Lecture 13: Gymnosperms Flashcards
Homosporous/Heterosporous
What are gymnosperms? Seedless vascular?
Homosporous: Plants where a single type of spore develops into a bisexual gamete
Heterosporous: Plants in which sporophyte produces 2 different types of spores that differ in size and develop into male or female
Gymnosperm
(Definition, 3 major innovations of the gymnosperm vs seedles vascular)
Naked seed because their seed is not enclosed in a fruit
1. Much reduced size and complexity of gametophyte (no longer free living)
2. Shift from motile to non motile male gametes (no more need for water)
3. Evolution of the seed ( an embryo of the sporophyte in a protective package that inclufes a food supply)
Name all the gymnosperms we need to know/mentioned in lecture
- Welwitschia- largest leaves
- ginko- large tree native to China, only 1 species
- pine trees- most important gymnosperm because of their lumber
- cycads- palm like plants but non flowering
- Ephedra- leafless plant but a powerful stimulant
What are all the new terms/definitions of the pine (gymnosperm) life cycle
Microsporangia- where male spores are made by meiosis
Megasporangia- where female spores are made by meiosis
Microspore- male spore
Megaspore-female spore
heterosporous- seperate male and female spores
ovule- a structure that contains the female gametophyte
pollen- an immature gametophyte
What are the steps of gymnosperm alteration of generation (COMPLEX)
- mature sporophyte drops two seperate types of cones (microspore and megaspore aka ovulate cones)
- Meiotically, haploid microspore forms pollen grain and ovules containing megasporongia are made
- Pollen disperses by wind (onto female cone) into female part of the plant called the megasporngium and develops into male gametophyte.
- Megaspore divides to form female gametophyte which forms eggs by mitosis (only one egg is fertilized)
- Sperm and egg get wrapped in protective tissue (2n) (like archegonium) which is the seed
- Seeds disperse via wind or animals into developing sporophyte then mature. sporophyte (process repeats)
What are the important notes aboute gymnosperms life cycle
- Megaspore and microspores are produced in seperate sporongia (aka cones)
- Female gametophyte is no longer freeliving and develops in the confines of the sporophyte (reduction of the gametophyte)
- Motile swimming sperm replaced by wind born pollen
- Fertilized zygote is contained within the megametophyte and undergoes cell division to become the embryo
- How is sperm delivered to the egg
- Also what does the seed consist of? (indicate which is dilpoid/haploid)
- Pollen tube
- -Seed coat- sporophytic tissue from mother (diploid)
-The food reserves derived from the megametophyte (haploid)
- The embryo derived from the union of sperm and egg (diploid)
Pine tree life cycle (5)
SIMPLE
- Mature sporophyte to microspore (pollen grain) and megaspore via meiosis
- Microspore to male gametophyte (via pollen tube and sperm cells) via mitosis AND megaspore to female gametophyte with development of archegonia and eggs
- Sperm and egg create zygote via fertilization
- Zygote to embryo via mitosis
- Embryo surrounded by megametophyte and wrapped by a protective layer to make seed
4 features of the pine life cycle
- heterosporous: Megaspore become the female gametophyte (egg) and microspore becomes male gametophyte (sperm)
- Fertilization not dependent on water (wind)
- Female gametophyte is not free living and attached and protected by sporophytic tissue
- Seed protects and provides food for the sporophyte embryo (gametophytoc tissue supplies food, sporophytic tissue makes seed coat)
Why do gymnosperms not need a moist environment
hint: more than 1 reason
Gametophyte is nurtured directly by sporophyte and there is no need for water to reproduce
Evolutionary significance of the seed
- Plays important role in dispersion of plants (carried by water or wind)
- Seeds can be dormant, germinate when the time is favorable
