Ferns Flashcards
what are tracheophytes
- Tracheophytes first arose among polysporangiates. They possess tracheids.
- These cells expand lengthwise when young
- they then developed thick secondary cell walls
- and right before they die - they produced a burst of a tough polymer called lignin.
what problems did vascularity solve
- These transport vessels occured in a central strand. This new tissue - the vascular bundle (bundle of transport fibres) provided one elegant solution to two engineering problems experienced by early plants
- Problem 1: how to prevent dessiccation
- by having a system of dead cells dedicated to water transport, plants could grow taller without desiccating. Since they could transport water up to the higher cells they stay hydrated through indoor plumbin. Unlike how mosses evade dessication.
- Problem 2: How to grow upwards against gravity
- Hardened cells provided structural support, allowing greater height and size. Taller plants dispersed spores farther. Larger plants could produce more sporangia, more spores. Overall, fitness increased due to further dispersal.
- Problem 1: how to prevent dessiccation
what did early vascular plants evolve to “assist” their vascularity
- To make this work they needed a few add ons
- A cuticle which covered the outer surface of the plant to prevent water loss
- small openings (stomates) which allow evaporation of water, which creates suction to draw water up through the plant
- helps with cooling and providing water for photosynthesis
what change in growth occurred early in vascular plant evolution
The earlies Polysporangiate plants only had primary growth. So they grew from a primary growing point pr meristem of the plant. Soon, a new secondary meristem would evolve that produce rings of tracheids, known as wood.
how were polysporangiates discovered
- These kinds of Polysporangiate plant fossils were first found in New Brunswick by Patricia Gensel and her team.
- They found plants which due to these evolutionary adaptations were taller, with more sporangia, branching stems, and photosynthetic surfaces.
- They are called Polysporangiates since they can possess more than one sporangium, unlike mosses which have only one.
how did the dual lifecycle work in vascular plants
- In vascular plants the sporophytes are separate from the gametophytes. And they are also much larger.
- Early vascular plants (400 mya) had independent generations. (resulting in different scientific names for fossil plants, though to be in the same species, called form genera)
- In these plants only sporophytes had tracheids so the new adaptation was restricted to them.
what had established themselves on land before plants
- 450 mya, land was occupied by early plants, protists, bacteria, and fungi (or possibly lichens)
- these fungi had established themselves on land before plants and could grow to 8m high, the tallest organisms on land.
describe fungal evolution in relation to plants
- ame to land before plants
- broke down rocks to liberate minerals and form soils
- Fungi had an initial parasitic relationship with plants, resulting in co-evolution producing in a symbiosis and certain plants like Phynia sporophytic cells containing hyphae
- Mycorrhizas developed i.e mutualistic relationships with plants, in exchange for sugars from the plant, the fungus supplies nutrients, water and defence.
what are the 6 steps from early to modern vascular plants
- ominance of sporophyte
- Acquisition of water transport system (Xylem made up of tracheids)
- Acquisition of roots, which were derived from stems
- Acquision of leaves, both microphylls and megaphylls (moss “leaves” are actually called phyllids but don’t count)
- Evolution of presentation of sporangia
- i.e different types of clusters
- sorus in ferns
- Elaboration of type of spores, from plants having only one type of spore (homospory) to plants having two types of spores (heterospory, where male spores → microgametophytes (like sperm) and female spores → megagametophytes (like eggs)
What are monilophytes
- ferns are tracheophytes (vascular polysporangiates) that have alternation of generation in which the sporophyte is dominant.
- Their sporophytes vary from miniscule plants to tall trees in the andes
- Gametophytes are always small
- Ferns were in their heyday during the carboniferous, when they were the dominant land plants. Since gametophytes require water for reproduction, they were largely confined to wet regions and swamps
what are fern lifecycles and reproduction like
Ferns have a two part lifecycle, including Gametophyte which grows from the spores, then releases sperm from the Antheridium which fertilized an egg in the Archegonium (both on the underside of the mature gametophyte). (this whole section prior to fertilization is haploid)
The sperm and Eggs form a zygote (which is diploid) which grows on the gametophyte to make the sporophyte (the big main frond bit)
On the underside of a mature sporophytes leaves there is sporangium (together clumping in sorus) which releases spores restarting the cycle.
how do ferns survive droughts
They survive by taking in moisture from the fog and air. (through their leaves)
they also take advantage of the rare rainfalls to clear the embolisms in their circulatory system.
how do fern spores be epic
The spores can survive travel over long distances by air, through cold, dry and high irradiation environments.
They then lie in wait till conditions are good to germinate for up to 63 years. Though most spores will never germinate.
how do ferns prevent inbreeding.
Fern gametophytes have both male and female gamete producing organs: i.e bisexual
This could result in inbreeding
to avoid inbreeding and promote outbreeding ferns do a couple things:
- the antheridia and archegonia develop asynchronously
- the fastest growing gametophyte to have archegonia first releases a compound called Antheridiogen, which turns the other gametophytes male.
