CHP 30

• Seeds


  Consist of an embryo and its food supply, surrounded by a protective coat
• Seeds


  • When mature, they are dispersed from their parent by wind or other means, enabling them to colonize distant locations
  • They can remain dormant for days, months, or even years after being released from the parent plant
• Seeds have a supply of stored food
• Seeds


  • They provide protection from harsh conditions and facilitate dispersal to new habitats
  • They are multicellular, consisting of an embryo protected by a layer of tissue, the seed coat
• Spores are usually single-celled, whereas seeds are multicellular
• Seed plants


  The dominant producers on land
• Seed plants have reduced gametophytes, heterospory, ovules, and pollen
• These adaptations helped seed plants cope with conditions such as drought and exposure to ultraviolet (UV) radiation in sunlight. They also freed seed plants from requiring water for fertilization, enabling reproduction under a broader range of conditions than in seedless plants.
• Gametophytes of seed plants

  • They are microscopic and can develop from spores retained within the sporangia of the parental sporophyte, which can protect them from environmental stresses
• Heterospory


  Producing two kinds of spores: Megaspores that give rise to female gametophytes, and microspores that give rise to male gametophytes
• Ovules


  The whole structure consisting of a megasporangium, megaspore, and their integument(s)
• Pollen


  A microspore that develops into a pollen grain containing a male gametophyte
• Pollen can be carried by wind or animals, eliminating the dependence on water for sperm transport
• The sperm of seed plants are carried to the eggs by pollen tubes, and do not require motility
• Seed plants are unique in retaining the megasporangium within the parent sporophyte
• In gymnosperms, the megasporangia are surrounded by one integument, whereas in angiosperms they usually have two integuments
• Inside each ovule, a female gametophyte develops from a megaspore and produces one or more eggs
• If a pollen grain germinates, it gives rise to a pollen tube that discharges sperm into the female gametophyte within the ovule
• Fertilization of the egg by the sperm initiates the transformation of the ovule into a seed, which consists of a sporophyte embryo, a food supply, and a protective seed coat derived from the integument(s)
• Seeds provide protection from harsh conditions and facilitate dispersal to new habitats, unlike the spores of seedless plants
• Seeds are multicellular, whereas spores are usually single-celled
• Seeds can remain dormant for days, months, or even years, whereas most spores have shorter lifetimes
• Conifers


  • Most species have woody cones, but a few have fleshy cones
  • Some have needlelike leaves, others have scalelike leaves
  • Some dominate vast northern forests, others are native to the Southern Hemisphere
• Evergreen conifers


  Retain their leaves throughout the year, limited photosynthesis occurs even in winter
• Common juniper "berries"


  Are actually ovule-producing cones consisting of fleshy sporophylls
• Nucleus


  Part of the male gametophyte (n) in a pollen grain
• Angiosperms may be more closely related to several extinct lineages of woody seed plants than they are to gymnosperms
• One such lineage is the Bennettitales, an extinct group with flowerlike structures that may have been pollinated by insects
• Molecular and morphological evidence suggests that extant gymnosperm lineages had diverged from the lineage leading to angiosperms by 305 million years ago
• Amborella is woody, supporting the conclusion that the angiosperm common ancestor was probably woody
• Early angiosperms were probably woody shrubs that had small flowers and relatively simple water-conducting cells
• Herbivores can reduce a plant's reproductive success by eating its roots, leaves, or seeds
• Flower shape can affect the rate at which new species form, perhaps by affecting the behavior of insect pollinators
• Recent DNA studies indicate that the species traditionally called dicots are paraphyletic
• The vast majority of species once categorized as dicots form a large clade, now known as eudicots ("true" dicots)
• Main angiosperm groups


  • Monocots
  • Eudicots
  • Basal angiosperms
  • Magnoliids
• Basal angiosperms consist of three lineages comprising only about 100 species
• Magnoliids consist of about 8,500 species, most notably magnolias, laurels, and black pepper plants
• Bee pollination mechanism


  1. Tripping mechanism arches the flower's stamens over the bee and dusts it with pollen

  2. Pollen may rub off onto the stigma of the next flower the bee visits

  
• Amborella trichopoda


  The first lineage to have diverged from other angiosperms, represented today by a single species