1/14
Flashcards about Gymnosperms
Name | Mastery | Learn | Test | Matching | Spaced |
---|
No study sessions yet.
Gymnosperm
Gymnosperm refers to plants with 'naked seeds,' meaning the seeds are not enclosed in ovaries.
Pine Tree Sporophyte
A mature pine tree is the 2n sporophyte and has both male 2n 'pollen cones' and female 2n 'ovulate cones'.
Male Cones
Small, soft, and transient cones that produce pollen in coniferous trees.
Male Gametophyte Production
Each 2n male pollen cone contains many 2n microsporangia holding 2n microsporocytes (cells) that undergo meiosis to produce n microspores.
Pollen Grain Development
Each n microspore grows (by mitosis) into a n pollen grain and contains the n male gametophyte (which will later produce sperm via highly reduced antheridium—literally 1 cell!).
Ovulate Cone Scales
Each 'scale' of a 2n ovulate cone contains two 2n ovules, each with an outer protective 2n integument and a micropyle opening (where a pollen grain will enter).
Female Gametophyte Production
Each 2n ovule has a 2n megasporangium with a 2n megasporocyte cell that produces a n megaspore by meiosis.
Megaspore Development
The n megaspore in the ovule develops into a n female gametophyte with an n archegonium that produces an n egg by mitosis. The female gametophyte will never leave the sporophyte (~few 100 cells!)
Pollination
Occurs when wind carries an n pollen grain to a female cone, entering an ovule’s micropyle opening, where the pollen grain’s male n gametophyte grows a pollen tube delivering haploid sperm.
Pollen Grain Function
Pollen grains disperse and protect sperm, and eliminate the need for water
Fertilization (Gymnosperms)
Occurs inside the female ovule, where an n sperm in the pollen tube reaches the n egg produced by the n female gametophyte creating a 2n zygote that grows into a new 2n sporophyte embryo.
Seed Formation
The whole ovule becomes a seed.
Seed Components
Protective seed coat (2n) from the ovule integument ; a 2n sporophyte embryo ; n food reserves (derived from the gametophyte).
Flowers
Modified leaves made of four rings, with reproductive structures (stamens and carpels)
Fruits
Mature ovaries that help disperse seeds