BIS 2C Lecture Notes - Lecture 21: Pollen Tube, Sporangium, Sporophyll
27 Apr 2018
School
Department
Course
Angiosperm - seed contained inside a vessel
Double fertilization of megagametophyte makes a zygote and an endosperm for nutrition (triploid endosperm)
•
Flowers
Anatomy
Receptacle: stem that rest of the floral organs are born from
○
Sepal: photosynthetic leaves that protect flower before it buds
○
Petal: showy part of flower
○
Stamen: male reproductive organ
Anther: has four microsporangium that house the microspores or pollen
§
○
Pistil: female reproductive organ made of one or many carpals to house the ovules
Stigma: pollen landing site
§
Style: tube that pollen falls down
§
Ovary place where fertilization happens
§
Ovule: result of egg division (tube)
§
○
•
Types of Flowers
Complete: flowers with the four types of organs
○
Perfect: both male and female parts
○
Imperfect: flowers without one of the male or female parts
Can be incomplete yet still perfect… think about it
§
○
Monoecious: male and female present and borne on same plant
○
Dioecious: Male and female present on separate part
○
Inflorescences: clusters of flowers
○
•
Function
Attract pollinators
○
Protect reproductive parts
○
Landing sites and rewards for pollinator
○
ALL HELP PROMOTE CROSS POLLINATION
○
•
Origin of Carpals
Started as modified leaf with sporangium (sporophyll)
•
Fused ends of leaf together to house the ovules
•
Origin of Stamen
used to be a leaf with sporangium for microspores which fused together to make this long stalk
•
Life Cycle of Angiosperm
Microspores develop into pollen grains 1.
Megasporangium holds the megasporocytes which then through meiosis create megaspores
Three of the megaspores die off and one keeps most energya.
2.
Cells in megagametophyte divide into 7 cells (one is the egg) with 8 nuclei cells ; one central cell has two polar nuclei 3.
Pollen goes down stigma and then through pollen tube reaches the megagametophyte with the seven cells4.
Pollen grain divides in the megagametophyte into two sperm one which fertilizes the central cell with two nuclei and
the egg creating endosperm with triploidy and fertilized zygote
5.
Zygote (2n) is surrounded by massively dividing endosperm (3n) for nutrition for developing sporophyte,6.
Seed made with this embryo, endosperm and two cotyledons for nourishment7.
Advantages of Double Fertilization
Can create zygote and nutritional source at the same time
•
Resources only allocated to fertilized ovules
•
Not wasteful allocations
•
More nutrition allocated in a precise manner
•
Evolution
Double fertilization, xylem vessels also found in gnetophytes which are not sister taxa of angiosperms but this came
through convergent evolution
•
Monocot vs Eudicots
Monocots have one cotyledon, parallel leaf veins, flower parts in multiple of three, scattered bundles so no
secondary growth
•
Eudicots, two cotyledons, branching veins, four to five plant parts, organized bundles
•
Angiosperms
Wednesday, February 14, 2018
12:12 PM
Angiosperm - seed contained inside a vessel
Double fertilization of megagametophyte makes a zygote and an endosperm for nutrition (triploid endosperm)
•
Flowers
Anatomy
Receptacle: stem that rest of the floral organs are born from
○
Sepal: photosynthetic leaves that protect flower before it buds
○
Petal: showy part of flower
○
Stamen: male reproductive organ
Anther: has four microsporangium that house the microspores or pollen
§
○
Pistil: female reproductive organ made of one or many carpals to house the ovules
Stigma: pollen landing site
§
Style: tube that pollen falls down
§
Ovary place where fertilization happens
§
Ovule: result of egg division (tube)
§
○
•
Types of Flowers
Complete: flowers with the four types of organs
○
Perfect: both male and female parts
○
Imperfect: flowers without one of the male or female parts
Can be incomplete yet still perfect… think about it
§
○
Monoecious: male and female present and borne on same plant
○
Dioecious: Male and female present on separate part
○
Inflorescences: clusters of flowers
○
•
Function
Attract pollinators
○
Protect reproductive parts
○
Landing sites and rewards for pollinator
○
ALL HELP PROMOTE CROSS POLLINATION
○
•
Origin of Carpals
Started as modified leaf with sporangium (sporophyll)
•
Fused ends of leaf together to house the ovules
•
Origin of Stamen
used to be a leaf with sporangium for microspores which fused together to make this long stalk
•
Life Cycle of Angiosperm
Microspores develop into pollen grains 1.
Megasporangium holds the megasporocytes which then through meiosis create megaspores
Three of the megaspores die off and one keeps most energya.
2.
Cells in megagametophyte divide into 7 cells (one is the egg) with 8 nuclei cells ; one central cell has two polar nuclei 3.
Pollen goes down stigma and then through pollen tube reaches the megagametophyte with the seven cells4.
Pollen grain divides in the megagametophyte into two sperm one which fertilizes the central cell with two nuclei and
the egg creating endosperm with triploidy and fertilized zygote
5.
Zygote (2n) is surrounded by massively dividing endosperm (3n) for nutrition for developing sporophyte,6.
Seed made with this embryo, endosperm and two cotyledons for nourishment7.
Advantages of Double Fertilization
Can create zygote and nutritional source at the same time
•
Resources only allocated to fertilized ovules
•
Not wasteful allocations
•
More nutrition allocated in a precise manner
•
Evolution
Double fertilization, xylem vessels also found in gnetophytes which are not sister taxa of angiosperms but this came
through convergent evolution
•
Monocot vs Eudicots
Monocots have one cotyledon, parallel leaf veins, flower parts in multiple of three, scattered bundles so no
secondary growth
•
Eudicots, two cotyledons, branching veins, four to five plant parts, organized bundles
•
Angiosperms
Wednesday, February 14, 2018
12:12 PM
