BIOL 371: Theme 2 - Plant Diversity and Classification

multicellularity

leads to specialized cells giving rise to tissues/organs with specialized functions

plants and animals divergence

~1.6 Ga - plant-animal common ancestor, mitochondria came before animals and plants split and plastids only came after, endosymbiotic events, animals can be photosynthetic, plants are sessile

classification

helps us to understand similarity and diversity of living organisms in an organized manner, organisms can be grouped together based on common characteristics, morphological and sequence homologies, provides information on evolutionary lineages

defining characteristics of land plants

eukaryotes, almost all are photoautotrophs (eg. monotropha can grow in the dark, obtains organic carbon from other plants), multicellular, sessile or stationary, cell walls, alternation of generations life cycle (sporophytes and gametophytes)

primary cell wall

in all plant cells, surrounds plasma membrane and cell contents (cytoplasm and organelles), cellulose fibres in matrix of hemicellulose, rigid but flexible, contains cellulose, hemicellulose, pectin and structural proteins

cellulose

unbranched polymer of glucose, most abundant, 50% of all biomass, hard to degrade

secondary cell wall

only in some plant cells, cellulose fibres anchored with lignin, stronger and more rigid, creates highly hydrophobic waterproof barrier, xylem and sclerenchyma cells

turgor pressure

provides rigidity from the vacuole pushing against the cell wall

plasmolyzed

due to a hypertonic environment, cell contracts, shrinks, membrane is pulled in

flaccid

due to an isotonic environment, cell lacks water, becomes droopy, wilted, incipient plasmolysis

turgid

due to a hypotonic environment, high pressure, cell is swollen and stiff

osmosis

how all water is lost or acquired

animal life cycles

one free diploid individual, haploid gametes are formed through meiosis, gametes are not free living

plant life cycles

alternation of generations (sporophytes and gametophytes)

sporophyte

diploid (2n), multicellular, produces spores through meiosis

spores

haploid (n), unicellular, germinate to produce gametophytes through mitosis

gametophyte

haploid (n), multicellular generation, produces haploid unicellular gametes through mitosis

embryo

diploid (2n), multicellular, forms from gametes

amplification of gametes

increases chances of successful off-springs, 1 sporophyte produces 1000 spores —> 1000 gametophytes —> 1000 × 1000 gametes

land plant classification

based on presence of vasculature and seeds

vasculature

consists of xylem, phloem, parenchyma cells, and fiber cells

its evolution allowed for increased height (moss to trees)

fiber cells

sclerenchyma cells that provide rigid support to the xylem and phloem, files run throughout the vascular system, lignified secondary cell walls, the strong fiber cells provide raw materials for the textile industry

xylem

water conducting cells, dead at maturity, structurally strengthened by secondary cell wall and lignin

phloem

cells that transport sugars and other solutes, live at maturity

lignin

second most abundant polymer after cellulose, hydrophobic and aromatic, covalently linked with cell wall polysaccharides (hemicellulose) providing the rigidity and strength for the cell wall

makes vegetables crunchy and is highly resistant to degradation by chemicals, degrades very slowly and slows down the fermentation process when biomass is used to produce biofuels

seeds

have the plant embryo, cotyledon (nutrition for embryo)

nonvascular plants

bryophytes (eg. mosses), lack vascular tissue, haploid generation is dominant (diploid generation small/shorter time)

vascular seedless plants

lycophytes (eg. selaginella) and pterophytes (eg. ferns), have well-developed vascular tissues but do not make seeds, diploid generation is dominant

vascular seed plants

gymnosperms (eg. conifers) and angiosperms (all flowering plants), have well developed vascular tissues and produce seeds, diploid generation is dominant (haploid generation microscopic/shorter time)

advantage to dominant diploid stage

diploid can compensate for deleterious mutations, genetic load (we all carry deleterious mutations), diploid generation accumulates favourable mutations