Topic 16: Seed Plants - Gymnosperms Flashcards
What are seeds?
An embryo and nutrients surrounded by a protective coat that allows for long-distance travel.
What are the 5 shared derived traits of Seed Plants?
- Reduced Gametophytes
- Heterospory
- Ovules
- Pollen
- Seeds
- Reduced Gametophytes
Gametophtyes develop within the wall of the sporophyte.
- Heterospory
All seed plants produce two gendered spores that are NOT dispersed.
- Ovules
Consists pf a megasporangium, megaspore, and one or more protective integument. These develop into seeds after fertilization.
How does an ovule become a seed?
The megasporangium (2n) produces a megaspore (1n) via meiosis. Pollination triggers female gametophyte development.
- Pollen
Microspores develop into male gametophytes within pollen grains with walls coated in sporopollen, which withstands desiccation, UV, and physical damage.
5.Seeds
A seed develops from a fertilized ovule.
Pollination
The transport of pollen to ovule for fertilization via wind or animals. Eliminates the need for water.
What happens if pollination is successful?
A pollen tube discharges sperm nuclei into the female gametophyte within the ovule.
What advantages does seed dispersal have?
- They are larger
- Have external coats to protect embryo
- Have energy dense supply of stored food to support early seed growth (Large seed plants = few seeds, lots of stored energy, Small seed plants = many seeds)
- Can be dormant until conditions are favourable
When did Gymnosperms dominate Earth?
During the Mesozoic period.
Four Gymno Phyla?
Cycadophata
Ginkgophyta
Gnephyta
Coniferophyta
Cycadophata
Are now limited to small population in the tropics. Grow very slowly, producing large palm leaves. Still have flagellated sperm.
Ginkgphyta
One living species - Ginkgo biloba.
Gnephyta
75 species in thee genera
Coniferophyta
Found in cold climates in boreal and alpine regions. Most are evergreen and can carry out photosynthesis year-round.
Small cones produce…
Microspores
Large cones produce…
Megaspores
