Biodiversity - Plants

random facts

• have cellulose cell walls (thick, meshed cellulose microfibrils)

• have many different types of organelles/plastids

• have larger genomes in some plants

• known as sessile (cannot move)

• virdiplantae (predominantly have chlorophyll a and b)

• water is needed for sperm motility in lower plants)

factors that affect plants

• temperature

• water (humidity and turgor)

• atmosphere (nitrogen, oxygen, carbon dioxide) (pressure and gravity)

• light and dark

• soil

food webs

• land dwelling

• non locomotory

• oxygen producing

• autotrophs

importance of plants to humans

• 60-70% calorific intake

• predominantly carbs, oils and proteins

• vitamins

• biofuels

• medicines

extant plant phyla descended from green algae

• bryophytes (non vascular)

• lycophytes (vascular seedless)

• monilophytes (vascular seedless)

• gymnosperms (vascular seeded)

• angiosperms (vascular seeded)

charophytes

plant-like multicellular protists

• found in freshwater lakes and ponds

• some called stoneworts due to brittle calcium carbonate outer layer

similarities between plants and charophytes

• rings of cellulose-synthesising protein complexes in plasma membrane

• presence of sporopollenin in spore walls

• similarities in DNA (similar RNA and genes)

• similar structure of flagellated sperm

• formation of a phragmoplast, the microtubule structure between daughter nuclei in a dividing cell

• peroxisome enzymes reduce effects of photorespiration and the inefficient loss of organic compounds (e.g. sugar)

rosette cellulose synthesis complexes

• cellulose (not found in animals)(important for cell rigidity)

• components of the cellulose synthesise complexes (assembled on the plasma membrane of the endoplasmic reticulum, processed by the Golgi apparatus)(vesicle trafficking to the cell plasma membrane surface)

• rosette shaped

• first found in charophytes

adaptations preventing desiccation

• sporopollenin (durable polymer reinforcing spore walls, preventing desiccation)

• sporopollenin is also found in plant spore and pollen walls, suggesting that it is a key trait to allow land colonisation by charophytes

• benefits = unfiltered sun, plentiful carbon dioxide, nutrient rich soil

• costs = water scarcity, lack of structural support

peroxisome enzymes

• found first in charophytes

• degrades anti-oxidant molecules which are toxic to cells

• other algal species lack them

• makes plant suited to life away from water (more efficient photosynthesis, protection against bacterial and fungal attack)

emergence of land plants

• 3.2 billion years ago: few prokaryotes on land 

• 2.4 Bya: atmosphere changed by ocean cyanobacteria 

• 1.2 Bya: evidence of land cyanobacteria and protists 

• 1-2 Bya: evidence of first rudimentary chloroplastid 

• 475-470 Mya: ancestral plants emerge on land 

  • basic vegetative and reproductive structures but multicellular e.g., Cooksonia sporangia 

  • Bryophytes (mainly mosses) predominate: unbranched, small (<5 cm tall). Dominant form of life cycle: gametophyte (1n) 

emergence of some complex traits

Emergence of some complex traits 

• 425 Mya: ancestral lycophytes with vascular systems and bifurcated branching emerges 

• 405 Mya:evidence of fossilised stomata 

• Sporophylls: 

  • modified leaf structures 

  • bear spore-forming structures called sporangia 

  • 410 Mya: microphylls first appear in fossil records. 

Lycophytes and then monilophytes are prevalent 

• 385 Mya: first forests appear, mainly lycophytes, many now extinct 

• 360-300 Mya: CO₂ removed from the atmosphere which, many large plants reliant on swimming sperm, die off. Dominant form of life cycle: sporophyte (2n): monilophytes and later lineages. 

bryophytes

• non vascular

• seedless

• non-woody

• 3 phyla (mosses, liverworts, hornworts)

• from charophyte has conserved cellulosee synthase complexes and flagellated sperm

• has swimming sperm

• some species are sensitive to pollution, making them useful ecosystem indicators

• homosporous (from one spore 2 types of gametophytes, male and female, can be produced)

• can reproduce asexually from gemmae held within cups

phylum hepatophyta : liverworts

• from fossil record of spores

• do not have a vascular system

• are either thalloid or leafy

phylum anthocerophyta : hornworts

• dominant form (gametophyte) are 1-2 cm in diameter and grow horizontally

• a sporangium occurs in the sporophyte tip. it will split open upon maturation, releasing thousands of spores

phylum Bryophyta : mosses

• gametophyte form, either male or female is dominant

• sporophytes are ephemeral (made up of sporangium, spores, sporophyte, gametophyte)

