Lecture notes
Evolution of Seedless Plants
- Module
- BIOL1029
- Institution
- University Of Southampton (UOS)
Lecture notes about seedless plants from first year. Covers colonisation of plants and lower plants.
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Lecture 1: colonisation of plantsThe first land plants appeared 500mya. Pre-colonisation, the earth's surface would've been a hostile
environment for plants and animals. The colonisation of land by plants is important because they
altered the composition of the air, increasing O2 content. They created habitats for other organisms,
provided a food source. Plants provide a means to harvest energy from the sun and convert us t
biomass and food.
Producers --> consumers --> decomposers
Around 420mya, vascular plants were formed (they had a system that allowed them to transport
molecules within their cells). In tidal areas or ponds which dry out, plants would have a period of
time of dry land-- this then evolved into plants that could live on land. Land plants have evolved
directly from a group called charophytes.
The evidence for this is that charophytes share distinct traits with land plants. They're multicellular
and eukaryotic. The structure of chlorophyll in land plants and charophytes were very similar. The
cell walls of both cells contain cellulose. In land plants, there are cellulose synthase complexes
arranged in rosettes. Non-charophyte algae have linear cellulose synthase protein arrangements.
Peroxisome enzymes in both land plants and charophytes have enzymes to minimise the loss of
organic compounds through photorespiration. Other algae lack these enzymes.
Another feature they both share is, structure of flagellated sperm (plants in damp environments)
In land plants having flagellated sperm, the structure is similar to charophytes. This is one way they
adapted for an aquatic environment.
Land plants and charophytes divide in similar ways. Plant cells divide by depositing cell wall material
in between the elongated cell, eventually forming a new cell wall.
process of cell division in plants
DNA sequence comparisons can be made between the nuclear and chloroplast genomes of existing
land plants and charophytes.
Sporopollenin is a tough polymer protecting exposed zygotes in charophytes (also found in encasing
spores of plants)
, Challenges that plants face moving from water to land:
Water provides support and allows nutrients to be transported from one place to another. However,
if they were moved to land, this would be a lot harder. The currents of water aided reproduction by
carrying pollen etc. water also maintains a stable temperature and acts as a buffer from solar
radiation. It also prevents desiccation (drying out)
How did plants solve these issues on land?
Desiccation on land - formation of cuticle layer with stomata which prevents water loss.
Water is a supportive medium but land isn't - cell wall thickenings (lignified cell walls).
Obtaining nutrients from soil - formation of rhizoid and later on, root systems, formation of
symbiotic associations with fungi networks (the fungi provides a nitrogen source and the plants
provide a carbohydrate source)
How to access and transport water - development of a vascular system
Main differences between charophytes and land plants:
Land plants have meristems whereas charophytes don't (found in roots and shoots)
LP have multicellular gamete forming structures called gametangia
Early LP have walled spores produced in sporangia.
Lecture 2: Lower plants
Major factors that distinguish different phyla is:
Mode of reproduction
Alteration of generations
Water relations - Prescence or absence of vascular systems
Habitat
Seed producing
Presence of leaves, roots, stems and flowers
12 phyla of extant plants
Non vascular plants
Vascular plants
Seed plants: gymnosperms and angiosperms
Phylogenetic relationship among extant land plants
Liverworts -- mosses -- lycophytes -- ferns -- gymnosperms -- angiosperms
Cryptogams refers to
Lower plants
Seedless plants
Spore-bearing plants
Non-flowering plants
Non-vascular cryptogams = mosses and allies
Vascular cryptogams = ferns and allies
Vascularisation provides a major distinction between plants
Non-vascular cryptogams (seedless)
Bryophytes
Small due to lack of vasculature
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