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Chapter 30. Plant Diversity II: the evolution of seed plants. Section 30-1. A lot of terrestrial adaptations contributed to the success of seed plants. These adaptations include the seed, the reduction of the gametophyte generation, heterospory , ovules, and pollen.

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chapter 30

Chapter 30

Plant Diversity II: the evolution of seed plants

section 30 1
Section 30-1
  • A lot of terrestrial adaptations contributed to the success of seed plants.
  • These adaptations include the seed, the reduction of the gametophyte generation, heterospory, ovules, and pollen.
  • Bryophyte life cycles are mainly dominated by the gametophyte generation, but seedless vascular plants mainly have sporophyte-dominated life cycles.
  • Seedless vascular plants have very small gametophytes however are visible to the naked eye.
  • The gametophytes of seed plants are VERY VERY small and develop from spores that are kept within the moist sporangia of the parental sporophyte.
continuation
COntinuation
  • Almost all seedless plants are homosporous, producing a single kind of spore that forms a hermaphroditic gametophyte.
  • It is thought that seeds most likely had homosporous ancestors
  • An important thing to remember is that all seed plants are heterosporous, producing two different types of sporangia that produce two types of spores.
  • Megasporangiamake megaspores, which produce a female (egg-containing) gametophytes.
  • Microsporangia on the other hand make microspores, which produce a male (sperm-containing) gametophytes.
slide4
Cont.
  • Seed plants produce ovules .
  • Layer over layer of sporophyte tissue, integuments, wrap , encase and help protect the megasporangium.
  • Gymnosperm megaspores are surrounded by one integument.
  • While on the other hand angiosperm megaspores are surrounded by two integuments.
  • An ovule is made of the megasporangium, megaspores, and integuments.
slide5
Cont.
  • The microspores develop into pollen grains that are released from the microsporangium.
  • The pollen grains are are covered with a tough coat that has sporopollenin.
  • Then they are carried by wind or animals and moved to a new location where pollination occurs.
  • The pollen grain germinates and grows as a pollen tube into the ovule, where it delivers one or two sperm into the female gametophyte.
section 30 2
Section 30-2
  • The ovules and seeds of gymnosperms develop on the surfaces of modified leaves that usually form cones .
  • When in contrast, ovules and seeds of angiosperms develop in enclosed chambers called ovaries.
  • There are four different types of gymnosperms that I while discuss in the next couple slides.
phylum ginkgophyta
Phylum Ginkgophyta
  • This is the smallest one out of all the groups because it only contains one species , Ginkgo biloba.
  • This is a popular ornamental species because of its fanlike leaves that turn gold in fall before they fall off.
  • Landscapers usually plant only male trees because the coats of seeds produced by female plants produce a repulsive odor as they decay. That smells really bad.
phylum cycadophyta
phylum Cycadophyta
  • the species in this phylum have have large cones and palmlike leaves.
  • As of right now 130 species of cycads are living right now with these characteristics .
  • They are the third largest phylum out of all four.
  • Cycads flourished mainly in the Mesozoic era, they even had it named after then as it became known as the “Age of the Cycads”
phylum gnetophyta
Phylum Gnetophyta
  • This phylum has three very different genera.
  • Weltwitschia plants, from deserts in southwestern Africa, have straplike leaves that are among the largest known leaves. Very weird and unheard of leaves but amazingly good.
  • Then there are the gentum species which are tropical plants and vines .
  • Ephedra is a shrub of the American deserts.
  • And those are the three genera .
coniferophyta
Coniferophyta
  • This is the class that the confifers belong to .
  • The word and concept conifer comes from the reproductive structure, the cone, which is a bunch of scalelikesporophylls bunched together.
  • Although there are only about 600 species of conifers, a few species dominate vey big and broad forested regions in the Northern Hemisphere where the growing season is short.
  • Conifers include pines, firs, spruces, larches, yews, junipers, cedars, cypresses, and redwoods.
continuation1
continuation
  • Most conifers are evergreen, retaining their leaves and photosynthesizing throughout the year pretty much meaning they never stop photosynthesis, and never really fall off.
  • Some conifers, like the dawn redwood and tamarack, are deciduous, dropping their leaves in autumn. Meaning that when autumn comes around they begin to lose there leaves.
section 30 3
Section 30-3
  • Angiosperms, mainly known as flowering plants, are vascular seed plants that produce flowers and fruits.
  • They are the most unique and geographically spread of all plants, including more than 90% of plant species.
  • There are about 250,000 known species of angiosperms.
  • The phylum Anthophyta is the phylum that all angiosperms belong to.
  • The flower is a structure the angiosperms have adapted for very successful sexual reproduction.
continuation2
Continuation
  • In the species of angiosperms, insects and other animals or the wind transfer pollen from one flower to female sex organs of another.
  • Most of the dense populations with a lot of the population in the same area of occurs because of wind pollination.
  • A flower is specialized to have up to four modified leaves on it : sepals, petals, stamens, and carpals.
  • The sepals are around at the base of the flower are modified leaves that are usually green and enclose the flower before it opens.
continuation3
Continuation
  • The petals lie inside the sepals.
  • These are often brightly colored in plant species that are pollinated by animals.
  • They usually lack bright coloration in wind-pollinated plant species.
  • Sepals and petals are sterile parts, not directly involved in reproduction.
  • Stamens which are the male reproductive organs, are sporophylls that make microspores that will being to make pollen grains containing male gametophytes.
continuation4
continuation
  • Carpals are female sporophylls that produce megaspores and their products, female gametophytes.
  • At the tip of the carpal is a sticky thing that receives pollen.
  • A style leads to the ovary at the base of the carpal.
  • Ovules are protected inside the ovary,
slide16
30-4
  • Like other organisms, we depend on photosynthetic organisms for food production and oxygen release.
  • However, we use technology to manipulate or select plants that maximize the harvest of plant products for human use.
  • We rely on seed plants for food, fuel, wood, and medicine.
  • Flowering plants provide nearly all our food.
  • Just six crops—wheat, rice, maize, potatoes, cassava, and sweet potatoes—yield 80% of all calories consumed by humans.
  • Modern crops are the products of a relatively recent burst of genetic change, resulting from artificial selection after the domestication of plants 13,000 years ago.
  • In maize, key changes such as increased cob size and removal of the hard coating of the kernels may have been initiated by as few as five gene mutations.