Topic 6

• Devonian period (400 million years ago) - plants started to cover the land; decline of CO2 levels
• End of the Devonian (After 60 millon years) - giant trees, Archaeopteris “early fern”, spread around the world
• 1920, Gilboa, New York - uncovered ancient trees dating back 390 million years
• Ordovician period (470 millon years ago) - plant first began colonizing the land
• Xylem - transports water from the bottom to the top of the plant
• Secondary Xylem / wood - consists of cellulose fibers and lignin
• Cellulose & Lignin - give support and structure to the plant
• Stomata - absorb carbon dioxide; allow for the evaporation of water
• Woody tissue - first appeared as an adaptation for keeping plants hydrated
• Convergent Evolution - wood evolved atleast 5 different times by the late Devonian
• Archaeopteris - reproduced like ferns, with spores, but had both male and female spores
• Humus - organic component of soil made up of broken down lignin
• pollen - male gametophyte
• gymnosperms - naked, sperm seed: presence of ovules are exposed at time of fertilization
• angiosperms - ovules enclosed by carpels
• Pollen grain with air bags orbladders - help in pollen dispersal
• Protogymnosperms - extinct group of primitive gymnosperms
• trilent - pollen is of a tetra head of cells
• heterosporous plants - all plants that produce seeds
• Seed - package that is made up of a protective seed coat that surrounds a sporophyte embryo and stored food that the young sporophyte can use early in its growth
• Ovule - structure that consists of megasporangium
• integuments - envelopes of tissue surrounding the megasporangium or nucellus
• Pollen Grain - microgametophyte in seed plants
• Micropyle - hole in the integument
• Pollination drop - process when the pollen lands on the tip of the ovule and enters the micropyle
• Ovary - enclosure of the ovule in flowering plants
• Stigma - where pollen lands and germinate
• Pollination - transfer of pollen grains from microsporangia to ovules or stigmas
• Fertilization - fusion of sperm and egg are separate processes in seed plants
• Zoidogamous - having motile swimming sperms
• Siphonogamous - seed plants have nonmotile sperm
• Endosperm: the part of a seed which acts as a food store for the developing plant embryo, usually containing starch with protein and other nutrients.
• epicotyl - short stem above the cotyledons
• hypocotyl - stem axis below the cotyledon
• embryo initials → 4 cells at the base of archegonium
• suspensor initials → 4 cells at the adjacent tier
• neck cells → entrance of archegonium
• venter - containing a single egg cell
• generative cells: sterile cell, spermatogenous cell
• lignophytes - woody plants that includes progymnosperms and spermatophytes