Chapter 30 Flashcards
Seed plants first began to diversify from their seedless ancestor when?
309 MYA
The earliest angiosperms appeared when?
192 MYA
Seed plants evolved from spore-bearing plants knows as?
progymnosperms (they share traits with modern gymnosperms like secondary vascular tissue)
(it is not known which group gave rise to the seed plants)
Success of angiosperms is attributed to evolution of seed. What does it do?
Protects and provides food for embryo.
Allows the “clock to be stopped” to survive harsh periods before germinating.
Later development of fruits enhanced dispersal.
As plants further evolve?
the size of the gametophyte reduces in small and corresponding to this is an increase in dominance of the sporophyte generation.
3 layers of the seed and their functions
(top layer to bottom layer)
- stored food (endosperm)
- integument (seed coat) (impermeable)
- An extra layer or two of sporophyte
tissue, creating the ovule - Hardens into seed coat.
- An extra layer or two of sporophyte
- embryo
What are the two types of gametophytes?
male and female
Male gametophytes
Pollen grains (multicellular male gametophyte)
Dispersed by wind or a pollinator, sometime a pollen tube grows to help move the sperm into the ovule
No need for water.
different from seedless plant because in this the whole gametophytes move to the female instead of just the sperm
Female gametophytes
Develop within an ovule.
forms within the protection of the integuments, collectively forming the ovule
Enclosed within diploid sporophyte tissue in angiosperms.
Ovule and protective tissue are the ovary.
The ovary develops into fruit (fruit only develops after fertilization)
Five Phyla of Extant Seed Plants
Coniferophyta - evergreen, pines (nonflagellated sperm)
Cycadophyta - motile sperm
Gnetophyta - nonflagellated sperm
Ginkophyta - only one species, motile sperm
Anthophyta - flowering plants (over 300,000)
Gymnosperms
Plants with “naked seeds”
There are four living groups
- Coniferophytes.
- Cycadophytes.
- Gnetophytes.
- Ginkgophytes.
All lack flowers and fruits of angiosperms
All have ovule exposed on a scale
Conifers (phylum Coniferophyta)
Pines, spruces, firs, cedars, hemlocks, yews, larches, cypresses, etc. (conifers r 40% of the world’s forests)
- Coastal redwood (Sequoia sempervirens) – Tallest living vascular plant. (NW Cali, SW OR) (100m/300ft)
- Bristlecone pine (Pinus longaeva) – Oldest living tree. (one specimen is 4900 yrs old)
Found in colder and sometimes drier regions of the world (Northern Regions )
Conifers are sources of important consumer products. Ex. timber, paper, resin, and paclitaxel (taxol - anti-cancer). THEY ARE NOT USED FOR FOOD
Pine reproduction
Male gametophytes (pollen grains)
- Develop from microspores in male cones by meiosis.
- Typically clusters on the Bottom of the tree
Female pine cones
- form on the upper branches of the same tree
- Female cones are larger, and have woody scales.
- Two ovules develop on each scale.
- Each contains a megasporangium that is known as the nucellus.
Female Pine Cones
The nucellus is surrounded by the integument
- Micropyle: small opening at end of integument.
- Seed coat forms from a layer of integument.
One megaspore mother cell within each megasporangium forms four megaspores via meiosis (MEIOSIS OCCURS IN THE MEGASPORANGIUM)
- 3 megaspores break down.
- 1 slowly develops into a female gametophyte via mitosis.
Pine Fertilization
Female cones usually take 2 or more seasons to mature
During the first spring, pollen grains drift down between open scales
- Pollen grains drawn down into micropyle.
- Scales close.
A year later, female gametophyte matures
- Pollen tube is digesting its way through.
- Mature male gametophyte has 2 sperm.
15 months after pollination, pollen tube reaches archegonium and discharges contents
- One sperm unites with egg = zygote.
- Other sperm degenerates.
Cycads (phylum Cycadophyta)
largest sperm cells of all organisms (LITERALLY ANY LIVING THING THAT PRODUCES SPERM)
Female cones can weigh 45 kg
Slow-growing gymnosperms of tropical and subtropical regions
Sporophytes resemble palm trees
Gnetophytes (phylum Gnetophyta)
Only gymnosperms with vessels in their xylem
Ginkgophytes
Only one living species remains
- Ginkgo biloba.
Flagellated sperm
Dioecious
- Male and female reproductive structures form on different trees.
Angiosperms
Flowering plants
Ovules are enclosed in diploid tissue at the time of pollination
Carpel, a modified leaf that covers seeds, develops into fruit
Unique angiosperm features aided abundance
- Flower production
- insect pollination
- broad leaves with thick veins.
Angiosperm origins
UNKOWN ORIGIN
Oldest known angiosperm in the fossil record is Archaefructus (OLD FRUIT LITERAL MEANING) (ITS EXTINCTTTTT)
- 125 million years old.
- Unlikely to have been the first angiosperm.
- Lack sepals and petals.
Closest living relative to the original angiosperm is Amborella
- Horizontal gene transfer explains the presence of moss mitochondrial genes in the genome of Amborella
Flower Morphology
Flowers house the gametophyte generation
Modified stems bearing modified leaves.
Primordium develops into a bud at the end of a stalk called the pedicel.
Pedicel expands at the tip to form a receptacle, to which other parts attach.
Flower parts are organized in circles called whorls.
Flower whorls
Outermost whorl – sepals
Second whorl – petals
Third whorl – stamens (androecium - male)
- Pollen is the male gametophyte.
- Each stamen has a pollen-bearing anther and a filament (stalk).
Innermost whorl – gynoecium - female
- Consists of one or more carpels.
- House the female gametophyte.
The Carpel
Carpel has 3 major regions
- Ovary – swollen base containing ovules.
- Later develops into a fruit.
- Stigma – tip where pollen lands.
- Style – neck or stalk.
Double Fertilization
One sperm unites with egg to form the diploid zygote.
- New sporophyte.
Other sperm unites with the two polar nuclei to form the triploid endosperm.
- Provides nutrients to embryo.
Seed may remain dormant for many years
- Germinate when conditions are favorable.