• asexual reproduction is also possible

ecological and economical value of mosses

• improve soil architecture, particularly in uncolonised land

• retain water and some harbour nitrogen-fixing cyanobacteria

• able to live in very cold and dry habitats

• are resistant to high levels of UV

sphagnum moss

• economically valuable but being used up too quickly

• compacted moss underground in peat lands is burned as fuel

• low temp, pH and oxygen inhibit bacterial activity

lycophytes

• seedless

• vascular

• less reliant on moisture

• diversity in phylum

• still have swimming sperm

• fossil loycophytes (tree-like)

• strobili (cone-like)

moniliophytes

• seedles

• vascular

• megaphylls rooting system

• sporophyte (2n) is dominant life form

• homospory

• ferns (pterophytes), horse tails (sphenophytes) and whisk ferns

horsetails (sphenophytes)

• grow in marshes and riverbanks

• stems have joints with small leaves in rings at the joints

• gives bushy appearance

whisk ferns

• reduced leaves

• yellow sporangia form on the sporophyte

• minute gametophytes (only found underground)

5 key traits in nearly all plants but are absent in charophytes

• multicellularity in alternation of generations

• walled spores produced in sporangia

• multicellular gametangia

• stomata and cuticles

• apical meristems

some plant lineages within groups have lost traits over time

multicellularity in both generations of plants

• single celled gametes

• multicellular gametophyte (haploid) plant form

• multicellular sporophyte (diploid) plant form

stomata and waxy cuticles

• early plants : sufficient levels of cumin in dermal tissue

• high carbon dioxide: low stomata count on the undersides of leaves

• pseudostomata (contain parts of sporophytes of hornworts and mosses

gymnosperms

• vascular

• seedless

• mainly woody

• 4 phyla (conifers, cycads, gnetophytes and Ginkgo globa)

• has a more developed root system and has megaphylls

• complex vascular bundling of xylem and phloem cells

• conifers do not need water for reproduction

cycads

• have flagellated motile sperm

• have large cones and palm-like leaves

• woody

• highly endangered

Ginkgo glioba

• have flagellated motile sperm

• fanlike leaves (known as maidenhair tree)

• separate male and female trees

• resistant to air pollution

• woody

gnetophyta

• Three genera are grouped based on molecular data 

  • Welwitschia mirabillis : only one species in this genus 

• Found in the desert regions of south western African countries 

• Long living, well adapted to dry environments 

  • Ephedra genus : 40 species 

• Herbaceous desert shrubs 

• Produce cones and seeds 

• Produce ephedrine which acts as a decongestant 

  • Gnetum genus : 35 species 

• Tropical trees, shrubs and vines 

• Leaves look like the broad leaves of many angiosperms 

conifers

• Wollemi nobilis pines 

• Many large trees found in the northern hemisphere 

• Many are evergreen and survive well in cold regions 

• Huge economic impact : timber and paper 

• 600 species 

• Adapted to colder climates 

• Don't have a fully closed ovule (for pollen to enter) 

angiosperms

• 299,000 species 

• Eusteles, complex roots and megaphylls 

• Reason for huge evolutionary success 

  • Interactions with pollinators (spread further) 

  • Floral structures 

  • Complex vascular systems 

• Seed complexity 

  • Double fertilisation 

  • Fully enclosed 

  • Fruit for dispersal 

• Vascular seed (floral) plants 

floral structures

• Sepal (protective) 

• Female structures (e.g. stigma) 

• Male structures (on a stalk) 

double fertilisation

• Unique to angiosperms: 

• Mature male gametophyte (microscopic) has two sperm cells: 

  • One sperm will fuse with the egg cell. This will become the embryo.

  • One sperm will fuse with the polar nuclei. This will become the endosperm 

5 derived traits of seed plants

• Reduced gametophytes (microscopic) which are nourished and protected by the sporophyte 

• Heterospory (microspore becomes male gametophyte, megaspore becomes female gametophyte), ensures the right pollen goes to the right egg 

• Ovule (open for pollen to fall through) 

• Pollen (makes water unnecessary for fertillisation) 

• Seeds (can survive better than unprotected spores)(have a protective coating and a food source) 

homosporous spore production

Sporangium on sporophyll -> single type of spore -> 2 types of gametophyte -> eggs / sperm 

heterosporous spore production

• Megasporangium on megasporophyll -> megaspore -> female gametophyte -> includes egg cells 

• Microsporangium on microsporophyll -> microspores -> male gametophyte -> sperm 

pollen

• Huge diversity in form and shape 

• The pollen rube will break through apertures (folds) once hydrated by stigma cells (only flowering plants)