom the Ovule Wall
Fruit Fruit –– From the OvaryFrom the Ovary
Life Cycle: Eudicot
Pollen sacs form in the mature sporophyte.
pollen sac anther (cutaway view)
filament
meiosisDiploid Stage
Fig. 30-8 (a-d), p. 512
Stepped Art
Haploid Stage
A pollen grain released from the anther lands on a stigma and germinates.
pollen tube
stigmaMature Male Gametophyte
carpelsperm cells (male gametes)
Double fertilization Double fertilization results from the results from the discharge of two sperm from the discharge of two sperm from the pollen tube into the embryo sacpollen tube into the embryo sac
One sperm One sperm �� the the eggegg
The other combines with the polar The other combines with the polar nuclei in ovule foodnuclei in ovule food--storing storing …………………………….…………………………….endosperm.endosperm.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Fig. 30-8 (e-i), p. 513
an ovuleovary wall
cell inside ovule tissueSporophyte
seedling (2n)
seed coatembryo (2n)
In a flower of a mature sporophyte, an ovule forms inside
an ovary. One of the cells in the ovule enlarges.
ovary (cutaway view)
Diploid Stagedouble fertilization meiosis
Haploid Stage
pollen tube
Female Gametophyte
endosperm mother cell (n + n)
egg (n)
The pollen tube grows down through stigma, style, and ovary tissues, then penetrates the ovule and releases two sperm nuclei.
endosperm (3n)
Flower Sex
� Recognition proteins on epidermal cells of the stigma bind to molecules in the pollen grain coat
� Species-specific molecular signals from the stigma stimulate pollen germination and guide pollen-tube growth to the egg
Life Cycle: EudicotType of flowers
Regular vs. Irregular - Symmetry
Complete vs. Incomplete - # whorls
Perfect vs. Imperfect – if both M & F
Inflorescence - Clusters
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Now let’s revise our model
1) How does the pollen take the sperm to the egg?
2) Where is the seed?
3) What part will become the fruit?
Pollination
The transfer of pollen from anther to stigma.
Cross pollination (dioecious plants)vs. Self pollination (monecious).
For discussion:Advantages?Disadvantages?
Why use animals as
agents of pollination?
Answer:
� There is a high degree of pollinator
specificity.
Plants attract animals using a variety of adaptations including:
> Color
> Scent
> Heat
> Rewards (pollen & nectar) The goods!
Special Features
Thermogenic – in cold climates
Nectar guides – UV reflected “runways.”
Landing platforms – umbels or large petals
Unusual shapes – usually in the tropics
Pheromones – sex attractant mimics
What a bee can see……
Fruit adaptations help disperse seeds
Seeds can be carried by:
> wind
> water
> animals
…………..to new locations
Adaptations for Fruit Dispersal
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Fruits
� Consists of a mature ovary but can also include other flower parts
� Fruits protect seeds and aid in their dispersal
� Mature fruits can be either:
I. Fleshy - eg: grapes, apricots,apples
II. Dry – eg: beans, grains, nuts
Simple Fruits
� Develops from a single carpel.
OR
� May develop from several fused carpels.
� Derived from one flower.
� Examples: Pea, lemon, beans, peanut.
Aggregate Fruit
� Develops from many separate carpels.
� From one flower.
� Examples:
- raspberry
- blackberry
- strawberry
Multiple Fruits
� Develops from many carpels.
� Many flowers i.e. an inflorescence.
� Examples:
� Pineapple.
� Fig
Accessory Fruit
� Develops from tissues other than the ovary.
� May be embedded
in the fleshy receptacle.
� Examples:
- Apple (only core develops from ovary).