Intro Gymnosperm Evolution Pine – Life Cycle
Gymnosperms are plants that have “naked” seeds are not enclosed in ovaries and usually on cones. Angiosperms seeds are enclosed in fruits, which are mature ovaries. Conifers – pines, firs, and redwoods Four of the ten plant phyla are gymnosperms : Cycadophyta, Ginkgophyta, Gnetophyta, and Coniferophyta.
Cycads have large cones and palm-like leaves. 130 species of cycads survive today.
Consists of only a single extant species, Ginkgo biloba. This popular ornamental species has fan-like leaves that turn gold before they fall off in the autumn.
Consists of three very different genera. Weltwitschia plants have strap-like leaves. Gentum species are tropical tress or vines. Ephedra (Mormom tea) is a shrub of the American deserts.
Conifers The cone which is a cluster of scale-like sporophylls. Pines, firs, sprices, larches, yews, junipers, cedaes, cypresses, and redwoods. Most confiners are evergreen. The needle-shaped leaves of some conifers are adapted for dry conditions. Coniferous trees are among the largest and oldest organisms of Earth.
Fossil evidence reveals that by the late Devonian Some plants, called progymnosperms, had begun to acquire some adaptations that characterize seed plants. Figure 30.5
Gymnosperms appear early in the fossil record And dominated the Mesozoic terrestrial ecosystems Living seed plants Can be divided into two groups: gymnosperms and angiosperms
Three Key Reproductive adaptations : The increasing dominance of the sporophyte generation The advent if the seed as a resistant, dispersible stage in life cycle Evolution of pollen as an airborne agent that brings gametes together
The life cycle of a pine 2 An ovulate cone scale has two ovules, each containing a mega- In most sporangium. Only one ovule is shown. 1 Key conifer species, Haploid (n) each tree has Ovule Diploid (2n) both ovulate and pollen A pollen grain cones. Ovulate Megasporocyte (2n) 4 enters through cone Integument the micropyle Longitudinal and germinates, section of Micropyle forming a pollen Pollen ovulate cone tube that slowly cone digests Mature Microsporocytes Germinating Megasporangium through the sporophyte (2n) Pollen pollen grain megasporangium. (2n) grains (n) MEIOSIS (containing male MEIOSIS gametophytes) While the Longitudinal Surviving pollen tube 5 section of Sporophyll megaspore (n) develops, the Microsporangium pollen cone contains many microsporangia megasporocyte A pollen cone 3 (megaspore Seedling held in sporophylls. Each microsporangium Germinating mother cell) contains microsporocytes (microspore mother grain pollen undergoes meiosis, cells). These undergo meiosis, giving rise to Archegonium producing four haploid microspores that develop into Egg (n) Integument haploid cells. One pollen grains. Female Seeds on surface survives as a gametophyte of ovulate scale megaspore. Fertilization usually occurs Germinating more pollen grain (n) than a year after pollination. All Food reservesSeed coat 6 The female gametophyte eggs (gametophyte(derived from Discharged develops within the megaspore 8 may be fertilized, but usually tissue) (n) parent and contains two or three sperm nucleus (n) only one sporophyte) (2n) archegonia, each with an egg. Pollen zygote develops into an embryo. By the time the eggs are mature, tube 7 The two sperm cells have developed in the ovule becomes a seed, consisting Embryo pollen tube, which extends to the of an FERTILIZATION (new sporophyte) female gametophyte. Fertilization occurs embryo, food supply, and seed Egg nucleus (n) (2n) when sperm and egg nuclei unite. Figure 30.6 coat.