Origin of Land Plants Flashcards
When did land plants first appear?
~0.46 Ga
Define the following terms:
- Bryophytes
- Pteridophytes
- Gynosperms
- Mosses and liverworts
- Seedless vascular plants
- Naked seeds
What 6 key challenges did plants have to overcome to colonize the land?
- Support structure
- Desiccation
- Access to nutrients
- Temperature variation (more severe)
- Damaging UV radiation
- High oxygen concentration (3.5% in water)
What reproductive issue does living on land pose?
No medium on land for sperm to swim, also danger of desiccation of sex cells and propagules
What were the 3 advantages of living on land?
- More photosynthetically active radiation
- High CO2 concentrations
- Escaping competition and herbivorous animals
How did early land plants deal with the problem of support?
Initially not a problem, spread out flat. Only developed later with increasing competition
How did early land plants deal with the problem of desiccation?
Only initially lived in watery environments. However developed rhizoids to anchor plants to the ground and a waxy cuticle to reduce water loss
How did early land plants deal with sexual challenges?
- Initially relied on water for sperm dispersal
2. Later to avoid desiccation, invention of sporopollenin (walled spores)
Why are the green algae group charophytes believed to be the likely ancestor of land plants?
- Common photosynthic pigments
- Have hexamic cellulose synthesis
- Phragmoplast formation during cell division
- Have plasmodesmata
- Have peroxisomes to protect from photorespiration
- Sequence ribosomal RNA
What 4 things define a land plant?
- Apical meristems (3 faces)
- Multicellular gametangia
- Alternation of generations
- Sporollenin
What are the two generations in the life cycle of a land plant?
- Sporophyte generation - asexual, diploid
2. Gametophyte generation - sexual, haploid
What phase was dominant in early land plants?
Gametophyte
In what way are bryophytes different from early land plants?
Sporophyte is dependent on gametophyte throughout its life
What makes liverworts unique from all other land plants?
They lack stomata (have pores for similar function but less efficient)
What are 2 other features of liverworts?
- Lack conductive tissue (hence size restraint)
2. Have unicellular rhizoids
What is the name of the liverwort:
- Male reproductive structure
- Female reproductive structure
- Female gamete
- Antheridium (Antheridia - sperm)
- Archegonium (archegonia - egg)
- Sessile
Describe the reproductive process of Mechantia
- Fertilised by rain splash mechanism, where rain splash splashes male gametes on to archegonium where sessile is then fertilised.
- Sporophytes then grow from under the female structure
- Seta enlarges 20 times its original size and spores are eventually released, with elators aiding their dispersal
How are mosses different to liverworts
a) structurally
b) sexually
a) Have stomata and conductive tissue. Also rhizoids are branched, multicellular and with opaque cell walls
b) Gametophytes are leafy and radially arranged
In spores, which generation supports the other?
Gametophyte generation supports the sporophyte. Meiosis in sporangia produces spores which are released as the capsule dries
Name 3 features of ferns
- First to develop megaphyll leaves whith a highly branched vascular system
- Multiple branched vascularised stem
- Siphonostele - pith with vascular cylinder
How is it hypothesized that ferns developed from bryophytes?
That sporophytes began to enlarge and develop autotrophic independence and outlive the gametophyte which is used as a food store. This allowed for increased size and complexity. Several gametophytes may be fertilised but only a few may develop to assure food abundance
Where can the spores be found in ferns?
On the underside of the leaf, called sori. Idusium dires up to release them.
How are the gametophytes of pteridophytes bisexual?
Can produce both male and female gametophytes at different times, dictated by hormones.
Name 3 features of gynosperms
- Development of SEEDS
- Well developed vascular system
- True roots, stems and leaves
What conditions in the Permian period contributed to the rise of seeds?
Dry and cold, lack of water for fertilisation
What are flying plant gametes called?
Progynosperms
Describe heterospory
Two types of gametophytes dispersed instead of spores
- Microspores (male) produced by microsporangia
- Megaspores (female) produced by megasporangia
Why did microspores become more abundant and develop increasingly for flight?
- Increase chance of reaching a megaspore
- In order to reach mother plant which can assist the sperms journey to the egg and also support the gametophyte and zygote after fertilisation (no need for dependence on water)
In what 3 ways did female gametes become spcialised?
- Size and complexity reduction
- Dependence on mother plant
- Enclosing (2n) structure
How could the mother plant support the zygote post fertilsation?
- Development of structures before release such as roots and leaves
- When released provide ingrument (2n) for protection
- Provide nucellus (2n deriver from sporangium) for nutrition
