Ch18: Gymnosperms Flashcards
What is a seed composed of?
A matured ovule containing an embryo.
What is the unit of dispersal corresponding to the evolution of the ovule?
Following fertilization, the ovule matures into a seed. This seed is the unit of dispersal.
What is the direct ancestor of seed-bearing plants?
- Late Devonian (365mya)
- Elkinsia
- integumentary lobes with no/little fusion between lobes began to curve inwards at the tips, forming a ring around the apex of the nucellus. Ovules surrounded by dichotomously branched, steril structures called cupules.
What is the mode of pollination in most gymnosperms?
Wind
Where does meiosis occur in the life cycle of pines/conifers?
Microsporangiate cones:
-microsporophylls
- early spring, microspore mother cells undergo meiosis to produce four haploid microspores.
Ovuliferous scales:
- each ovule consists of a megasporangium, containing a single megasporocyte (megaspore mother cell) which undergoes meiosis to give four megaspores, only one functional.
What must occur for pollen germination in pine life cycle?
- pollination occurs in spring
- scales of ovulate are widely spread
- as pollen grains settle on scales from wind dispersal, they adhere to pollinatino drops exhuded from the ovules.
- After pollen grain lies in the chamber, the scales grow together to protect the ovule
- the pollen grain then germinates to form a pollen tube
What is located ar the micropylar end of an embryo for gymnosperms?
-opening for pollen to reach depression in nucellus
- pollen chamber
What kind of sperm do cycads produce?
multiflagellated sperm
*dioceous plants
Which group of gymnosperms are closest related to angiosperms?
Gnetophyta
1. similarity of their stobili to angiosperm inflorescences
2. presense of vessels in xylem
3. lack of archegonia in Gnetum and Welwitschia
Be able to label the parts of the seed and cone
