BIOL 371 Early Land Plants

In what order did life develop?

• true colonization began with fungi

• early embryophytes (land plants)

• vascular plants

• arthropods

• terapods (first vertebrates)

• seed plants

Why would aquatic plants want to move out of the water?

• no competition

• unlimited untapped mineral resources

• unlimited space for establishment and growth

• full access to light

• no predators

Are algal mats considered aquatic or land plants?

Aquatic

Where did land plants begin?

freshwater algal mats first began photosynthesizing on land having to withstand wet-dry cycles

How did algal mats begin diversifying?

through forming symbiotic relationships with fungi they established the first soils allowed for further diversification as near these wet zones more organisms could take whole

What were the first embryophytes?

the bryophytes

embryophytes vs bryophytes

Embryophyte is the broader, overarching classification for all land plants, while bryophyte refers to a specific, non-vascular group within the embryophyte lineage

What were the first terrestrial animals?

arthropods in the Silurian period

What are the challenges that came with life on land?

• desication (drying)

• respiration

• reproduction

• locomotion and support

• nutrients

• senses

How did desication cause problems for land plants

they required protection from drying out like a resistant coat or skin to prevent body fluids from evaporation and having to deal with scarce water like the cuticle

How did respiration cause problems for land plants

in water dissolved oxygen and CO2 are exchanged so now organisms had to dead with atmospheric gas exchange instead lik using stomata

How did reproduction cause problems for land plants?

in water eggs and sperm could be released into the water or broadcast

land organisms had to develop successful reproductive strategies under desiccating conditions using the alternation of generations

How did locomotion and support cause problems for land plants?

they no longer had propulsion through a viscous medium , no more support or buoyancy from the water meaning they required a new locomotive system and support like limbs, types of joints or reinforced tissues to help with upward growth

How did nutrients cause problems for land plants?

in the water mineral nutrients and ions are diffused and are readily taken up through diffusion and maintaining osmotic balance while on land mineral nutrients remain in the substrate

How did sense cause problems for land plants?

organisms on land had to adapt to the changes in light, sound, and smell which were perceived very different in water

What is the purpose of the cuticle?

a waxy layer that prevents water loss from stems and leaves ensuring they don’t dry out

also protects from microbes and pathogen attacks

Where were cuticles found in fossil records?

early land plants and spores

How is the cuticle produced?

photosynthetic cells transfer metabolites to the epidermis where wax is produced and deposited outwards

What are epidermal layers?

transparent and lack chloroplasts

What are stomata?

pores that allow exchange of gases across photosynthetic surfaces

What are guard cells?

specialized cells that control the opening and closing of stomata

How do guard cells regulate gas exchange?

although covered by the cuticle, they create a pore by swelling and pulling apart allowing gas exchange to occur when water is plentiful limiting uneccesary water loss

Describe the formation of the epidermal layer and why they are formed this way

epidermal layers are arranged in a jigsaw puzzle growth pattern allows for complete intricate seals between neighboring cells regardless of swelling or contracting preventing them from ripping apart

How do guard cells swell and contract in response to water amounts?

• water moves in (plentiful) → swell to sausage shape → pore opens

• water moves out (lacking) → contract to flaccid straight sided shape → pore closes

What are the two different multicellular growth forms of the plant life cycle?

• diploid (2n) phase = multicellular sporophyte → makes spores (n) through meiosis

• haploid (n) phase = multicellular gametophyte → makes gametes (n) through mitosis

spores vs gametes

• spores: haploid, unicellular but will germinate to produce gametophytes (n) through mitosis

• gametes: sperm and egg cells fuse (fertilization) to form a unicellular zygote (2n) that will quickly develop into an embryo through mitosis

What happens to the plant embryo?

diploid (2n), multicellular and will develop into a sporophyte through mitosis

Where is the embryo of land plants retained?

on the female gametophyte

The alternation of generations steps

• The Gametophyte (1n): This generation produces gametes (sperm and egg) through regular cell division (mitosis).

• Fertilization: A sperm and egg fuse to create a (2n) zygote, which grows into the next generation sporophytes/

• The Sporophyte (2n): This generation creates spores through division that halves the chromosome number (meiosis).

• Spore Development: These spores are released into the environment, where they grow via mitosis back into a gametophyte, starting the cycle over

What is the purpose of the alternation of generations?

to amplify gametes and chances of successful fertilization events and offspring

What is the main difference between algae reproduction and alternation of generations of land plants?

In algae, the zygote immediately undergoes meiosis to form spores, whereas in land plants the zygote first develops into a multicellular diploid sporophyte, which later undergoes meiosis to produce spores.

Do algae or land plants have a longer gametophyte stage?

algae

How does alternation of generation improve land plants’ reproductive success?

Algae:

1 fertilization → zygote → spores

Land plants:

1 fertilization → large sporophyte → thousands of spores

So the sporophyte acts like a spore factory. That's why land plants have much greater reproductive success than algae.

What are defining characters of all LAND plants?

• cuticles

• stromata

• alternation of generations (diphasic life cycle)

Do all land plants share a common ancestor?

Yes, all land plants (embryophytes) share a single common ancestor

What are land plants classified/seperated by?

1. presence of vasculature

2. presence of seeds