Seedless plants Flashcards
Which of the main evolutionary thresholds involved plants?
Endosymbiotic events
Multicellularity
Sexual Reproduction
Colonisation of land by lichens, then plants
Trees
Seeds
Agriculture (incl medicinal plants)
How did plants massively change the climate?
Increase in oxygen as a result of the first plants.
444 mya at the end of the Ordovician, there were glaciations. Expansion of non-vascular plants accelerated the chemical weathering, and may have drawn enough atmospheric carbon dioxide (out of the atmosphere) to trigger the growth of the ice sheets.
May have led to many marine species dying out.
The research suggests that the first plants caused the weathering of calcium and magnesium ions from silicate rocks, such as granite, in a process that removed carbon dioxide from the atmosphere, forming new carbonate rocks in the ocean. This cooled global temperatures by around five degrees Celsius.
Where do land plants fit into the plant phylogeny?
Are plants or algae monophyletic groupss?
Plants are a monophyletic group, resulting from an endosymbiotic event 1.2 mya (resulted in chloroplast formation from cyanobacteria).
Algae don’t all form monophyletic groups.
Oldest multicellular organism?
Bangiomorpha pubescens was the oldest complex multicellular, sexually reproducing organism.
Sister group to land plants?
Green algae
First terrestrial organism?
Thought to be lichen. Fossils found which have a massive resemblence to current lichens.
Benefits of being haploid?
Lethal mutations get immediately elimintated from the gene pool, no chance of ending up with a masked lethal mutation. Diploids have twice the mutation load.
What are charophytes and how does their lifecycle work?
Closest sister group to land plants.
Produce gametes by mitosis, which join to form a zygote. Sporic meiosis occurs straight away to form the gametophyte.
Forms 4 halpoid meiospores which divide to make a multicellular algae.
Mutations get deleted from population, but recombination still occurs to test different combinations and find optimum.
What are embryophytes?
The land plants. Where the embryo is retained in maternal tissue.
What is the alternation of generations?
Life history has alternate haploid and diploid stages.
Male and female gametophytes are haploid. The gametes are produced by mitosis.
Male gametes produced in anteridium, female in the archegonium. Male gametes swim about 1mm to eggs. Chemical signalling with chemo-attractants or travel on animals.
Fertilisation occurs to produce a zygote. The embryo is fed by the female gametphyte. Develops into a diploid embryo (meaning a multicellular diploid organism is made and meiosis delayed). Develops into a diploid sporophyte. Releases spores by meiosis.
Haploid spores germinate into a protonema forming a gametophyte.
When did the stomata develop?
After liverworts, before mosses.
What are the monilophytes?
Ferns.
Most produce one size, shape and colour of spore.
Spores are released from the sporangia, they are flung out. The spores germinate and grow into prothallus, gametophyte. Releases gametes of either sex (bisexual). Fertilisation. Risk of self-fertilisation and lack of genetic diversity.
Got rid of mutations by being haploid. End up with 100% homozygous individual however which isn’t good either. Eggs are produced before the sperm, so only the first sperm have a chance of fertilising eggs if they haven’t already been fertilised. Means will have the chance of self-fertilisation as reproductive assurance, if only plant, for example.
The embryo and young sporophyte are fed by the gametophyte/prothallus. Then free living when big enough to grow by itself. Then produces spores by meiosis which turn into gametophytes.
What are the bryophytes?
Non monophyletic group of seedless plants.
Mosses, hornworts and liverworts.
Small, mostly haploid. No roots or leaves. Have a sporophyte with a stalk. Tolerant of dessication and rehydration. Can survive for months without water.
All mosses produce one size, shape and colour of spore.
2nd most speciose group of land plants.
When did trees and seeds evolve?
Trees evolved 385 mya.
Seed evolved 365 mya.
Describe gymnosperms?
Dominant in the Permian, as continents drifted to cooler places. 250 mya.
Beetle and Weevil pollinated. Old lineage but still developing.
What is heterospory?
Evolved at least 4 times independently so polyphyletic.
Angiosperms and gymnosperms.
Evolutionary significance is debated.
Describe macrospores?
Larger woody structures. Small opening is filled with the pollen drop. Pollen must land on the pollen drop, which is close to the female mega-gametophyte produced in the nucellus.
The eggs are contained in a very strong woody structure.
Pollen germinates in the pollen drop and grows towards the female mega-gametophyte by producing a tube.
The fertilised egg forms a zygote which grows into an embryo which is a long way from the soil. The seed enables the embryo to drop to the ground.
The coat is female and derived from the walls of the ovule.
The food comes from the female haploid gametophyte.
The embryo is heterozygous male and female.
When did angiosperms evolve?
125 mya.
Split mostly into magnolids, monocots and eudicots.
New characters found in angiosperms: carpel, stamens and pollen grains.
Carpels are found in the flower. In the bisexual flowers, the stamens are situated close to the carpels. Pollen has to be moved from stamen to the stigmatic surface, hopefully on a different plant.
The pollen tube has to grow down the style to the female gametophyte in the ovary.
