Evolution of seed plants Flashcards
(23 cards)
What were the first plants to develop seed-like structures?
Seed ferns. Appeared 400 mya but are extinct
What were the traits of progymnosperms?
Had spores instead of seeds, may have evolved from seed ferns. Branched off 390 mya
When did the radiation of gymnosperms happen?
250 mya. They took over the world from the seedless vascular plants after the Permian extinction
When did angiosperms appear in the fossil record?
130-150 mya
When did pollen first appear in the fossil record?
250 mya
What are the 2 reasons why pollen was a huge competitive advantage?
- No longer reliant on water for gamete exchange, pollen can go a lot further than just the neighbours, which increases genetic diversity
- Sperm is very easy to kill, and pollen isn’t
What are the 3 components of a pollen grain?
Generative cell
Tube cell
Pollen wall
What does the generative cell of pollen do?
The sperm cell that will fertilize the egg
What does the tube cell of pollen do?
Transports the sperm cell to the egg
What does the pollen wall do?
Mechanical stability, gas exchange, and provides a chemically inert environment
What is the pollen wall made of that makes it so strong?
Partly made of sporopollenin, which is completely inert and basically indestructible
Why are seeds an adaptive advantage over spores?
Embryo is protected and encased in a seed, and can be transported far from the parent plant. Seeds also last a lot longer than spores
Where does the embryo get nutrients from in a gymnosperm seed?
Female gametophyte tissue
What are 2 ways seeds are dispersed?
Wind: often have modifications to increase drag
Animal based
How developed is the cuticle of seed plants?
Very complex and well developed. Covers the hypodermis. Much more complex than Monilophytes
How many gymnosperms and angiosperms show secondary growth?
Only present in woody angiosperm species, but is in almost all gymnosperms
How is having secondary growth an advantage for gymnosperms and angiosperms?
They can grow outwards to expand their stems, which allows them to grow taller and opens up possibilities for mechanical support
What 7 traits are common to both gymnosperms and angiosperms?
Pollen is all that remains of the microgameteophyte Fertilization occurs via the pollen tube Use seeds for dispersal Lacks antheridia Heterosporous Secondary cell walls Woody species have secondary growth
How are gymnosperms and angiosperms different in terms of ovule placement?
Gymnosperms: ovules are exposed
Angiosperms: ovules are enclosed in the carpel
How are gymnosperms and angiosperms different in terms of pollination?
Gymnosperms: direct pollination by the pollen landing directly on the ovule. Often wind pollinated
Angiosperms: indirect pollination by the pollen landing on the stigma then the pollen tube growing down the style to fertilize the ovule. Often animal pollinated
How are gymnosperms and angiosperms different in terms of fertilization?
Gymnosperms: single fertilization. One generative cell fertilizes the egg and the female gametophyte tissue provides nutrition to the embryo
Angiosperms: double fertilization. The generative cell splits into two before fertilizing the egg, one will fertilize the embryo and the other fertilizes the polar nuclei. The endosperm provides nutrition to the embryo
How are gymnosperms and angiosperms different in terms of the megagametophyte?
Gymnosperms: larger megagametophyte with 2 archegonia each with one egg. Completely parasitic on the sporophyte at all life cycle stages
Angiosperms: 7 celled, 8 nucleated with no archegonia. Has a large cell in the middle with 2 polar nuclei, 3 antipodal cells, 2 synergids, and one egg cell
How are gymnosperms and angiosperms different in terms of fruits?
Gymnosperms: no fruits
Angiosperms: fruit
